Arid Corridor Research Articles

Climate cycling did not affect haplotype distribution in an abundant Southern African avian habitat generalist species, the familiar chat (Oenanthe familiaris).

Avian species diversity in Southern Africa is remarkably high, yet the mechanisms responsible for that diversity are poorly understood. While this is particularly true with respect to species endemic to the subregion, it is unclear as to how more broadly distributed African species may have colonized southern Africa. One process that may in part account for the high bird species diversity in southern Africa is a "species pump" model, wherein the region was repeatedly colonized by lineages from areas further north: a pattern related to climate cycling and the eastern African arid corridor. Once occupying southern Africa, with its many varied biomes, it is possible that climate cycling further affected lineages by generating genetic diversity in multiple refugia, a pattern recently shown for several southern African bird species. Here, we used mtDNA to address these questions in a widespread, sedentary habitat generalist bird species, the familiar chat (Oenanthe familiaris). The phylogenetic structure suggests a north-to-south colonization pattern, supporting the "species pump" model. Haplotype diversity was partitioned into two distinct clusters: southern Africa and Malawi (East Africa). Southern African haplotypes were not geographically partitioned, and we hypothesize that this pattern has arisen because this species is a habitat generalist, and as such resilient to habitat-altering climate perturbations. Based on our phylogenetic results, we discuss the validity of currently recognized subspecies.

Evaluation of water supply and demand and optimization under the planting structure of cultivated land in the Hengshao Arid Corridor

Evaluation of water supply and demand and optimization under the planting structure of cultivated land in the Hengshao Arid Corridor

The first Miocene fossils from coastal woodlands in the southern East African Rift

The Miocene was a key time in the evolution of African ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here, we report the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique. We provide the first 1) radiometric ages of the Mazamba Formation, 2) reconstructions of paleovegetation in the region based on pedogenic carbonates and fossil wood, and 3) descriptions of fossil teeth. Gorongosa is unique in the East African Rift in combining marine invertebrates, marine vertebrates, reptiles, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossils including new species.

Phylogenetic and morphological investigation of the Mochlus afer-sundevallii species complex (Squamata: Scincidae) across the arid corridor of sub-Saharan Africa

The aridification of Africa resulted in the fragmentation of forests and the expansion of an arid corridor stretching from the northeast to southwest portion of sub-Saharan Africa, but the role this corridor has had in species-level diversification of southern African vertebrates is poorly understood. The skink species Mochlus afer and M. sundevallii inhabit wide areas of the arid corridor and are therefore an ideal species pair for studying patterns of genetic and phenotypic diversity associated with this landscape. However, species boundaries between these taxa have been controversial. Using multi-locus molecular and morphological datasets, we investigate diversification patterns of the M. afer-sundevallii Species Complex across the arid corridor. Although analyses of genetic data reveals some genetic structure among geographic populations, results of phylogenetic and morphological analyses provide little support for two distinct evolutionary lineages, suggesting that populations previously referred to as M. afer and M. sundevallii represent a single species, Mochlus sundevallii. Genetic diversity is unequally distributed across the arid corridor, with observed patterns consistent with aridification-facilitated diversification southward across southern Africa. Additional geographic and population-level sampling is necessary before more conclusive inferences can be drawn about the role historical climate transitions have played in skink diversification patterns across southern Africa.

Lifting the blue-headed veil – integrative taxonomy of the Acanthocercus atricollis species complex (Squamata: Agamidae)

We present the first integrative review of the African agamid lizard Acanthocercus atricollis, a broadly distributed species found from Ethiopia through East Africa to Angola and South Africa. Since the original description of the species approximately 170 years ago six subspecies have been described, mainly on the basis of coloration characters. Our study presents new morphological and genetic data, which together suggest that A. atricollis is a complex of multiple species. External morphological characters and cranial osteology support some of the taxonomic differentiation implied by coloration. We also provide complementary 16S rRNA mitochondrial DNA (mtDNA) sequence data analysed in the context of species delimitation. Our integrated data support several systematic and taxonomic changes, including (1) Acanthocercus branchi is part of the A. atricollis complex, (2) the subspecies A. gregorii, A. minutus, A. ugandaensis, and A. kiwuensis merit species rank, (3) A. atricollis loveridgei is a synonym of A. a. gregorii, (4) Agama cyanocephalus, a former synonym of A. atricollis, is now recognized as full species distributed in Angola, Zambia and extreme northern Namibia. The distribution and diversity of the A. atricollis species complex supports the presence of a biogeographic arid corridor connecting eastern and southern Africa.

Gisekia (Gisekiaceae): Phylogenetic relationships, biogeography, and ecophysiology of a poorly known C4 lineage in the Caryophyllales

Gisekiaceae are a monogeneric family of the core Caryophyllales distributed in arid regions of Africa and Asia. The only widespread species of the genus, Gisekia pharnaceoides, performs C4 photosynthesis based on CO2 compensation point measurements. This study investigates the C4 syndrome and its evolution in Gisekia. The infrageneric relationships, distribution and bioclimatic preferences of Gisekia are also investigated. Leaf gas exchange characteristics, activity of Rubisco and major C4 cycle enzymes, and ultrastructural characteristics of mesophyll and bundle sheath cells are studied for Gisekia pharnaceoides. δ(13)C values and leaf anatomy are analyzed for all species. A dated molecular phylogeny of 39 accessions representing all species of Gisekiaceae and 14 representatives of closely related core Caryophyllales families is generated using four cp markers and ITS. The precise current distribution and bioclimatic niche of Gisekia is assessed on the basis of 520 georeferenced specimen localities. All traditionally recognized species of Gisekia are C4 plants with atriplicoid Kranz anatomy. Gisekia pharnaceoides uses the NAD-ME biochemical type. The molecular phylogeny demonstrated two East African clades nested within South African clades, demonstrating migration along the arid areas of eastern Africa during the Late Miocene/Pliocene Epochs. Most traditionally defined species are polyphyletic. Gisekia represents an isolated C4 lineage within core Caryophyllales dating back to the Miocene Epoch and probably spread along the African arid corridor from a South African center of origin. The seven currently recognized species should be treated as one polymorphic species or species complex, Gisekia pharnaceoides agg.

Influence of drainage divides versus arid corridors on genetic structure and demography of a widespread freshwater turtle, Emydura macquarii krefftii, from Australia.

The influence of Pleistocene climatic cycles on Southern Hemisphere biotas is not yet well understood. Australia's eastern coastal margin provides an ideal setting for examining the relative influence of landscape development, sea level fluctuation, and cyclic climatic aridity on the evolution of freshwater biodiversity. We examined the impact of climatic oscillations and physical biogeographic barriers on the evolutionary history of the wide-ranging Krefft's river turtle (Emydura macquarii krefftii), using range-wide sampling (649 individuals representing 18 locations across 11 drainages) and analysis of mitochondrial sequences (∼1.3-kb control region and ND4) and nuclear microsatellites (12 polymorphic loci). A range of phylogeographic (haplotype networks, molecular dating), demographic (neutrality tests, mismatch distributions), and population genetic analyses (pairwise FST, analysis of molecular variance, Bayesian clustering analysis) were implemented to differentiate between competing demographic (local persistence vs. range expansion) and biogeographic (arid corridor vs. drainage divide) scenarios. Genetic data reveal population genetic structure in Krefft's river turtles primarily reflects isolation across drainage divides. Striking north-south regional divergence (2.2% ND4 p-distance; c. 4.73 Ma, 95% higher posterior density (HPD) 2.08–8.16 Ma) was consistent with long-term isolation across a major drainage divide, not an adjacent arid corridor. Ancient divergence among regional lineages implies persistence of northern Krefft's populations despite the recurrent phases of severe local aridity, but with very low contemporary genetic diversity. Stable demography and high levels of genetic diversity are inferred for southern populations, where aridity was less extreme. Range-wide genetic structure in Krefft's river turtles reflects contemporary and historical drainage architecture, although regional differences in the extent of Plio–Pleistocene climatic aridity may be reflected in current levels of genetic diversity.

Genetic diversity of Angiopolybia pallens (Lepeletier) (Hymenoptera, Vespidae, Polistinae) explained by the disjunction of South American rainforests

Angiopolybia pallens is a swarm-founding wasp that occurs in Atlantic and Amazonian rainforests, which have been isolated from each other by a large arid corridor in central Brazil since the Tertiary. In this study, we used data from polymerase chain reaction-restriction fragment length polymorphism of 16S rDNA to infer some aspects of the genetic diversity and evolutionary history of this social wasp population. Samples collected across the species range in both rainforests showed remarkable differences that separated them into two distinct haplogroups. However, some samples from isolated areas in northeastern Bahia were more related to Amazonian lineages than to southern Bahia populations. Vicariant divergenc is discussed under South American rainforests biogeographical proposals.

Application of trait-based mechanisms to resilience of ecosystem service provision in an arid riparian corridor

Application of trait-based mechanisms to resilience of ecosystem service provision in an arid riparian corridor

Identifying optimal barriers to halt the invasion of cane toads Rhinella marina in arid Australia

Summary Spatial heterogeneity in environmental conditions may restrict the spread of invasive species to narrow corridors between extensive patches of suitable habitat; thus, we may be able to curtail invasions by identifying such corridors, and focusing control efforts in these areas. Invasive cane toads Rhinella marina have spread rapidly through northern Australia, but to invade further into Western Australia, the toads must traverse a narrow arid corridor where artificial waterbodies may serve as critical stepping stones for range expansion. We focus on the cane toads' imminent expansion into north‐western Australia and use stochastic simulation to identify areas in which removal of artificial waterbodies would be most effective at stopping their spread. Our model predicts that toads will spread from the Kimberley to the Pilbara regions of Western Australia through a narrow coastal corridor, but that they will depend upon artificial waterbodies to do so. Importantly, excluding toads from artificial waterbodies is predicted to prevent toads from colonizing c. 268 200 km2 of their potential range in Western Australia. We identified three locations where closure of a relatively small subset of artificial waterbodies is predicted to halt the spread of toads. Synthesis and applications. We present a modelling framework that can be used to focus management activities within invasion corridors. Our analyses suggest that strategic removal of potential invasion hubs along such corridors can halt the spread of an invasive species.

Phylogenetic relationships of elephant‐shrews (Afrotheria, Macroscelididae)

Elephant-shrews or sengis (Macroscelidea, Afrotheria) are grouped into two subfamilies, Rhynchocyoninae with a single genus and four species, and Macroscelidinae represented by three genera and 13 species. Our current understanding of the evolutionary relationships within this group is largely based on a molecular phylogeny that suffers from incomplete species representation. We present the first complete phylogeny (with the exception of the recently described East African Rhynchocyon udzungwensis) for Macroscelidea based on mitochondrial and nuclear markers. Novel cytogenetic characters as well as previously described allozyme variation and various morphological features are evaluated and mapped to the molecular topology. Our analyses indicate that Elephantulus is paraphyletic, and that Petrodromus and Macroscelides should be subsumed in Elephantulus. A relaxed Bayesian dating approach supports the hypothesis that an arid-adapted Macroscelidinae lineage dispersed from east Africa at ∼11.5 MYA via an African arid corridor to south-western Africa. The timing of speciation within the east African Rhynchocyoninae (8–10 MYA) is coincidental with the diversification of some other forest specialists. In turn, divergence within the Macroscelidinae coincides with major aridification events across Africa.

Old-New World and trans-African disjunctions of Thamnosma (Rutaceae): Intercontinental long-distance dispersal and local differentiation in the succulent biome

The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we used Thamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra. We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange. Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene. We conclude that the Old-New World disjunction of Thamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of Thamnosma.

Phylogeny of the tribe Indigofereae (Leguminosae–Papilionoideae): Geographically structured more in succulent‐rich and temperate settings than in grass‐rich environments

This analysis goes beyond many phylogenies in exploring how phylogenetic structure imposed by morphology, ecology, and geography reveals useful evolutionary data. A comprehensive range of such diversity is evaluated within tribe Indigofereae and outgroups from sister tribes. A combined data set of 321 taxa (over one-third of the tribe) by 80 morphological characters, 833 aligned nuclear ribosomal ITS/5.8S sites, and an indel data set of 33 characters was subjected to parsimony analysis. Notable results include the Madagascan dry forest Disynstemon resolved as sister to tribe Indigofereae, and all species of the large genus Indigofera comprise just four main clades, each diagnosable by morphological synapomorphies and ecological and geographical predilections. These results suggest niche conservation (ecology) and dispersal limitation (geography) are important processes rendering signature shapes to the Indigofereae phylogeny in different biomes. Clades confined to temperate and succulent-rich biomes are more dispersal limited and have more geographical phylogenetic structure than those inhabiting tropical grass-rich vegetation. The African arid corridor, particularly the Namib center of endemism, harbors many of the oldest Indigofera lineages. A rates analysis of nucleotide substitutions confirms that the ages of the oldest crown clades are mostly younger than 16 Ma, implicating dispersal in explaining the worldwide distribution of the tribe.

Disjunctions in the Diptera (Insecta) fauna of the Mediterranean Province and southern Africa and a discussion of biogeographical considerations

This paper explores disjunctions in the Diptera fauna of the Mediterranean Province and southern Africa, drawing from eight families of Diptera, the more ancient Psychodidae and Vermileonidae, and the more recent Acroceridae, Asilidae, Bombyliidae, Dolichopodidae, Pipunculidae and Sciomyzidae. Information from recent published revisions is geo-referenced and plotted onto maps using GIS software. These distribution patterns are interpreted and probable means and routes of dispersal between the two regions are discussed. The concept of an Afrotropical sub-Saharan boundary is outlined and it is argued that although the vast, arid and virtually abiotic Sahara acts as a barrier to dispersal today, relict floral and faunal populations of Mediterranean provincial origin still occur on the Hoggar and Tibesti Mountains of the central Sahara, indicating that the aridification of the Sahara is a very recent event. The presence of extensive palaeolakes formerly covering ca 10% of the present-day Sahara is regarded as evidence in support of this hypothesis. These lakes and their associated catchments, situated in basins between the central Saharan mountains, could clearly have acted as a humid route of dispersal as recently as 4000 BP, when these lakes began to recede, and this route is here regarded as a “central high Africa corridor”; a filter-bridge between the Mediterranean Province and southern Africa. Examples of Mediterranean provincial species of Ephydridae and the muscid genus Lispe Latreille, 1796, occurring as far south as the Aïr Massif in northern Niger are cited as examples of relict montane Diptera of Mediterranean provincial origin in the southern Hoggar Mountains; these groups being associated with the margins of standing water. Balinsky's (1962) concept of an “arid corridor” is also re-examined, using examples from the larger, less mobile Diptera, and it is concluded that such a pattern may not be the result of aridity, but represent an “eastern high Africa corridor”, broadly corresponding to the “African Superswell”. Other perceived distribution pathways between the Holarctic and Afrotropical Regions are mapped. Anemochore dispersal is considered, and the extent of the Afrotropical Region is discussed. Mediterranean tectonic evolution on both a globe of constant size and on a smaller Jurassic globe is also considered. It is concluded that if all the transitional zones between the zoogeographical regions are to be given more-or-less equivalent treatment, we must avoid setting boundaries based on earlier faunal distributions. For this reason the current boundary between the Palaearctic and Afrotropical Regions, arbitrary as it is, should be retained, despite evidence suggesting recent continuity between sub-Saharan Africa, North Africa and the Arabian Peninsula, corresponding broadly to the African and Arabian lithospheric plates.

The genus <i>Wellstedia</i> (Boraginaceae: Wellstedioideae) in southern Africa

This regional taxonomic revision of the genus Wellstedia Balf.f., a member of the family Boraginaceae s.I. (including Hydrophyllaceae s.str.), is part of a series of publications on the Boraginaceae in southern Africa. Wellstedia comprises six species, five in Socotra, Somalia and Ethiopia with the remaining one. W. dinteri Pilg.. occurring in southern Africa. W dinteri Pilg. subsp. dinteri occurs in Namibia and the Northern Cape, whereas the newly instated subspecies W. dinteri subsp. gracilior (D.R.Hunt) Retief A.E.van Wyk, based on W. dinteri Pilg. var. gracilior D.R.Hunt, is confined to Namibia only. The disjunct distribution of Wellstedia and numerous other plant and animal taxa between the arid regions of northeastern Africa and southern Africa is usually explained by the postulated periodic existence of an arid corridor between the two regions during the arid phases of the Pleistocene and even earlier. Wellstedia is treated here in Wellstedioideae, a subfamily of Boraginaceae s.I. but is sometimes placed in a family of its own, Wellstediaceae Pilger. Morphologically Wellstedia displays strong similarity to genera of the Ehretioideae and also to certain members of the Hydrophyllaceae. The genus is characterized by a perennial, dwarf shrub habit, densely hairy leaves. 4-merous flowers, a terminal, bifid style and a 1- or 2-seeded capsule. A key to the two subspecies, diagnostic characters, a distribution map and illustrations of various macro- and micromorphological features are provided.

Molecular biogeography of Mediterranean and southern African disjunctions as exemplified by pollen beetles of the Meligethes planiusculus species-group and related taxa (Coleoptera: Nitidulidae; Meligethinae)

Biogeographia vol. XX/X - 2008 (Pubb/icato il 30 dice-mbre 2008) The Mediterranean—southern African disjunct distribution pattern Molecular biogeography of Mediterranean and southern African disjunctions as exemplified by pollen beetles of the Melzgetbesplnniusculus species—group and related taxa (Coleoptera: Nitidulidae; Meligethinae) PAOLO AUDISIO, ALESSIO DE BIASE, ASHLEY H. KIRK-SPRlGGS*, ANDREW R. CLINE**, MARCO TRIZZINO, GLORIA ANTONINI, EMILIANO MAN CINI D1jgczr'ti772e72to di Bio/ogizz Animzz/e e r2'elZ’U0mo, Szzpierzzzz Urziz/ersitfz dz’ Rama, z/izz A. Bore!/z’ 50, [-0016] Rome, Italy *De]gzzrtmem‘ of Entomology, Nzztiomzl MZl5€Zl77Z, Bl0emfi77zZ'ei7Z, 9300 South Afiicrz *”‘P[zzm‘ Pest Diagnostic: Center, Czzlzfbmirz Depamvzerzt of Food fl7ZdAgTiCZt[tZl7€, 3294 Men:/ow:/iew Road, Szzcranzerzto, CA 95832-1448, USA Key words: Mcliger/Jet, biogeography, disjunctions, dispersal, cytochrome oxidase I SUMMARY We investigated the apparent disjunction expressed in two related assemblages of species of the genus Me/{get/Jar, i.e. M. fiwrico/zz and its allies in the Cape region of South Africa and the M. plrtnizrscu/115 group in the Mediterranean region. We also inferred possible dynamics in the radiation of the Mt’/{get/Jr’: plmz/'1z.rr:11l1t.r complex within Macaronesia utilizing morphological, molecular and bionomical data, exploring potential historical and palaeoecological scenarios regulated by a molecular clock dating system. We reconstructed phylogenetic relationships of the M. p/zznizzxcu/115 complex and of related Mediterranean (ll/I. zfistis), tropical (ll/I. ream) and soud1ern African (/l/I. c/Jeuro/ati, /VI. rmzfizrmir, and /l/I.fiqm‘1'm/zz) species, using CO1 mitochondrial gene sequences. Phylogenetic reconstructions support an unambiguous distinction of two major clades grouping European—Mediterranean M czzmtriensir, ll/I. iroplexidit and ll/I. [1/arziiuczz/11: specimens in one clade and the South—African specimens related to Mfi*z/fica/a in another. Molecular markers suggested that the European— Mediterranean taxon Il/I. tristi: is unambiguously more distantly related to the partly sy1npatricM £1171/z7'I'mxi:, M. iso/7/exit/it and M p/mzimcu/m, than to the geographically isolated Southern African taxon, /l/I. fivzfiw/:1. However, morphological data revealed that /l/[. t7'i.rtz': is more closely related to A4. p/tzriiitmz/1/5 and its allies while occupying a position internal to the [VI /2/rzzzimcnl1z.r species group, but external to the A/[. p/arlizlmzlrzs complex. Results of divergence estimation analyses suggest a splitting between ancestors of the European-Mediterranean species of the M. p/tzzzirzrcu/zzr complex and that of the African species M. flzitica/(I at —2l—23 MYA. Molecular results also demonstrated that the remaining Afrotropical species are more related to the M p//zniz/5:1//m and A4. fi'z/rim//1 complexes than to M. trirtis. This evidence clearly indicates that the Holarctic M. ]1/zzziimczz/11: group represents a paraphyletic assemblage with heterochronic Afrotropical origin. The estimated times of divergence supports evidence from other researchers of an ‘Arid Corridor’, or of a ‘Central or Eastern

The biogeographical patterns of disjunt distribution with special emphasis on the Mediterranean and southern African model

Biogeographia vol. XXIX — 2008 (Pubblicato il 30 dicembre 2008) The Mediterranean—southern African disjunct distribution pattern The biogeographical patterns of disjunct distribution with special emphasis on the Mediterranean and southern African model MARCO A. BOLOGNA, PAOLO A. AUDlSIO*, MAURIZIO BlONDI**, ACHILLE CASALE*** Dipzzrtimmto di Biologia Arnbientrzle, Um'z/erritfz Roma Tre, via/e G. Marconi 446, 00146 Rome, Italy e—mzzz'[: bologna @um'r0mrz3. it *Dz}uzrtz'me7zto di Biologirz Arzimzzle e a'el[’U0mo, Sapienza Universitfz dz’ Roma, z/idle del/’Uniz2er5z't£z 32, 00185 Rome, Italy ”‘*Dz‘pzzrtimmto di Scienze Am/vientzzli, Universitfz del/1/lqziilzz, via Vetoio 57%‘, 67100 L i/lqui/zz, Italy ***Dz‘partin2e7zto di Z00/ogia e Gmetiaz evoluzionistiaz, Universitiz di Sasszzri, Via Muroni 25, 07100 Szzmzri, Italy Key words: biogeographical models, disjunction, Mediterranean, southern Africa SUMMARY The authors introduce and shortly discuss the intriguing issue of biogeographical disjunctions, with special emphasis on the Mediterranean—southern African disjunctions, analyzed considering both dispersal and vicariance models. Combined data sets based on both mot holo ical and molecular cues from a relativel lar 6 series ofdifferent . P . . . . V g . . animal and ve etal taxa some of them extensivel discussed in the resent volume) indicate true and si nificant E . . _ Y _ _ 5 _ phylogenetic relationships between Mediterranean and southern African biota. Where molecular data are available, . . . - a . . ., (L the estimated times of divergence frequently supports evidence of an Arid Corridor , or of a Central or Eastern High Africa Corridor”, which connected a number of times in the last 20—25 MY s the European—Mediterranean and eastern/southern African areas, and facilitated species migration northwards and southwards. These corridors allowed the dispersal southwards of several taxa of European—Mediterranean origin, frequently teaching at least the main mountain systems and the coasts of Eastern and SE Africa. On the other hand, several taxa of eastern and southern African origin migrated northwards, colonizing the Mediterranean and southern Palaearctic areas. Finally, secondary radiations at specific level frequently occurred in the last MYs both in Mediterranean and African areas, involving taxa of African and Mediterranean origins, respectively. INTRODUCTION Among the most relevant topics in biogeography, a fundamental role is played by the analysis of the origin and theevolutionary timing of disjunct

Evidence of repeated migrations through the African arid corridor as revealed by a molecular phylogeny of southern African members of the genus Zygophyllum

Evidence of repeated migrations through the African arid corridor as revealed by a molecular phylogeny of southern African members of the genus Zygophyllum

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

AbstractAim 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.

The evolution of arid ecosystems in eastern Africa

The present aridity of Africa contrasts with the lush environments that existed over most of the continent in the early Cenozoic. The extinction of large terrestrial herbivores at the end of the Mesozoic, and relatively warm global climatic conditions in the early Cenozoic contributed to the spread of forests and woodlands in regions today occupied by grasslands and deserts. The increase in aridity after the Eocene climate optimum has been complex, characterized by multiple reversals and modulated by rifting in eastern Africa. The paleobotanical evidence indicates that ecological differentiation within the continent existed early in the Cenozoic, with some areas dominated by moist forests and others by drier Acacia woodlands. C4 grasslands began to spread during the Late Miocene, and became more prominent during the Pleistocene. In parallel to the spread of grassland mosaics during the Cenozoic there was an increase in the diversity of large herbivorous mammals (with body mass >350 kg). This diversity in megafauna peaked in the Pliocene. One of the key ecological roles of the megafauna was to create and maintain complex mosaics that included open habitats. Faunal evidence of paleoenvironments in the Turkana Basin of Kenya corroborates conclusions derived from other lines of evidence, but raises new questions. Hypsodont and cursorial bovids increased in abundance in the Late Miocene about 6 Ma, in the Pliocene after 3 Ma, and again in the Plio-Pleistocene after 2 Ma. But this faunal evidence also demonstrates that not all parts of the Turkana Basin responded in the same way to climatic changes. The lower Omo valley of Ethiopia, a northern extension of the Turkana Basin, remained significantly more forested than the areas near the western margins of the basin. Major river valleys like the Omo served as refuges and centers of endemism during intervals of significant climatic fluctuations. A similar role was played by the coastal and montane forests of eastern Africa, which were separated from the Central African forests by an arid corridor that stretched from northeast Africa to Namibia, and probably originated in the Miocene. The complex mosaic of environments in eastern Africa today continues to support an immensely diverse range of plants and animals, many of them found nowhere else on earth.