Trachemys scripta gene expression data under constant and fluctuating incubation temperatures

There is ample research demonstrating that temperature can have complex
effects on biological processes, including the timing of when organisms
respond to temperature; some responses occur rapidly while others require
an extended exposure time. However, most of what we know about temperature
effects comes from studies using constant temperature conditions, which
are not reflective of natural, fluctuating temperatures. Species with
temperature-dependent sex determination (TSD) present an ideal system to
study the temporal aspects of the temperature response because prior
research has established a number of temperature-responsive genes involved
in TSD, albeit under constant temperatures. To investigate potential
differences in the timing of sexual development between constant and
fluctuating incubation temperatures, we exposed Trachemys scripta embryos
to two conditions that produce males (constant 26°C and 26 ± 3°C) and two
that produce females (constant 31°C and 31 ± 3°C), and sampled embryonic
gonads for gene expression analysis via qPCR.We analyzed three genes
involved in testis differentiation (Kdm6b, Dmrt1, and Sox9) and two genes
involved in ovary differentiation (Foxl2 and Cyp19A1). Results show that
Kdm6b expression was significantly lower under fluctuating temperatures
compared to constant temperatures. Foxl2 and Cyp19A1 expression were also
lower under fluctuating temperatures, but not at all stages of
development. These results suggest that constant temperatures caused
increases in both Foxl2 and Cyp19A1 expression earlier (developmental
stage 20) than fluctuating temperatures (stages 22 and 23). Dmrt1 and Sox9
expression did not differ between constant and fluctuating temperatures.
These results highlight that not all genes in a temperature-dependent
process respond to temperature in the same manner. Whether there are
functional consequences of this variation remains to be determined.