Temperature-sex determination in Podocnemis expansa (Testudines, Podocnemididae)

Abstract

This study has been carried out at the central region of the Araguaia river on the border between the states of Goiás and Mato Grosso in the Brazilian Amazon Basin from September to December 2000. We recorded temperature fluctuation, clutch-size, incubation period and hatching success rate and hatchlings' sex ratio of five nests of Podocnemis expansa (Schweigger, 1812). Despite the relatively small sample size we infer that: a) nests of P. expansa in the central Araguaia river have a lower incubation temperature than nests located further south; however, incubation period is shorter, hatching success rate is lower and clutch-size is larger; b) Podocnemis expansa may present a female-male-female (FMF) pattern of temperature sex-determination (TSD); c) thermosensitive period of sex determination apparently occur at the last third of the incubation period; and, d) future studies should prioritize the relationship between temperature variation (i.e., range and cycle) and embryos development, survivorship and sex determination.

Morphology and immunolocalization of intertubular steroidogenic cell in mesonephros of Podocnemis expansa during gonadal differentiation

“…This finding is common in cells with endocrine function, as the proximity to blood vessels favors the secretion of their products, possibly hormones (Schaeffer et al, 2011). It is known that high temperatures predispose the increase in aromatase enzymatic activity (Plewes and Burns, 2018), which would lead to the conversion of androgens into estrogens and favor the emergence of females in this species (Bonach et al, 2011).…”

“…The nesting of this species is influenced by the water levels of the river, in which spawning, and hatching are carried out in the dry season and the hatching of eggs coincides with the beginning of the rainy season and the rise of rivers (Vanzolini, 2003;Piña et al, 2006). This species lays an average of 92 eggs (63-134) and the hatching period is between 55 and 70 days (Bonach et al, 2011). It presents sexual determination influenced by incubation temperature (Temperature-dependent sex determination -TSD), in which high temperatures promote birth more females, while low temperatures increase male births (Valenzuela, 2001;Bonach et al, 2011).…”

“…This species lays an average of 92 eggs (63-134) and the hatching period is between 55 and 70 days (Bonach et al, 2011). It presents sexual determination influenced by incubation temperature (Temperature-dependent sex determination -TSD), in which high temperatures promote birth more females, while low temperatures increase male births (Valenzuela, 2001;Bonach et al, 2011). There is usually a time window known as thermosensitive period (TSP), during the second third of incubation period, in which physical temperature stimulus is transformed into biological stimulus acting on gonadal tissues and triggering sexual determination (Radhakrishnan et al, 2018).…”

Ecotoxicological Perspectives of Sex Determination

“…Gonads may still be sex-reversed after the thermosensitive period when exposed to exogenous hormones or inhibitors that affect the maintenance of gonadal differentiation [Dorizzi et al, 1996;Belaid et al, 2001]. The duration of the thermosensitive period may vary by species, by temperature, and even by population [Yntema, 1979;Pieau and Dorizzi, 1981;Wibbels et al, 1991;Valenzuela, 2001;Hewavisenthi and Parmenter, 2002;Bonach et al, 2011;Rhen et al, 2015]. Under fluctuating temperature regimes, as occur in natural nests, sex is determined by the cumulative effect of the temperatures above the pivotal temperature (or above the value that causes development to halt) experienced during the thermosensitive period Neuwald and Valenzuela, 2011].…”

Pronephros and mesonephros characterization during the embryonic development of the giant South American river turtle, Podocnemis expansa (Podocnemididae: Testudines)

“…It is widely distributed in the Amazon basin, the Tocantins/Araguaia, and the Orinoco basin (Vogt, 2008). P. expansa presents temperature‐controlled sexual determination (Alho et al, 1985; Bonach et al, 2011; Valenzuela, 2001), depositing 63–134 eggs per nest, with an incubation period varying according to ambient temperature, displaying faster rates at high temperatures (Vogt, 2008). It should be noted that, in addition to controlling sex determination, incubation temperatures influence incubation duration and degree of development.…”