Physiological benefits as precursors of sociality: why banded geckos band

Abstract

Aggregating has been widely studied in a variety of animals and found to have important benefits in terms of sociality, courtship, predator avoidance and physiology. Several species of nocturnal geckos form diurnal aggregations; however, little is known about the benefits of these groupings. We conducted a series of experiments to determine the benefit of aggregation for the desert-dwelling western banded gecko, Coleonyx variegatus. We found that banded geckos benefit from aggregation by a reduction in evaporative water loss (EWL). No social or mating benefits were detected, and geckos did not group to avoid predators. Geckos did not select diurnal retreat sites based solely on the scent of conspecifics, although they aggregated readily when conspecifics were present. Thus, C. variegatus appear to achieve physiological but not social benefits from grouping. Banded geckos belong to an ancestrally tropical lineage whose descendants invaded present-day North American deserts at a time when these regions were more mesic. This may explain their relatively high rate of EWL. Aggregating seems to be a solution to this physiological handicap. Our study also suggests a path for the evolution of social behaviour: as animals aggregate for physiological benefits, the stage is set for the evolution of more complex social interactions.

Scatting behaviour of the sleepy lizard,Tiliqua rugosa

“…A conclusion from this comparison is that scat piling in the Egernia lineage is associated more with refuge defence than with social aggregation. This is consistent with the observation that scat piling is regularly observed in other lizard (Shah et al, 2003;Lancaster et al, 2006) and snake families (Chiszar et al, 1980;Heller & Halpern, 1982;Aubert & Shine, 2009) where social aggregations are rarely observed.…”

A hot knot of toads: Aggregation provides thermal benefits to metamorphic Andean toads

“…Animals aggregate for a variety of reasons ranging from strictly physiological to primarily social (Krebs and Davies, 1993;Alcock, 2001;Krause and Ruxton, 2002;Lancaster et al, 2006). For the population of metamorphic R. spinulosa we studied, the reason appears to be physiological-specifically a thermal benefit-but several alternative hypotheses are worth considering.…”

“…Wells, 1977;Arnold and Wassersug, 1978;Boersma, 1982;Sillen-Tullberg and Leimar, 1988;Watt et al, 1997;Wikelski, 1999;Krause and Ruxton, 2002;Spieler, 2003). Thus, the cues or selective forces favoring aggregation vary along a continuum from strictly abiotic to primarily social (Lancaster et al, 2006).…”

“…behavioral inertia; sensu Huey et al, 2003), such as low moisture availability (e.g. Cohen and Alford, 1996;Lancaster et al, 2006) or thermal extremes (e.g. Boersma, 1982;Kearney et al, 2001;Shah et al, 2003;Bloomstein et al, 2004;Schradin et al, 2006).…”

Sharing refuges on arid islands: ecological and social influence on aggregation behaviour of wall geckos

“…Social aggregations which allow the control of thermal exchange rates via huddling were reported for thick-tailed geckos Underwoodisaurus milii  (Shah, 2002; Shine et al, 2003) and common brown geckos Woodworthia maculatus (Bauer, 1990). Reduction of evaporative water loss was suggested for the western banded gecko Coleonyx variegatus, which forms large groups under shelters during the day (Lancaster, Wilson & Espinoza, 2006) where often several males and females can be found together (Greenberg, 1943). Pianka & Vitt (2003) suggested the existence of long term pair bond aggregations of the small diurnal naked-toed gecko genus Gymnodactylus in southern Brazil.…”