High food abundance permits the evolution of placentotrophy : evidence from a placental lizard, Pseudemoia entrecasteauxii

Mechanisms of reproductive allocation are major determinants of fitness because embryos cannot complete development without receiving sufficient nutrition from their parents. The nourishment of offspring via placentas (placentotrophy) has evolved repeatedly in vertebrates, including multiple times in squamate reptiles (lizards and snakes). Placentotrophy has been suggested to evolve only if food is sufficiently abundant throughout gestation to allow successful embryogenesis. If scarcity of food prevents successful embryogenesis, females should recoup nutrients allocated to embryos via abortion, reabsorption, and/or cannibalism. We tested these hypotheses in the placentotrophic southern grass skink Pseudemoia entrecasteauxii. We fed females one of four diets (high constant, high variable, low constant, and low variable) during gestation and tested the effects of both food amount and schedule of feeding on developmental success, cannibalism rate, placental nutrient transport, offspring size, and maternal growth and body condition. Low food availability reduced developmental success, placental nutrient transport, offspring size, and maternal growth and body condition. Cannibalism of offspring also increased when food was scarce. Schedule of feeding did not affect offspring or mothers. We suggest that high food abundance and ability to abort and cannibalize poor-quality offspring are permissive factors necessary for placentotrophy to be a viable strategy of reproductive allocation.