Abstract
Larks constitute an avian family of exceptional cryptic diversity and striking examples of convergent evolution. Therefore, traditional morphology-based taxonomy has recurrently failed to reflect evolutionary relationships. While taxonomy ideally should integrate morphology, vocalizations, behaviour, ecology, and genetics, this can be challenging for groups that span several continents including areas that are difficult to access. Here, we combine morphometrics and mitochondrial DNA to evaluate the taxonomy of Calandrella larks, with particular focus on the African C. cinerea and the Asian C. acutirostris complexes. We describe a new range-restricted West African taxon, Calandrella cinerea rufipecta ssp. nov. (type locality: Jos, Plateau State, Nigeria), with an isolated relic population 3000 km from its closest relative in the Rift Valley. We performed molecular species delimitation, employing coalescence-based multi-rate Poisson Tree Processes (mPTP) on cytochrome b sequences across 52 currently recognized lark species, including multiple taxa currently treated as subspecies. Three species-level splits were inferred within the genus Calandrella and another 13 across other genera, primarily among fragmented sub-Saharan taxa and taxa distributed from Northwest Africa to Arabia or East Africa. Previously unknown divergences date back as far as to the Miocene, indicating the presence of currently unrecognized species. However, we stress that taxonomic decisions should not be based on single datasets, such as mitochondrial DNA, although analyses of mitochondrial DNA can be a good indicator of taxa in need of further integrative taxonomic assessment.
Highlights
Despite being a central entity in biology, the definition of a species is under constant debate, e.g., [1,2,3], and the application of different species definitions—with focus varying from, e.g., reproductive isolation, diagnosable characters, or monophyly [4,5]—result in widely different delineations [6]
Taxonomy has traditionally been based on morphology, including plumage patterns, and convergent as well as divergent evolution has often led to misclassifications at every taxonomic level, e.g., [17,18,19,20,21,22]
Our study suggests that opposing patterns of phenotypic differentiation and convergence in the open-habitat specialist family Alaudidae have resulted in a taxonomy that often does not reflect the evolutionary history as inferred by mitochondrial markers, and previously by multilocus data [25]
Summary
Despite being a central entity in biology, the definition of a species is under constant debate, e.g., [1,2,3], and the application of different species definitions—with focus varying from, e.g., reproductive isolation, diagnosable characters, or monophyly [4,5]—result in widely different delineations [6]. Whereas gene flow could theoretically homogenize the full genomes between interbreeding species, save a few specific genes that maintain striking difference in, e.g., coloration and perception [12,13], other lineages may have been isolated so long that they are—or would be—reproductively isolated upon secondary contact, but differ ever so slightly in morphology or/and behaviour, e.g., [14,15]. Such cryptic taxa are often discovered through DNA sequencing and open a new window to diversity and conservation [16]. Taxonomy has traditionally been based on morphology, including plumage patterns, and convergent as well as divergent evolution has often led to misclassifications at every taxonomic level, e.g., [17,18,19,20,21,22]
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