Geographic Variation in Sex Determination Patterns in the River TurtlePodocnemis lewyana: Implications for Global Warming

An Approximation of the Sex Determination Parameters in the Savanna Side-Necked Turtle Podocnemis vogli (Podocnemididae)

“…Prior to this study, information on the sex determination parameters of P. vogli was lacking, but we now know that all 6 species in the genus Podocnemis exhibit TSD, apparently with a TSD Ia pattern with a high pivotal temperature in comparison with other turtle species (Valenzuela 2001a; Vogt 2001, 2008; de Souza and Vogt 1994; Páez and Bock 2004; Hulin et al 2009; Páez et al 2009; Gallego-García and Páez 2016; Camillo et al 2022; present study). We could not characterize the entire TSD reaction norm for this species, but we documented a masculinizing temperature of 31°C and produced results that suggest the species has a T piv presumably slightly higher than 33°C, because at this regime we obtained a 7:3 male–female ratio.…”

“…Quantifying levels of intra- and interpopulational variation in TSD parameters is important if we want to characterize them at the species level, not only because they might vary between populations (Bobyn and Brooks 1994; Ewert et al 2005; Gallego-García and Páez 2016), but also particularly because for podocnemidid species, one of the most common management strategies is ex situ egg incubation or nest transfer (Páez et al 2015b). Also, climate change could have a rapid and drastic negative effect on their long-term population viability (Valenzuela et al 2019) by feminizing sex ratios.…”

“…These TSD parameters have been documented using constant or semiconstant temperatures in 5 of the 6 species of the genus Podocnemis (de Souza and Vogt 1994; Valenzuela 2001a; Vogt 2001, 2008; Páez and Bock 2004; Hulin et al 2009; Páez et al 2009; Camillo et al 2022). All of these species have been shown to exhibit a TSD Ia pattern and variable TRTs (Gallego-García and Páez 2016; Camillo et al 2022). Although not as frequently quantified, in these species the hatching success rate and other aspects of the hatching phenotype, such as size, shape, body growth rates, and behavior, may be influenced by different forms of maternal effects and their interactions with incubation temperature regimes (de Souza and Vogt 1994; Valenzuela 2001b; Escalona 2003; Páez et al 2015a; Camillo et al 2022).…”

Podocnemis expansa Turtles Hint to a Unifying Explanation for the Evolution of Temperature-Dependent Sex Determination in Long-Lived and Short-Lived Vertebrates

“…One hypothesis is that TSD might be retained in P. expansa via phylogenetic inertia due to lack of genetic variation that precludes this lineage from evolving out of TSD. However, this explanation can be ruled out because variation exists among populations of P. expansa in their TSD pattern, as observed also within and among congeneric species (P. unifilis, P. erythrocephala, and P. leywana) [Lance et al, 1992;de Souza and Vogt, 1994;Valenzuela et al, 1997;Valenzuela, 2001a, c;Lubiana and Ferreira, 2009;Paez et al, 2009;Bonach et al, 2011;Gallego-Garcia and Paez, 2016;Gómez-Saldarriaga et al, 2016], as well as in their incubation time [Hildebrand et al, 1997;Valenzuela, 2001c;Lubiana and Ferreira, 2009], clutch size, and other life history traits [Vanzolini, 2003]. Furthermore, variation in the thermal response of the gene network regulating sexual development in turtles and the general lability of sex determination in this clade (TSDIa, TSDII, XX/XY, and ZZ/ZW systems have evolved in turtles) also argue against this hypothesis as an overall explanation for chelonians [Bull, 1980;Ewert et al, 2004;Valenzuela, 2004;Grossen et al, 2010;Uller and Helantera, 2011;Valenzuela et al, 2013;Holleley et al, 2015].…”