Explosive Pleistocene diversification and hemispheric expansion of a “great speciator”

Abstract

Factors that influence speciation rates among groups of organisms are integral to deciphering macroevolutionary processes; however, they remain poorly understood. Here, we use molecular phylogenetic data and divergence time estimates to reconstruct the pattern and tempo of speciation within a widespread and homogeneous bird family (white-eyes, Zosteropidae) that contains an archetypal ''great speciator.'' Our analyses show that the majority of this species-rich family constitutes a clade that arose within the last 2 million years, yielding a per-lineage diversification rate among the highest reported for vertebrates (1.95-2.63 species per million years). However, unlike most rapid radiations reported to date, this burst of diversification was not limited in geographic scope, but instead spanned the entire Old World tropics, parts of temperate Asia, and numerous Atlantic, Pacific, and Indian Ocean archipelagos. The tempo and geographic breadth of this rapid radiation defy any single diversification paradigm, but implicate a prominent role for lineage-specific life-history traits (such as rapid evolutionary shifts in dispersal ability) that enabled white-eyes to respond rapidly and persistently to the geographic drivers of diversification.diversification rate ͉ speciation ͉ Zosterops ͉ white-eye ͉ evolution D isparity in diversification rates among groups of organisms is well documented and provides unique opportunities for studying evolutionary processes underlying the genesis of biological diversity (1-7). A few groups of organisms that diversified recently and rapidly have contributed disproportionately to speciation theory by providing comparatively accessible opportunities to evaluate factors that drive speciation (1-4). These groups are also characterized by a restricted geography (e.g., archipelagos, lakes, mountain tops, etc.) circumscribed by the more extensive distribution shared by the group and its close relatives. The reduced faunas, stark geographic boundaries, and limited set of earth history influences of these confined geographies make such systems attractive for studies of diversification.Island settings are especially well known for variable speciation rates. For example, some island bird taxa spread across scattered insular landscapes with little or no differentiation, whereas others appear to have diversified rapidly across the same geographies (8). In the wake of island biogeographic theory and its antecedents (9-11), recognition of this pattern in birds resulted in characterization of a set of ''great speciator'' lineages (12), as well as a famous paradox: how can these lineages show such high degrees of differentiation across oceanic islands when their excellent dispersal ability should limit differentiation?Discussions of this paradox have appealed to intermediate dispersal ability (8,12) or to evolutionary shifts in dispersal ability (12) to explain the seeming conflict between large geographic range, implying good dispersal ability, and the high degree of morphological differentiation be...

Bird assemblage vulnerability depends on the diversity and biogeographic histories of islands

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Evolution along the Great Rift Valley: phenotypic and genetic differentiation of East African white‐eyes (Aves, Zosteropidae)

“…While the genus is generally recognized as a “great speciator” (Moyle et al. 2009; Melo et al. 2011), comparatively few species are described from East Africa.…”

Ancient host specificity within a single species of brood parasitic bird

“…In the absence of independently derived calibration points, and given that Piciformes have relatively high rates of mtDNA sequence evolution (33), we used maximum rate estimates to conservatively estimate a minimum divergence time between the two lineages. Even using the fastest estimated rates of mtDNA sequence evolution in birds (33)(34)(35), the 14.8% mtDNA divergence between Greater Honeyguide lineages corresponds to an evolutionary age of ∼3 My. For comparison, the common cuckoo C. canorus host races (gentes) appear to have diverged on the order of ∼80,000 y ago (13) and have shown imperfect host fidelity since that time (13,17).…”