Open access journal: http://periodicos.uefs.br/ojs/index.php/sociobiology ISSN: 0361-6525 DOI: 10.13102/sociobiology.v68i4.7430Sociobiology 68(4): e7430 (December, 2021) Introduction Ants are among the most ubiquitous organisms in terrestrial habitats, being highly diverse and comprising a significant part of the terrestrial arthropods’ biomass (Holldöbler & Wilson, 1990; Lach et al., 2010). Ants are terrestrial and cursorial organisms adapted for living on different solid surfaces, from the soil underground to the canopies of tropical rain forests. Although water is present in 70% of the planet, interactions with water represent a formidable obstacle for such terrestrial organisms. Successfully overcoming this obstacle can be essential to determine their persistence in some specific habitats. Among these habitats are those constantly flooded, such as the intertidal zone and seasonally flooded areas, like floodplains and riparian forests. While some species avoid the water by constraining their foraging activities to drier habitats or climbing taller objects (Adis, 1997), others developed ways to overcome this obstacle by swimming. Abstract Ants are among the most abundant organisms on Earth, being adapted for living on different solid surfaces. However, in some habitats, like riparian forests and flooded plains, water can be a constant obstacle, and overcoming this obstacle can be essential to determine the persistence of ants in such habitats. While most ant species avoid the water during a flood by foraging at higher elevations or climbing on trees, a few species developed ways to overcome this obstacle by swimming. Here, we report, for the first time, ants of the species Linepthema micans (Forel 1908) performing rafts. We observed 14 rafts in three consecutive days at approximately 1400 meters a.s.l. in Serra do Cipó, Brazil. Notably, this is the first record of ant rafting in tropical mountaintop grasslands, extreme habitats with shallow and sandy soils, where small temporary water pools are extremely common in the wet season. Sociobiology An international journal on social insects Geraldo W. Fernandes, Flávio S. de Castro, Flávio Camarota, Jessica C Blum, Renata Maia Article History Edited by Evandro Nascimento Silva, UEFS, Brazil Received 24 September 2021 Initial acceptance 27 September 2021 Final acceptance 06 October 2021 Publication date 19 November 2021 Keywords Campo rupestre, Linepthema micans, Mountaintop grassland, Rupestrian grassland, Serra do Cipó. Corresponding author Flávio Camarota Universidade Federal de Minas Gerais CEP: 31270-901, Belo Horizonte, Brasil. E-Mail: camarotaflavio@gmail.com While ant swimming is not usual, it has been known for over a century that ants have some swimming ability (Field, 1903; Wheeler, 1910). The swimming behavior occurs in multiple ant genera distributed in different clades, and there is often considerable variation across different ant groups and even among species within genera (Yanoviak & Frederick, 2014). Usually, larger ant species, like Pachycondyla spp. and Odontomachus bauri, are efficient swimmers, using their long legs to provide propulsion (Yanoviak & Frederick, 2014). Perhaps, the most extreme cases involve ant species inhabiting mangroves (Nielsen, 1997; Robson, 2010). The Australian ant Polyhachis sokolova can have their colonies submerged for 3.5 hours during a normal tide cycle and covered by two meters of water under extreme tides (Shuetrim, 2001). Another interesting adaptation is related to ant species associated with pitcher plants and other epiphytes, such as Camponotus schmitzi ants that live in symbiosis with the pitcher plant Nepenthes bicalcarata, Universidade Federal de Minas Gerais, Departamento de Genética, Ecologia e Evolução, Belo Horizonte, Brazil SHORt NOtE Ant Rafting in an Extreme Ecosystem Geraldo W. Fernandes, Flávio S. de Castro, Flávio Camarota, Jessica C Blum, Renata Maia – Ant rafting in an extreme ecosystem2 in Bornean rain forests (Clarke & Kitching, 1995; Merbach et al., 2007). This interaction is unique because the ants actively forage on the water to prey on the insects captured by the pitcher plant (Bohn et al., 2012). In the ground of tropical forests, some large-bodied ants, such as Ectatomma ruidum and Acromyrmex lundii, can walk to overcome small pools of water (Adis, 1982; Yanoviak & Frederick, 2014). While most of the mentioned taxa are from tropical habitats, some cases were also reported for temperate forest ants, including the genera Camponotus and Formica (DuBois & Jander, 1985; Yanoviak & Frederick, 2014). Some ant species, usually small-bodied, can overcome the lack of morphological adaptations for swimming by linking their body together in a kind of self-assemblage, the ant rafting, consisting of floating conglomerations of ants (Purcell et al., 2014; Avril et al., 2016). Rafting is extremely important in habitats where colonies are often exposed to floods, and these floating masses can persist from some hours to even a few weeks (Adams et al., 2011). The rafts comprise interconnected workers connected mainly by their tarsi and curling their appendages, forming Velcro-like connections in the structure (Adams et al., 2011). The rafting behavior gained much attention since it is used by one of the most prominent invasive ant species, Solenopsis invicta, which can form rafts of thousands of individuals (Mlot et al., 2011; 2012). The native habitats of S. invicta are mostly comprised of seasonally flooded plains, like the Brazilian Pantanal. This adaptation could have been extremely important in defining S. invicta as one of the numerically dominant ant species (Adams et al., 2011). While rafting appears to be a formidable adaptation for those species living in constantly flooding habitats, only a few species have been recorded performing rafting. One common feature is that they were all found in habitats prone to inundation. On three consecutive days in April 2021, we observed the formation of 14 rafts at a small first order wash at approximately 1400 meters a.s.l. in Serra do Cipó, Brazil (19•10’19,7” S 043• 60’ 49,2” W) (Fig 1). On the first day, nine rafts were observed. These varied from 3 to 10 cm in diameter and were composed of a single ant species, Linepithema micans (Fig 2 a, b). The form of the rafts was mostly a circle, with a very large number of ants. Only workers were observed in the rafting. Curiously, ants swam actively towards the rafting, even against the wash’s weak but constant water flow. Yet another interesting behavior was the jumping of many individuals into the water from some grass stems. This jumping behavior was observed in the morning (9:00 – 11:00) and lasted for ca. 15 minutes. On the following day, six rafts were observed; they had similar sizes. After the raft observations, we collected ant individuals to assure their species-level identification. The ants were stored in vials with 70% ethanol and brought to the laboratory. The ant identification was performed by Flávio Siqueira de Castro, by comparisons with the extensive collection of Formicidae from campo rupestre of the Laboratory of Insect Ecology at the Universidade Federal de Minas Gerais, Brazil. All ants collected are held at this referred collection of Formicidae, which consists mostly of specimens from the PELD/CRSC Project (Silveira et al., 2019). Here, we show, for the first time, ants of the species Linepthema micans (Forel, 1908) performing rafts. While this is not the first record for rafting on the genus Linepithema (see Nondillo et al., 2013), it is the first record of such complex social behavior in a tropical mountaintop grassland. L. micans is very common in the study area (Costa et al., 2016; Monteiro et al., 2020; Calazans et al., 2020; Castro et al., 2020) and generally exhibit high recruitment rates with many individuals Fig 1. Ant raft in a small water pool in Serra do Cipó, Minas Gerais, Brazil. Sociobiology 68(4): e7430 (December, 2021) 3 foraging on the ground (Nondillo et al., 2013). The formation of rafts by L. micans has purposes similar to other species with this behavior. That essentially means the ants gather a significant part of the colony to find drier places to forage. The soils in the harsh and nutritionally poor habitats at high elevation in the Espinhaço mountains are mostly shallow and sandy. During the wet season, the formation of small temporary water pools is extremely common (see reviews in Fernandes, 2016). Thus, while rafting is relatively uncommon among ant species, our observation suggests that this behavior may be more widespread than previously thought. Although no specific swimming adaptation has been reported for this species, this is the first record of such a phenomenon. The region where the observations were taken is known for its high precipitation and rapid flood events due to the orographic rains and strong winds. During the winter, the moisture-laden clouds may bring important water and humidity to the region, representing another stressing variable among the others known for this mountaintop area (see Fernandes, 2016). While we do not know the relevance of this behavior to colony success, it may represent an important observation on the plasticity of ants to deal with abrupt changes in extreme tropical environments. Acknowledgements We thank the support provided by the Brazilian National Research Council – CNPq, Minas Gerais Foundation for Science (Fapemig), Anglo American, and the Project Peld- CRSC-17 (CNPq-MCTI). Author contributions All authors contributed to the study’s conception and design. All authors performed data collection and analysis. Conflicts of Interest/Competing Interests All authors certify that they have no affiliations with or involvement in any organization or entity with any financial or non-financial interest in the subject matter or materials discussed in this manuscript. References Anstett, D.N., Naujokaitis-Lewis, I. & Johnson, M.T. (2014). Latitudinal gradients in herbivory on Oenothera biennis vary according to herbivore guild and specialization. Ecology, 95: 2915-2923. doi: 10.1890/13-0932.1 Adams, B.J., Hooper-Bùi, L.M., Strecker, R.M. & O’Brien, D.M. (2011). Raft formation by the red imported fire ant, Solenopsis invicta. Journal of Insect Science, 11: 171. doi: 10.1673/031.011.17101 Adis, J. (1982). Eco-entomological observations from the Amazon: III. How do leaf-cutting ants of inundation-forests survive flooding? Acta Amazonica, 12: 839-840. Avril, A., Purcell, J. & Chapuisat, M. (2016). Ant workers exhibit specialization and memory during raft formation. The Science of Nature, 103: 36. doi: 10.1007/s00114-016-1360-5 Bohn, H.F., Thornham, D.G. & Federle, W. (2012). Ants swimming in pitcher plants: kinematics of aquatic and terrestrial locomotion in Camponotus schmitzi. Journal of Comparative Physiology A, 198: 465-476. doi: 10.1007/ s00359-012-0723-4 Calazans, E.G., Costa, F.V.D., Cristiano, M.P. & Cardoso, D.C. (2020). Daily dynamics of an ant community in a mountaintop ecosystem. Environmental Entomology, 49: 383- 390. doi: 10.1093/ee/nvaa011 Castro, F.S., Da Silva, P.G., Solar, R., Fernandes, G.W. & Neves, F.S. (2020). Environmental drivers of taxonomic Fig 2. Lateral (a) and frontal (b) view of a Linepithema micans worker. Geraldo W. Fernandes, Flávio S. de Castro, Flávio Camarota, Jessica C Blum, Renata Maia – Ant rafting in an extreme ecosystem4 and functional diversity of ant communities in a tropical mountain. Insect Conservation Diversity, 13: 393-403. doi: 10.1111/icad.12415 Clarke, C.M. & Kitching, R.L. (1995). Swimming ants and pitcher plants: a unique ant-plant interaction from Borneo. Journal of Tropical Ecology, 11: 589-602. Costa, F.V., Mello, M.A., Bronstein, J.L., Guerra, T.J., Muylaert, R.L., Leite, A.C. & Neves, F.S. (2016). Few ant species play a central role linking different plant resources in a network in rupestrian grasslands. PloS one, 11: e0167161. doi: 10.1371/ journal.pone.0167161 Fernandes, G.W. (Ed.) (2016). Ecology and conservation of mountaintop grasslands in Brazil. Switzerland: Springer International Publishing. Fielde, A.M. (1903). Experiments with ants induced to swim. Proceedings of the Academy of Natural Sciences of Philadelphia, 55: 617-624. Hölldobler, B. & Wilson, E.O. (1990). The Ants. Cambridge: Harvard University Press, 732 p Lach, L., Parr, C. & Abbott, K. (Eds.) (2010). Ant ecology. Oxford: Oxford University Press. Merbach, M.A., Zizka, G., Fiala, B., Merbach, D., Booth, W.E. & Maschwitz, U. (2007). Why a carnivorous plant cooperates with an ant-selective defense against pitcher- destroying weevils in the myrmecophytic pitcher plant Nepenthes bicalcarata Hook. f. Ecotropica, 13: 45-56. Mlot, N.J., Tovey, C.A. & Hu, D.L. (2011) Fire ants self- assemble into waterproof rafts to survive floods. Proceedings of the National Academy of Sciences USA, 108: 7669-7673. doi: 10.1073/pnas.1016658108 Mlot, N.J., Tovey, C. & Hu, D.L. (2012). Dynamics and shape of large fire ant rafts. Communicative and Integrative Biology, 5: 590-597. doi: 10.4161/cib.21421 Monteiro, G.F., Macedo-Reis, L.E., Dáttilo, W., Fernandes, G.W., Castro, F.S. & Neves, F.S. (2020). Ecological interactions among insect herbivores, ants and the host plant Baccharis dracunculifolia in a Brazilian mountain ecosystem. Austral Ecology, 45: 158-167. doi: 10.1111/aec.12839 Nielsen, M.G. (1997). Nesting biology of the mangrove mud-nesting ant Polyrhachis sokolova Forel (Hymenoptera, Formicidae) in northern Australia. Insectes Sociaux, 44: 15-21. Nondillo, A., Ferrari, L., Lerin, S., Bueno, O.C. & Botton, M. (2014). Foraging activity and seasonal food preference of Linepithema micans (Hymenoptera: Formicidae), a species associated with the spread of Eurhizococcus brasiliensis (Hemiptera: Margarodidae). Journal of Economic Entomology, 107: 1385-1391. doi: 10.1603/EC13392 Purcell, J., Avril, A., Jaffuel, G., Bates, S. & Chapuisat, M. (2014). Ant brood function as life preservers during floods. PloS one, 9: e89211. doi: 10.1371/journal.pone.0089211 Robson, S.K.A. (2010). Ants in the intertidal zone: colony and behavioral adaptations for survival. In Ant Ecology (ed. L. Lach, C.L. Parr and K.L. Abbott), pp. 185-186. New York, NY: Oxford University Press. Silveira, F.A., Barbosa, M., Beiroz, W., Callisto, M., Macedo, D.R., Morellato, L.P.C., Neves, F.S., Nunes, Y.R.F., Solar, R.R. & Fernandes, G.W. (2019). Tropical mountains as natural laboratories to study global changes: a long-term ecological research project in a megadiverse biodiversity hotspot. Perspectives in Plant Ecology, Evolution and Systematics, 38: 64-73. doi: 10.1016/j.ppees.2019.04.001 Wheeler, W.M. (1910). Ants: Their Structure, Development, and Behavior. Columbia University Press. Yanoviak, S.P. & Frederick, D.N. (2014). Water surface locomotion in tropical canopy ants. Journal of Experimental Biology, 217: 2163-2170. doi: 10.1242/jeb.101600 https://doi.org/10.1111/aec.12839 https://doi.org/10.1603/EC13392 https://doi.org/10.1371/journal.pone.0089211 https://doi.org/10.1242/jeb.101600