Maternal effects in a placental live-bearing fish

Maternal effects often provide a mechanism for adaptive transgenerational phenotypic plasticity. The maternal phenotype can profoundly influence the potential for such environmentally-induced adjustments of the offspring phenotype, causing correlations between offspring and maternal traits across a variety of taxa. We studied the effects of maternal phenotype on offspring provisioning prior to and during pregnancy in the placental live-bearing fish species Poeciliopsis retropinna. Specifically, we examined how maternal traits such as body fat, lean mass and length influence pre- (i.e. allocation to eggs prior to fertilization) and post-fertilization (i.e. allocation to embryos during pregnancy) maternal provisioning and how this ultimately affects offspring size and body composition at birth. We found that maternal length proportionally increases egg mass at fertilization and offspring mass at birth, notably without changing the ratio of pre- to post-fertilization maternal provisioning. By contrast, maternal body fat strongly increases the amount of post-fertilization maternal provisioning and hence offspring mass at birth. We furthermore found that females invest first in embryo lean mass, and allocate fat reserves to embryos only very late in pregnancy. We propose the delay in fat allocation to be adaptive, because it delays an unnecessary high reproductive burden to the mother earlier in pregnancy. Our study herewith suggests that offspring provisioning is a phenotypically plastic trait that is strongly determined by maternal phenotype.