Sex of incubation neighbours influences hatchling sexual phenotypes in an oviparous lizard

Abstract

In many litter-bearing mammals and in a few viviparous reptiles the sex ratio of the entire brood or the sex of the adjacent fetuses induces sex-specific differences in the hatchling's phenotype. This study examines whether the sex of incubation neighbours affects hatchling characteristics in oviparous common lizards (Lacerta vivipara). Oviparous common lizards lay eggs with thin eggshells and, therefore, are an optimal model organism for studying the effects of hormone leakage among developing embryos since the strongest evidence for prenatal sex ratio effects on offspring development comes from viviparous populations of the same species. Groups of three eggs were incubated together and were categorised according to the sex of the resulting hatchlings as either homosex (three hatchlings of the same sex) or heterosex (one male or one female hatchling plus two siblings of the opposite sex). Hatchlings incubated adjacent to siblings of the same sex had larger body mass and body condition. Males tended to have lower ventral scale counts when incubated with other males. Conversely, females tended to have more ventral scales when incubated with other females, indicative of a more feminised phenotype. There was also a significant interaction between hatchling sex and incubation environment with respect to the length of the fourth digit of the hindlimb, likely indicative of masculinisation in heterosex females. This study suggests steroid diffusion between adjacent eggs in a minimally manipulative experiment and provides the first evidence for developmental effects of the exogenous hormonal environment in near natural conditions in an oviparous amniote. Implications of these results for the evolution of within-clutch sex ratio are discussed.

Digit Ratio, Color Polymorphism and Egg Testosterone in the Australian Painted Dragon

“…Our study is the first to provide direct evidence of such a link in a reptilian species. It corroborates indirect evidence from a study on common lizards ( Lacerta vivipara ) which suggested an influence of prenatal sex hormones on digit development in reptiles [21]. In this study, female common lizard embryos tended to have longer, male-like digits when developing together with two male embryos implying hormone leakage between developing embryos.…”

“…Although the second (2D) and the fourth (4D) digit are the most commonly measured digits (because of the frequently used 2D:4D digit ratio) other digit lengths appear to be informative as well [21], [45], [46]. In an initial test we therefore measured the second, third and fourth toe on the right hind foot of 12 adult individuals (6 males and 6 females) twice within the interval of an hour.…”

Shift in Thermal Preferences of Female Oviparous Common Lizards During Egg Retention: Insights into the Evolution of Reptilian Viviparity

“…As has been previously found in the same population (Braña 2008;Rodríguez-Díaz et al 2010), SVL, abdomen, and tail length of hatchlings varied according to sex, with the SVL and abdomen being longer in females (SVL: F 1,117 = 68.69, P \ 0.001; abdomen length: Table 1), and the tail being longer in males (Table 1). Furthermore, hatchling males were more robust than females (body mass with SVL as covariate; Table 1).…”

Sex-specific fitness returns are too weak to select for non-random patterns of sex allocation in a viviparous snake

“…Symbols are staggered in b for purposes of presentation. Unbroken curves correspond to the prediction from a logistic regression and dashed curves correspond to point-wise confidence bounds effects of sex ratio biases for the fitness of juveniles, for example due to hormonal interactions between male and female embryos (Brana 2008;Uller 2003); the costs of sex ratio control (Pen and Weissing 2002); and a life history characterized by small litters of large offspring and substantial costs of reproduction (Baron et al 1996;Pen and Weissing 2002). The occurrence of sex ratio biases and facultative sex allocation strategies in other snakes suggest Total clutch size Body mass at birth (g) b Fig.…”