Environmental sex determination
Encyclopedia
Environmental sex determination or ESD is any sex-determination system
in which sex is established by a nongenetic cue (e.g. nutrient availability) experienced within a discrete period after conception. In contrast, genotypic sex determination (GSD) occurs when sex is established by genetic factors (e.g. sex chromosomes) at conception. Environmental sex determination should also not be confused with some forms of hermaphroditism in which the sex is determined flexibly after birth, such as dichogamy
.
s, however, the clade in which this it is perhaps most common.
Most amniote vertebrates have genetic sex determination, but a small highly diverse set of taxa in this clade show environmental sex determination. In these latter animals, environmental sex determination occurs as temperature-dependent sex determination
(TSD), wherein sex of individuals is permanently determined by thermal conditions experienced approximately during the middle one-third of embryonic development. Mammals and birds only have genetic sex determination, whereas crocodilians and sphenodontians exclusively have temperature-dependent sex determination. In contrast, squamates (lizard
s and snake
s) and turtle
s exhibit both genotypic sex determination and temperature-dependent sex determination, although the latter is much more common in turtles than in squamates.
Daphnia Magna, parthenogenetically produces male progeny in response to environmental conditions.
Yasuhiko Kato, Kaoru Kobayashi, Hajime Watanabe, Taisen Iguchi (2011). “Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation of a Doublesex Gene in the Sex-Determining Pathway”. PLoS Genet 7: (3) 1-12
Sex-determination system
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...
in which sex is established by a nongenetic cue (e.g. nutrient availability) experienced within a discrete period after conception. In contrast, genotypic sex determination (GSD) occurs when sex is established by genetic factors (e.g. sex chromosomes) at conception. Environmental sex determination should also not be confused with some forms of hermaphroditism in which the sex is determined flexibly after birth, such as dichogamy
Dichogamy
Sequential hermaphroditism is a type of hermaphroditism that occurs in many fish, gastropods and plants. Here, the individual is born one sex and changes sex at some point in their life. They can change from a male to female , or from female to male...
.
Examples
In the season in the amphipod Gammarus duebeni, photoperiod induces production of males earlier, and females later. Because male fitness improves more than female fitness with increased size, environmental sex determination is adaptive in this system by permitting males to experience a longer growing season than females. The adaptive significance of environmental sex determination is not so clear for amnioteAmniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
s, however, the clade in which this it is perhaps most common.
Most amniote vertebrates have genetic sex determination, but a small highly diverse set of taxa in this clade show environmental sex determination. In these latter animals, environmental sex determination occurs as temperature-dependent sex determination
Temperature-dependent sex determination
Temperature-dependent sex determination is type of environmental sex determination in which the temperatures experienced during embryonic development determine the sex of the offspring. It is most prevalent and common among amniote vertebrates that are classified under the reptile class, but is...
(TSD), wherein sex of individuals is permanently determined by thermal conditions experienced approximately during the middle one-third of embryonic development. Mammals and birds only have genetic sex determination, whereas crocodilians and sphenodontians exclusively have temperature-dependent sex determination. In contrast, squamates (lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s and snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s) and turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s exhibit both genotypic sex determination and temperature-dependent sex determination, although the latter is much more common in turtles than in squamates.
See also
- Sex-determination systemSex-determination systemA sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...
Daphnia Magna, parthenogenetically produces male progeny in response to environmental conditions.
Yasuhiko Kato, Kaoru Kobayashi, Hajime Watanabe, Taisen Iguchi (2011). “Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation of a Doublesex Gene in the Sex-Determining Pathway”. PLoS Genet 7: (3) 1-12