Selection for increased maternal body volume does not differ between two Scincella lizards with different reproductive modes

Body size and shape are among the most important determinants of reproductive output in diverse animal taxa. We compared morphology and reproductive output between two Scincella lizards (Scincidae), Scincella modesta (oviparous) and Scincella reevesii (viviparous), to examine whether viviparous females compensate for their lower reproductive output by modifying maternal body size and/or shape. As predicted, reproductive output was lower in S. reevesii than in S. modesta when corrected for body size. The two lizards differed morphologically, but were similar in three aspects: females were the larger sex, the relative head size was greater in adult males, and the relative abdomen size was greater in adult females. Sexual dimorphism in abdomen length (AL) was more evident in S. reevesii than in S. modesta, but this difference was attributable to a smaller sexual difference in AL in S. modesta, rather than to the greater relative maternal AL in S. reevesii. Female S. reevesii on average were larger than female S. modesta in snout–vent length (SVL), but this increase in overall body size cannot be viewed as a way of allowing female S. reevesii to compensate for lower reproductive output, as the linear slope of reproductive output against maternal SVL did not differ between the two species. Our data show that selection for increased maternal body volume does not differ between the two Scincella lizards with different reproductive modes.