Hatchling Sex Ratios are Independent of Temperature in Field Nests of the Long-necked Turtle, Chelodina longicollis (Testudinata : Chelidae)

Abstract

Eastern long-necked turtles, Chelodina longicollis, are known to lack heteromorphic sex chromosomes and to lack temperature-dependent sex determination when incubated under constant conditions. This study determined whether sex ratios of hatchlings emerging from natural nests of C. longicollis were different from that expected from constant temperature experiments. Temperatures in the eight nests monitored varied considerably each day (by 1.7-12.6°C), with eggs at the top of the nest experiencing the greatest variation (mean range 9.0°C) and eggs at the bottom experiencing least variation (mean range 5.3°C). Temperatures experienced by the top and bottom eggs differed by as much as 5.7°C at any one time. No monotonic seasonal trend was evident, but rainfall caused a sharp drop in nest temperatures. Sex ratios in hatchlings from 14 field nests of C. longicollis did not differ significantly from 1:1, a result in agreement with previous studies conducted at constant incubation temperatures in the laboratory.