Many species—such as several species of turtle and lizards, like the green iguana—have X and Y sex chromosomes again, like mammalswith females being "homogametic," that is, having two identical X chromosomes. Bibcode : GCBio.
However, in the bipotential gonads of those turtles raised at male-promoting temperatures, Sox9 expression was retained in the medullary sex cords destined to become Sertoli cells Spotila et al. In this Page. Consequently, the adaptive significance of TSD in all but the most recent origins of TSD may have been obscured by the passage of deep time, with TSD potentially being maintained in many amniote clades simply because it works 'well enough' i.
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Location-dependent sex determination in Bonellia and Crepidula As mentioned in Chapter 3, the sex of the echiuroid worm Bonellia depends on where a larva settles. Therein it differentiates into a minute 1—3-mm-long male that is essentially a sperm-producing symbiont of the female see Figure 3.
It is quite possible that there are other species of reptiles with more complicated scenarios of temperature reversal of chromosomal sex. PLOS Biology.
Figure A study found that hot temperatures altered the expression of the sex chromosomes in Australia's bearded dragon lizards. Turtle species that display TSD are thought to follow one of two patterns of temperature dependence. At certain levels of PCBs, the feminizing effects can override the influence of temperature, negating the effects of TSD in an organism.
The developmental period during which sex determination occurs can be discovered by incubating eggs at the male-producing temperature for a certain amount of time and then shifting the eggs to an incubator at the female-producing temperature and vice versa.
However, there is evidence that during climactic extremes, changes in the sex determining mechanism itself to GSD are selected for, particularly in the highly-mutable turtles. PCBs can act as an estrogen replacement, causing feminization of sex organs in growing reptiles.
Sinauer Associates: Massachusetts.