Orientation and dispersal to suitable habitat affects fitness in many animals, but the factors that govern these behaviors are poorly understood. In many turtle species, hatchlings must orient and disperse to suitable aquatic habitat immediately after emergence from subterranean nests. Thus, the location of nest sites relative to aquatic habitats ideally should be associated with the direction of hatchling dispersal. At our study site, painted turtles (Chrysemys picta) nest to the west (on an island) and east (on the mainland) of a wetland, which determines the direction that hatchlings must travel to reach suitable aquatic habitat. To determine if hatchling orientation is intrinsically influenced by the location where their mothers nest, we employed a two-part cross-fostering experiment in the field, whereby half the eggs laid in mainland nests were swapped with half the eggs laid in island nests. Moreover, because C. picta hatchlings overwinter inside their nests, we performed a second cross-fostering experiment to fully decouple the effects of (1) the maternally chosen nest location, (2) the embryonic developmental location, and (3) the overwinter location. We released hatchlings into a circular arena in the field and found that turtles generally dispersed in a westerly direction, regardless of the maternally chosen nest location and independent of the locations of embryonic development and overwintering. Although this westerly direction was towards suitable aquatic habitat, we could not distinguish whether naïve hatchling turtles (i) use environmental cues/stimuli to orient their movement, or (ii) have an intrinsic bias to orient west in the absence of stimuli. Nevertheless, these findings suggest that the orientation behavior of naïve hatchling turtles during terrestrial dispersal is not dependent upon the location of maternally-chosen nest sites.
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Acknowledgments We thank R. Alverio, A. Durso, J. Maciel, A. Sethuraman, J. Strickland, and J. Ward for assistance in the field and laboratory. We are grateful to E. Britton and the staff with the Army Corps of Engineers for making this research possible. Thanks to G. Cordero, F. Janzen, J. Refsnider, A. Sethuraman, and R. Telemeco for insightful comments on earlier drafts of this paper. This research was approved by the Institutional Animal Care and Use Committee at Iowa State University (protocol # 12-03-5570-J), the United States Fish and Wildlife Service (permit # 0A022), and the Illinois Department of Natural Resources (permit # NH10.0073). This work was supported by the National Science Foundation (LTREB DEB-0640932 to F.J. Janzen).
- Cross-fostering experiment
- Maternal effects
- Nest-site selection