The Role of Nest Depth and Site Choice in Mitigating the Effects of Climate Change on an Oviparous Reptile

Abstract

Climate change is likely to have strong impacts on oviparous animals with minimal parental care, because nest temperature can impact egg development, sex, and survival, especially in the absence of mitigation via parental care. Nesting females may compensate for increasing temperatures by altering how, when, and where they nest. We examined the factors determining nest depth and site choice as well as the effects that nest depth and location have on nest temperature and hatching success in the diamondback terrapin (Malaclemys terrapin). We found that nest depth was not correlated with nesting female size, egg characteristics, or daily temperatures. Nest temperatures and hatching success were correlated with different environmental and nest characteristics between 2004, a cool and wet year, and 2005, a hot and dry year. Females selected nests with lower southern overstory vegetation in 2005. These results suggest that nest depth and location can play an important yet varying role in determining nest temperature and hatching success in more extreme warm and dry environmental conditions and, therefore, may mitigate the impacts of climate change on oviparous reptiles. However, we found minimal evidence that turtles choose nest locations and depths that maximize offspring survival based on short-term environmental cues.

Can Reptiles Use Nest Site Choice Behavior to Counter Global Warming Effects on Developing Embryos? Potential Climate Responses in a Turtle

“…Oviparous ectothermic animals can theoretically offset climate warming effects on developing embryos by nesting in cooler microhabitats, given certain assumptions such as the heritability of nest site choice behaviors, the rate of climate change relative to the rate of evolutionary response, and the availability of cooler potential nest sites. Surprisingly few studies have quantified the availability of thermally heterogeneous potential nest sites in oviparous animals within the context of climate change (but see Refsnider et al, 2013a;Czaja et al, 2020). Our study produced four lines of evidence that softshell turtle mothers may be able to use nest site choice behavior to offset climate warming effects on incubation temperatures.…”

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

“…Research has focused on nesting phenology and non-squamates generally start nesting earlier in response to increased temperatures (Cherkiss et al 2020 ; Janzen et al 2018 ; Lamont and Fujisaki 2014 ; Monsinjon et al 2019 ; Schwanz and Janzen 2008 ; Weishampel et al 2004 , 2010 ) preceding the nesting season (Janzen et al 2018 ; Lovich et al 2012 ). Nesting females may also be able to select nest sites or depths that mitigate the effects of altered incubation conditions, if they are available (Czaja et al 2020 ; Liles et al 2019 ; Mitchell et al 2008 ; Reboul et al 2021 ; Refsnider and Janzen 2012 ; Staines et al 2019 ).…”

Turtle Nest-Site Choice, Anthropogenic Challenges, and Evolutionary Potential for Adaptation

“…The ambient temperature eggs experience depends on many external factors (Czaja et al, 2020), including air temperature, which is influenced by clouds, solar radiation, and time of day. Cloud cover reduces the shortwave solar radiation reaching the ground, leading to a lower maximum daily temperature and increasing the minimum daily temperature by enhancing the longwave radiation (Janzen and Morjan, 2001).…”

“…Deeper nests are cooler than shallower nests and are less affected by extreme temperature fluctuations detrimental to hatchling viability (Valenzuela, 2001a;Marco et al, 2018). For instance, hatching success in diamondback terrapins (Malaclemys terrapin) improved with nest depth (which ranges from 13 to 17 cm) during an unusually hot and dry season, but not during a more favorable season (Czaja et al, 2020). Further, no evidence was detected that females altered their nesting location to improve offspring survival short-term.…”

“…Temperature variability within nests can accelerate the feminization of TSD turtle populations and cause increased mortality of developing embryos, such as in painted turtles (Valenzuela et al, 2019) and potentially in other shallow nesting taxa, with long-lasting consequences (Noble et al, 2018). In contrast, the observation in Malaclemys terrapin that greater nest depth can protect against extreme and fluctuating temperatures (Czaja et al, 2020), even though nests in this turtle are only 13-17 cm below the surface, suggests that deeper-nesting taxa may be somewhat buffered against climate change. But shallower-nesting taxa, such as painted turtles, whose nests are 7-11 cm below the surface, remain vulnerable to accentuated thermal fluctuations.…”