Nick's research focuses on diversification patterns in an endemic radiation of Malagasy passerine birds and how those patterns can broadly inform on topics like taxonomy, conservation, and speciation. The focus of his research is the family Bernieridae, which comprises 11+ species of warbler-like birds found mostly in the eastern rainforests of Madagascar. The history of the family is unique in that its members were previously classified in three very different families: Old World warblers, babblers, and greenbuls. Only recently, through analysis of DNA sequences, were the members realized to belong to their own endemic family, which has been evolving on Madagascar for perhaps 20 million years! Nick uses DNA sequencing as the primary tool in his research as well. Using data from mitochondrial DNA sequences, nuclear DNA sequences, and microsatellites, he is examining unexpected patterns of cryptic diversity within several members of the family. Despite showing virtually no phenotypic differences, these species harbor significant genetic diversity. In one case, the data show that one species is actually three very cryptic species that first began diverging ~7.5 million years ago. These cryptic species are roughly separated along elevational and ecological lines, highlighting the underemphasized role that elevation has played in the diversification of birds in Madagascar. In another case, one species comprises four lineages that are as genetically distinct (or more so!) than many sister bird species that look nothing alike! Amazingly, these four lineages appear to now be merging back into one despite having first separated ~3.5 million years ago or more, which is an unprecedented scenario in birds (and possibly in all vertebrates). The reasons behind this are also a focus of Nick's research, and he is exploring the role that widespread deforestation of lowland rainforests might have played.
In addition to DNA from the birds, Nick collects DNA sequence from some of the birds' ectoparasites, particularly chewing lice. One genus, Myrsidea, is very host-specific and can be used as a proxy to confirm or to clarify certain questions about the birds' evolutionary history. When trying to untangle the novel scenario of these birds' cryptic diversity, it is very important to assemble as many types of datasets as possible to establish a comparative framework, and the lice are a perfect example of how useful this approach can be. Comparing these datasets across species in the Bernieridae will help answer questions regarding the role that genetic divergence plays in maintaining species boundaries, the taxonomy of allopatric cryptic taxa, the role of elevation in generating diversity in tropical forests, and others. Additionally, although Madagascar's native forests are diminishing rapidly everywhere, the rate of lowland deforestation in the relatively unprotected southeastern region is the highest, and Nick hopes his research will support the growing evidence that this region harbors unique biodiversity in need of conservation.
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