Wednesday, August 8, 2012

[Ornithology • 2007] Phylogenetic conservatism and antiquity of a tropical specialization: Army-ant-following in the typical antbirds (Thamnophilidae)

Researchers found some tropcial birds that are completely reliant on army ants for food. (Credit: Image courtesy of Dan Lebbin)
Map: Species-richness maps of (a) occasional/non-following species that are sister to ant-following clades A, B, and C (Fig. 1); (b) obligate army-ant-followers, with distributions of Myrmeciza fortis (obligate) and M. melanoceps (occasional) outlined; (c) regular army-ant-followers (pooling thamnophilid and furnariid species); (d) regular thamnophilid army-ant-followers.

One of the most novel foraging strategies in Neotropical birds is army-ant-following, in which birds prey upon arthropods and small vertebrates flushed from the forest floor by swarm raids of the army-ant Eciton burchellii. This specialization is most developed in the typical antbirds (Thamnophilidae) which are divisible into three specialization categories: (1) those that forage at swarms opportunistically as army-ants move through their territories (occasional followers), (2) those that follow swarms beyond their territories but also forage independently of swarms (regular followers), and (3) those that appear incapable of foraging independently of swarms (obligate followers). Although army-ant-following is one of the great spectacles of tropical forests, basic questions about its evolution remain unaddressed. Using a strongly resolved molecular phylogeny of the typical antbirds, we found that army-ant-following is phylogenetically conserved, with regular following having evolved only three times, and that the most likely evolutionary progression was from least (occasional) to more (regular) to most (obligate) specialized, with no reversals from the obligate state. Despite the dependence of the specialists on a single ant species, molecular dating indicates that army-ant-following has persisted in antbirds since the late Miocene. These results provide the first characterization of army-ant-following as an ancient and phylogenetically conserved specialization.

Keywords: Ancestral character state reconstruction; Army-ant-following; Ecological specialization; Eciton; Foraging strategies; Thamnophildae

Some Tropical Birds Depend Completely On Army Ants To Flush Out Prey

Phylogenetic conservatism and antiquity of a tropical specialization: Army-ant-following in the typical antbirds (Thamnophilidae)