The reproductive ecology drivers of egg attendance in amphibians

Abstract

Parental care is extremely diverse but, despite much research, why parental care evolves is poorly understood. Here we address this outstanding question using egg attendance, the simplest and most common care form in many taxa. We demonstrate that, in amphibians, terrestrial egg deposition, laying eggs in hidden locations and direct development promote the evolution of female egg attendance.Male egg attendance follows the evolution of hidden eggs and is associated with terrestrial egg deposition but not with direct development. We conclude that egg attendance, particularly by females, evolves following changes in reproductive ecology that are likely to increase egg survival, select for small clutches of large eggs and/or expose eggs to new environmental challenges. While our results resolve a long-standing question on whether reproductive ecology traits are drivers, consequences or alternative solutions to caring, they also unravel important, yet previously unappreciated, differences between the sexes.

Benefits and costs of female and male care in amphibians: a meta-analytical approach

“…Our findings also show that the benefits of egg attendance are not dependent on the type of breeding site. A comprehensive comparative study has found that the emergence of both male and female egg attendance in amphibians is associated with egg deposition in concealed sites [29]. There are two non-mutually excluding hypotheses to explain this association: (i) eggs laid in exposed sites may be easier for predators to find [23,28] and (ii) concealed sites may decrease parental mortality imposed by predators [29].…”

“…To test whether the magnitude of benefits and costs differ according to the caring sex, we ran models with sex (female or male) as moderator. To test whether egg survival is affected by the type of breeding site (concealed or exposed sites, following classification in [29]), we ran models with this moderator. We also tested whether non-reproductive costs are affected by the form of parental care.…”

“…The dataset includes only cases of egg attendance in which parental presence may decrease mortality by predation and dehydration. In total, we have data for 9 species with maternal care (29 effect sizes), 21 with paternal care (44 effect sizes) and 2 with biparental care (3 effect sizes) in which the identification of the caring sex was determined by the egg-tending sex (females: 29 We found 22 studies (68 effect sizes, 15 species) exploring the non-reproductive costs of parental care, from which we extracted several measurements commonly employed to evaluate body condition in amphibians (reviewed and discussed in [33]): (a) different indices of body condition, usually residuals of a regression between body size and body mass; (b) fat content, usually comparing parental and non-parental individuals; (c) body mass, usually measured at the beginning and end of the caring period; (d) gut content, usually comparing parental and non-parental individuals; (e) growth or mass change in species with continuous growth during the breeding season (such as some salamanders included in our dataset); and (f) locomotor performance while carrying eggs or tadpoles on the dorsum, a behaviour that increases parental expenditure and may affect body condition. Given that the number of studies quantifying mortality risk during the caring period was small (e.g.…”

“…The forms of parental care in amphibians vary widely, from egg attendance to trophic egg feeding during tadpole development ( [26][27][28], figure 1). A recent comparative study has shown that male and female egg attendance in amphibians primarily occurs when eggs are laid in concealed places like subterranean burrows, tree holes, or underneath rocks, logs or leaf litter [29]. The authors suggest that oviposition in concealed places, which precedes the evolution of egg attendance, enhances egg survival, particularly in terrestrial environments.…”

“…In the case of females, terrestrial eggs with direct development also favour the evolution of egg attendance, probably because the eggs are large and few in number. Therefore, they represent a significant maternal investment, and the loss of a clutch would entail a high cost to the females [29]. Finally, tadpole feeding with trophic eggs is associated with oviposition in phytotelmata where predation pressure is low, but food resources for tadpole development are scarce [30].…”