Population genetic structure of Grauer's Swamp Warbler Bradypterus graueri, an Albertine Rift endemic

Abstract

The endangered warbler Bradypterus graueri is endemic to the Albertine Rift, where it is restricted to montane swamps above 1900 m across the region. We studied genetic structure among six populations sampled across the species' distribution in northern Burundi, Rwanda, Uganda and the eastern Democratic Republic of Congo. A total of 2117 base pairs of mitochondrial data were sequenced. Phylogenetic analyses and network reconstruction of B. graueri haplotypes recovered three clades with a defined geographical pattern: clade 1, Virunga Volcanoes and Kigezi Highlands; clade 2, Rugege Highlands; and clade 3, Kahuzi‐Biega Highlands; clades 2 and 3 are sisters to each other. Both landscape dynamics and historical climate are likely to have played a role in the diversification of this species. The divergence between clade 1 and clades 2 and 3 (168.5 ka, 95% HPD 108.5, 244.4) coincides with a prolonged period of aridity in tropical Africa between 130 and 270 ka. Similarly, the divergence between clades 2 and 3 (99.4 ka, 95% HPD 55.4, 153.8) corresponds with a period of aridity just prior to 94 ka. Populations sampled from the eastern arm of the central Albertine Rift (Kigezi and Rugege Highlands) show a coincident increase in effective population size after the Last Glacial Maximum at c. 15 ka, whereas those sampled from Kahuzi‐Biega on the western arm of the rift do not. Despite the perceived higher vagility of bird species relative to other vertebrates, the degree of phylogeographical structure among populations of B. graueri is similar to that reported for small mammals (Hylomyscus vulcanorum, Lophuromys woosnami, Sylvisorex vulcanorum) and a frog Hyperolius castaneus sampled across the central Albertine Rift. Collectively our results suggest that climate dynamics associated with late Pleistocene cycles had a significant influence on driving the population genetic structure and associated levels of genetic diversity in B. graueri and other small terrestrial vertebrates. Our results have implications for the conservation of B. graueri and other endemics to the Albertine Rift, particularly in the context of other phylogegeographical studies centred on this biodiversity hotspot.

The critically endangered forest owlet Heteroglaux blewitti is nested within the currently recognized Athene clade: A century-old debate addressed

“…Endemic and endangered species are often ecologically specialized and there is an urgent need to better understand the ecology and phylogenetic history of endangered species to uncover features that might be crucial for conservation. Such species could be viewed as model species to understand evolutionary processes in the landscape of their occurrence [ 1 – 3 ]. However, our knowledge of the evolutionary history of highly restricted, endemic species in the tropics is limited, due to their rarity and incomplete genetic sampling [ 4 ].…”

Comparative niche modeling of two bush-shrikes (Laniarius) and the conservation of mid-elevation Afromontane forests of the Albertine Rift

“…Evidence for elevational structuring of avian communities in the region is based on data for the Rwenzori Mountains (Willard et al 1996, Dehn andChristiansen 2001) and the Itombwe Plateau (Prigogine 1980). The primary conservation focus in the Albertine Rift has been on montane forests, with less consideration of geography and species distributions (Kahindo et al 2007(Kahindo et al , 2017, although recent models predict regional montane forest connectivity for some endemic birds in the face of climate change and intervening habitat (Bagchi et al 2018). The region's flagship animals include endangered species such as the eastern gorilla (Gorilla beringei) and Grauer's Swamp Warbler (Bradypterus graueri; Kahindo et al 2017), but the region is a hotspot for .40 endemic species of birds (Prigogine 1980, Bober et al 2001, Plumptre et al 2007.…”

“…The primary conservation focus in the Albertine Rift has been on montane forests, with less consideration of geography and species distributions (Kahindo et al 2007(Kahindo et al , 2017, although recent models predict regional montane forest connectivity for some endemic birds in the face of climate change and intervening habitat (Bagchi et al 2018). The region's flagship animals include endangered species such as the eastern gorilla (Gorilla beringei) and Grauer's Swamp Warbler (Bradypterus graueri; Kahindo et al 2017), but the region is a hotspot for .40 endemic species of birds (Prigogine 1980, Bober et al 2001, Plumptre et al 2007. New vertebrate species are still being described from the area, including birds (Engel et al 2014), small mammals (Kerbis Peterhans et al 2013a, 2013b, lizards (Greenbaum et al , 2012, and amphibians (Evans et al 2011, Greenbaum et al 2013, Portillo and Greenbaum 2014a, 2014b.…”

Genetic isolation in an endemic African habitat specialist

“…During this time, dramatic landscape changes have occurred in eastern Africa. First, habitats here have been affected by longterm aridification with episodic periods of extreme humidity (Maslin et al 2014, Voelker et al 2014, Kahindo et al 2017. Secondly, mountain ranges and deep lake basins continued to form as the central plateau of Africa uplifted.…”

“…Although it is not possible to date the divergence of the two subspecies without further molecular clock analyses, studies in a range of African bird species have highlighted the importance of palaeoclimatic events and habitat changes on patterns of dispersal, vicariance and speciation (Fjelds a & Bowie 2008, Voelker & Light 2011, Oatley et al 2012, Kahindo et al 2017. Open savannah and grassland habitats have dominated much of sub-Saharan Africa (with the exception of the Guinea-Congolian forests) for the last few million years .…”