Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: paul.fr on 26/04/2007 07:34:09

Title: it's a frog..it's a boy!..no, it's a girl !
Post by: paul.fr on 26/04/2007 07:34:09

I heard that frogs can change their sex!, one minute their male the next their female. is this right? If it is then, why, how and can they make themselves pregnant?

Title: it's a frog..it's a boy!..no, it's a girl !
Post by: DoctorBeaver on 26/04/2007 09:11:16

Quote from: paul.fr on 26/04/2007 07:34:09

I heard that frogs can change their sex!, one minute their male the next their female. is this right? If it is then, why, how and can they make themselves pregnant?

Can Belgians do that too?  [???]

Title: it's a frog..it's a boy!..no, it's a girl !
Post by: another_someone on 26/04/2007 12:02:34

No, I don't think frogs are able to do that.  Certainly, some fish are able to do that - what usually happens then is that the young fish will be male (males have less investment in procreation, and if they are not subject to the competitive pressures that mammalian males place themselves under, can need not be that large - in insects too, the male is smaller than the female); and as the grow, they become female.

With reptiles (and possibly amphibians) the sex of the animals is determined by the context in which it is born (changes in temperature are often a determining factor as to whether the ground will have more males or more females in the clutch).

Title: it's a frog..it's a boy!..no, it's a girl !
Post by: another_someone on 26/04/2007 12:52:55

http://www.rbej.com/content/4/1/59

Quote

Determining sexual fate is an integral part of reproduction, used as a means to enrich the genome. A variety of such regulatory mechanisms have been described so far and some of the more extensively studied ones are being discussed.

For the insect order of Hymenoptera, the choice lies between uniparental haploid males and biparental diploid females, originating from unfertilized and fertilized eggs accordingly. This mechanism is also known as single-locus complementary sex determination (slCSD). On the other hand, for Dipterans and Drosophila melanogaster, sex is determined by the ratio of X chromosomes to autosomes and the sex switching gene, sxl. Another model organism whose sex depends on the X:A ratio, Caenorhabditis elegans, has furthermore to provide for the brief period of spermatogenesis in hermaphrodites (XX) without the benefit of the "male" genes of the sex determination pathway.

Many reptiles have no discernible sex determining genes. Their sexual fate is determined by the temperature of the environment during the thermosensitive period (TSP) of incubation, which regulates aromatase activity. Variable patterns of sex determination apply in fish and amphibians. In birds, while sex chromosomes do exist, females are the heterogametic (ZW) and males the homogametic sex (ZZ). However, we have yet to decipher which of the two (Z or W) is responsible for the choice between males and females.

In mammals, sex determination is based on the presence of two identical (XX) or distinct (XY) gonosomes. This is believed to be the result of a lengthy evolutionary process, emerging from a common ancestral autosomal pair. Indeed, X and Y present different levels of homology in various mammals, supporting the argument of a gradual structural differentiation starting around the SRY region. The latter initiates a gene cascade that results in the formation of a male. Regulation of sex steroid production is also a major result of these genetic interactions. Similar observations have been described not only in mammals, but also in other vertebrates, emphasizing the need for further study of both normal hormonal regulators of sexual phenotype and patterns of epigenetic/environmental disruption.

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Amphibians

The thermosensitivity of the gonads has been demonstrated not only in reptiles, but also in several fish and some amphibians. These tend to combine a genotypic sex determination mechanism -either male heterogamety, female heterogamety or polygenic- with the mechanism demonstrated above. The result is a phenomenon known as sex reversal, where the effects of temperature may go against the genotypic directions, allowing the existence of animals in genotypic and phenotypic sex discordance.

In particular, male or female heterogamety has been described in various species of anurans and urodeles. Sex chromosomes of various types may be present, following both the XY/XX and WZ/ZZ pattern that usually apply to mammals and birds, respectively. The exact mechanism by which temperature regulates sex determination in amphibians is not yet deciphered, but it doesn't seem to apply to the TSP-aromatase regulation model of reptiles. Hormonal action may also act in the process of acquisition of sexual phenotype, either independently or in conjunction with temperature variation.

Gene studies in amphibian sex determination are not as extensive as in other animal models. Of the various genes so far associated with sex determination in other species, amphibians appear to express DMRT1. However, it is not yet clear whether this is a downstream product in the sex differentiation cascade or a factor with a more central role in sex determination

Title: it's a frog..it's a boy!..no, it's a girl !
Post by: elegantlywasted on 26/04/2007 12:57:36

Jurrasic Park Lied?!!??!?