ILLINOIS NATURAL HISTORY SURVEY Natural History of the Wood Frog (Rana sylvatica) in the Shawnee National Forest, Southern Illinois Michael Redmer linois Natural History Survey Bulletin » Volume 36, Article 4 March 2002 Illinois Natural History Survey, David L. Thomas, Chief A Division of the Illinois Department of Natural Resources A catalog of the publications of the Illinois Natural History Survey is available without charge — from the address below. A price list and an order blank are included with the catalog. This catalog may also be accessed on the World Wide Web at http://www.inhs.uiuc.edu/chf/pub/ pub-catalog/spring00/index00. html Illinois Natural History Survey Distribution Office 607 E. Peabody Dr. Champaign, IL 61820 Editors: Thomas Rice and Charles Warwick Citation: | Redmer, Michael. 2002. Natural History of the Wood Frog (Rana sylvatica) in the Shawnee National Forest, Southern Illinois. Illinois Natural History Survey Bulletin 36(4):163-194. Michael Redmer ts a biologist with the United States Fish and Wildlife Service, Chicago Illinois Field Office. He completed work on this project while a graduate student in the Department of Zoology, Southern Illinois University at Carbondale. US ISSN 0073-4918 Printed by authority of the State of Hlinois (RRV2926—1M—02-02) Printed with soy ink on recycled and recyclable paper. ILLINOIS NATURAL Fuss EO Rey SU REV EY: Natural History of the Wood Frog (Rana sylvatica) in the Shawnee National Forest, Southern Illinois Michael Redmer Hlinois Natural History Survey Bulletin Volume 36, Article 4 March 2002 Acknowledgments For assistance with field work, I thank M. Blanford, R.A. Brandon, B. Burke, D. Corgiat, C. Lechowicz, K. Tolch, and A. Wilson. Research permits were facilitated by L. Odegaard and E. Shimp (United States Forest Service, Shawnee National Forest). R. Stotlar (Department of Plant Biology, SIUC) identi- fied a club moss. M. Doran (SIUC School of Medicine) graciously allowed me to work in the SIUC Histology Center. C.A. Phillips (Center for Biodiversity, Illinois Natural History Survey), R.A. Brandon, C. Redmer, D.R. Ludwig (Forest Preserve District of DuPage County), and two anonymous review- ers commented on drafts of the manuscript. Edits and helpful suggestions for improving the manuscript were made by JoAnn Jacoby, Thomas Rice, and Charles Warwick, all from the [Illinois Natural History Survey. Funding was provided by a grant from the National Biological Service, Northern Prairie Science Center. C.A. Phillips kindly invited submis- sion of the manuscript and helped to defray page charges. This paper is based in part on an M.S. thesis submitted to the Department of Zoology, Southern [linois University at Carbondale. Contents Acknowledgements 11 Introduction 163 Methods 165 Study Area 165 Distribution 165 Habitat 165 Breeding Ponds 165 Terrestrial Habitat 165 Population Studies 165 Breeding Phenology 165 Demography 166 Clutch Size 167 Other Natural History Notes 167 Data Analyses 167 Results 168 Distribution 168 Habitat 168 Breeding Ponds 168 Terrestrial Habitat 169 Population Studies 169 Breeding Phenology 169 Demography and Skeletochronology 171 Clutch Size 176 Other Natural History Notes 177 Discussion 178 Distribution 178 Habitat 178 Breeding Ponds 178 Terrestrial Habitat 179 Population Studies 180 Breeding Phenology 180 Demography 181 Clutch Size 186 Other Comments 187 Summary 187 Digitized by the Internet Archive in 2021 with funding from University of Illinois Urbana-Champaign https://archive.org/details/winterstonefliesS365webb March 2002 Introduction In the past 20 years, a number of studies have documented considerable intraspecific geographic variation in life history traits of wide-ranging amphibians (Augert and Joly 1993; Berven 1982a, 1982b, 1988; Berven and Gill 1983; Dushane and Hutchinson 1944: Hemelaar 1988; Miaud et al. 1999, 2000). Regionally limited studies that provide data on local amphibian populations can also contrib- ute to the understanding of geographic variation in wide-ranging species by providing baseline data necessary to compare various life-history and population characteristics. Regional studies of amphibian popula- tions may also contribute to the understanding of amphibian declines. Since 1990, reports of such declines from various parts of the world have led to well-publicized concern about amphibian populations (Blaustein 1994; Blaustein and Wake 1995; Wake 1991, 1993; Wyman 1990). An effort to identify research needs and to begin monitoring amphibian populations was started in the early 1990s by the International Union for the Conservation of Nature and Natural Resources (IUCN). The possibility of global decline has been difficult to assess because amphibian populations are known to undergo cycles of increase and decrease (McCoy 1994; Pechmann and Wilbur 1994; Travis 1994). Although amphibian biology is an active field of study, there is a general lack of baseline data against which to measure population changes (Wake 1993), and important population characteristics (i.e., fecundity, demography, longevity, their interrelationships, and phenology) remain poorly understood even for many common species (Duellman and Trueb 1986). Once gathered, such baseline data can be useful for planning long-term study of population characteristics. In addition, documenting vulnerability to decline will require application of methodologies to obtain data on population cycles. Such methods can be best developed and tested on populations of common species not currently undergoing declines. The wood frog, Rana sylvatica, is a small North American ranid characterized by distinct dorsolateral folds; brown, tan, or dark gray Wood Frog in Southern Illinois 163 coloration; light stripes on the upper lips; and dark masks along the sides of the face (Fig. 1A). Tadpoles have high tail fins, primarily black bodies with scattered iridophores, and light lines along the ventrolateral edges of the head (Fig 1B). The male breeding vocaliza- tion is a fast two-note chuckle that can be heard over only short distances. Although its range is primarily boreal, R. sylvatica is the most widespread North American amphibian species (Martof 1970). It occurs from the southern Appalachian Mountains of Georgia, north into Canada above the Arctic Circle, and west to Alaska (Conant and Collins 1998: Martof 1970). The western edge of its range runs roughly diagonally from Alaska and the Northwest Territories southeast through eastern North Dakota and other upper midwestern states (Minnesota, Wisconsin, Illinois) to northeastern Alabama. There are disjunct populations in Colorado, Wyoming, and the Ozark Plateau (Conant and Collins 1998; Martof 1970). The range includes much of the eastern region of the continent, which is highly populated by humans. Rana sylvatica has been used extensively by ecologists as a study organism. There have been many regional studies of its life history, including populations near the periphery of its range (Camp et al. 1990; Corn and Livo 1989; Davis and Folkerts 1986; Meeks and Nagel 1973; Trauth et al. 1989, 1995). Because of its large geographic distribution and its occurrence in many habitats at a broad range of elevations, significant phenotypic and life history varia- tion has been reported (Berven 1982a, 1982b; Berven and Gill 1983; Martof and Humphries 1959). Throughout most of its range in Illinois, the wood frog has been an uncom- monly collected species (Redmer 1998; Smith 1961) and there are few data on its natural history in the state. I studied several aspects of the natural history and population biology of R. sylvatica in the Shawnee National Forest (SNF) between 1993 and 1997. The primary objective was to conduct the first extensive study of this species in Illinois. The first portion of this study documented the distribution of R. sylvatica in the SNF. Observations of general aspects of natural history (predation, amphibian commu- Illinois Natural History Survey Bulletin Vol. 36 Art. 4 Figure 1A. An adult male Rana sylvatica from Jackson County, Illinois. Figure 1B. Tadpole of R. sylvatica from Jackson County, Illinois. Photographs by Michael Redmer. March 2002 nity associates, and larval period) were also recorded. I then identified and qualitatively characterized types of breeding ponds and woodland habitats in which the species occurs, and recorded the phenology of breeding activity and weather conditions at which they occurred. I then used skeletochronology to estimate individual ages of wood frogs, and compared statistical correlations between age and body length of individuals and female age and body length with clutch size and ovum size. Methods Study Area This study took place within the boundaries of the United States Forest Service (USES), Shawnee National Forest (SNF) in southern Illinois, between 1993 and 1997. The SNF is located roughly between 37° and 38° North latitude, and 88° to 100° West longitude. Distribution Before 1992, there were few records of R. sylvatica from the region (Redmer 1998). To document new localities, searches were conducted during or immediately following the breeding season (late February through early March). Individual vouchers were collected on roads or at breeding ponds. Potential breeding ponds (vernal ponds and flooded depressions) were located by listening for chorus frogs (Pseudacris feriarum) and spring peepers (P. crucifer) after late winter thaws in February, or by visiting man-made “wildlife ponds” plotted on USFS-SNF topographical maps. During early spring, ponds were inspected for wood frog choruses or searched for the distinctive egg masses or tadpoles. Upon discovery in ponds at new localities, <50 eggs or tadpoles were collected and raised through metamorphosis in the laboratory. All surviving metamorphs were preserved and vouchers were deposited in the Fluid Vertebrate Collection, Department of Zoology, Southern [Illinois University at Carbondale (SIUC). Habitat Breeding Ponds. Breeding ponds were both Wood Frog in Southern IIlinois 165 natural and human-made. Natural ponds included ephemeral woodland pools (with variable basins, little or no aquatic vegetation, and dried in summer of all years) and semi- permanent ponds (with distinct basins and aquatic vegetation, and dried in some years). Human-made ponds or depressions included flooded roadside ditches, ruts caused by vehicle traffic on earthen or clay-based roads, and wildlife ponds. Maximum depth (to the nearest cm) of breeding ponds was measured with a meter stick while egg masses were still present. Terrestrial Habitat. Terrestrial habitats around breeding ponds or wherever else R. sylvatica was collected were floodplain or upland forest, classified on the basis of published plant community descriptions (Voigt and Mohlenbrock 1964). Dominant species of trees and other general observations on vegetative cover were recorded. Canopies over ponds were classified as closed (> 75% canopy cover after leaf-out) or open (< 75% canopy after leaf-out). Population Studies A population of R. sylvatica in southern Jackson County (37°39'N, 89°04’ W) was studied intensively between 1993 and 1997. This population bred in at least 12 breeding pools or ponds in Cave Creek floodplain 1—1.5 km N of Pomona and another pond along an arm of Cedar Lake ca. 1.8-km E of Pomona and 2.5 km ESE of the center of the Cave Creek area. | Breeding Phenology. Oviposition dates at the Cave Creek floodplain were recorded from 1993 through 1997 and at Cedar Lake from 1995 through 1997. From 1994 through 1997, weather conditions at the center of the Cave Creek study site were monitored every 24 h from | February until at least one week after secession of breeding activity. Minimum- maximum thermometers (VWH Scientific) were mounted on a stake 0.2 m above ground, and buried 5-10 cm below the soil surface. Mean daily temperatures were calculated by averaging daily minimum and maximum air and soil temperatures. Precipitation (to the nearest 0.1 cm) was measured with a scientific rain gauge (Productive Alternatives, Inc., 166 Illinois Natural History Survey Bulletin Fergus Falls, MN). Correlations between minimum-maximum air and soil temperatures were determined by bivariate regression analyses. Oviposition dates were plotted against trends in weather variables in an attempt to determine whether wood frog emergence and breeding behavior followed consistent annual patterns during this study. Demography. The ages of 188 individuals were estimated by skeletochronology. Skeletochronology allows estimation of individual age from the number of annular lines of arrested growth (LAGs) on cross- sectioned diaphyses of long bones such as femora or phalanges. This method has proven effective in seasonally variable climates where growth is greatly reduced or prevented by low winter temperatures (Halliday and Verrell 1988). Studies on post-release mortality of toe-clipped amphibians are few, but generally show an insignificant reduction in survivorship (Clarke 1972; Ott and Scott 1999; Reaser and Dexter 1996). Thus, skeletochronology is a relatively harmless method with which to sample age within anuran populations. This technique has been popular in Europe for nearly 20 years and appears (based on increas- ing publications) to have gained increased use in North America since 1986 (Bastien and LeClair 1992; Redmer 1999). In most studies, amputated toes were preserved, cross-sec- tioned, stained with hematoxylin, and peri- osteal LAGs were counted under a micro- scope. The total number of LAGs (more intensely stained lines) indicates the number of winter dormancies through which an indi- vidual has lived. Since endosteal bone growth can cause resorbtion and remodeling of the periosteal bone cortex (and thus obliteration of some periosteal LAGs), application of statistical methods to estimate loss of peri- osteal LAG has been recommended (Hemelaar 1985; Sagor et al. 1998). In this study, most (n = 172) wood frogs were collected during 26—28 February and 3-6 March 1995. Eight amplexed pairs were collected on 5 March 1996. The sample consisted of 119 males and 69 females, of which 139 (93 M:46 F) were from Cedar Lake and 49 (26 M:23 F) were from Cave Creek. Vol. 36 Art. 4 Frogs were collected by hand, with a dipnet, or with 36-cm-tall nylon drift-fence/funnel trap arrays erected along parts of the margins of three Cave Creek ponds. Captured frogs were transported to the laboratory in insulated coolers (naturally amplexed pairs were kept together in plastic bags separate from individuals). In the laboratory, sexes and snout-vent lengths (SVL; measured with a plastic ruler to the nearest 1.0 mm) were recorded and each individual was assigned a unique number. The fourth toe of one hind foot of each frog was amputated at or below the joint between the penultimate and third phalanges and fixed for at least 24 h in 10% formalin, rinsed in running tap water for 12 h, and stored in 70% ethanol. Most frogs were returned within 12 h to the place of capture. Twenty-four gravid females were euthanized by immersion in 20% ethanol, fixed in 10% formalin, stored in 70% ethanol, and dissected later for counts of oviductal eggs. Amplexed pairs were kept together in glass bowls in the laboratory for 24-48 h to allow oviposition and all resultant egg masses were preserved in 5% formalin so counts and measurements of pre-yolk plug embryos could be made later. Glass-mounted cross-sections of phalan- ges were prepared. Each preserved toe was defleshed manually and the penultimate phalanx from each separated from the others. The penultimate phalanges were decalcified in . Kristensen’s formic acid solution for 6 h and rinsed for 24 h in running tap water. After initial decalcification, bones were dehydrated automatically (V.I.P.® Tissue-Tek machine), infiltrated with paraffin, embedded individu- ally in paraffin blocks, and cross-sectioned at 10 ttm with a microtome. Some bones found to be brittle when sectioned were decalcified further at the tissue face for 15 min in RAPID® nitric acid solution. Ten to 30 mid- diaphysial cross-sections of each bone were attached with adhesive gelatin to microscope slides. Sections then were cleared, hydrated, stained, and dehydrated by immersion 1n the following sequence of solutions and reagents: (1) three baths, 3 min each in Histoclear; (2) two baths, 2 min each in 100% ETOH; (3) 2 min in 95% ETOH; (4) 10 sec in distilled March 2002 water; (5) 15 min in Shandon® instant regressive hematoxylin; (6) 10 sec in distilled water; (7) two dips, | sec each, in acid ETOH; (8) 1 min in LiCO,; (9) two baths, 2 min each, in 100% ETOH; and (10) two baths, 2 min each, in 100% ISOH. Processed sections were mounted in Permont® mounting medium under glass cover slips. Bone cross-sections were interpreted by the procedures and criteria of previous skeletochronology studies (Castanet and Smirina 1990; Castanet et al. 1993; Hemelaar 1985; Hota 1994; Sagor et al. 1998; Smirina 1994). Diameters of bone characteristics were measured at 160X to the nearest 5 um with a calibrated ocular micrometer mounted in a binocular compound microscope. From the medullary cavity (MC) to the exterior, the bone layers are metamorphosis line (ML), endosteal bone (EB), and subsequent lines of arrested growth (LAGs) in cortical periosteal bone. ML and EB were not always present. Because bone cross-sections were oval or irregular in outline, their diameters were calculated as the square root of the product of the greatest diameter and the greatest diameter perpendicular to it as suggested by Hemelaar (1985) and Sagor et al. (1998). Because remodeling was detected in some bone samples, age estimates were made as follows. If metamorphosis lines were present, or if endosteal and periosteal LAGs were present in a 1:1 ratio, age was estimated by counting periosteal LAGs (each LAG = | yr). Because tissues were collected from frogs that had just emerged from hibernation, the LAG deposited during the winter was not discern- ible from the outer bone perimeter; thus, the outer perimeter was counted as a LAG. In some instances, EB was broken or absent (as evidenced by resorbtion patterns in periosteal bone layers), probably because of damage caused by the microtome blade. In these instances, the diameter of the space where MC and EB had been was recorded as the diameter of EB. To determine what percentage of early LAGs may have been obliterated by endosteal bone growth, | compared the mean diameter of endosteal bone with mean diameters of the innermost and second visible LAGs. If the diameter of the endosteal region was > 2 SD Wood Frog in Southern I[Ilinois 167 more than the group mean, LAG | was considered to be resorbed, and the innermost LAG was counted as LAG 2. If only part of a LAG was obscured by endosteal bone remod- eling, the area of endosteal bone was calcu- lated. If it was > 2 SD smaller than the mean of the next LAG, the partial visible LAG was counted as LAG |. Estimated age was compared to SVL for both males and females using bivariate regression analyses. Clutch Size. Preserved gravid females were dissected and oviductal ova were removed from egg envelopes. Diameters of 10 ova from each clutch were measured to the nearest 0.05 mm with a calibrated ocular micrometer mounted in a binocular dissecting microscope. Because most preserved ova were aspherical, average diameter was recorded as the square root of the longest axis multiplied by the longest axis perpendicular to it. Females that spawned in the laboratory as well as their spawned eggs and any eggs remaining in the oviducts were preserved. Ova and pre-yolk plug-stage embryos were counted and 10 from each clutch were measured as above. Clutches in which embryos developed past the yolk- plug stage were not included in these analyses because such embryos can achieve diameters significantly larger than those of earlier developmental stages (Rugh 1948; Kaplan beh? We Other Natural History Notes Observations of predation, associations with other amphibians, larval periods of 22 cohorts (from wild-collected eggs raised in the lab), and the dates metamorphosed frogs were first observed in the wild also were recorded. Data Analyses All statistical analyses were made with StatView® (Abacus Concepts, Inc.) version 4.5 software for Windows. Two-tailed f-tests were used to test for differences between age and size distributions. Bivariate regression analysis was used to calculate correlations between the following variables: (1) age and SVL, by sex; (2) age and fecundity; (3) SVL and fecundity; and (4) fecundity and mean ovum diameter. Descriptive statistics such as 168 Illinois Natural History Survey Bulletin sample size (N), range, mean, squared product moment coefficient (r?), standard errors (SE), standard deviation (SD), degrees of freedom (df), and t values (t), were calculated as appropriate. All alpha levels were set at = 3: Results Distribution Wood frogs were found at 20 localities within the SNF (Redmer 1998; Fig. 2). All localities were in the Shawnee Hills and Ozark Natural Divisions (Schwegman 1973) in Jackson (8), Union (4), Hardin (1), Pope (6), and Saline (1) counties. No wood frogs were found in the central portion of the SNF (Johnson and Williamson counties), Alexander County, or in the Cretaceous Hills Section of the Coastal Plain Natural Division in Massac, Pulaski, and southern Pope counties despite extensive searches (Redmer 1998). Vol. 36 Art. 4 Habitat Breeding Ponds. Thirty ponds or flooded depressions in which oviposition was observed were at or near 18 of the documented locali- ties. Of these, 21 (70%) were natural, and 9 (30%) were human-made or modified. Natural ponds included 14 (47%) ephemeral pools, 6 (20%) semi-permanent ponds, and | (3%) depression in a grassy field. Human-made or modified ponds included four (13%) flooded tire ruts, three (10%) wildlife ponds, and two (7%) roadside ditches. All oviposition sites were lentic. Although most (70%) ponds were in floodplains and thus may have been subject to periodic flooding (and invasion by fishes) from nearby streams, fishes (Gambusia affinis, Fundulus sp.) were observed in only three (10%) semi-permanent ponds. Twenty-one (70%) breeding ponds were under closed canopies, eight (27%) were under open canopies, and one (3%) was in a field about 50 m from mesic forest. Ponds were variable in Figure 2. Distribution of Rana sylvatica in the Shawnee National Forest, southern Illinois. Solid circles indicate localities confirmed by the author. The triangles indicate the locations within the Pomona study site (Cave Creek and Cedar Lake) mentioned in the text. March 2002 size, depth, and shape. Ephemeral woodland ponds with egg masses present were 22—78 cm (mean = 41 cm) deep. Semi-permanent ponds were 60—95 cm (mean = 74 cm) deep, tire-ruts 10—40 cm (mean = 24 cm) deep, and roadside ditches 40 and 60 cm (mean = 50 cm) deep. Wildlife ponds were 40—90 cm (mean = 60 cm) deep, and the flooded grassy field was 65 cm deep. Terrestrial Habitat. Twenty-one (70%) breeding ponds were in upland floodplains (the valleys of second- or third-order streams) and nine (30%) were on hills or ridges. In the western part of the SNF (Jackson and Union counties), 21 (91%) ponds were in floodplains and 2 (9%) were in uplands. In the eastern part of the SNF (Pope and Hardin counties), six (85%) ponds were in uplands (on ridges) and one (15%) was in a floodplain. The localities of R. sylvatica in the SNF were associated with mixed mature and second growth deciduous forest at six (30%) locali- ties, mature deciduous forest at seven (35%), mixed deciduous and planted pine (Pinus sp.) at five (25%), and monotypic planted conifer groves at two (10%) localities, both in Pope County. Trees most frequently noted in the mature deciduous forests included beech (Fagus grandifolia), sugar maple (Acer saccharum), tulip poplar (Liriodendron tulipifera), American elm (U/mus americana), sweet gum (Liquidambar stryaciflua), and sycamore (Platanus occidentalis). This composition indicates a community intermedi- ate between moist lowland and ravine forests as described by Voigt and Mohlenbrock (1964), but scattered red bud (Cercis americanus) and flowering dogwood (Cornus florida), as well as lush ephemeral herbaceous cover, indicated greater similarity to the latter one. Mixed mature-second growth woodlands were primarily in floodplains and usually not far from mature forest. Several trees (espe- cially A. saccharum and L. tulipifera) occurred in thickets of box elders (A. negundo) and green ash (Fraxinus lanceolata), often with dense patches of cane (Arundinaria gigantea) and the vines poison ivy (Rhus radicans) and catbriar (Smilax sp.). Mixed deciduous- coniferous forests usually included canopies of Wood Frog in Southern Illinois 169 pine (primarily Pinus taeda) along with F: lanceolata, A. negundo, A. saccharum, L. tulipifera, oaks (Quercus spp.), and hickories (Carya spp.). The ground where R. sylvatica occurred in two planted Pinus groves was covered by mats of needles and little vegeta- tion other than abundant R. radicans and patches of club moss (Diphasiatrum digitatum). In systematic searches through areas where R. sylvatica was known to occur, adults were rarely encountered after the breeding season. I observed seven alive on roads at night, and two during the day in shallow leaf litter near the bases of overhanging bluffs. All were found in April in forested ravines or valleys with plant communities similar to those described above. Population Studies Breeding Phenology. Rana sylvatica breed- ing activities (chorusing and oviposition) were explosive. Few males were heard calling and no amplexed pairs were found during daylight hours. In all years, a few males called one or two nights before oviposition was observed, and egg masses were found only after nights when numerous males called. The first dates of breeding activity were as follows: 17 March (1993), 19 February (1994), 27 February (1995), 26 February (1996), and 22 February (1997). The mean date of the onset of breed- ing activity was 26 February, and the mean date when breeding activity occurred was 28 February. At both Pomona-area study sites, oviposition took place over two to six nights (mean = 4) per year, but was not observed to occur more than two nights in any one pond. The peak of chorusing and oviposition was not always on the same night in neighboring ponds, and the breeding season throughout the study site usually lasted longer than it did in individual ponds. Breeding activity took place after several days of warming air and soil temperatures (Figs. 3-5). Mean air and mean soil tempera- tures were highly correlated (1° = 0.72, P< 0.001, df = 148) before, during, and after the breeding seasons of 1994-1997. The mini- mum/maximum surface air temperatures on the dates of first oviposition were -1/21°C (1994), 4/19°C (1995), 6/22°C (1996), and 10/ 170 Illinois Natural History Survey Bulletin Vol. 36 Art. 4 a o g @ 3 s a P= © oO o pe o. a = £ it) (7) E i = & <_< ea “Sh hh Sh “SS. Wh OA Sh Sh Wa Wa Oven, en SN aa a ave Dat th EON NOOR 3 4 9) 4 5 6 Female Age (yr) Figure 8. Age-frequency distributions of skeletochronologically estimated age classes of Rana sylvatica from a population in the vicinity of Pomona, Jackson County, Illinois. (A) males, N = 119; (B) females, N = 69. March 2002 long (mean = 51.3), three-year-olds 49-56 mm (mean = 51.8), four-year-olds 51-57 mm (mean = 54), and a five-year-old was 54 mm. The presence of a few one-year-old males (both in choruses and in amplexus) and two- year-old gravid females indicates that at least some males matured after their first growing season and that some females matured after two years. There was a low positive correlation between SVLs of mates found in amplexus (r? 50 45 40 Sen EON: NON RON PIT ey Y, e 35 WY ® 30 Ye eZ 5 -° gY = Lf 4 “ 20 LA ZO a Be oe o 4 Af, V4 4 19 Y iY oe, Se Oy 10 Wyae 5 GY 5 g ee 46 Wood Frog in Southern Illinois \ : SNS es SA a i \ RONSON 175 = 0.17, P=0.01, N = 18) and no correlation between their ages (1? = 0.07, P= 0.3, N = 18). Males of all four age classes were found in amplexus with females in the two- to four- year-old age classes. Amplexed pairs included the smallest (49 mm SVL) and largest (57 mm SVL) females observed. The mean SVL (51.5 mm) of amplexed females was not signifi- cantly different (P = 0.10) from that of non- amplexed females. Two, three- and four-year- old females were found in amplexus and their & 31 Male SVL (mm) 20 fae ® rei Ze) iy Sof, ———- £ Yy (we 10 ALA “fy =) A y 7 KL, : es Af Zz Guay ee sy i J G LA ity Guas fo r/ 2 3) Mf VA, DL a fee Y a “) ie Lh, VI ig “A LY, SS, Jf Os Af iy 0 Y} ZZ YZ 53 58 99 54 Female SVL (mm) Figure 9. Length frequency distributions of Rana sylvatica from a population in the vicinity of Pomona, Jackson County, Illinois. (A) Males, N = 119; (B) females, N = 69. 176 Illinois Natural History Survey Bulletin Vol. 36 Art. 4 mean age (2.8 yr) was not statistically different Clutch Size. Mean size of 24 clutches (15 (P > 0.95) from that of nonamplexed females. oviductal and 9 oviposited in the lab) was 575 Males captured in amplexus ranged from the (SE = 28.08, range = 304-874). Mean ovum/ shortest (43 mm SVL) to second-longest (49 pre-yolk plug embryo diameter was 2.45 mm mm) observed. The mean SVL (46.1 mm) was (SE = 0.04, range = 1.95-2.75). Mean not significantly different (P = 0.31) than that diameter in oviductal clutches was 2.40 mm of all males. Ages of amplexed males ranged (SE = 0.06, range = 1.94—2.74) and in ovipos- from one to four years old and their mean age ited clutches 2.48 mm (SE = 0.07, range = (2.4 yr) was not significantly different (P = 2.14—2.70). There was strong positive 0.51) from the mean age of all males. correlation (r° = 0.53,.P < 0.0001T;Ni= 24) oye A 43 15 ao = = 56 _} 48 > ” ® chs 5 = 42 1 2: 3 4 Male Age (yr) on CO —_ on 35 oO oO) 18 Female SVL (mm) nn On NO a oO © bh foe) 4 o 2 3 4 5 Female Age (yr) Figure 10. Length-age distributions of Rana sylvatica from a population in the vicinity of Pomona, Jackson County, Illinois. (A) Males, (B) females. Key: numbers = sample sizes; extreme upper and lower lateral lines = range of data; upper and lower edges of boxes = interquartile values; lines in boxes = mean values. March 2002 between female SVLs and clutch size (Fig. 11A) but no correlation (r? = 0.02, P= 0.52, N = 24) between female age and clutch size (Fig. 11B). There were strong negative correlations (overall r? = -0.71, P< 0.001, N = 24) between clutch size and mean ovum diameter (r? = - 0.67, P = 0.002, N = 15) and pre-gastrulation embryo diameter (r* = -0.81, P = 0.009, N = 9). All females from which oviductal ova were counted had only granular, non-pigmented or 1000 900 800 700 600 500 Number of Ova 400 300 200 46 48 50 Wood Frog in Southern Illinois 177 weakly pigmented ovarian ova remaining; thus all mature ova had been ovulated and counted. Only single ova were found to remain in the oviducts of five females that had oviposited. Other Natural History Notes Predation on different life-stages was observed on a number of occasions. In each year of the study, egg masses frequently were found hauled out of breeding ponds and left partially 54 56 58 60 Female SVL (mm) 800 600 Number of Ova 400 200 Female Age (yr) Figure 11. The relationships of (A) length (SVL) and clutch size, and (B) age and clutch size of female Rana sylvatica from a population near Pomona, Jackson County, Illinois. 178 Illinois Natural History Survey Bulletin consumed on the banks, probably by raccoons (Procyon lotor). In March 1993, marbled salamander (Ambystoma opacum) larvae were observed eating eggs from egg masses of R. sylvatica and southern leopard frogs (R. sphenocephala) oviposited the previous evening. During 1995-1997, A. opacum larvae were observed eating R. sylvatica tadpoles in a flooded tire-rut. In 1996 and 1997, crayfishes (Cambarus diogenes and Procambarus acutus) were observed eating eggs from R. sylvatica and R. sphenocephala egg masses. In 1996, a large C. diogenes ina funnel trap (at a drift fence next toa R. sylvatica breeding pond) was found consum- ing a dead gravid female wood frog captured in the same trap. Two other dead adults in the same trap had injuries indicating the crayfish probably had killed them as well. In April 1994, common grackles (Quiscalus quiscula), and a garter snake (Thamnophis sirtalis) were observed eating R. sylvatica tadpoles in shallow tire ruts. In 1995, the stomach of a 78-mm male bullfrog (R. catesbeiana) collected at the Cedar Lake pond on the night of peak chorusing by R. sylvatica was found to contain a partially digested P. crucifer and a freshly consumed, 45-mm male R. sylvatica. All of the above predators are well known to opportunistically prey upon various life-stages of amphibians. Late winter and early spring breeding amphibian species observed breeding in the same SNF ponds (and frequency of occurrence in 30 ponds) as R. sylvatica included Pseudacris crucifer (73%), P. feriarum (83%), Rana sphenocephala (57%), Ambystoma maculatum (76%), A. texanum (53%), and A. tigrinum (3%). Other amphibians noted in these ponds, or that bred in them later in the year, included B. americanus (13%), B. woodhousi (13%), Hyla chrysoscelis (50%), Hyla cinerea (3%), R. blairi (3%), R. catesbeiana (13%), R. clamitans (39%), A. opacum (57%), and Notophthalmus viridescens (27%). On 6 March 1996, a gravid female R. sylvatica and male R. sphenocephala were found in amplexus in a pond at Cave Creek. No R. sylvatica males were heard, and none were observed to oviposit on or after 6 March. Vol. 36 Art. 4 The interspecific pair was taken to the labora- tory where they remained in amplexus for over 60h. The female oviposited unfertilized ova after amplexus was ended. Amplexus between these two Rana spp. was previously reported by Nelson (1971). In the laboratory, R. sylvatica embryos hatched in 5 to 8 d, and the tadpoles trans- formed after 47-63 d (mean = 51 d). Numer- ous metamorphosing frogs were observed at Cave Creek on 19 May 1996 and 10 May 1997, indicating development takes 70-87 d in the wild. Discussion Distribution In Illinois, R. sylvatica occurs in forested areas in the state’s northeastern corner, east-central perimeter, south to and across the Shawnee Hills, and northwest into Monroe County (Redmer 1998; Smith 1961). There are old museum specimens from JoDaviess and Rock Island counties in extreme northwestern Illinois (Martof and Humphries 1959; Redmer 1998; Smith 1961). A literature record from central Illinois (Garman 1890) was accepted by Smith (1961) but this and another (Blanchard and Princen 1976) not documented by vouchers are questionable (Redmer 1998). Thurow (1994) has been criticized for intro- ducing wood frogs into western Illinois (McDonough County) well outside of the documented range (Redmer 1998; Szafoni et al. 1999). Previous to this study, R. sylvatica was known from few localities in southern Illinois (Redmer 1998). Cagle (1942) stated that this species was uncommon in Jackson and Union counties, and Smith (1961) showed only two records from southern Illinois (from Jackson and Monroe counties). There were later reports from localities in Pope County (Applegate and Zimbleman 1978; Thompson 1972). I docu- mented additional localities in Hardin, Jackson, Pope, Saline, and Union counties (Redmer, 1998; Fig. 2). The apparent distribution gap in the central SNF counties 1s discussed under “Terrestrial Habitat” (pp. 179-180). Habitat Breeding Ponds. In the SNF, R. sylvatica March 2002 Oviposited in a variety of pond types, including a significant number of human-made ones. Colonization of human-made aquatic habitats by amphibians (including R. sylvatica) is a commonly reported phenomenon and a variety of such pools or ponds are used (Burkett and Thompson 1994; Cortwright 1998; Stuart and Davidson, 1999) including tire ruts (Adams and Lacki 1993; Camp et al. 1990; Cortwright 1998). Frequent use of human-made aquatic breeding habitat by R. sylvatica in the SNF has several conservation implications. These habitats could benefit populations by provid- ing additional oviposition sites. In the Ozark National Forest (Arkansas), Trauth et al. (1989, 1995) reported that most R. sylvatica breeding sites were in human-made wildlife ponds. In the SNF, 10% of the ponds I located _ were mapped as USFS-inventoried wildlife ponds or waterholes. However, small, human-made aquatic habitats also pose some risks. for amphibian larvae. In shallow habitats, eggs or larvae may be vulnerable to insufficient hydroperiod, which could cause total mortality in some years. Although the eggs of R. sylvatica can withstand some desiccation caused by tempo- rary terrestrial standing (Forester and Lykens 1988), tadpoles cannot. One SNF tire-rut in which R. sylvatica spawned during every year of this study was never deeper than 10 cm when egg masses were in it, and it always dried before tadpoles metamorphosed. Small aquatic habitats (such as tire ruts) may have insufficient food resources for large cohorts of larvae and, thus, fitness, recruitment, or both could be reduced. Most tire-ruts in which R. sylvatica oviposited in the SNF were in clay- based roads or trails, and were largely devoid of aquatic macrophytes and other cover. Besides the potential of insufficient food, this could make larvae more vulnerable to preda- tors. Because tire-ruts are usually located on existing trails, they are also prone to distur- bance. In 1995 at Cave Creek, an off-road vehicle was driven through a tire-rut that contained 44 fresh R. sylvatica egg masses. Several egg masses were damaged or de- stroyed by tires that rolled over them, and most of the others were covered with silt churned up by the tires as they passed through Wood Frog in Southern IIlinois 179 the water. Other tire tracks 1n that pool indicated that there was periodic traffic through it in all years of the study. Despite the above factors, tadpoles metamorphosed and left this and one other large tire-rut pond at Cave Creek in 1996 and 1997 (the only years they were monitored during metamorphosis), so these must provide adequate aquatic habitat in some years. The frequency of ponds in closed-canopy sites (70%) vs. open sites (30%) in the SNF is similar to that reported from Michigan (Werner and Glennemeier 1999) where R. sylvatica tadpoles hold a competitive advan- tage over sympatric R. pipiens and B. americanus under closed canopies. Terrestrial Habitat. Although the range of R. sylvatica is mostly boreal, this species has been reported from a variety of habitats including tundra, subalpine woodlands, willow thickets, wet meadows, bogs, and coniferous, deciduous, and other temperate forests of various canopy species (Behler and King 1979; Conant and Collins 1998; Hammerson et al. 1986; Harding 1997; Martof 1970; Martof and Humphries 1959; Oldfield and Moriarty 1994: Russell and Bauer 1993; Trauth et al. 1995). The Shawnee Hills Natural Division 1s characterized by non-glaciated hills underlain by limestone or sandstone bedrock and covered with loess soils. Most of the division was heavily forested during presettlement times (Schwegman 1973). Uplands are dominated by oak-hickory forests while more mesic ravines contain mixed oak-beech-tulip poplar-maple forest, and the floodplain forests consist of these species and sycamore, ash, and box elder (Schwegman 1973; Voigt and Mohlenbrock 1964). The Ozark Natural Division is part of the Ozark Plateau. It is characterized by dry loess soils over limestone bedrock and forests of somewhat similar composition to the Shawnee Hills. The flora is characteritic of the Ozarks, but otherwise this division has much natural similarity to the Shawnee Natural Division (Schwegman 1973). The lack of records of R. sylvatica from the center of the Shawnee Hills Division and from the Cretaceous Hills Section of the Coastal Plain Natural Division 1s interesting. I 180 Illinois Natural History Survey Bulletin searched many human-made wildlife ponds in these areas but found no wood frogs. The forest habitat appeared suitable and egg masses of Ambystoma maculatum (a species that commonly breeds in the same ponds as R. sylvatica elsewhere in the SNF) were abundant in these ponds. Johnson County and the eastern Cretaceous Hills receive more precipi- tation than any other part of Illinois (Schwegman 1973), so it is unlikely that lack of moisture precludes R. sylvatica from these areas. However, while forests of the Creta- ceous Hills are similar in species composition to those of the Shawnee Hills Natural Divi- sion, the soils (composed of tertiary sands, gravels, and clays) differ (Schwegman 1973). Also, woodlands in the Cretaceous Hills are interspersed with dryer barrens communities that are characterized by floras more often associated with prairie outliers or woodlands of the southeatsern United States (Stritch 1987). The distributions of two plethodontid salamanders (two-lined salamander, Eurycea cirrigera; zigzag salamander, Plethodon dorsalis) have some similarities to that of R. sylvatica in the SNF. Eurycea cirrigera 1s common in rocky, wooded stream valleys in Saline, Hardin, Gallatin, and northern Pope counties, but in the Cretaceous Hills it is documented only from one disjunct population in a few ravines in southeast Pulaski County and seems to be absent from the hills of southern Pope County (Mierzwa 1989). Like R. sylvatica, P. dorsalis occurs in two appar- ently disjunct populations separated by the central Shawnee Hills (Smith 1961), although it is common in the Cretaceous Hills in Pope County (Redmer pers. obs.). It is possible that the currently known wood frog and zigzag salamander populations in the eastern and western SNF may not be disjunct at all, but simply remain undiscovered in the intervening area. Until recently, there were so few wood frog records in the SNF that despite the recent records, microdistribution remains poorly known. Additional surveys for tadpoles following the breeding season could find additional localities. I observed few R. sylvatica after the breeding season, and have little data on habitat use. My only observations after the breeding Vol. 36 Art. 4 season were nocturnal encounters (frogs on roads) and two individuals in shaded ravines. D. Corgiat (pers. comm.) conducted extensive field studies of the golden mouse (Ochrotomys nuttali) in the Cave Creek valley, and was familiar with R. sylvatica but never encoun- tered one after the breeding season. E. Ulaszek (pers. comm.) found individuals buried in deep, cool accumulations of leaves in shaded rocky ravines in the SNF during summer. Thompson (1972) found individuals on wooded hillsides around Little Lusk Creek (Pope County). In Arkansas, wood frogs occur ...[near the mouths of caves and bluff crev- ices| following the breeding season (Trauth et al. 1995:47). Adults from southern popula- tions have higher critical thermal maxima (CTM) then nonacclimated individuals from more northern populations but there is no difference in tolerance to low temperatures - (Lotshaw 1977; Manis and Claussen 1986). Southern wood frogs have CTM temperatures of 34.2°-36.8°C (Lotshaw 1977; Manis and Claussen 1986). Daily high temperatures in southern [linois often reach or exceed this range in summer. Either this species must have adaptations to survive hot southern [linois summers or perhaps soil temperature in closed-canopy woodlands remains cool enough to provide refuge then. Heatwole (1961) reported that R. sylvatica sought refuge under leaf litter as ground humidity decreased. Observations of nocturnal activity and presence of individuals in cool microhabitats indicate that southern wood frogs are active during cool periods or seek refuge in cool habitats during warm weather. Further study of the summer habitat and movements in southern Illinois (or elsewhere near the southern edge of its range) could add to the understanding of mean physiological longevity of this species (see “Demography” section pp. 181-186). Population Studies Breeding Phenology. Rana sylvatica usually is reported to have an explosive breeding season (Herreid and Kinney 1967; Howard 1980; Meeks and Nagel 1973; Seale 1982). It was explosive in all five years that I studied this species at Cave Creek and Cedar Lake. March 2002 Air temperatures at which breeding took place in the SNF varied, but generally were similar to those reported elsewhere (Herreid and Kinney 1967; Howard 1980; Meeks and Nagel 1973; Seale 1982; Wright and Wright 1949). Rana sylvatica 1s known to hibernate terrestri- ally near the soil surface (Bellis 1962; Heatwole 1961; Howard 1980; Licht 1991; Schmid 1982; Storey 1984; Storey and Storey 1987; Zweifel 1989). As an adaptation to the effects of freezing winter temperatures, this species is somewhat resistant to dehydration (Schmid 1965) and produces physiological cryoprotectants (Storey 1984; Storey and Storey 1987). At Cave Creek, breeding occurred with rising soil temperatures. In three of five years, breeding was interrupted by cold air temperatures but resumed immedi- ately when air temperatures re-warmed (Fig. 3). In these instances, soil re-warmed more slowly, and did not reach 9°C before breeding resumed (Fig. 4). While freeze tolerance may persist for some time after emergence from hibernation (Storey and Storey 1987), not all wood frogs returned to terrestrial dormancy after reaching the ponds. Some were observed resting on pond bottoms, while others were partially hidden under sunken leaves during cold nights in 1995 and 1996. It is likely that most adults already in the ponds when air temperatures dropped did not leave, and they resumed breeding after air and water tempera- tures rose sufficiently. Similar observations have been made elsewhere (Davis and Folkerts 1986; Meeks and Nagel 1973; Trauth et al. 1995). Post-emergent wood frogs can survive at least 10 days submerged in water under a frozen surface (Licht 1991). As would be expected of a species with a broad latitudinal range, and in which breeding is triggered by temperature, breeding of R. sylvatica is somewhat predictable along a south to north gradient (Guttman et al. 1991). Considering latitude and year-to-year variation in weather, the dates at which breeding occurred in the SNF were comparable to dates reported elsewhere in the southern portion of its range (Table 2). Demography. Two previous studies (Bastien and LeClair 1992; Sagor et al. 1998) used skeletochronology to estimate age in popula- Wood Frog in Southern Illinois 18] tions of R. sylvatica. Both examined samples of phalangeal cross-sections from populations in southern Quebec, Canada, and both detected LAGs. Bastien and LeClair (1992) estimated that LAG | was obliterated by endosteal remodeling in up to 29% of individuals. Sagor et al. (1998) estimated that LAG | was obliterated in 6% of individuals. In my sample, endosteal remodeling partially obscured LAG | in 11% and completely obliterated it in 4% of phalanges. Studies by Berven (1982a,b; 1988) and Berven and Gill (1983) documented geo- graphic variation in life history and demo- graphic traits of R. sylvatica. Growing season and elevation affect body size in this species (Berven 1982a,1982b, 1988; Berven and Gill 1983; Davis and Folkerts 1986; Martof and Humphries 1959; Sagor et al. 1998). Snout- vent lengths have been reported from a number of localities in the southern part of the range (Table 3). The only previous size data on Illinois specimens were given by Smith (1961), who found SVL to be greater in the southern part of the state than in the northeast corner. The largest SVL I observed in a Jackson County sample (a 57-mm female) was greater than the maxima of all of Smith’s samples from Illinois. Body size and age at maturity are environ- mentally plastic traits in some amphibians (Augert and Joly 1993; Berven 1981, 1982a; Scott 1994; Tilley 1973, 1980). Several studies have reported ages of individual R. sylvatica (Table 4). The proportions of age classes in southern I]linois are most similar to those reported from Quebec, Canada, by Bastien and LeClair (1992), who also esti- mated age from skeletochronology. They obtained mean ages of 2.8 yr (range = 2—4) for males, and 3.2 yr (range = 2—5) for females, compared with 2.6 and 3.0 yr in southern linois. In southern Illinois some males matured by the beginning of their second year and females by the beginning of their third year. Elsewhere, males have been reported to mature in 1-3 yr and females in 2-4 yr (Bellis 1962; Berven 1982a; Bastien and LeClair 1992, Sagor et al. 1998). Sexual differences in age at maturity have also been reported in other Rana as well (Ryser 1988, 1996; Shirose and Brooks 1995). 182 Illinois Natural History Survey Bulletin Vol. 36 Art. 4 Table 2. Earliest reported dates (d/m/y) of Rana sylvatica breeding activity in the southern part of the species’ range. Source Location Date (Approximate Latitude) Berven (1982) Lowland Maryland (38°N) 15/02/76 Mountain Virginia (38°N) 28/02/76 Camp et al. (1990) N Georgia (35°N) 12/02/87 Davis and Folkerts (1986) E Alabama (33°—34°N) 21/02/79 17/01/80 Guttman et al. (1991) EC Missouri (38°N) 26/02/87 Meeks and Nagel (1973) E Tennessee (36°N) 22/0247 1 Redmer (this study) Jackson Co., Illinois (37°N) 17/03/93 19/02/94 27/02/95 26/02/96 22/02/97 Trauth et al. (1989, 1995) N Arkansas (36°) 07/02/87 01/02/88 25/01/89 01/02/90 02/02/91 31/01/92 183 Wood Frog in Southern IIlinois March 2002 Table 3. Reported sizes (SVL) of Rana sylvatica from the southern part of the species’ range. Source Be rv en (1 98 2a ) Da vi s an d Fo lk er ts (1 98 6) G u t t m a n et al . (1 99 1) Ma rt of an d Hu mp hr ie s (1 95 9) M e e k s an d N a g e l (1 97 3) M i n t o n (1 97 2) R e d m e r (t hi s st ud y) Sm it h (1 96 1) Tr au th et al . (1 99 5) Location Maryland (lowland) Virginia (mountain) Alabama Missouri Georgia & Carolinas Tennessee N Indiana S Indiana Jackson Co., linois SW Illinois EC Illinois NE Illinois Arkansas Maximum (mm) 67 75 2 62 .5 > 50.8 54.4 49.3 104 M e a n ( m m ) 41 .7 Ses 50.0 Sule 54.8 ay 38.4 43.8 46 .1 ake Range (mm) 42-62 55-63 35-42 43-54 43 -5 0 46-65. 1 Mean (mm) 47 .7 64.4 60.0 60.3 66.8 69 43 .8 2: 0 O 2 2 65.6 Range (mm) 59.9-76.7 184 Ilinois Natural History Survey Bulletin Vol. 36 Art. 4 Table 4. Age structure (percent frequency) in populations of Rana sylvatica. Source Location Age Males Females Berven (1982a)* Maryland l 86.0 1.1 (low elevation) 2 14.0 98.9 3 0 0 Virginia 0 0 (high elevation) 2 13.6 0 4 Goa), 44.2 4 aes 55.8 Bastien and LeClair (1992) Quebec l 0 0 2 Seal 8.7 2 53.6 69.6 4 14.3 13.0 2 0 8.7 Redmer (this study) S. Illinois | 4.2 0 gi 47.5 26.1 : BAIS 50.7 4 12.5 2A > 0 tS Sagor et al. (1998) Quebec l 4.1 0 2 49.0 45.5 a 40.8 33.8 4 6.1 2 *A ges at maturity. March 2002 An alternative to expressing mean longevity in years is mean physiological longevity (MPL = mean age in years multi- plied by the average number of frost-free days in the region). Bastien and LeClair (1992) commented on possible variation in MPL of different wood frog populations. From theirs and other published data (Berven 1982a), they calculated MPL for three populations (Quebec, Maryland, and Virginia). Assuming 195 frost- free days for southeastern Jackson County (Schwegman 1973), the MPL of wood frogs is much greater in Jackson County than those calculated for other populations (Table 5) by Bastien and LeClair (1992). They speculated that MPL was relatively constant in females but geographically more variable in males, and that earlier maturity curtailed the potential life span of males. Considering the greater MPL of Pomona wood frogs (both males and females), the former does not appear to be the case in southern Illinois. Local environmental factors (1.e., larval density, size and fitness at metamorphosis) may contribute to consider- able plasticity in growth and longevity, as well as the timing of and size at sexual maturity in amphibians (Berven 1988, 1990; Berven and Gill 1983; Scott 1994; Tilley 1973, 1980). Numerous studies of factors influencing mate selection in anurans have been conducted (Berven 1981; Fellers 1979; Halliday 1983; Howard 1978, 1980, 1983; Howard and Palmer 1995; Howard et al. 1994; Howard and Kluge 1985; Lykens and Forester 1987; Ryan Wood Frog in Southern Illinois 185 1980). In some species, large females mate more frequently with large males (Duellman and Trueb 1986; Halliday 1983; Howard and Kluge 1985; Ryan 1980). Because large males often are thought to be the oldest males and have a history of reproductive success, they might advertise fitness (through physical characteristics of vocalization or other cues) and be more attractive to females (Lykens and Forester 1987; Ryan 1980). However, despite previous assumptions that females probably choose mates, most studies have indicated that this occurs in only a minority of anurans (Halliday 1983). The lack of correlations between R. sylvatica mate SVL and mate age in the SNF suggests that mate selection is not strongly related to either variable. Previous studies of mated R. sylvatica (Berven 1981; Howard 1980; Howard and Kluge 1985) found non- random pairing in which larger males had a reproductive advantage over smaller ones because once in amplexus larger size and limb length allowed males to amplex longer and more easily defend their mates from chal- lenges by smaller males. To date, there is no evidence of mate choice by female wood frogs. In the SNF, older and larger adults were statistically no more likely to mate than younger and smaller ones. Berven (1981) found no correlations (r? = 0.05 and 0.08) between male and female sizes in mated pairs in two Maryland ponds, and a low positive correlation (1° = 0.16) in a third pond. He Table 5. Comparison of mean age and mean physiological longevity of R. sylvatica from Quebec (Bastien and LeClair 1992), Maryland (Berven 1982a), Virginia (Berven 1982a), and the Shawnee National Forest (this study). Quebec Maryland Parameter M F M i Mean age 2.8 Sy hd 2.4 Frost-free days 130 130 Ly Lay Physiological longevity (d) 364 416 290 42] Virginia SNF M F M F 3.6 3.8 2.6 ot 121 121 195 195 438 458 507 585 186 Illinois Natural History Survey Bulletin suggested that male-male competition and mate choice by males occur in R. sylvatica. I and others (Berven 1981; Howard 1980; Phillips and Wade 1990) have observed competition for females by males that at- tempted to dislodge each other from amplexed females. Several males often attempt to amplex the same female. Amplexus by multiple males sometimes leads to female mortality (Howard 1980; Phillips and Wade 1990), although I did not observe this in the SNF. Smith-Gill and Berven (1980) found that larger (probably older) males produced more sperm and thus have greater reproductive potential than smaller males, so offspring of females that mate with larger males should be at a selective advantage. Rana sylvatica usually is described as an explosive synchro- nously breeding species with males and females arriving at breeding ponds simulta- neously and completing oviposition in a few days (Berven 1981; Howard 1980; Phillips and Wade 1990; Trauth et al. 1989, 1995). This is true in southern Illinois. Clutch Size. Studies of anuran fecundity generally have shown a negative correlation Vol. 36 Art. 4 between clutch size and ovum diameter and a positive correlation between female size and clutch size (Berven 1988; Duellman and Trueb 1986; Salthe and Duellman 1973; Salthe and Mecham 1974). The positive correlation between body size and age implies a positive correlation between clutch size and age as well (Duellman and Trueb 1986). However, in some species considerable reproductive variation among populations, or among females in the same populations, has been reported (Berven 1982b, 1988; Crump 1984; Dushane and Hutchinson 1944; Kaplan 1980; Pettus and Angleton 1967). Clutch sizes of R. sylvatica in southern Illinois are within the ranges reported else- where in the southern part of the range (Table 6). Single eggs were found in the oviducts of five spawned females, so it is likely that nearly all oviductal ova were oviposited and yolked ovarian or oviductal ovum compliments are validly used as measures of fecundity. Some older studies (Minton 1972; Mount 1975; Pope 1944; Smith 1961; Wright and Wright 1949) have reported a general range of 1,000 to 3,000 eggs per clutch. More recent studies in the southern part of the range have consis- Table 6. Reported clutch sizes and ovum diameters in Rana sylvatica from the southern part of its range. Source Location Berven (1982a) Maryland (low) Virginia (mountain) Camp et al. (1990) Georgia Davis & Folkerts (1986) Alabama Meeks & Nagel (1973) Tennessee Redmer (this study) Jackson Co., Illinois Trauth et al. (1989) Arkansas 'Ranges are + standard deviation from mean. Clutch Size Ovum Size (mm) Mean Range Mean Range 642 642 + 200! 1.8 1.83 + 0.29! 920 920 + 217! 20 2.28 + 0.13! 553 295-706 2.8 2.2-3.3 496 350-709 9 — 465 386-543 250 2.1-2.4 Sis 304-874 ke 1.95-2.75 883 510-1433 28 2.2—3.3 March 2002 tently reported smaller clutches (range = 295— 1,433; Table 6). Adult R. sylvatica are well known to have physiological adaptations to cold (Layne and Lee 1987; Lotshaw 1977; Storey 1984; Storey and Storey 1987). In addition, thick, insulative egg envelopes, large ova, and communal oviposition have been reported as adaptations that protect embryos from low temperatures that occur suddenly during the breeding season (Howard 1980; Seale 1982; Waldman 1982; Waldman and Ryan 1983). Larger eggs are more resistant to desiccation caused by terrestrial stranding (Forester and Lykens 1988). Ovum diameters (mean = 2.5 mm, range = 1.95—2.75) in the SNF are within the range of diameters reported from other southern populations (Table 6). Because Oviposition in the SNF usually took place in late February when there was still a risk of cold weather that could freeze ponds, large ova may be a necessary adaptation to cold weather there as well. . In the SNF, wood frog clutch and ovum sizes collected in 1995 and 1996 were nega- tively correlated. This follows a pattern reported previously from other amphibian species (Kaplan 1979, 1980; Kaplan and Salthe 1979; Salthe and Duellman 1973). Numerous studies of reproductive investment in amphibians (and other organisms) have examined the trade-off between number and size of offspring (the model of “optimal parental investment” [Smith and Fretwell 1974]). There is considerable evidence that environmental factors greatly influence these traits (Berven 1988; Crump 1981, 1984; Crump and Kaplan 1979; Kaplan and King 1997; Kuramoto 1978). In R. sylvatica, environmental factors affect traits such as female age and size, which may in turn affect clutch and ovum size (Berven 1988). How- ever, in 1995 and 1996, the SVL of SNF female R. sylvatica was strongly correlated with clutch size, but female age was not (Fig. 11). While the reasons for this are beyond the scope of this study, this is interesting because in my sample female age and SVL were positively correlated. Other Comments. Age and size structure and reproductive characteristics of adult amphib- Wood Frog in Southern Illinois 187 ians may be influenced strongly by variation in larval survival and recruitment (Berven 1990; Miaud et al. 2000; Semlitsch et al. 1996). In amphibians, ovum size, competition, growth rate, and mass at metamorphosis are known to contribute to larval fitness and recruitment of metamorphs (Berven and Gill 1983; Berven 1988, 1990; Parris and Semlitsch 1998; Semlitsch and Pechmann 1988; Smith 1987). Significant geographic variation in life history and reproductive traits of R. sylvatica has profound effects on local population dynamics (Berven 1982a,b; Berven 1988; Berven and Gill 1983). Future regional studies or monitor- ing efforts designed to include this and other wide-ranging amphibians should continue to investigate or account for how these factors regulate adult populations. Skeletochronology has been shown to be an effective method for obtaining age estimates for many species of amphibians. However, when used in single years, this technique reveals nothing about population trends. It should be used over several years to detect fluctuations in age structure among years (Friedl and Klump 1997). Regional studies of amphibian popula- tions should combine methods (such as skeletochronology) for determining demogra- phy of adult populations with studies of reproductive traits and relationships between larval and adult life stages. Such comprehen- sive studies may be more useful for tracking regional trends in amphibian populations, and could potentially help to identify reasons contributing to regional rarity or declines of some species. Summary The wood frog (Rana sylvatica), an uncom- mon species in Illinois, was studied in the Shawnee National Forest in the extreme southern part of the state. Frogs were docu- mented from 20 localities in 5 counties (Jackson, Hardin, Pope, Saline, and Union) in the Shawnee Hills and Ozark Natural Divi- sions. Eggs or tadpoles were observed in 30 aquatic breeding sites, including ephemeral ponds and depressions, semi-permanent ponds, human-made ponds, roadside ditches, and ruts (caused by vehicles) in dirt trails. Surrounding 188 [linois Natural History Survey Bulletin habitat included floodplain and upland deciduous, coniferous, and mixed deciduous/ coniferous forests. 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R « ee : LiQpte f ce oe > Aer « as + on Pe te COP RE GS Pest MR is, * c es. pa <5 i “_e sa Dag es HE Be? be ‘ a y A Rte Fe Reh: 7a wert Wo Ned the Ree ee id vodeie A ae Tar ee b. i Rex: : 3 a ee bee Ae o tia, Tie hy es 4 ae *. igs eee ia Z ae Xe ae e ri : mie ae r et * AY DEPARTMENT OF oh A a om " so $ hd Oe a ay * re Si e Pag + \: ™ ’ bas « ‘ 7 : i) Illinois Natural History Survey Natural Resources Building 607 Hast Peabody: Drives", etna ie a Oa Champaign, Hingis G1820. (U2 ak ae ee 317-33326880 us hoses en ne eve er eee & ; . h ai O “i PIT Ae ; Gy Sat avd inad i ; AS SN " % : otk é ILLINOIS ic a are a ble MENT GIR gi, heat A Division of the Illinois Department of Natural Resources — z a + NATURAL | : Pe MEAT Oe Ne RESOURCES y=) g Aa mS ra oa Ag - i, et % f a i ¢ “4 eee: on x