Does the oviparity-viviparity transition alter the partitioning of yolk in embryonic snakes?

Abstract

BackgroundThe oviparity-viviparity transition is a major evolutionary event, likely altering the reproductive process of the organisms involved. Residual yolk, a portion of yolk remaining unutilized at hatching or birth as parental investment in care, has been investigated in many oviparous amniotes but remained largely unknown in viviparous species. Here, we used data from 20 (12 oviparous and 8 viviparous) species of snakes to see if the oviparity-viviparity transition alters the partitioning of yolk in embryonic snakes. We used ANCOVA to test whether offspring size, mass and components at hatching or birth differed between the sexes in each species. We used both ordinary least squares and phylogenetic generalized least squares regressions to test whether relationships between selected pairs of offspring components were significant. We used phylogenetic ANOVA to test whether offspring components differed between oviparous and viviparous species and, more specifically, the hypothesis that viviparous snakes invest more in the yolk as parental investment in embryogenesis to produce more well developed offspring that are larger in linear size.ResultsIn none of the 20 species was sex a significant source of variation in any offspring component examined. Newborn viviparous snakes on average contained proportionally more water and, after accounting for body dry mass, had larger carcasses but smaller residual yolks than did newly hatched oviparous snakes. The rates at which carcass dry mass (CDM) and fat body dry mass (FDM) increased with residual yolk dry mass (YDM) did not differ between newborn oviparous and viviparous snakes. Neither CDM nor FDM differed between newborn oviparous and viviparous snakes after accounting for YDM.ConclusionsOur results are not consistent with the hypothesis that the partitioning of yolk between embryonic and post-embryonic stages differs between snakes that differ in parity mode, but instead show that the partitioning of yolk in embryonic snakes is species-specific or phylogenetically related. We conclude that the oviparity-viviparity transition does not alter yolk partitioning in embryonic snakes.Electronic supplementary materialThe online version of this article (10.1186/s12862-017-1083-z) contains supplementary material, which is available to authorized users.

Can snakes use yolk reserves to maximize body size at hatching?

“…2015). There is also evidence that yolk partitioning in embryonic snakes is phylogenetically related or species-specific (Wu et al. 2017).…”

“…2006), snakes (Ji et al. 1997, 1999; Ji and Sun 2000; Wu et al. 2017), and turtles (Filoramo and Janzen 1999; Lance and Morafka 2001; Alava et al.…”

Stage-Dependent Corticosterone Production and Response to Maternal Toxin Exposure in Embryos of a Viviparous and Genetically Toad Toxin-Resistant Snake (Thamnophis elegans)

“…Many viviparous squamates have retained varying degrees of lecithotrophy (i.e., substantial yolk retention), depending on the species and maternal life history. In some reptiles, parity mode does not significantly impact yolk volume (Wu et al, 2017). In viviparous reptiles, the relationship between maternal, embryonic, and yolk-derived hormones is complex.…”

“…In viviparous reptiles, the relationship between maternal, embryonic, and yolk-derived hormones is complex. Embryos begin to produce their own hormones as the adrenal gland develops (Rupik, 2002; Elinson et al, 2014; Wu et al, 2017). Tritium from labeled maternal hormone has also been found to cross the placenta in a viviparous skink (Itonaga et al, 2011), though the degree varies by embryonic stage and time from exposure.…”