Anthropogenic nest sites provide warmer incubation environments than natural nest sites in a population of oviparous reptiles near their northern range limit
Oviposition site choice affects a host of offspring phenotypes and directly impacts maternal fitness. Recent evidence suggests that oviparous reptiles often select nest sites where the landscape has been altered by anthropogenic activity, whereas natural nest sites are less often used. We leverage a long-term study of snapping turtle (Chelydra serpentina) to identify natural nest sites and anthropogenic nest sites and to compare habitat variables among nest site types. Natural and anthropogenic nest sites did not differ in average canopy closure, distance to nearest water, substrate composition, or aspect. However, anthropogenic nest sites had less ground-level vegetation and greater soil brightness, and were 3.3 °C warmer than natural nests during incubation. We used the Schoolfield model of poikilotherm development to assess differences in development rate between natural and anthropogenic nests. Because of the difference in temperature, embryos in anthropogenic nests were predicted to have undergone nearly twice as much development as embryos in natural nests during incubation. We outline why the evolution of fast embryonic development rate cannot compensate indefinitely for the low temperature incubation regimes that become increasingly prevalent at northern range margins, thereby underlining why maternal nest site choice of relatively warm anthropogenic sites may help oviparous reptiles persist in thermally constrained environments. Future research should aim to quantify both the thermal benefits of anthropogenic nest sites, as well as associated fitness costs (e.g., increased adult mortality) to elucidate whether anthropogenic disturbance of the landscape can be an ecological trap or serve a net benefit to some reptiles in northern environments.
KeywordsChelydra serpentina Ecological trap Embryonic development Nest microhabitat Thermal performance
We would like to thank Jacqueline D. Litzgus and Ronald J. Brooks for collaborative use of long-term study site and system; Algonquin Park/Ontario Parks for permission to conduct research; and Algonquin Wildlife Research Station for field accommodation; Nicole Brunet, Taylor Wynia, and Steven Kell for assistance in the field; Lin Schwarzkopf and one anonymous reviewer for helpful comments that improved this paper. All applicable institutional and national guidelines for the care and use of animals were followed.
Author contribution statement
PDM conceived and designed the experiment. EAF and PDM conducted fieldwork. EAF, MAG, and NR analyzed the data. EAF, PDM, MAG, and NR wrote the manuscript.
We acknowledge and thank the University of Toronto Faculty of Arts and Science Research Excursion Program, an NSERC Discovery Grant (# 2016-06469) to NR, a postdoctoral fellowship from the University of Toronto Department of Ecology and Evolutionary Biology to MAG, and Algonquin Park/Ontario Parks for funding that supported this research.
Compliance with ethical standards
Conflict of interest
All authors declare no conflict of interest.
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