Avian Species Concepts in the Light of Genomics

Abstract

What is a species? This seemingly simple question has occupied the minds of numerous biologists and philosophers, resulting in the formulation of many species concepts. From a theoretical point of view, the species problem has been resolved by equating species with independently evolving lineages (i.e. the evolutionary species concept or the general lineage concept). However, the practical issues with describing and delineating species remain. The origin of species is a gradual process that typically requires thousands to millions of years, creating a grey zone of species delimitation in which taxonomy is often controversial. To account for this, an integrative taxonomy has been proposed in which different taxonomic concepts and methods are integrated in the delimitation of species. In this chapter, I argue that genomics provides another line of evidence in this pluralistic approach to species classification. Indeed, genomic data can be combined with classical species criteria, such as diagnosability, phylogeny and reproductive isolation. First, genomic data can provide an extra diagnostic feature in species delimitation. Compared to `old-school' genetic markers, the use of genome-wide markers leads to a significant rise in statistical power. Second, phylogenomic analyses can resolve the evolutionary relationships within rapidly diverging or hybridizing groups of species while taking into account gene tree discordance. Third, genomic data can be used to pinpoint the genetic basis of reproductive isolation and provide a detailed description of the speciation process. All in all, the genomic era will supply avian taxonomists with a new tool box that can be applied to old concepts, leading to better informed decisions in cataloguing biodiversity.