Abstract
Understanding and resolving conflicts between phenotypic and genetic differentiation is central to evolutionary research. While phenotypically monomorphic species may exhibit deep genetic divergences, some morphologically distinct taxa lack notable genetic differentiation. Here we conduct a molecular investigation of an enigmatic shorebird with a convoluted taxonomic history, the White-faced Plover (Charadrius alexandrinus dealbatus), widely regarded as a subspecies of the Kentish Plover (C. alexandrinus). Described as distinct in 1863, its name was consistently misapplied in subsequent decades until taxonomic clarification ensued in 2008. Using a recently proposed test of species delimitation, we reconfirm the phenotypic distinctness of dealbatus. We then compare three mitochondrial and seven nuclear DNA markers among 278 samples of dealbatus and alexandrinus from across their breeding range and four other closely related plovers. We fail to find any population genetic differentiation between dealbatus and alexandrinus, whereas the other species are deeply diverged at the study loci. Kentish Plovers join a small but growing list of species for which low levels of genetic differentiation are accompanied by the presence of strong phenotypic divergence, suggesting that diagnostic phenotypic characters may be encoded by few genes that are difficult to detect. Alternatively, gene expression differences may be crucial in producing different phenotypes whereas neutral differentiation may be lagging behind.
Highlights
Explaining the occurrence and maintenance of phenotypic variation has been a central theme in evolutionary biology for more than 150 years
Phenotypic species delimitation We used the species delimitation criteria recently proposed by Tobias et al [24] to assess the biological species status of dealbatus based on the morphometric, ecological, behavioral and plumage characters presented by Kennerley et al [23] (Table 1)
The total score amounted to 8, which is greater than the ‘‘species threshold’’ set by Tobias et al [24] at 7, indicating that alexandrinus and dealbatus display a phenotypic differentiation that is typical for members of different species
Summary
Explaining the occurrence and maintenance of phenotypic variation has been a central theme in evolutionary biology for more than 150 years. Darwin [1] derived many of the insights and ideas for his seminal work by observing the phenotypic diversity of pigeon breeds. When present in natural populations, phenotypic variation still provides challenges for taxonomy and systematics today, and the molecular machinery behind it has only just begun to be unraveled. Phenotypic characters have been the traditional taxonomic tool of choice and continue to contribute a major share to our current understanding of the Earth’s zoological diversity. Apart from corroborating most of our long-standing classification of animals, these new molecular data routinely refine our insights into relationships between groups for which phenotypic characters seem to have been exhausted [3]. Molecular results are at odds with previous phenotype-based hypotheses, which sometimes leads to a re-examination of the latter under more appropriate assumptions and an eventual removal of conflict [4]
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