Natural nest substrates influence squamate embryo physiology but have little effect on hatchling phenotypes

Abstract

Vertebrate embryos require access to water; however, many species nest in terrestrial habitats that vary considerably in moisture content. Oviparous, non‐avian reptiles have served as models to understand how environmental factors, like moisture availability, influence development because eggs are often exposed to prevailing environments in the absence of parental care. Though much research demonstrates the importance of water absorption by eggs, many ecological factors that influence moisture availability in natural nests have received little attention. For example, the type of substrate in which nests are constructed is understudied. We experimentally incubated eggs of the brown anole lizard (Anolis sagrei) in 2 naturally occurring nest substrates that were treated with varying amounts of water to determine how natural substrates influence development at different moisture concentrations. One substrate consisted of sand and crushed seashells and the other was mostly organic material (i.e. decayed plant material). Both are common nesting substrates at our field site. When controlling for water uptake by eggs, we found that egg survival and hatchling phenotypes were similar between substrates; however, embryos developed more quickly in the sand/shell substrate than the organic substrate, indicating substrate‐specific effects on embryo physiology. These results demonstrate that different natural substrates can result in similar developmental outcomes if the water available to eggs is comparable; however, some aspects of development, like developmental rate, are affected by the type of substrate, independent of water availability. Further study is required to determine how natural substrates influence embryo physiology independent of water content.

A general framework for jointly modelling thermal and hydric constraints on developing eggs

“…Our framework and its incorporation into the NicheMapR package create new opportunities to understand the joint effects of temperature and moisture in limiting the distribution and abundance of species. Soil moisture below a certain threshold (around −1500 J/kg) can kill eggs in the laboratory and in nature (Andrews & Sexton, 1981; Bodensteiner et al, 2015; Hall et al, 2022; Muth, 1981; Porter & Tracy, 1983). Although sublethal water potentials may have limited effects on hatchling success or phenotypes (Du & Shine, 2008; Flatt, 2001; Ji & Du, 2001; Plummer & Snell, 1988; Shine & Brown, 2002), they can affect post‐hatching growth (Overall, 2014).…”

The diverse terminology of reptile eggshell microstructure and its effect on phylogenetic comparative analyses

“…During incubation, the eggshell provides calcium to the embryo and controls water and gas exchange with its surrounding environment (Ackerman, Dmi'el, & Ar, 1985; Ackerman, Seagrave, et al, 1985; Ar, 1991; Ar & Rahn, 1985; Deeming & Thompson, 1991; Paganelli, 1980) – generally through a system of pores, which in birds can present a highly complex structure (Board, 1982; Grellet‐Tinner et al, 2017; Mikhailov & Zelenkov, 2020; Tyler & Simkiss, 1959). In extant birds and crocodilians, the egg‐laying site is a nest or a mound made from vegetation (Ackerman & Lott, 2004; Hall et al, in press; Mainwaring et al, 2014; Murray et al, 2020). Conversely, lepidosaur and turtle eggs are laid either in a tunnel dug into the ground or above ground with substrate covering (e.g.…”