RESEARCH OUTLINE
Grassland birds have traditionally not received much attention from a phylogenetic or phylogeographic point of view. Grassland bird habitats are largely continuous in most parts of the world. This makes these taxa a poor study subject in terms of investigating the role of landscape-level processes such as orogeny and riverine dynamics on the shaping of gene flow. However, widespread gene flow through the lack of drivers of vicariance and the accompanying absence of reciprocally monophyletic groups within taxa are illustrative of their ecology and life history. Especially in birds of open landscapes, which are generally strong fliers (Voelker 2001), a lack of phylogeographic structure is often assumed. However, Zink (2002), in one of the few comparative studies addressing phylogeographic structure of open country birds, duly remarks that ‘it is just as important to know that a group’s history is one of population and range expansion as it is to document a history of isolation’.
Unlike in the Holarctic, Neotropical grasslands are not continuously distributed and are a mosaic of various temperate (pampa), montane (puna, páramo), and (sub)tropical (cerrado, campo, llanos) grassland types. Grasslands were much more widespread in the Neotropics during the Last Glacial Maximum (~21,000 years ago) according to several lines of evidence, including palynology (Salgado-Labourieau 1991, Van der Hammen 1979), climatic models (Markgraf 1993), and fossil deposits (Webb 1978). Many of the grassland biomes were presumably connected during the Pleistocene and have only recently become isolated, in pockets surrounding the more humid and centrally located Amazon forest. This has resulted in grassland faunas becoming isolated in these pockets, while humid biota expanded (Haffer 1969). In spite of these inferred landscape patterns, the evolution of Neotropical grassland biomes and their geographic locations are poorly known (Bush 1994), preventing meaningful comparisons between the phylogeographic history of single species and historical landscape development (Antonelli et al. 2010, Brumfield 2012).
Testing the effects of historical landscape changes on the evolution of Neotropical grassland birds will therefore necessarily involve multiple species, to find potential common population signatures indicative of joint evolution in response to landscape changes (‘comparative phylogeography’). More recently, comparative phylogeography gained momentum by the incorporation of next-generation sequencing techniques, which allow for the comparison of large parts of the genome between individuals (Smith et al. 2014). Relative to traditional sequencing, next-generation sequencing is an important tool in reducing the amount of error associated with gene flow analyses, population assignment, and divergence time estimation, among others. For this reason, it will be helpful in accurately establishing common phylogeographic and population genetic patterns among grassland birds.
Neotropical grassland bird dispersal hypotheses. Dry
habitats inluding grasslands were presumably more
widespread during the Pleistocene, providing corridors
of dispersal between different pockets of grasslands.
A. Andean corridor, B. central Amazonian corridor,
C. Atlantic coast corridor. From Da Silva & Bates 2002.
