ABSTRACT
Molecular genetic studies shed light on the processes and constraints that led to present species distributions. DNA sequences have become instrumental in constructing a modern phylogeny of plovers with subsequent comparative analyses revealing that plover ancestors evolved in the Northern hemisphere. Detailed molecular investigations have helped to clarify taxonomic relationships and species delimitations of controversial plover taxa. The results of molecular studies have practical implications for conservation management, helping to delineate species and populations. For example, an analysis of molecular characters identified substantial differences between the threatened American Snowy Plover (Charadrius nivosus) and the Eurasian Kentish Plover (C. alexandrinus) leading to restoration of full species status for Snowy plovers. Yet taxonomic analyses are ongoing and phylogenetic studies constantly bring up new questions and challenges. Whether Charadrius plovers form a monophyletic clade or some species are more closely related to lapwings (Vanellus spp.) is currently under debate. Some species such as Kentish/White-faced Plover (C. alexandrinus) and Greater Sand-Plover (C. leschenaultii) may harbor further cryptic species and are awaiting a more detailed investigation. At the population level, genetic analyses show patterns of high gene flow and a general lack of genetic structure over large geographic distances within many plover species. The extent of gene flow and lack of population differentiation across entire continental distributions shown by some plover species is remarkable even in comparison with other highly dispersive birds. Variation in the patterns of gene flow among plover species is explained by four characteristics: (1) habitat specialization, (2) mating behavior and breeding dispersal, (3) colonization of oceanic islands, and (4) past population fluctuations due to climatic changes. Surprisingly, the role of seasonal migration in maintaining gene flow appears to be of less importance in plovers. Methodological improvements, such as high throughput sequencing, offer great promise for the future. New molecular studies are likely to resolve many open questions on the past and present status of plover populations that are of interest to conservationists, ecologists, and evolutionary biologists alike.
