Temperature dependent sex determination Wikipedia. Temperature dependent sex determination TSD is a type of environmental sex determination in which the temperatures experienced during embryoniclarval development determine the sex of the offspring. It is only observed in reptiles and teleost fish. TSD differs from the chromosomal sex determination systems common among vertebrates. It is the most popular and most studied type of environmental sex determination ESD. Some other conditions, e. H, and environmental background color, are also observed to alter sex ratio, which could be classified either as temperature dependent sex determination or temperature dependent sex differentiation, depending on the involved mechanisms. As sex determining mechanisms, TSD and genetic sex determination GSD should be considered in an equivalent manner,7 which can lead to reconsidering the status of fish species that are claimed to have TSD when submitted to extreme temperatures instead of the temperature experienced during development in the wild, since changes in sex ratio with temperature variation are ecologically and evolutionally relevant. While TSD has been observed in many reptile and fish species, the genetic differences between sexes and molecular mechanisms of TSD have not been disclosed. The cortisol mediated pathway and epigenetic regulatory pathway are thought to be the potential mechanisms involved in TSD. The eggs are affected by the temperature at which they are incubated during the middle one third of embryonic development. This critical period of incubation is known as the thermosensitive period TSP. The specific time of sex commitment is known due to several authors resolving histological chronology of sex differentiation in the gonads of turtles with TSD. Thermosensitive period TSPeditThe thermosensitive, or temperature sensitive, period TSP is the period during development when sex is irreversibly determined. It is used in reference to species with temperature dependent sex determination, such as crocodilians and turtles. The TSP typically spans the middle third of incubation with the endpoints defined by embryonic stage. The extent of the TSP varies a little among species,1. Temperature pulses during the thermosensitive period are often sufficient to determine sex, but after the TSP, sex is unresponsive to temperature. After this period, however, sex cannot be reversed see sex reversal. Some reptiles use incubation temperatures to determine sex. In some species, this follows the pattern that eggs in extremely high or low temperatures become male and eggs in medium temperatures become female. Within the mechanism, two distinct patterns have been discovered and named Pattern I and Pattern II. Pattern I is further divided into IA and IB. Pattern IA has a single transition zone, where eggs predominantly hatch males if incubated below this temperature zone, and predominantly hatch females if incubated above it. Pattern IA occurs in most turtles, with the transition between male producing temperatures and female producing temperatures occurring over a range of temperatures as little as 12C. Pattern IB also has a single transition zone, but females are produced below it and males above it. Pattern IB occurs in the tuatara. Stata 9.0 Software there. Pattern II has two transition zones, with males dominating at intermediate temperatures and females dominating at both extremes. Pattern II occurs in some turtles, lizards, and crocodilians. Very near or at the pivotal temperature of sex determination, mixed sex ratios and more rarely intersex individuals. It has been proposed that essentially all modes of TSD are actually Pattern II and those that deviate from the expected female male female pattern are species whose nests have simply never been observed exposed to extreme temperature ranges on one end of the range or the other. The distinction between chromosomal sex determination systems and TSD is often blurred because the sex of some species such as the three lined skink Bassiana duperreyi and the central bearded dragon Pogona vitticeps is determined by sex chromosomes, but this is over ridden by temperatures that are tolerable but extreme. Also, experiments conducted at the pivotal temperature, where temperature is equivocal in its influence, have demonstrated an underlying genetic predisposition to be one sex or the other. ExampleseditTemperature dependent sex determination was first described in Agama agama in the year 1. Madeleine Charnier fr. A 2. 01. 5 study found that hot temperatures altered the expression of the sex chromosomes in Australias bearded dragon lizards. The lizards were female in appearance and were capable of bearing offspring, despite having the ZZ chromosomes usually associated with male lizards. Hormones in TSD systemseditSynergism between temperature and hormones has also been identified in these systems. Administering estradiol at male producing temperatures generates females that are physiologically identical to temperature produced females. The reverse experiment, males produced at female temperatures, only occurs when a nonaromatizable testosterone or an aromatase inhibitor is administered, indicating that the enzyme responsible for conversion of testosterone to estradiol, aromatase, plays a role in female development. Nonetheless, the mechanisms for TSD are still relatively unknown, but in some ways, TSD resembles genetic sex determination GSD, particularly in regards to the effects of aromatase in each process. In some fish species, aromatase is in both the ovaries of female organisms who underwent TSD and those who underwent GSD, with no less than 8. TSD and suggesting that there must be another factor in addition to it that is also affecting TSD. Interestingly, hormones and temperature show signs of acting in the same pathway, in that less hormone is required to produce a sexual shift as the incubation conditions near the pivotal temperature. It has been proposed2. GSD pathways has provided a genic starting point. Yet, the genetic sexual determination pathway in TSD turtles is poorly understood and the controlling mechanism for male or female commitment has not been identified. While sex hormones have been observed to be influenced by temperature, thus potentially altering sexual phenotypes, specific genes in the gonadal differentiation pathway display temperature influenced expression. In some species, such important sex determining genes as DMRT12. Wnt signalling pathway2. TSD. While aromatase is involved in more processes than only TSD, it has also been shown to play a role in certain tumor development. Adaptive significanceeditThe adaptive significance of TSD is currently not well understood. Dragon Nest Ph' title='Dragon Nest Ph' />This update will see the death of the old email program Outlook Express, as well as the depreciation of the popular Paint application. As Microsoft told Gizmodo back. The DragoninChief is when The Dragon serves as the Big Bad of the story in spirit, even if not technically the one in charge. Theyre nominally. Extremely aggressive to members of its own species, they will fight to the death. At no point should two male bettas be kept together. At no point should a male and. You are logged out. Sign in and Get Lucky Dont have an account yet Toggle navigation. Updated world stock indexes. Get an overview of major world indexes, current values and stock market data. Whether youre looking to train a new puppy, find the best toy for your cat or set up a tropical aquarium, eHow has answers to all of your petrelated questions. One possible explanation that TSD is common in amniotes is phylogenetic inertia TSD is the ancestral condition in this clade and is simply maintained in extant lineages because it is currently adaptively neutral or nearly so. Rob Zombie Past Present &Amp; Future Rar'>Rob Zombie Past Present &Amp; Future Rar. Indeed, recent phylogenetic comparative analyses imply a single origin for TSD in most amniotes around 3. TSD in squamates2. GSD. 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. Other work centers on a 1. Dragon Nest Ph' title='Dragon Nest Ph' />LYCOPHRON of Chalcis was a Greek poet and scholar of the Library of Alexandria who flourished in the C3rd B. C. His cryptic poem Alexandra tells the stories of the. The Encyclopedia of House Plants Click a link for description, or click a picture to see a larger image. CharnovBull model,3.