Do you know the chances of that with a 50/50 chance of m/f for every egg? If this is further combined with with a thermal modification of expression of gender then you could easily see all of one sex or another. Sex determination in fish may be due to a lot of different factors including multiple sex chromosomes or none at all..I was told by a lady in the US that is studying the Azureiventris that the Azureiventris actually has no toxins like other darts do, and I know the males like to sit up high in the open and call very loud and if it is true that they don't carry any "dart" toxins then it could be that the males get picked off at an alarming rate and maybe that is why the outragous ratio of m/f so that in the wild if they get eaten the ratio would be even by the time they are of breeding age? in the cases where sex is not genetically determined then there may not be any sex chromosomes. If the theory is true, then in the wild the frogs are not exposed to temperatures that cause a enzyme or receptor to malfunction resulting in the skewed sex ratio.The closest to the scenario practiced by protogynous fish is a Hyperolius (see JSTOR: An Error Occurred Setting Your User Cookie) but this is a seperate case from is being seen in the dendrobatid in question.Ed It depends on what you mean by disproportional...Does raising the tads in groups have any effect on sex? I still can't figure out why out of 60 offspring they were all male? If this is the case (and I'm only theorizing here) then breeding two frogs (both genetically the same sex but one expressing the opposite sex) together would result in an extreme disproportion of the frogs being one sex.
Now if this species is of the ZZ (male)/ZW (female) system then a breeding between a functional female and a (I don't want to use the word phenotype as its not correct in this usage) temperature altered female would only produce 25% genetic males... The other possible causes seem more difficult to test (i.e.endocrine disruption, epigenetics, survivability and maternal diet.)Yes, temperature would be an easy way to tell.As an alternative, one could also perform karyotyping on adults of known sexes to see if there are some different genetic sexes.Ed, is this what you described as changing the expression of the sex?I remembered the bit in Lotters as well which was parthly behind my explination. The problem is that while the frogs may be genetically female they are not going to produce ova, behave or be able to function as a female. Can a genetic female produce viable sperm, and a genetic male produce ova?endocrine disruption, epigenetics, survivability and maternal diet.) As for azureiventris, assuming you had real males and females (not altered ones), wouldn't it be simple to confirm or eliminate temperature as a source for the large percentage of males.