Change in Aquatic Life by Climate
Vertebrates with separate sexes, sex determination can be genotypic (GSD) or temperature-dependent (TSD). TSD is very common in reptiles, where the ambient temperature during sensitive periods of early development irreversibly determines whether an individual will be male or female. The number of males and females in a population is the sex ratio, a key demographic parameter crucial for population viability. A number of studies have also suggested that TSD may also be very common in many species of fish, with increasing temperatures generally affecting the sex ratio of a species in one of three ways: 1.) Increased numbers of males, 2.) Increased numbers of females or 3.) Increased numbers of males at high and low temperatures, with a balanced sex ratio at intermediate temperatures. However, to elicit a sex-ratio response to temperature, past experiments were often conducted only in the laboratory and not in the field, and the temperatures used were beyond the natural range of temperatures that the species experience in nature. the researchers show that even small changes of just 1-2°C can significantly alter the sex ratio from 1:1 (males: females) up to 3:1 in both freshwater and marine species. study provides evidence that many cases where the observed sex ratio has shifted in response to temperature reveal thermal alterations of an otherwise predominately GSD mechanism rather than the presence of TSD. The results also show that in fish species with TSD, increasing temperatures invariably result in highly male-biased sex ratios. this studies gives two main questions to be solved by research,
Firstly, whether the predicted effects can be observed in sensitive, natural populations.
Secondly, while it is already known that high temperatures inhibit the synthesis of estrogens, which are essential for female sex differentiation in fish and reptiles, more work needs to be done into the molecular mechanism linking environmental temperature and estrogen synthesis.
So far, predicted effects of climate change on fish populations include distribution shifts , alterations in developmental time and larval dispersal , decrements in aerobic performance , and mismatches in species interactions . Climate change effects on the sex ratio have already been inferred for some sea turtles with TSD, , but are lacking for fish. Thus, knowledge of the extent to which temperature affects sex ratios is relevant in order to gauge potential threats of rising temperatures on fish populations. Further, knowing the prevalence of TSD is essential for the correct theoretical and empirical study of the evolution of sex determining mechanisms , because otherwise inferences on the distribution and prevalence of a particular type of mechanism may be biased .
Keywords - T.S.D, Sex Determination in Fish by Temperature, G.S.D, Climate Change effect in Fish Sex