Environmental sex determination .

January 13, 2021 By Swapnil Suryawanshi

Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after fertilization. Environmental factors which often influence sex determination during development or sexual maturation include light intensity and photoperiod, temperature, nutrient availability, and pheromones emitted by surrounding plants or animals. This is in contrast to genotypic sex determination, which establishes sex at fertilization by genetic factors such as sex chromosomes. Under true environmental sex determination, once sex is determined, it is fixed and cannot be switched again. Environmental sex determination is different to some forms of sequential hermaphroditism in which the sex is determined flexibly after fertilization throughout the organism’s life.

The sex of the green spoonworm, Bonellia viridis, a marine annelid .

Taxonomic range :

Crustaceans :

The amphipod crustacean Gammarus duebeni produces males early in the mating season, and females later, in response to the length of daylight, the photoperiod. 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 .

Annelids :

Bonellia viridis, a marine worm, has location-dependent sex determination; sex depends on where the larvae land.

Vertebrates :

The sex of alligators is determined by nest temperature.

The sex of most amniote vertebrates, such as mammals and birds, is determined genetically.  However, some reptiles have temperature-dependent sex determination, where sex is permanently determined by thermal conditions experienced during the middle third of embryonic development.

Moss :

Moss gametophytes (green photosynthetic tissue) and sporophytes (upright, brown structures). The presence of many sporophytes, indicates that the moss is likely either monoicous and self fertilizing or dioicous with fertile males and females. This can be rare as females often outcompete males in mosses.

Moss gametophytes can be either asexual, female, male, or hermaphroditic like ferns. Unlike homosporous ferns, moss gametophytes can be either monoicous or dioicous (similar to monoecious and dioecious in vascular plants),