Meeting Abstract
Most turtles possess temperature-dependent sex determination where eggs incubating above a threshold temperature (pivotal temperature; Tpiv) develop as females and eggs incubating below the Tpiv develop as males. Despite inhabiting broad geographic ranges, turtles have a similar Tpiv across species and populations (~29°C), making the production of both sexes in different climates enigmatic. To help resolve how TSD operates naturally, we hypothesized that populations vary in “thermal responsiveness,” a novel trait defined as the amount of thermal exposure (an interaction of time and magnitude above the Tpiv) necessary to trigger female development. Functionally, this would result in populations and species differing in the duration of exposure to temperatures above the Tpiv (i.e. heat waves) necessary to induce the production of females, and would not necessitate variation in the Tpiv itself. We predict that northern populations will be more “thermally responsive,” requiring shorter heat waves to produce females than southern populations. To test this, Trachemys scripta eggs were collected from LA, SC, and IL, and incubated under daily fluctuating temperatures (27±3°C) known to produce only males. After 20 days of incubation, eggs were switched to a female producing condition (29.5±3°C) for variable durations (0-30 d). This incubation schema allows us to determine how much exposure to warm conditions is required to shift sex from male to female, and whether the amount of exposure to warm conditions required to produce females differs across populations. Variation in “thermal responsiveness” should help explain how populations and species produce mixed sex ratios naturally, despite possessing similar Tpiv’s.
