Evolution of nesting behavior in megapodes.

Aim: Unique among birds, megapodes (family Megapodiidae) have exchanged the strategy of incubating eggs with the warmth of their bodies for novel incubation behaviors that rely entirely on environmental heat sources. Typically, mound-builders capture the heat released from decomposition of organic materials, while burrow-nesters lay their eggs in solar or geothermally heated soils. The evolutionary path towards novel incubation behaviors has led to ecological and physiological adaptations unique to megapodes. Here, we present a species tree for all extant megapodes that settles long-standing debates about megapode evolution, namely, their biogeographic origins and ancestral nesting behavior.
Methods: A time-calibrated multilocus species tree for all extant megapodes was constructed using the Bayesian species tree reconstruction method *BEAST. We estimated and compared divergence dates for megapodes obtained from molecular rates, fossils, and a combination of fossils and rates. Using this phylogeny, Bayesian estimation of ancestral nesting behavior was conducted in BayesTraits and ancestral ranges were estimated in BioGeoBEARS.

Results: Recent dispersal has led to the reintroduction of Megapodius to mainland Australia and New Guinea. Bayesian estimation of ancestral states indicates that mound building is the most probable ancestral nesting behavior in megapodes (posterior probability = 0.75). Burrow nesting was acquired early in the diversification of the family (at least 1.2 million year ago), followed by a single switch back to mound building.

Main Conclusions: Divergence dates and biogeographic reconstructions demonstrate that dispersal, and not vicariance, led to the isolation of megapodes in Australasia We propose that flight mediated dispersal to environmentally variable islands is responsible for the behavioral lability in nesting behaviors observed in some Megapodius species today.

Collaborators: Sharon M. Birks, Adam D. Leaché
Funding: UW Sargent Award
Progress: Early View, Journal of Biogeography
Poster: I presented the phylogenetics part of this project at NAOC-V2012 in Vancouver, BC. Check out my poster.

Never seen a megapode? Watch Daryl Jones stalking a megapode.