A review of the effects of incubation conditions on hatchling phenotypes in non-squamate reptiles

Abstract

Developing embryos of oviparous reptiles show substantial plasticity in their responses to environmental conditions during incubation, which can include altered sex ratios, morphology, locomotor performance and hatching success. While recent research and reviews have focused on temperature during incubation, emerging evidence suggests other environmental variables are also important in determining hatchling phenotypes. Understanding how the external environment influences development is important for species management and requires identifying how environmental variables exert their effects individually, and how they interact to affect developing embryos. To address this knowledge gap, we review the literature on phenotypic responses in oviparous non-squamate (i.e., turtles, crocodilians and tuataras) reptile hatchlings to temperature, moisture, oxygen concentration and salinity. We examine how these variables influence one another and consider how changes in each variable alters incubation conditions and thus, hatchling phenotypes. We explore how incubation conditions drive variation in hatchling phenotypes and influence adult populations. Finally, we highlight knowledge gaps and suggest future research directions.

Can nesting behaviour allow reptiles to adapt to climate change?

“…body size and behavioural performance) and a highly biased sex ratio in TSD reptile species [89,137,138], but longitudinal studies that can provide direct evidence of phenotypic changes induced by climate change are still rare. Nonetheless, numerous studies have documented the effects of incubation temperatures on offspring phenotypes in reptiles ( [24,114]; see reviews in [118,128,139]). High developmental temperatures at the embryonic stage produce small hatchlings that might have poor locomotor and growth performance [125,[140][141][142].…”

“…The small hatchlings resulting from higher-temperature incubation may be less able to compete for food or to evade predation, although such fitness-reducing effects [126] are not universal [127]. Additionally, flooding or rainfall can affect embryonic development rate directly or indirectly by interacting with nest temperatures [128]. For example, eggs of painted turtles had longer incubation duration in watered nests without any change in nest temperatures because of water saturation-induced hypoxic conditions that disrupted embryonic development in eggs [129].…”

Mitigating the effects of climate change on the nests of sea turtles with artificial irrigation

“…However, irrigation decreases the temperature and usually results in higher NWC (Erb et al., 2018 ; Hill et al., 2015 ), and NWC can influence other environmental variables, including PO 2 and salinity (Booth, 1998 ; Foley et al., 2006 ). Gatto and Reina ( 2022 ) reviewed the effect that changes in NWC have on other environmental variables. Generally, elevated NWC results in lower temperature and oxygen availability (Ackerman, 1997 ).…”

“…However, NWC may directly influence sex determination in sea turtles (Lolavar & Wyneken, 2017 , 2020 ). Gatto and Reina ( 2022 ) extensively reviewed the effects of moisture on reproductive success and offspring traits in nonsquamate reptiles. There are currently no reviews on birds or insects, but moisture affects offspring phenotypes in both (Klimstra et al., 2009 ; Norhisham et al., 2015 ).…”

Sand characteristics do not influence hatching success of nests at the world’s largest green turtle rookery

“…Sea turtle embryos develop successfully only at incubation temperatures between approximately 25°C and 33°C (Ackerman 1997;Howard et al 2014), although embryos can survive temperatures up to 36°C during the latter stages of their development (Booth 2017). The influence of substrate moisture and oxygen partial pressure on embryonic development are less well studied, but under extreme conditions are associated with decreased hatching success (McGehee 1990;Ackerman 1997;Bézy et al 2014Bézy et al , 2015Gatto and Reina 2022), and in the case of moisture content, can also influence hatchling size (McGehee 1990;Erb et al 2018), and sex, although the moisture effect on sex may be a consequence of the moisture content on incubation temperature (Lolavar and Wyneken 2017). In theory and in practise, both water and oxygen availability to the developing embryos are dependent on the physical properties of the nest substrate, particularly substrate particle size (Mortimer 1990).…”