Effects of maternal basking and food quantity during gestation provide evidence for the selective advantage of matrotrophy in a viviparous lizard

Abstract

The evolution of matrotrophy (i.e., direct supply of nutrients by the mother during gestation) may be associated with high maternal energy availability during gestation. However, we lack knowledge about the selective advantages of matrotrophic viviparity (live-bearing) in reptiles. In reptiles, the interaction between body temperature and food intake affect maternal net energy gain. In the present study, we examined the effects of basking and food availability (2 by 2 factorial design) during gestation on offspring phenotype in a matrotrophic viviparous lizard (Pseudemoia entrecasteauxii). Subsequently, we investigated if the maternal effects were context-dependent using offspring growth rate as an indicator of the adaptive significance of matrotrophy. Offspring were exposed either to the same thermal conditions as their mothers experienced or to thermal conditions different from those experienced by their mothers. We provide the first evidence that an interaction between maternal thermal and maternal food conditions during gestation strongly affects offspring phenotype, including date of birth, body size and performance ability, which affect offspring fitness. Offspring growth rate was dependent on offspring thermal conditions, but was not influenced by maternal effects or offspring sex. Matrotrophic viviparity provided gravid females with the means to enhance offspring fitness through greater energetic input to offspring when conditions allowed it (i.e., extended basking opportunity with high food availability). Therefore, we suggest that selective advantages of matrotrophic viviparity in P. entrecasteauxii may be associated with high maternal energy availability during gestation.

Figure 1. Frequency of births (3 day increments) for Pseudemoia entrecasteauxii.

White bars indicate high food availability during gestation, while black bars indicate low food availability during gestation. Graph A shows date of birth in offspring from females given extended basking availability during gestation. Graph B shows date of birth in offspring from females given restricted basking availability during gestation. Three day increments begin with the first recorded births on Dec 7 2007.

Figure 2. Effects of maternal gestation conditions on offspring Pseudemoia entrecasteauxii.

A: snout-vent length (SVL), B: body mass, C: sprint speed and D: fat reserves relative to body mass at birth from females given combinations of extended and restricted basking opportunities and food supply during gestation. Values are means ± S.E. •: Offspring from females given high food availability during gestation. ○: Offspring from females given low food availability during gestation.

Figure 3. Offspring growth rate over five weeks in Pseudemoia entrecasteauxii under the two thermal regimes.

•: Offspring from females given 12 hours basking opportunity with high food availability during gestation. ○: Offspring from females given 12 hours basking opportunity with low food availability during gestation. ▪: Offspring from females given 4 hours basking opportunity with high food availability during gestation. □: Offspring from females given 4 hours basking opportunity with low food availability during gestation. Sample sizes among offspring given 12 hours basking opportunity per day are • = 17, ○ = 13, ▪ = 16 and □ = 14. Sample sizes among offspring given 4 hours basking opportunity per day are • = 18, ○ = 17, ▪ = 13 and □ = 12. Values are means ± S.E. Some overlapping points have been displaced laterally to aid clarity.