Substrate Influences Turtle Nest Temperature, Incubation Period, and Offspring Sex Ratio in the Field

Timothy S. Mitchell, Fredric J. Janzen

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Temperature-dependent sex determination, where egg incubation temperature irreversibly determines offspring sex, is a common sex-determining mechanism in reptiles. Weather is the primary determinant of temperature in reptile nests, yet the effects of weather are mediated through the nest microhabitat selected by the mother (e.g., overstory canopy cover). One potentially important aspect of the nest microhabitat is the physical substrate used for nesting. However, the influence of substrate type on nest temperature and offspring sex determination has never been experimentally assessed in the field. We incubated eggs of Painted Turtles (Chrysemys picta) in three substrate types similar to those commonly selected for nesting within our study population. Within a single study site, we constructed pits, which we refilled with loam, sand, or gravel. Then, we created artificial nests in each substrate type, and randomly assigned eggs to a substrate treatment. Substrate type influenced nest temperature and soil moisture, and affected incubation duration, but no other phenotype measured beyond offspring sex ratios. The cooler loam yielded the most male-biased outcome. This finding illustrates the potential importance of nesting substrate as a component of nest-site choice and as a factor in modeling future nest-temperature scenarios.

Original languageEnglish (US)
Pages (from-to)57-62
Number of pages6
JournalHerpetologica
Volume75
Issue number1
DOIs
StatePublished - Mar 2019

Bibliographical note

Funding Information:
We thank B. Bodensteiner, M. Piñon, and G. Purnell for field assistance, M. Honeyman and N. Howell for logistical help, and two anonymous reviewers for constructive comments. B. Carr and R. Horton kindly performed laboratory soil analyses. Funding was provided by Iowa State University (ISU) Research Farms and the National Science Foundation (DEB-1242510 to FJJ and DBI-1402202 to TSM). Research was approved by an ISU IACUC protocol (12-03-5570-J), and conducted under permits from the Illinois Department of Natural Resources (NH14.0073) and the U.S. Fish and Wildlife Service (SUP 32576-028).

Funding Information:
Acknowledgments.—We thank B. Bodensteiner, M. Piñon, and G. Purnell for field assistance, M. Honeyman and N. Howell for logistical help, and two anonymous reviewers for constructive comments. B. Carr and R. Horton kindly performed laboratory soil analyses. Funding was provided by Iowa State University (ISU) Research Farms and the National Science Foundation (DEB-1242510 to FJJ and DBI-1402202 to TSM). Research was approved by an ISU IACUC protocol (12-03-5570-J), and conducted under permits from the Illinois Department of Natural Resources (NH14.0073) and the U.S. Fish and Wildlife Service (SUP 32576-028).

Keywords

  • Chrysemys picta
  • Hydric conditions
  • Nest-site choice
  • Painted Turtles
  • Sex determination
  • Soil temperature

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