Contrasting Phylogeography and Speciation History of Birds in The Northern Andes: a comparative phylogeographic approach

Abstract

Biological diversity is generally very high in mountain systems around the world, with the Andes containing one third of the world's bird species with many restricted species. Species with similar geographic distributions have been proposed as probably having a shared evolutionary history. Several speciation models for the origin and diversification of mountain organisms are 1) vicariance and isolated populations with posterior allopatric speciation, and 2) parapatric/peripatric speciation along elevational gradients. I explored the phylogeography of five separate lineages of co-distributed Andean mountain bird sister species with different trophic affinities (insectivores, nectarivores, frugivores, and frugivore/insectivores). Sister species belong to two different Orders and four Families: Ovenbirds Treerunners Margarornis and Tuftedcheeks Pseudocolaptes; Hummingbirds Aglaiocercus; Tanagers Anisognathus; and a Sparrow Chlorospingus. In each pair one sister is range-restricted to the Pacific Andean slopes of Western Colombia and NW Ecuador and in partial syntopy with its widespread sister found also in other mountain ranges. By contrasting their phylogeographies, I tested which speciation mode better explained their relationships, and whether a single biogeographic event explained the geographical distributions and divergence times. I co-estimated the relationships and divergence times using a Bayesian analysis (StarBEAST) with two mitochondrial genes Cyt-b - ND2 and two nuclear introns FIBi7 - TGFB2i5. The five groups showed non-concordant topologies, suggesting different evolutionary histories between the sisters' species. The geographical branching patterns are somewhat similar, but not the divergence times. Results suggest speciation in allopatry with posterior secondary contact, with forms divided to the west (Pacific slope or Panama) and east (other two Mountain ranges), but with individual complex evolutionary histories and geographical relationships. In Chlorospingus, the contested sister species belongs to two different and separate lineages. Divergence times with mitochondrial genes and "molecular clock rates", assuming they reflect species divergences, are different for each group, and happened in the last 3.4 million years. These differences in timing and branching are probably related to repeated climatic changes in the same locations, linked to glacial/interglacial cycles. Similar geographic distributions today do not mean that all species have diverged at the same time, but the same type of events could influence them.