Egg of the red-eared slider (Trachemys scripta). Note the vascularized portion surrounding the embryo. The temperature experienced during the middle third of incubation initiates the cellular and molecular cascades that result in male or female offspring. Incubation temperature is believed to activate genes encoding for the steroidogenic enzymes aromatase and reductase, steroidogenic factor 1, and steroid hormone receptors.
Hatching in the red-eared slider turtle (Trachemys scripta). Eggs are incubated in trays and, depending upon the temperature, will hatch in 45 to 60 days.
The leopard gecko (Eublepharis macularius). Incubation temperature influences body coloration, with individuals from warmer temperatures having a lighter coloration. In this picture the male (from a 32.5° C incubation temperature) is on the left and the female (from a 26° C incubation temperature) is on the right. In addition to determining the gonadal sex of the hatchling, incubation temperature also influences growth rate and, in adulthood, the pattern of secretion of sex hormone secretion, aggressive and sexual behavior, and the size and metabolic activity of brain nuclei.
Pseudosexual behavior in the all-female desert grasslands whiptail (Cnemidophorus uniparens). This is the characteristic mating posture observed in all sexual whiptail lizards. Although males do not exist in this parthenogenetic species, the individuals continue to display male-like and female-like pseudosexual behavior. The male-like individual is postovulatory and the female-like individual is preovulatory.
The green anole lizard (Anolis carolinensis). The picture shows a territorial males in a full aggressive display. Not the saggital display and erection of the crest on the neck and back. The colored throat fan, or dewlap, is extended, indicating that the male is challenging another male.
During most of the warm summer months, the Canadian red-sided garter snake (Thamnophis sirtalis parietalis) leads a solitary existence. At two times of the year, spring and summer, however, the animals mass together as they emerge from, or later return to, underground overwintering hibernacula. Only during the spring is the intense mating activity observed. All males emerge together and await the solitary emergence of females over the next two-to-four weeks.
The picture shows a female as she emerges from the underground hibernaculum. The males are attracted to a specific pheromone produced normally by females. This results in “mating ball” forming. Usually on a single female will be at the center of this writhing mass of snakes. There are some male, however, who produce the female pheromone and confuse other males in the mating ball. These “she-males” are more likely to mate with a female in the mating ball.