Comparative Population Genomics of African Montane Forest Mammals Support Population Persistence across a Climatic Gradient and Quaternary Climatic Cycles

The Eastern Afromontane biodiversity hotspot (EABH) has the highest concentration of biodiversity in tropical Africa, yet few studies have investigated recent historical diversification processes in EABH lineages. Herein, we analyze restriction-site associated DNA-sequences (RAD-Seq) to study recent historical processes in co-distributed mouse (Hylomyscus) and shrew (Sylvisorex) species complexes, with an aim to better determine how historical paleoenvironmental processes might have contributed to the EABH’s high diversity. We analyzed complete SNP matrices of > 50,000 RAD loci to delineate populations, reconstruct the history of isolation and admixture, and discover geographic patterns of genetic partitioning. These analyses demonstrate that persistently unsuitable habitat may have isolated multiple populations distributed across montane habitat islands in the Itombwe Massif and Albertine Rift to the west as well as Mt Elgon and Kenyan Highlands to the east. We detected low genetic diversity in Kenyan Highland populations of both genera, consistent with smaller historical population sizes in this region. We additionally tested predictions that Albertine Rift populations are older and more persistently isolated compared to the Kenyan Highlands. Phylogenetic analyses support greater historical isolation among Albertine Rift populations of both shrews and mice compared to the Kenyan Highlands and suggest that there are genetically isolated populations from both focal genera in the Itombwe Massif, Democratic Republic of Congo. The Albertine Rift ecoregion has the highest mammalian tropical forest species richness per unit area on earth. Our results clearly support accelerating efforts to conserve this diversity.     

Speciation mirrors geomorphology and palaeoclimatic history in African laminate-toothed rats (Muridae: Otomyini) of the Otomys denti and Otomys lacustris species-complexes in the 'Montane Circle' of East Africa

We adopted an integrated systematic approach to delimit evolutionary species and describe phylogeographic, morphometric and ecological relationships in Otomys denti (from the Albertine Rift, Southern Rift in Malawi and the northern Eastern Arc Mountains) and Otomys lacustris (from the Southern Rift in Tanzania and Zambia, and the southern Eastern Arc Mountains). Molecular [cytochrome (cyt) b sequences, 1143 bp, N  = 18], craniometric (classical, N  = 100 and geometric, N  = 60) and ecological (Partial Least Squares regression of shape and ecogeographic variables) approaches show a profound, parallel disjunction between two groups: (1) Eastern Arc and Southern Rift (including the Malawi Rift) ( O. lacustris and Otomys denti sungae ) and (2) Albertine Rift ( Otomys denti denti and Otomys denti kempi ) taxa. Within both groups, cyt b sequences or craniometric analysis provided evidence for the differentiation of both southern and northern Eastern Arc from Southern Rift lineages (across the so-called Makambako Gap). Within the Albertine Rift ( denti – kempi ) lineage, populations from individual mountain ranges differed significantly in skull shape (but not size), but were similar genetically. Over-reliance in the past on very few morphological characters (e.g. number of molar laminae) and a polytypic species concept has obscured phylogenetic relationships and species discrimination in this group. We recognize at least three species in this group, and distinct lineages within two of these species. Each species or lineage was endemic to one of three regions: the Albertine Rift, the Malawi Rift or the Eastern Arc. Our result echo conclusions of recent studies of other mammalian and bird taxa and reflect the geomorphology and palaeoclimatic history of the region.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 913–941.     

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

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.     

Molecular evolution in space and through time: mtDNA phylogeography of the Olive Sunbird (Nectarinia olivacea/obscura) throughout continental Africa

This study constitutes the first investigation of the phylogeographic structure of a forest bird distributed throughout the montane and lowland forest biomes of Africa. The key objective was to investigate the importance of Pleistocene climatic cycles on avian diversification across Africa. The Olive Sunbird is a relatively large polytypic sunbird widely distributed throughout evergreen, montane and coastal forests in Africa. Recently, it was split into two species, the Eastern Olive Sunbird (Nectarinia olivacea) and the Western Olive Sunbird (Nectarinia obscura), based on morphological grounds. Analyses of a 395bp fragment of the mtDNA NADH subunit 3 gene with flanking tRNA sequences, from 196 individuals of N. olivacea and 86 from N. obscura indicate that genetic divergence levels are low (1.0-2.4%) across some 9000km, from Ghana in the northwest of Africa to KwaZulu-Natal in eastern South Africa. Neither currently recognized Olive Sunbird species were monophyletic using either parsimony or likelihood tree-building methods. [Formula: see text] (ST) values suggested that there was less variation partitioned among species than between most neighboring regions. Genetic diversity within the N. olivacea/obscura complex was dominated by three star-like phylogenies linked to each other by a single mutational step and two subnetworks (IV and V) separated from the core star-like phylogenies (subnetworks I, II, and III) by five to six mutational steps. The dominant evolutionary mechanism shaping genetic variation within the N. olivacea/obscura complex as identified by nested-clade analyses, appears to be one of range expansion possibly out of East Africa associated with a period of forest expansion during the mid-Pleistocene, some 1.1-0.7 million years ago. Mismatch profiles suggested that secondary contact has occurred between eastern and western lineages within the Ufipa Escarpment and possibly Zimbabwe, as well as between eastern lineages in the Kenyan Highlands and northern Eastern Arc Mts.     

Pliocene forest dynamics as a primary driver of African bird speciation

Aim Montane tropics are areas of high endemism, and mechanisms driving this endemism have been receiving increasing attention at a global scale. A general trend is that climatic factors do not explain the species richness of species with small to medium‐sized geographic ranges, suggesting that geological and evolutionary processes must be considered. On the African continent, several hypotheses including both refugial and geographic uplift models have been advanced to explain avian speciation and diversity in the lowland forest and montane regions of central and eastern Africa; montane regions in particular are recognized as hotspots of vertebrate endemism. Here, we examine the possible role of these models in driving speciation in a clade of African forest robins. Location Africa. Methods We constructed the first robustly supported molecular phylogenetic hypothesis of forest robins. On this phylogeny, we reconstructed habitat‐based distributions and geographic distributions relative to the Albertine Rift. We also estimated the timing of lineage divergences via a molecular clock. Results Robust estimates of phylogenetic relationships and clock‐based divergences reject Miocene tectonic uplift and Pleistocene forest refugia as primary drivers of speciation in forest robins. Instead, our data suggest that most forest robin speciation took place in the Late Pliocene, from 3.2 to 2.2 Ma. Distributional patterns are complex, with the Albertine Rift region serving as a general east–west break across the group. Montane distributions are inferred to have evolved four times. Main conclusions Phylogenetic divergence dates coincide with a single period of lowland forest retraction in the late Pliocene, suggesting that most montane speciation resulted from the rapid isolation of populations in montane areas, rather than montane areas themselves being drivers of speciation. This conclusion provides additional evidence that Pliocene climate change was a major driver of speciation in broadly distributed African animal lineages. We further show that lowland forest robins are no older than their montane relatives, suggesting that lowland areas are not museums which house ‘ancient’ taxa; rather, for forest robins, montane areas should be viewed as living museums of a late Pliocene diversification event. A forest refugial pattern is operating in Africa, but it is not constrained to the Pleistocene.     

Comparative phylogeography of three endemic rodents from the Albertine Rift, east central Africa

The major aim of this study was to compare the phylogeographic patterns of codistributed rodents from the fragmented montane rainforests of the Albertine Rift region of east central Africa. We sampled individuals of three endemic rodent species, Hylomyscus denniae, Hybomys lunaris and Lophuromys woosnami from four localities in the Albertine Rift. We analysed mitochondrial DNA sequence variation from fragments of the cytochrome b and control region genes and found significant phylogeographic structuring for the three taxa examined. The recovered phylogenies suggest that climatic fluctuations and volcanic activity of the Virunga Volcanoes chain have caused the fragmentation of rainforest habitat during the past 2 million years. This fragmentation has played a major role in the diversification of the montane endemic rodents of the region. Estimation of the divergence times within each species suggests a separation of the major clades occurring during the mid to late Pleistocene.     

Ancient forest fragmentation or recent radiation? Testing refugial speciation models in chameleons within an African biodiversity hotspot

Aim East Africa is one of the most biologically diverse regions, especially in terms of endemism and species richness. Hypotheses put forward to explain this high diversity invoke a role for forest refugia through: (1) accumulation of new species due to radiation within refugial habitats, or (2) retention of older palaeoendemic species in stable refugia. We tested these alternative hypotheses using data for a diverse genus of East African forest chameleons, Kinyongia. Location East Africa. Methods We constructed a dated phylogeny for Kinyongia using one nuclear and two mitochondrial markers. We identified areas of high phylogenetic diversity (PD) and evolutionary diversity (ED), and mapped ancestral areas to ascertain whether lineage diversification could best be explained by vicariance or dispersal. Results Vicariance best explains the present biogeographic patterns, with divergence between three major Kinyongia clades (Albertine Rift, southern Eastern Arc, northern Eastern Arc) in the early Miocene/Oligocene (> 20 Ma). Lineage diversification within these clades pre‐dates the Pliocene (> 6 Ma). These dates are much older than the Plio‐Pleistocene climatic shifts associated with cladogenesis in other East African taxa (e.g. birds), and instead point to a scenario whereby palaeoendemics are retained in refugia, rather than more recent radiations within refugia. Estimates of PD show that diversity was highest in the Uluguru, Nguru and East Usambara Mountains and several lineages (from Mount Kenya, South Pare and the Uluguru Mountains) stand out as being evolutionarily distinct as a result of isolation in forest refugia. PD was lower than expected by chance, suggesting that the phylogenetic signal is influenced by an unusually low number of extant lineages with long branch lengths, which is probably due to the retention of palaeoendemic lineages. Main conclusions The biogeographic patterns associated with Kinyongia are the result of long evolutionary histories in isolation. The phylogeny is dominated by ancient lineages whose origins date back to the early Miocene/Oligocene as a result of continental wide forest fragmentation and contraction due to long term climatic changes in Africa. The maintenance of palaeoendemic lineages in refugia has contributed substantially to the remarkably high biodiversity of East Africa.     

Climatic fluctuations and orogenesis as motors for speciation in East Africa: case study on Parepistaurus Karsch, 1896 (Orthoptera)

Mechanisms of speciation of flightless grasshoppers in mountainous and coastal East Africa are inferred considering (i) phylogenies estimated with a combination of molecular markers (16S rRNA locus, COI and H3), (ii) ecological data and (iii) the geographic distribution of Parepistaurus species. The study suggests that coastal taxa of Parepistaurus belong to ancestral lineages from which evolved the high diversity of species found in the Eastern Arc Mountains of Tanzania and Kenya, which are geologically ancient mountain formations. Network analyses and a molecular clock approach, calibrated with the geological age of the volcanoes, suggested that speciation was boosted by climatic fluctuations affecting large areas of East Africa. With the aridification beginning 2.8 Ma, forest taxa were isolated due to forest fragmentation and populations were separated by extended grasslands, which are avoided by Parepistaurus species. However, a humid period between 2.7 and 2.5 Ma triggered a spread of coastal taxa along the Eastern Arc Mountains. Forests expanded again and riparian vegetation along rivers draining into the Indian Ocean probably served as corridors for the dispersal of coastal taxa to the hinterland. The inland volcanoes such as Mount Kilimanjaro are therefore good time markers because their geological age is known, limiting the available time for speciation processes of mountainous Parepistaurus in the area to a maximum of about 1–2 Ma. A third humid but cold period between 1.1 and 0.9 Ma probably further boosted the spread of several flightless and montane‐adapted Orthoptera taxa.     

Diversification in a biodiversity hot spot: landscape correlates of phylogeographic patterns in the African spotted reed frog

The Eastern Afromontane Biodiversity Hotspot is known for microendemism and exceptional population genetic structure. The region's landscape heterogeneity is thought to limit gene flow between fragmented populations and create opportunities for regional adaptation, but the processes involved are poorly understood. Using a combination of phylogeographic analyses and circuit theory, I investigate how characteristics of landscape heterogeneity including regional distributions of slope, rivers and streams, habitat and hydrological basins (drainages) impact genetic distance among populations of the endemic spotted reed frog (Hyperolius substriatus), identifying corridors of connectivity as well as barriers to dispersal. Results show that genetic distance among populations is most strongly correlated to regional and local hydrologic structure and the distribution of suitable habitat corridors, not isolation by distance. Contrary to expectations, phylogeographic structure is not coincident with the two montane systems, but instead corresponds to the split between the region's two major hydrological basins (Zambezi and East Central Coastal). This results in a paraphyletic relationship for the Malawian Highlands populations with respect to the Eastern Arc Mountains and implies that the northern Malawian Highlands are the diversity centre for H. substriatus. Although the Malawian Highlands collectively hold the greatest genetic diversity, individual populations have lower diversity than their Eastern Arc counterparts, with an overall pattern of decreasing population diversity from north to south. Through the study of intraspecific differentiation across a mosaic of ecosystem and geographic heterogeneity, we gain insight into the processes of diversification and a broader understanding of the role of landscape in evolution.     

Evidence for altitudinal migration of forest birds between montane Eastern Arc and lowland forests in East Africa

Burgess, N.D. & Mlingwa, C.O.F. 2000. Evidence for altitudinal migration of forest birds between montane Eastern Arc and lowland forests in East Africa. Ostrich 71 (1 & 2): 184–190.

In this paper we assess the evidence for altitudinal movements of forest birds from the montane forests of the Eastern Arc mountains of East Africa to nearby lowland forest patches. For 34 montane species, including all the Eastern Arc endemics except Banded Green Sunbird Anthreptes rubritorques there is no evidence that they undertake seasonal movements to lower altitudes. An additional 26 montane species, of somewhat wider distribution, have been recorded at low (<500 m) altitudes during the cold/dry season (June to September). Most records of these montane birds at lower altitudes are from sites adjoining montane forest areas, although a few records are from lowland coastal forests at 100–240 km distance from montane areas. Only five of the 26 species (White-chested Alethe Alethe fulleborni, White-starred Forest Robin Pogonocichla stellata, Orange Ground Thrush Zoothera gurneyi, Evergreen Forest Warbler Bradypterus mariae and Barred Long-tailed Cuckoo Cercococcyx montanus) are regularly and commonly reported in the lowlands. They are also found in the lowlands in small numbers during the warm/wet season (October to February), when they may breed. The abundance of at least four, and probably more, of the forest birds with a more widespread distribution in the lowland and montane forests of East Africa declines greatly at high altitudes from the onset of the cold/wet season (February) and only increases again at the start of the warm/wet season (September). It is not known how far these species move as they cannot be easily separated from resident populations in lowland forests, and there are no ringing recoveries in different forests. Altitudinal migration of a proportion of the Eastern Arc avifauna is the most likely explanation for available data, although source-sink metapopulation theories may be helpful to explain the distributions of some species. As the movement of forest birds from the Eastern Arc to the lowland forests does not involve the rare endemics, they are of lower conservation concern, but the presence of montane and lowland forest may be important for the long-term survival of some more widely distributed forest species.     

Four New Bat Species (Rhinolophus hildebrandtii Complex) Reflect Plio-Pleistocene Divergence of Dwarfs and Giants across an Afromontane Archipelago

Gigantism and dwarfism evolve in vertebrates restricted to islands. We describe four new species in the Rhinolophus hildebrandtii species-complex of horseshoe bats, whose evolution has entailed adaptive shifts in body size. We postulate that vicissitudes of palaeoenvironments resulted in gigantism and dwarfism in habitat islands fragmented across eastern and southern Africa. Mitochondrial and nuclear DNA sequences recovered two clades of R. hildebrandtii senso lato which are paraphyletic with respect to a third lineage (R. eloquens). Lineages differ by 7.7 to 9.0% in cytochrome b sequences. Clade 1 includes R. hildebrandtii sensu stricto from the east African highlands and three additional vicariants that speciated across an Afromontane archipelago through the Plio-Pleistocene, extending from the Kenyan Highlands through the Eastern Arc, northern Mozambique and the Zambezi Escarpment to the eastern Great Escarpment of South Africa. Clade 2 comprises one species confined to lowland savanna habitats (Mozambique and Zimbabwe). A third clade comprises R. eloquens from East Africa. Speciation within Clade 1 is associated with fixed differences in echolocation call frequency, and cranial shape and size in populations isolated since the late Pliocene (ca 3.74 Mya). Relative to the intermediate-sized savanna population (Clade 2), these island-populations within Clade 1 are characterised by either gigantism (South African eastern Great Escarpment and Mts Mabu and Inago in Mozambique) or dwarfism (Lutope-Ngolangola Gorge, Zimbabwe and Soutpansberg Mountains, South Africa). Sympatry between divergent clades (Clade 1 and Clade 2) at Lutope-Ngolangola Gorge (NW Zimbabwe) is attributed to recent range expansions. We propose an “Allometric Speciation Hypothesis”, which attributes the evolution of this species complex of bats to divergence in constant frequency (CF) sonar calls. The origin of species-specific peak frequencies (overall range = 32 to 46 kHz) represents the allometric effect of adaptive divergence in skull size, represented in the evolution of gigantism and dwarfism in habitat islands.     

Major gaps in the distribution of protected areas for threatened and narrow range Afrotropical plants

We investigated the major patterns of plant rarity in sub-Saharan Africa, and looked for the most significant gaps in the reserve network of the region in terms of representing the distribution of threatened and geographically rare plants. Comparisons of the species ranges captured by the network of reserves were made against the proportion of species captured by randomly generated sets of areas and against a theoretical near minimum set of areas that represent all species once. At this scale of analysis, the network of large IUCN-coded reserves (the official ‘protected areas’) performs poorly against random and systematic selection procedures. Significant gaps in the IUCN-coded protected areas are in coastal Gabon/Cameroon, in the various tropical montane forest areas (Cameroon Highlands, Eastern Arc Mountains, Ethiopian Mountains), in lowland coastal eastern Africa, and in the South African Cape. Some of these gaps, for example in the Eastern Arc and eastern African coastal regions, are covered on the ground by a network of Forest Reserves under the management of national Forestry Authorities. The networks of Forest Reserves in Ghana, Nigeria, Cameroon, Uganda, Kenya, Zimbabwe, Zambia and Sierra Leone also fill reservation gaps for rare African plants in these countries. Upgrading the conservation status of some key Forest Reserves, which has been gradually happening for some decades, is proposed as an efficient way to enhance the protected area network of the Afrotropical region for the conservation of rare African plant species.     

Colonization and diversification in the African 'sky islands' by Eurasian Lychnis L. (Caryophyllaceae)

Aim Many plants occurring on the isolated mountain peaks of Africa have their closest relatives in very remote areas, even in temperate Europe and Asia. Their biogeographical history is poorly understood. The Afro‐montane element of the primarily Eurasian genus Lychnis is a typical example of such a disjunction. Here, we aim to reconstruct the phylogeny of the Afro‐montane endemics of Lychnis and to infer the history of immigration into Africa and of the subsequent dispersal and speciation. Location The Afro‐montane representatives of Lychnis occur in Ethiopia, Kenya, Tanzania, Uganda, Rwanda, Burundi, the Democratic Republic of Congo, Cameroon, and Nigeria. Methods Silica‐dried plant materials collected in Ethiopia in 2004 as well as herbarium material were used for DNA extractions. We used parsimony analysis of nucleotide data from the rps16 intron and psbE‐petL region in plastids, and the internal transcribed spacer (ITS) and a region spanning exon 18–24 in the second largest subunit of RNA polymerase II (RPB2) from the nucleus. DAPI‐flow cytometry was used to determine relative genome size and to infer polyploidization events. Results Monophyly of the Afro‐montane Lychnis with the Eurasian diploid L. flos‐cuculi resolved as sister was strongly supported by the phylogenetic analyses. The Afro‐montane group was further divided into two strongly supported groups correlated with DNA ploidy levels. The relative genome size was species‐specific except for L. abyssinica, which had two genome‐size variants. Main conclusions Our results demonstrate that the biogeographical history of the Afro‐montane Lychnis has been highly dynamic, including polyploidization and both old and recent long‐distance dispersal events, even between Eastern and West Africa. The ancestor is inferred to have immigrated once from Eurasia via the Arabian Peninsula to the Ethiopian highlands. Divergence in the lineage containing diploid taxa was followed by several dispersals from Ethiopia to the Eastern and Western Rift Mountains, and recently to West Africa. Divergence of the lineage including the tetraploid L. crassifolia may have taken place in Ethiopia, from where it dispersed to the Eastern and Western Rift Mountains; alternatively, it may have taken place in the Eastern Rift Mountains, followed by dispersal from there to the Western Rift Mountains and then to Ethiopia.     

Diversification across an altitudinal gradient in the Tiny Greenbul (Phyllastrephus debilis) from the Eastern Arc Mountains of Africa

Background  

The Eastern Arc Mountains of Africa have become one of the focal systems with which to explore the patterns and mechanisms of diversification among montane species and populations. One unresolved question is the extent to which populations inhabiting montane forest interact with those of adjacent lowland forest abutting the coast of eastern Africa. The Tiny Greenbul (Phyllastephus debilis) represents the only described bird species within the Eastern Arc/coastal forest mosaic, which is polytypic across an altitudinal gradient: the subspecies albigula (green head) is distributed in the montane Usambara and Nguru Mountains whereas the subspecies rabai (grey head) is found in Tanzanian lowland and foothill forest. Using a combination of morphological and genetic data, we aim to establish if the pattern of morphological differentiation in the Tiny Greenbul (Phyllastrephus debilis) is the result of disruptive selection along an altitudinal gradient or a consequence of secondary contact following population expansion of two differentiated lineages.     

A new genus of African Karniellina (Orthoptera,Tettigoniidae, Conocephalinae,Conocephalini): integrating morphological,molecular and bioacoustical data

Melanoscirtes gen.n. is established within Karniellina. The members of this subtribe are small conocephaline bush crickets, confined to Africa. Melanoscirtes is erected on Phlesirtes kibonotensis, a species restricted to forest clearings and forest edge in the submontane and montane zones of Mt. Kilimanjaro. A subspecies, M. kibonotensis uguenoensis, is described from the North Pare mountains, a mountain range of the Eastern Arc adjacent to Mt. Kilimanjaro. Further species of Melanoscirtes occur on other mountain ranges of the northern branch of the Eastern Arc mountains of northern Tanzania and southern Kenya. The South Pare mountains harbour M. shengenae; the West Usambaras, M. usambarensis, and the Taita Hills, M. taitensis. All species and subspecies of Melanoscirtes exhibit a similar morphology and occupy analogous habitats on the respective mountains. The song patterns for all species found within this genus are very similar, and this, together with evidence from molecular data, suggests that allopatric speciation is the reason for the biogeographic pattern found in this genus. A key for the subspecies and species of Melanoscirtes is provided.     

Dispersal to or from an African biodiversity hotspot?

Biodiversity hotspots are centres of endemism and thus contain many range-restricted species. In addition, within these hotspots occur widespread species that might have originated within a hotspot before dispersing to neighbouring or distant regions. We test this hypothesis with a phylogeographic analysis of a miniature leaf litter frog, Arthroleptis xenodactyloides , that has a large distribution throughout the Eastern Arc biodiversity hotspot and other regions in East Africa. Maximum-likelihood and Bayesian estimates of the mitochondrial gene phylogeny are used as a proxy for understanding the evolutionary history of diversification and the historical relationships between populations. The north–south range of this species extends for approximately 1900 km; our sampling covers approximately 85% of this range. Using phylogenetic comparative methods, we estimate the region of origin and direction of dispersal within A. xenodactyloides . We compare contrasting hypotheses of latitudinal range expansion using bayes factors. The ancestral region of origin of A. xenodactyloides is reconstructed as having occurred within the Eastern Arc before dispersing southwards into the southern Rift Mountains, probably in the Pleistocene. The phylogeographic structure within this leaf litter frog is surprisingly similar to that of forest birds, revealing that similar geographic features might have had a driving role in diversification of these very dissimilar taxa. Latitudinal expansion occurred early in the evolutionary history of A. xenodactyloides , which may indicate that physiological adaptation facilitated its wide geographic distribution.     

Amphibian Diversity in East African Biodiversity Hotspots: Altitudinal and latitudinal Patterns

The Eastern Arc mountain chain and adjoining coastal forests of Tanzania and Kenya have been listed as world biodiversity hotspots. We report on an ongoing attempt to estimate amphibian diversity on the three best studied mountains of the Eastern Arc, the East Usambara, Uluguru and Udzungwa mountains of Tanzania, complemented by an estimate of diversity on the adjoining coastal lowland. This proves to be a complex task, which introduces a note of caution into evaluating global biodiversity estimates. Most amphibian species in eastern Tanzania occur on the coastal lowlands and are widely distributed, extending at least north or south of Tanzania and, to a variable extent, westwards to the elevated interior. Diversity patterns along the length of the lowlands are complex, with the presence of a Sahelian element in the extreme north. On the three Eastern Arc mountains studied, species turnover associated with rising altitude is greater than turnover associated with latitudinal distance between the mountain blocks, leading to greater altitudinal than latitudinal diversity in this equatorial region. A long-standing divergence is indicated between montane and lowland endemics. Although forest-associated species are not the largest contributor to the eastern Tanzanian total species diversity (some 48%), the uniqueness of these species both in lowland and montane forests, combined with their evident vulnerability to disturbance, makes them a subject for particular conservation concern, and justifies hotspot status for both montane and lowland forests.     

Differentiation between populations of a termite in eastern Africa: implications for biogeography

Aim  African forests are divided by an arid corridor which runs from the Horn of Africa to the Namib Desert. Several forest species occur in the forests of eastern Africa as well as in the Guineo-Congolian forest block. We evaluate the possibility that such species may have crossed the arid corridor along a route through the Kenyan Highlands and down the eastern drainages during climatologically favourable periods in the past.
Locations  Eastern Africa, Ivory Coast.
Methods  We used the termite species Schedorhinotermes lamanianus (Sjöstedt). This species occurs in lowland forests and woodland throughout Africa south of the Sahara. We sampled termites from 12 populations. We evaluated the differentiation between populations using amplified fragment length polymorphisms as well as morphometrical measurements.
Results  Genetic and morphometrical analysis demonstrated substantial differentiation between populations west and east of the arid corridor in Kenya. To the east of this corridor we found an increase of morphological distance with geographical distance. Schedorhinotermes lamanianus occurs not only along the coast but also at isolated locations (e.g. ground-water forests in foothills) within the arid hinterland.
Main conclusions  We interpret these populations as remnants of a wider distribution during wet climatic periods. At these times, populations of S. lamanianus were apparently able to establish along extensive gallery forests protruding into the arid belt of the Kenyan hinterland. There have been no connections between populations of this species east and west of the arid corridor across the Kenyan Highlands.     

Phylogeny of Acridocarpus-Brachylophon (Malpighiaceae): implications for tertiary tropical floras and Afroasian biogeography

Abstract.— A major tenet of African Tertiary biogeography posits that lowland rainforest dominated much of Africa in the late Cretaceous and was replaced by xeric vegetation as a response to continental uplift and consequent widespread aridification beginning in the late Paleogene. The aridification of Africa is thought to have been a major factor in the extinction of many African humid-tropical lineages, and in the present-day disparity of species diversity between Africa and other tropical regions. This primarily geologically based model can be tested with independent phylogenetic evidence from widespread African plant groups containing both humid- and xeric-adapted species. We estimated the phylogeny and lineage divergence times within one such angiosperm group, the acridocarpoid clade (Malpighiaceae), with combined ITS, ndhF , and trnL-F data from 15 species that encompass the range of morphological and geographic variation within the group. Dispersal-vicariance analysis and divergence-time estimates suggest that the basal acridocarpoid divergence occurred between African and Southeast Asian lineages approximately 50 million years ago (mya), perhaps after a southward ancestral retreat from high-latitude tropical forests in response to intermittent Eocene cooling. Dispersion of Acridocarpus from Africa to Madagascar is inferred between approximately 50 and 35 mya, when lowland humid tropical forest was nearly continuous between these landmasses. A single dispersal event within Acridocarpus is inferred from western Africa to eastern Africa between approximately 23 and 17 mya, coincident with the widespread replacement of humid forests by savannas in eastern Africa. Although the spread of xeric environments resulted in the extinction of many African plant groups, our data suggest that for others it provided an opportunity for further diversification.     

Genetic structure offers insights into the evolution of migration and the taxonomy of the Barred Long‐tailed Cuckoo Cercococcyx montanus species complex

Barred Long‐tailed Cuckoo (Cercococcyx montanus) currently comprises two morphologically distinct subspecies, one resident in the Albertine Rift (montanus) and one in east and southeast Africa (patulus) in which there are migrations that are poorly understood. Based on nuclear and mitochondrial DNA sequences, we find that two specimens collected in relatively low‐elevation forest in the Albertine Rift were correctly identified from plumage as the migratory subspecies whose closest known breeding area is > 800 km to the east. We discuss ways in which this unique migratory pattern could have evolved and argue that migration was gained and then lost in the C. montanus complex. Based on consistent morphological and genetic differences, we suggest that Barred Long‐tailed Cuckoo is best treated as two species, one of which (C. montanus) is a non‐migratory Albertine Rift endemic.