Sunday, August 28, 2011

Female Taiwanese Kukrisnakes Defend Territories Around Sea Turtle Nests

Oligodon formosanus. Photo courtesy

of Hans Breuer, and Snakes of Taiwan.

Kukrisnakes of the genus Oligodon are specious, with 69 species currently recognized, but poorly studied species. Although, several of them have been reported to feed on the eggs of other reptiles. Huang and colleagues (2011) report territorial behavior in the Taiwanese Kukrisnake (Oligodon formosanus). Territorial defense of an area containing resources (such as food or shelter) is widespread in lizards but poorly documented in snakes. The authors found the insland population of Oligodon formosanus have females that actively defend sea turtle nests by repelling other snakes of the same species for long periods (weeks) until the turtle eggs hatch or are consumed. A clutch of turtle eggs comprises a large, long-lasting food resource, unlike the prey types exploited by other types of snakes. Kukrisnakes of this species have greatly enlarged teeth that are used for slitting eggshells, and when threatened, these snakes wave their tails toward the aggressor (an apparent case of head-tail mimicry). Bites to the tail during intraspecific combat bouts thus can have high fitness costs for males should the hemipenes be damaged. In combination, unusual features of the species (ability to inflict severe damage to male conspecifics) and the local environment (a persistent prey resource, large relative to the snakes consuming it) render resource defense both feasible and advantageous for female kukrisnakes. When males arrived first, and outnumbered females, all of the turtle eggs in a nest were consumed rapidly (in three nests where we had accurate records of snake arrival and departure, all snakes departed within 5 days, no new snakes entered the nest after that time, and excavation of these nests confirmed that all eggs had been consumed). As soon as female snakes arrived at a nest, the authors saw other snakes being forcefully expelled (rapid retreat, sometimes with fresh wounds). Males that had been expelled often remained nearby and tried to reenter nests. The probability that a late-arriving male would remain within a nest was lower if a female snake was already present in the nest than if no female snakes were present in the nest. The (apparently unique) evolution of territorial behavior in this snake species thus provides strong support for the hypothesis that resource defensibility is critical to the evolution of territoriality.

W.-S. Huang, H. W. Greene, T.-J. Chang,and R. Shine 2011. Territorial behavior in Taiwanese kukrisnakes (Oligodon formosanus). Proc Natl Acad Sci. 108:7455–7459.

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