F:\ALCES\Vol_38\Pagemaker\3815. ALCES VOL. 38, 2002 BOWYER ET AL. - MORPHOLOGY OF MOOSE ANTLERS 155 GEOGRAPHICAL VARIATION IN ANTLER MORPHOLOGY OF ALASKAN MOOSE: PUTATIVE EFFECTS OF HABITAT AND GENETICS R. Terry Bowyer1, Kelley M. Stewart1, Becky M. Pierce1,2, Kris J. Hundertmark1,3, and William C. Gasaway4 1Institute of Arctic Biology, and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA, e-mail ffrtb@uaf.edu; 2California Department of Fish and Game, 407 West Line Street, Bishop, CA 93514, USA; 3Alaska Department of Fish and Game, 43961 Kalifornsky Beach Road, Soldotna, AK 99669, USA; 4Alaska Department of Fish and Game (Deceased) ABSTRACT: We assessed antler size of Alaskan moose (Alces alces gigas) with respect to the geographic region and dominant vegetation community (taiga or tundra) from which they were harvested from 1968 to 1983. Our retrospective analysis indicated that moose from the Copper River Delta and Alaska Peninsula possessed the largest antlers, whereas those from southeast Alaska, USA, had the smallest antlers. Delta flood plains of the Copper River offer a rich food supply for moose, and browse on the Alaska Peninsula also is plentiful; both areas have mild maritime climates and longer growing seasons than tundra and taiga habitats in interior Alaska—large antlers in those moose populations likely were the result of superior nutrition. After controlling for age, antlers of moose from tundra communities were significantly larger than those inhabiting taiga. Willows (Salix spp.), which are an important food for moose, dominate braided rivers and associated riparian areas in tundra habitat, and provide a high-quality and stable food supply over time. Fire and subsequent successional changes dominate taiga landscapes, which results in a variable food supply that is sometimes low in quality and quantity. Again, forage abundance and quality likely play important roles in determining antler size for populations of Alaskan moose inhabiting those plant communities. Nonetheless, antlers of A. a. gigas from taiga regions in Alaska, USA, were larger than those of A. a. andersoni from similar habitat in northeastern Minnesota, USA, and Saskatch- ewan, Canada. In addition, moose from tundra habitat on the Seward Peninsula, Alaska, which have colonized that area within the last ~30 years from the boreal forest, possessed antlers intermediate in size between moose inhabiting taiga and tundra. Moreover, moose from forested areas of southeast Alaska, which have a unique mitochrondial DNA haplotype from other subspecies of moose, also had comparatively smaller antlers than other moose in Alaska. Those outcomes indicated that differences in antler size likely have a genetic in addition to a nutritional basis. We hypothesize that differences in antler size of Alaskan moose in relation to habitat may have genetic as well as nutritional underpinnings related to openness of habitat, but more research is needed. Finally, our results on antler morphology, in concert with information on pelage coloration and recent data on genetics, do not support hypotheses concerning a double migration, or eastern and western races of moose, forwarded to explain morphological variation in moose inhabiting the New World. Likewise, we reject the hypothesis that ecotypical differences are primarily responsible for morphological variation in subspecies of moose inhabiting North America. ALCES VOL. 38: 155-165 (2002) Key words: age, Alaskan moose, Alces alces, antlers, ecotypes, genetics, habitat, morphology, nutrition, size, taiga, tundra MORPHOLOGY OF MOOSE ANTLERS - BOWYER ET AL. ALCES VOL. 38, 2002 156 Size and conformation of cervid antlers are influenced by genetics, age, and nutri- tion (Goss 1983). How those factors inter- act to determine antler size and shape, and whether antler morphology characterizes populations or subspecies, however, contin- ues to be debated (Bubenik 1983, Gasaway et al. 1987). For instance, Geist (1998) proposed that that there were eastern and western races of moose (Alces alces). Other geographical variation in morphology for subspecies of this large cervid was thought to be nutritional, and such differ- ences were best regarded as ecotypes (Geist 1998). Bubenik (1998), however, hypoth- esized that smaller-antlered moose inhabit- ing forested regions (taiga moose) were genetically distinct from larger-antlered moose living in more open areas (tundra moose), and that such distinctions were worldwide. He proposed a double-migra- tion hypothesis for moose entering the New World to explain extant morphological vari- ation (Bubenik 1998). Peterson (1955) delineated 4 subspe- cies of moose in North America based on skull morphology, and Bowyer et al. (1991) described pelage and behavioral differences among subspecies. Hundertmark et al. (2003) confirmed those subspecific differ- ences using mitochondrial DNA (mtDNA). Moreover, Gasaway et al. (1987) docu- mented clear differences in antler size among subspecies of moose, allowing the possibility of genetic underpinnings of that variability. Whether such differences are the result of genetics, nutrition, or both factors, however, remain unresolved. Moose are a useful species to evaluate effects of nutrition and genetics on antler morphology because antlers of this large cervid have been well studied (Bubenik et al. 1978, Bubenik 1998), including relations with body mass (Sæther and Haagenrud 1985; Solberg and Sæther 1993, 1994; Stewart et al. 2000), age (Sæther and Haagenrud 1985, Stewart et al. 2000, Bowyer et al. 2001), mineral composition (Moen and Pastor 1998), and theoretical interactions of population density, harvest, and genetics (Hundertmark et al. 1998). In addition, differences in morphology among subspecies have been confirmed with ge- netic analyses (Hundertmark et al. 2002a, 2002b, 2003). Finally, data on age and antler size are available from Alaska, for moose (A. a. gigas) inhabiting taiga and tundra habitats, and from northeastern Min- nesota, USA, and Saskatchewan, Canada, for another subspecies (A. a. andersoni) living in taiga (Gasaway et al. 1987). We hypothesized that if nutrition was influential in determining antler size, we would find the largest-antlered Alaskan moose (A. a. gigas) living in areas where forage was abundant, as well as differences in moose living in tundra compared with those from taiga habitat. Conversely, if genetics were the overriding determinant of antler size, we postulated that the largest difference would be between A. a. gigas from taiga and A. a. andersoni from that same habitat type. We recognize that these hypotheses are not mutually exclusive, but contend that, in concert with other data on morphology and genetics, we could test ideas concerning the evolution and mor- phology of subspecies of moose in North America. STUDY AREA We subset our data by game manage- ment units (GMUs) established by the Alaska Department of Fish and Game, and assigned a habitat type based on the pre- dominant vegetation community in each unit (Fig. 1). Taiga extended from the eastern boarder with Canada westward across the interior; moose harvested in that habitat were from GMUs 12-15, 20-22, and 24. Moose from southeast Alaska inhabited coastal coniferous forests and were har- ALCES VOL. 38, 2002 BOWYER ET AL. - MORPHOLOGY OF MOOSE ANTLERS 157 vested from GMU 1. Moose killed in the remaining GMUs, which were classified as tundra, included 5, 7, 11, 16-17, 19, 23, and 25-26. We further subdivided our data regionally because habitat in the Copper River Delta (GMU 6) and Alaska Peninsula (GMU 9) differed markedly from other areas. Likewise, we separated data from the Seward Peninsula (GMU 22) because moose had recently colonized that tundra area from nearby taiga. METHODS Antler measurements used in our retro- spective analysis were collected originally from hunter-harvested moose during 1968- 83 across game management units in Alaska (Gasaway et al. 1987). Those measure- ments were made mostly by employees of the Alaska Department of Fish and Game, who were experienced in gathering such data. Data on antler spread, palm length and width, beam circumference, and number of antler tines were obtained from a subset of data that included associated information on age (n = 1,501). Methods used to measure antlers were provided by Gasaway et al. (1987), Stewart et al. (2000), and Bowyer et al. (2001). Age of moose was determined by counts of tooth cementum annuli (Sergeant and Pimlott 1959, Gasaway et al. 1978). We used principal component analysis (McGarigal et al. 2000) to obtain an overall index to antler size. Principal component 1 (PC1) explained 73% of the variation in m e a s u r e m e n t s o f m o o s e a n t l e r s ; eigenvectors associated with PC1 had simi- lar loadings (0.30-0.35) for the various ant- ler characteristics (Stewart et al. 2000, Bowyer et al. 2001). PC1 exhibited pat- terns of rapid increase with age from 1 to 6 Fig. 1. Map of game management units (GMUs) and vegetation types in Alaska, USA, used in our analysis of antler size of moose (adapted from Albert et al. 2001). MORPHOLOGY OF MOOSE ANTLERS - BOWYER ET AL. ALCES VOL. 38, 2002 160 (Peek 1974, Weixelman et al. 1998). Moose populations throughout much of Alaska are held at low density by large mammalian carnivores (Van Ballenberghe 1987, Gasaway et al. 1992, Van Ballenberghe a n d B a l l a r d 1 9 9 4 , B a l l a r d a n d V a n Ballenberghe 1998, Bowyer et al. 1998). Consequently, biases from density-depend- ent effects on physical condition of cervids (sensu McCullough 1979, Bowyer et al. 1 9 9 9 ) a n d , u l t i m a t e l y , a n t l e r s i z e (McCullough 1982, Stewart et al. 2000) would not be expected. Declines in body and antler size, which are positively corre- lated in cervids (Clutton-Brock 1982, McCullough 1982, Bowyer 1986, Stewart et al. 2000), would be expected with increas- ing population density relative to carrying capacity (K). Those well-documented rela- tionships offer strong evidence against the ecotype hypothesis of Geist (1998). If morphological differences among subspe- cies were mostly the result of nutrition, then the magnitude of morphological variation observed among subspecies should be present in a population undergoing a rapid change in population size. Although nutri- tional stunting can occur among cervids, sufficiently large changes in morphology, including differences in pelage markings, within a population undergoing even enor- mous changes in numbers have not been described (Klein 1968, McCullough 1979). Indeed, we are unaware of a nutritional mechanism that would cause the marked differences in pelage color and behavior described for subspecies of moose in North America (Bowyer et al. 1991). The pres- ence of a white morph in moose that is not an albino, and white females giving birth to reddish-brown young (Franzmann 1981, Armstrong and Brown 1986), strongly sup- port the hypothesis of a genetic component to differences in pelage coloration that can- not be attributed to ecotypes. That same interpretation likely holds for subspecific differences in antlers of moose. Over the past ~30 years, moose have colonized the Seward Peninsula, which is mostly tundra, from nearby taiga habitat. Those moose possess antlers that are inter- mediate in size between moose inhabiting tundra and taiga habitats (Fig. 2). Although we believe that the intermediate antler size of moose on the Seward Peninsula likely has nutritional underpinnings, we cannot completely rule out genetics as a cause for that difference because the response in size was neither immediate nor as large as those in other tundra regions of the state (Fig. 2). Subspecies of cervids inhabiting more open terrain tend to be more social, and have larger body and antler sizes, and more con- spicuously marked pelage than those from densely vegetated forests (Cowan 1936, Peek et al. 1974, Hirth 1977, Geist 1987, Bowyer et al. 1991, Molvar and Bowyer 1994). More research is needed to deter- mine if antler size was under selection re- lated to more open habitat for moose living on the Seward Peninsula, as well as for moose inhabiting other open landscapes. Antler conformation for Alaskan moose (A. a. gigas) differs from other subspecies in North America in their tendency to ex- hibit a “butterfly” configuration of main and brow palms (Gasaway et al. 1987, Bowyer et al. 2001). Bubenik (1983) further pro- posed that in forest-dwelling subspecies (i.e., A. a. andersoni, A. a. shirasi, and A. a. americana) the orientation of palms curved upward to form a dish, whereas in moose from the tundra (e.g., A. a. gigas) the palms were comparatively flat. Gasaway et al. (1987), however, rejected that hypoth- esis by comparing ratios of antler charac- teristics from various subspecies of moose— few differences existed in the overall shape of antlers. Moose from wooded habitats also were postulated to have a narrower antler spread than those living in tundra (Bubenik et al. 1978, Bubenik 1983). ALCES VOL. 38, 2002 BOWYER ET AL. - MORPHOLOGY OF MOOSE ANTLERS 161 Gasaway et al. (1987) concluded that if forest-dwelling moose have evolved antlers that are adapted to dense woodlands, they have done so by altering size rather than shape of antlers—a supposition supported by our results (Figs. 2 and 3). Moreover, we hypothesize that differences in antler size between Alaskan moose inhabiting taiga and moose from forested areas of north- eastern Minnesota are mostly genetic. Moose from both of those areas are sub- jected to predation (Peek et al. 1976, Gasaway et al. 1992); consequently, nutri- tion is not likely the cause of that disparate difference in antler spread (Fig. 3). We further hypothesize that differences be- tween the size of antlers of A. a. andersoni from northeastern Minnesota and Saskatch- ewan may be nutritional (Fig. 3). Such differences would be expected because of more intense predation in the Minnesota population (Peek et al. 1976), and the con- comitant increase in physical condition of those moose from being farther away from K than moose from Saskatchewan (sensu McCullough 1979, Bowyer et al. 1999). The hypothesis of Bubenik (1998) that taiga and tundra moose are genetically dis- tinct also can be rejected, as can the hy- pothesis of Geist (1998) for the existence of eastern and western races of moose. Moose subspecies inhabiting tundra in the Russian Far East (A. a. buturilini) possess a differ- ent chromosome number (2n = 68) and are not closely related to A. a. gigas (2n = 70) from tundra in Alaska (Hundertmark et al. 2002b). Moreover, Alaskan moose, which Geist (1998) places with moose from the Russian Far East, have the same funda- mental chromosome number as other sub- species of moose in North America, and are more closely related to other subspecies in the New World than subspecies from Eura- sia (Hundertmark et al. 2002b). Similar morphology of A. a. gigas and A. a. buturilini likely is a result of convergent evolution resulting from living in more open habitats than other subspecies of moose (Hundertmark et al. 2002b). Differences in antler size between A. a gigas from taiga in Alaska, and A. a. andersoni from that same habitat in Min- nesota and Saskatchewan (Fig. 3), impli- cate genetics as the cause of such geo- graphic variation. Moreover, moose from forested areas of southeast Alaska recently have been identified as possessing a unique haplotype of mtDNA lacking in other sub- species of moose (Hundertmark et al. 2003). Although we caution that our sample size was small (Fig. 2), males from southeast Alaska also had much smaller antlers than moose from taiga habitat in other regions of Alaska, further indicating that selection operating in isolated populations affects antler size. Consequently, differences in antler size among populations of moose are not completely a result of the type of habitat they occupy. In addition, moose from south- east Alaska may be a unique subspecies. We believe, however, that morphological data presented herein, and genetic data from Hundertmark et al. (2002a, 2002b, 2003) are not yet sufficient to draw that conclusion—more research is needed. Neither the hypothesis of Geist (1998) nor Bubenik (1998) was supported by our study of antler size in moose. Clearly, both nutrition and genetics are involved in the size and shape of antlers (Williams et al. 1994), but not in the manner proposed by either Geist (1998) or Bubenik (1998). More research is required to understand precisely how nutritional and genetic factors interact, and how they might be related to founder effects during dispersal into new habitat, and how natural selection operates on the size of moose inhabiting more open habitat compared with those living in closed boreal forest. We proposed that studies of DNA microsatellites, which would allow greater resolution of genetic differences among MORPHOLOGY OF MOOSE ANTLERS - BOWYER ET AL. ALCES VOL. 38, 2002 162 populations (Broders et al. 1999), would be a fruitful next step in resolving this impor- tant question. ACKNOWLEDGEMENTS We are indebted to those individuals who originally made measurements of moose antlers, and who are properly acknowl- edged in Gasaway et al. (1987). The Alaska Department of Fish and Game, and the Institute of Arctic Biology at the University of Alaska Fairbanks funded this research. 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