Floral paedomorphy leads to secondary specialization in pollination of Malagasy Dalechampia (Euphorbiaceae)

The traditional evolutionary interpretation of Von Baer’s “laws” of embryology is that retention of early developmental forms into adulthood (paedomorphosis) leads to the evolution of simpler or more generalized morphology and ecology. Here we show that paedomorphosis can also be involved in an increase in ecological specialization, in this case of plant-pollinator relationships. A paedomorphic transition from generalized pollination (by several functional types of pollinators) to specialized pollination (by one or a few species in one functional type) occurred in a clade of endemic Malagasy vines (Dalechampia spp., Euphorbiaceae). This evolutionary transition involved staminate flowers that fail to develop “normally,” instead holding mature pollen inside virtually unopened, bud-like flowers. This paedomorphic morphology restricts reward access to “buzz-pollinating” bees, specifically Xylocopa sp. (carpenter bees), which can remove pollen by sonication. This is one of very few reports o...