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

Abstract

The moist and cool cloud forests of East Africa represent a network of isolated habitats that are separated by dry and warm lowland savannah, offering an opportunity to investigate how strikingly different selective regimes affect species diversification. Here, we used the passerine genus Zosterops (white‐eyes) from this region as our model system. Species of the genus occur in contrasting distribution settings, with geographical mountain isolation driving diversification, and savannah interconnectivity preventing differentiation. We analyze (1) patterns of phenotypic and genetic differentiation in high‐ and lowland species (different distribution settings), (2) investigate the potential effects of natural selection and temporal and spatial isolation (evolutionary drivers), and (3) critically review the taxonomy of this species complex. We found strong phenotypic and genetic differentiation among and within the three focal species, both in the highland species complex and in the lowland taxa. Altitude was a stronger predictor of phenotypic patterns than the current taxonomic classification. We found longitudinal and latitudinal phenotypic gradients for all three species. Furthermore, wing length and body weight were significantly correlated with altitude and habitat type in the highland species Z. poliogaster. Genetic and phenotypic divergence showed contrasting inter‐ and intraspecific structures. We suggest that the evolution of phenotypic characters is mainly driven by natural selection due to differences in the two macro‐habitats, cloud forest and savannah. In contrast, patterns of neutral genetic variation appear to be rather driven by geographical isolation of the respective mountain massifs. Populations of the Z. poliogaster complex, as well as Z. senegalensis and Z. abyssinicus, are not monophyletic based on microsatellite data and have higher levels of intraspecific differentiation compared to the currently accepted species.

Environmental correlates of phylogenetic endemism in amphibians and the conservation of refugia in the Coastal Forests of Eastern Africa

“…Broad biogeographic breaks are common in many other vertebrate taxa across other parts of sub‐Saharan Africa including ungulates (Arctander, Johansen, & Coutellec‐Vreto, ; Lorenzen et al., ), small mammals (Mynhardt et al. ), birds (Habel et al., ) and reptiles (Tolley et al., ). This points towards the importance of refugia in the persistence of biodiversity during long‐term climate change (Fjeldså & Lovett, ).…”

“…These measures are a useful proxy for historical climatic stability through deeper time (see Sandel et al, 2011) and can help to explain biogeographic breaks and endemism at the species level not only in many amphibians (e.g., Barratt et al, 2017;Loader et al, 2014;Zimkus et al, 2017) but also across other taxonomic groups. Broad biogeographic breaks are common in many other vertebrate taxa across other parts of sub-Saharan Africa including ungulates (Arctander, Johansen, & Coutellec-Vreto, 1999;Lorenzen et al, 2012), small mammals (Mynhardt et al 2015), birds (Habel et al, 2015) and reptiles (Tolley et al, 2011). This points towards the importance of refugia in the persistence of biodiversity during long-term climate change (Fjeldså & Lovett, 1997).…”

Divergence of morphological characters in two white‐eye species (Passeriformes: Zosteropidae) in sympatry

“…Habel et al. () observed a significant increase in wing length and body weight with the altitude for this species. This variation has also been documented in other similar avian systems.…”

“…Habel et al. () found that wing length and body weight were significantly correlated with altitude and habitat type in the highland species Zosterops poliogaster in East Africa. Habel et al.…”

Patterns of contact call differentiation in the panmictic East African Abyssinian White‐eye Zosterops abyssinicus (Aves: Passeriformes)

“…), phenotypic (Borghesio and Ndanganga ; Habel et al. ) and bioacoustic differences (Habel et al. ; Husemann et al.…”