Amphibian sex determination and sex reversal

Abstract

Amphibians employ a genetic mechanism of sex determination, according to all available information on sex chromosomes or breeding tests. Sex reversal allows breeding tests to establish which sex is heterogametic and provides an indication of the mechanism of sex determination. Cases of spontaneous and experimental sex reversal (by temperature, hormones or surgery) are reviewed and illustrated by previously unpublished studies on crested newts. These newts respond conventionally to temperature and hormone treatment but provide anomalous results from breeding tests. It is suggested that both the evolution from temperature dependency to a genetic switch and from ZZ/ZW to XX/XY are superimposed on a generally uniform mechanism of sex determination in all vertebrates.

Effects of Atrazine on Metamorphosis, Growth, and Gonadal Development in the Green Frog (Rana Clamitans)

“…Unlike African clawed frogs (X. laevis), R. clamitans are not feminized when exposed to exogenous estradiol, but instead are masculinized when exposed to exogenous androgens, such as DHT (Foote & Witschi, 1939). This difference in responses to hormones demonstrates that endocrine regulation of maturation and sexual development is different among frog species (Wallace et al, 1999). Therefore, hormones and hormone mimics could induce different responses in different frog species.…”

“…In particular, testicular oocytes have been reported to be a natural developmental occurrence in some strains of ranid species, including, but not limited to, Rana temporaria (Witschi, 1929), Rana catesbeiana (Hsu & Liang, 1970), and Rana curtipes (Gramapurohit et al, 2000). In addition, Bufonid toads, whether genetic males or genetic females, develop ovaries, which become compressed into the Bidder's organs in front of the definitive gonad at the time of metamorphosis (Wallace et al, 1999). Therefore, based on the results of this study and the reported incidences of natural background levels of hermaphroditism in the scientific literature, gonadal anomalies in R. clamitans do not appear to be related specifically to the presence or absence of atrazine.…”

Females Have Larger Ratio of Second‐to‐Fourth Digits Than Males in Four Species of Salamandridae, Caudata

“…All birds are female heterogametic; however, amphibians and reptiles possess two types of chromosomal sexdetermination system, namely, male heterogametic or female heterogametic (Wallace et al, 1999;Nakamura, 2009). During the first half of the twentieth century, before the development of chromosome banding techniques, the prevalent view was that amphibians lacked sex chromosomes (Solari, 1993).…”

Haldane's rule in the 21st century

“…Similarly, Teleostei (Volff, 2005) and Gastropoda (Avise et al, 2004) show a great diversity in sex determination systems and many groups have male heterogamety, female heterogamety and hermaphroditism in closely related taxa. Another promising approach may be to look for HR in groups that regularly or occasionally undergo sex change, such as some Teleostei (Pandian and Sheela, 1995), or that can be artificially induced to change sex (certain Amphibia; Wallace et al, 1999). Perrin (2009) realized that sex reversal may halt the differentiation of sex chromosomes following the cessation of recombination in the heterogametic sex.…”