Resources and offspring provisioning: a test of the Trexler-DeAngelis model for matrotrophy evolution.

Theoretical models of the evolution of matrotrophy from a lecithotrophic ancestor suggest that resource availability plays a major role in selective scenarios favoring a change in offspring provisioning. We examined effects of feeding level on embryo provisioning in the livebearing fish Gambusia geiseri, a species with dual provisioning of embryos via both yolk sequestered in large eggs and post-fertilization mother-to-embryo nutrient transfer. Females were fed either once per day or once every three days for three months. Females fed daily had marginally larger brood size, significantly larger embryos, and a higher rate of nutrient transfer (assayed directly by injection of radiolabeled nutrients) than females fed every third day. There was no difference in the size of unfertilized eggs between the feeding treatments. Resource effects on matrotrophic provisioning in G. geiseri suggest that matrotrophy plays an important role in provisioning and allows females to adjust offspring size in response to resource availability.