Sex‐specific DNA in reptiles with temperature sex determination

Abstract

Banded krait minor ("Bkm") satellite DNA, originating in the W-chromosome of the snake Bungarus fasciatus, has been found in the genome of diverse eukaryotic species including fruit fly, quail, and horse. Concentrations of Bkm have been found in the presumptive W-chromosome of snakes with isomorphic sex chromosomes and in the male-determining region of the Y-chromosome in mouse and man. We therefore asked whether Bkm-related DNA might be present in quantitative excess in DNA from males or females in two related species of sea turtle, Chelonia mydas, in which sex is determined by the temperature of the incubating egg, and Lepidochelys kempi, in which the critical sex-determining temperature has recently been described. Filter hybridization with the Bkm 2(8) probe revealed male-specific fragments in both species; female-specific fragments were also revealed in C. mydas. Sex-specific DNA sequences in temperature-sex-determined species such as Kemp's ridley and the green turtle were unexpected, but could be explained if there were an underlying genetic mode of sex determination in these animals, or alternatively, if temperature-influenced sex determination involved structural modifications in DNA adjacent to, or directly concerned with, the sex-determining genes. If these results are confirmed across a broader sample of sea turtles, the techniques described in this paper might be used routinely to identify gener in the young of these endangered animals, in which male and female are grossly indistinguishable.

Molecular Cytogenetic Search for Cryptic Sex Chromosomes in Painted Turtles <b><i>Chrysemys picta</i></b>

“…How do we reconcile our findings with previous studies that suggest there is an underlying GSD mechanism in TSD turtles [Engel et al, 1981;Bull et al, 1982;Demas et al, 1990;Girondot et al, 1994;Rhen and Lang, 1998;Mork et al, 2014]? Several explanations are possible.…”

“…This evidence derives from studies of TSD heritability [e.g. Bull et al, 1982;Janzen, 1992;Rhen and Lang, 1998] as well as population genetics and molecular studies where markers appear to segregate by sex in TSD turtles [Engel et al, 1981;Demas et al, 1990;Girondot et al, 1994]. Furthermore, a recent experimental study detected evidence consistent with the existence of an underlying genotypic sex-determining mechanism in the TSD slider turtle Trachemys scripta , which may be expressed at the pivotal temperature but overridden by higher and lower temperature values [Mork et al, 2014].…”

Single locus inheritance and joint segregation analysis of minisatellite (VNTR) DNA loci in brown trout (Salmo trutta L.)

“…Other types of repetitive DNA have also been linked to sex determining locations. For example Bkm satellite DNA, which contains numerous GATA-GACA repeats, is associated with sex determining chromosomes in snakes (Singh et a!., 1980); mice (Jones & Singh, 1982) and sea turtles (Demas et a!., 1990). While Bkm sequences have been shown to detect DNA fingerprint patterns in both rainbow trout (Lloyd et al, 1989) and in the coral reef fish, Anthias squamipinnis (Wachtel & Demas, 1991), no evidence of sex association was found in either study.…”

The ends of a continuum: genetic and temperature‐dependent sex determination in reptiles

“…(72) Unfortunately, the two phenomena were not investigated in a simultaneous study, so the possibility remains that the two investigations were of cryptic variants of the one species. In another example, the minisatellite DNA sequence Bkm, originally isolated from the W-chromosome of the banded krait, was shown by Demas et al (73) to exhibit sex-specific bands when hybridized to genomic DNA of wild-caught adult green sea turtles (Chelonia mydas) and Kemp's Ridley sea turtles (Lepidochelys kempi). Both species have TSD when incubated at constant temperatures.…”

“…In this way, temperature may have imposed sex-reversal on an underlying genetic mechanism of sex determination. Demas et al (73) did not consider the alternatives that these two species may exhibit GSD when incubated under natural conditions or that TSD and GSD may interact to produce less-viable sex-reversed hatchlings that are selected against under natural conditions. Additional investigations are required to fully explain this intriguing observation.…”