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

Yan-Qing Wu,Xiang Ji,Jian-Fang Gao,Yan-Fu Qu,Xue-Ji Wang

doi:10.1186/s12862-017-1083-z

Yan-Qing Wu, Xiang Ji + Show 3 more

Open Access

https://doi.org/10.1186/s12862-017-1083-z

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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.

Highlights

The oviparity-viviparity transition is a major evolutionary event, likely altering the reproductive process of the organisms involved
In none of the 20 species did we find that total body dry mass, carcass dry mass (CDM), fat body dry mass (FDM), or yolk dry mass (YDM) differed between the sexes after accounting for wet body mass (ANCOVA: all P > 0.093)
We found that newborn viviparous snakes on average contained proportionally more water and, after accounting for body dry mass, they had larger carcasses but smaller residual yolks than did newly hatched oviparous snakes (Fig. 2). These findings suggest that viviparous snakes generally produce more fully developed offspring than oviparous snakes, but they do not support the hypothesis that the partitioning of yolk between Parental investment in embryogenesis (PIE) and Parental investment in care (PIC) differs between snakes with different parity modes for two reasons

Summary

Introduction

The oviparity-viviparity transition is a major evolutionary event, likely altering the reproductive process of the organisms involved. We used phylogenetic ANOVA to test whether offspring components differed between oviparous and viviparous species and, 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. It is widespread and perhaps ubiquitous among invertebrates and non-mammalian vertebrates that embryos complete development without depleting the entire yolk reserve [1,2,3,4,5]. Residual yolks seem to be essential in species that have less developed feeding appendages, organs, behaviors, gut flora and/or enzyme systems at hatching or birth [2, 10, 32,33,34]

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