Climatic change as an engine for speciation in flightless Orthoptera species inhabiting African mountains

Whole genome data confirm pervasive gene discordance in the evolutionary history of Coenonympha (Nymphalidae) butterflies

Phylogenetic inference is challenged by genealogical heterogeneity amongst molecular markers. Such discordance is driven predominantly by incomplete lineage sorting (ILS) and interspecific gene flow, and bears attendant consequences for the accurate resolution of species relationships. Understanding the distribution of gene conflict in organismal genomes is, therefore, a key aspect of phylogenetic analysis. In this study, three large phylogenomic datasets (i.e., whole mitogenomes, conserved nuclear protein-coding loci, and genomic windows) are used to probe the extent to which discordance pervades the unresolved phylogeny of Coenonympha (Nymphalidae) butterflies. Gene tree discordance is found to be elevated at multiple historically recalcitrant phylogenetic positions. In particular, species relationships near the crown of Coenonympha and within a rapidly diversifying subclade (the hero group) remain difficult to resolve, suggesting that ILS and gene flow have obscured the evolution of this genus. These findings have implications for the taxonomy of this butterfly group and the study of its diversification history. In addition, this work lends support to a growing body of evidence that gene conflict driven by biological processes stands to confound phylogeny, even when extensive data are used.

Origin, Persistence, and Vulnerability to Climate Changes of Podocarpus Populations in Central African Mountains

Background and objectives—Podocarpus latifolius (synonym of P. milanjianus) is a key tree representative of Afromontane forests where it is highly threatened by climate and land-use changes. While large populations occur in East Africa, only a few isolated and usually small populations remain in western Central Africa (Cameroon to Angola). Studying the evolutionary history of such relictual populations can thus be relevant to understand their resilience under changing environments. Materials and Methods—we developed nine polymorphic nuclear microsatellites (nSSRs) to estimate genetic variability, (historical) gene flow, and demographic changes among natural populations from Central to East Africa. Results—despite the extended distribution range of P. latifolius, a strong isolation-by-distance pattern emerges at the intra-population scale, indicating low seed and pollen dispersal capacities. Central African populations display a lower genetic diversity (He = 0.34 to 0.61) and are more differentiated from each other (FST = 0.28) than are East African populations (He = 0.65 to 0.71; FST = 0.10), suggesting high genetic drift in the Central African populations. Spatial genetic structure reveals past connections between East and West Africa but also a gene flow barrier across the equator in western Central Africa. Demographic modelling anchors the history of current lineages in the Pleistocene and supports a strong demographic decline in most western populations during the last glacial period. By contrast, no signature of demographic change was detected in East African populations. Conclusions—in Cameroon, our results exclude a recent (re)colonization from one source population of all mountain ranges, but rather indicate long-term persistence of populations in each mountain with fluctuating sizes. A higher impact of genetic drift and further loss of diversity can be expected by survival through climatically unfavorable periods in such small refugial populations. Tracking the Quaternary legacy of podocarp populations is thus essential for their conservation since there is a temporal gap between environment crises and an ecological/genetic answer at the population level.

Highly divergent karyotypes and barcoding of the East African genus Gonatoxia Karsch (Orthoptera: Phaneropterinae)

East Africa is a hotspot of biodiversity of many orthopteran taxa, including bushcrickets. Gonatoxia Karsch, 1889 species are fully alate Phaneropterinae, which are perfectly adapted to the foliage of forests. We examined five species using combined cytogenetic and molecular data to determine the inter- and intraspecific genetic diversity. The variation in the diploid number of chromosomes in males ranged from 2n = 28 + X0 and 26 + X0 to 2n = 6 + X0. Fluorescence in situ hybridization showed from one to many 18S rDNA loci as well as interstitial sequences, especially in G. helleri. 18S rDNA loci coincided with active NOR and C-banding patterns. The isolation of populations of the species explains differences in the number of chromosomes (G. maculata), chromosomal polymorphism and chromosomal heterozygosity (G. helleri). Our molecular phylogeny based on the COI locus supported the monophyly of the genus Gonatoxia and separateness of the five examined species in accordance with their morphological features and chromosome numbers as well as the species' distribution.

Studying genetic population structure to shed light on the demographic explosion of the rare species Barbitistes vicetinus (Orthoptera, Tettigoniidae)

Insect outbreaks usually involve important ecological and economic consequences for agriculture and forestry. The short-winged bush-cricket Barbitistes vicetinus Galvagni & Fontana, 1993 is a recently described species that was considered rare until ten years ago, when unexpected population outbreaks causing severe defoliations across forests and crops were observed in north-eastern Italy. A genetic approach was used to analyse the origin of outbreak populations. The analysis of two mitochondrial regions (Cytochrome Oxidase I and II and 12S rRNA-Control Region) of 130 samples from the two disjunct ranges (Euganean and Berici Hills) showed high values of haplotype diversity and revealed a high geographical structure among populations of the two ranges. The high genetic variability observed supports the native origin of this species. In addition, results suggest that unexpected outbreaks are not a consequence of a single or few pestiferous haplotypes but rather the source of outbreaks are local populations which have experienced an increase in each area. The recent outbreaks have probably appeared independently of the genetic haplotypes whereas environmental conditions could have affected the outbreak populations. These findings contribute to a growing understanding of the status and evolutionary history of the pest that would be useful for developing and implementing biological control strategies for example by maximizing efforts to locate native natural enemies.

Tectonics, climate and the diversification of the tropical African terrestrial flora and fauna

Tropical Africa is home to an astonishing biodiversity occurring in a variety of ecosystems. Past climatic change and geological events have impacted the evolution and diversification of this biodiversity. During the last two decades, around 90 dated molecular phylogenies of different clades across animals and plants have been published leading to an increased understanding of the diversification and speciation processes generating tropical African biodiversity. In parallel, extended geological and palaeoclimatic records together with detailed numerical simulations have refined our understanding of past geological and climatic changes in Africa. To date, these important advances have not been reviewed within a common framework. Here, we critically review and synthesize African climate, tectonics and terrestrial biodiversity evolution throughout the Cenozoic to the mid-Pleistocene, drawing on recent advances in Earth and life sciences. We first review six major geo-climatic periods defining tropical African biodiversity diversification by synthesizing 89 dated molecular phylogeny studies. Two major geo-climatic factors impacting the diversification of the sub-Saharan biota are highlighted. First, Africa underwent numerous climatic fluctuations at ancient and more recent timescales, with tectonic, greenhouse gas, and orbital forcing stimulating diversification. Second, increased aridification since the Late Eocene led to important extinction events, but also provided unique diversification opportunities shaping the current tropical African biodiversity landscape. We then review diversification studies of tropical terrestrial animal and plant clades and discuss three major models of speciation: (i) geographic speciation via vicariance (allopatry); (ii) ecological speciation impacted by climate and geological changes, and (iii) genomic speciation via genome duplication. Geographic speciation has been the most widely documented to date and is a common speciation model across tropical Africa. We conclude with four important challenges faced by tropical African biodiversity research: (i) to increase knowledge by gathering basic and fundamental biodiversity information; (ii) to improve modelling of African geophysical evolution throughout the Cenozoic via better constraints and downscaling approaches; (iii) to increase the precision of phylogenetic reconstruction and molecular dating of tropical African clades by using next generation sequencing approaches together with better fossil calibrations; (iv) finally, as done here, to integrate data better from Earth and life sciences by focusing on the interdisciplinary study of the evolution of tropical African biodiversity in a wider geodiversity context.

Rapid chromosomal evolution in the bush-cricket Gonatoxia helleri Hemp, 2016 (Orthoptera, Phaneropterinae)

Gonatoxia helleri Hemp, 2016 is one of the most widespread bush-crickets of the genus Gonatoxia Karsch, 1889 in East Africa. This species with seven large chromosomes (2n♂ = 7) differs from other representatives of the genus Gonatoxia drastically by its reduced chromosome number, the asymmetrical karyotype including karyomorphs rarely found in tettigoniids, as well as in irregularities in the course of meiosis. To better understand the origin of such an exceptional karyotype, chromosomes of 29 specimens from four populations/localities were studied using classical techniques, such as C-banding, silver impregnation, fluorochrome double staining and fluorescence in situ hybridization (FISH) technique with 18S rDNA and (TTAGG) _n telomeric probes. FISH showed many 18S rDNA loci as well as interstitial telomeric sequences, where chromosome morphology varied in these components in terms of quantity and distribution. The 18S rDNA loci coincided with active NORs and C-banding patterns. We suggest that a combination of Robertsonian rearrangements and/or multiple common tandem fusions involving the same chromosomes contributed to the formation of this karyotype/karyomorphs. The results are the first step towards a better understanding of chromosomal reorganization and evolution within the genus Gonatoxia. Low chromosome number, together with the incidence of chromosomal polymorphism that is higher in G. helleri than previously reported in bush-crickets, implies that this species can be a valuable new model for cytogenetic and speciation studies. Our findings suggest that chromosomal translocations lead to diversification and speciation in this species and could be the driving force of adaptive radiation.

The comparative biogeography of Philippine geckos challenges predictions from a paradigm of climate-driven vicariant diversification across an island archipelago

A primary goal of biogeography is to understand how large-scale environmental processes, like climate change, affect diversification. One often-invoked but seldom tested process is the "species-pump" model, in which repeated bouts of cospeciation are driven by oscillating climate-induced habitat connectivity cycles. For example, over the past three million years, the landscape of the Philippine Islands has repeatedly coalesced and fragmented due to sea-level changes associated with glacial cycles. This repeated climate-driven vicariance has been proposed as a model of speciation across evolutionary lineages codistributed throughout the islands. This model predicts speciation times that are temporally clustered around the times when interglacial rises in sea level fragmented the islands. To test this prediction, we collected comparative genomic data from 16 pairs of insular gecko populations. We analyze these data in a full-likelihood, Bayesian model-choice framework to test for shared divergence times among the pairs. Our results provide support against the species-pump model prediction in favor of an alternative interpretation, namely that each pair of gecko populations diverged independently. These results suggest the repeated bouts of climate-driven landscape fragmentation have not been an important mechanism of speciation for gekkonid lizards across the Philippine Archipelago.

Relic populations of Fukomys mole-rats in Tanzania: description of two new species F. livingstoni sp. nov. and F. hanangensis sp. nov

Previous studies of African mole-rats of the genera Heliophobius and Fukomys (Bathyergidae) in the regions of East and south central Africa have revealed a diversity of species and vicariant populations, with patterns of distribution having been influenced by the geological process of rifting and changing patterns of drainage of major river systems. This has resulted in most of the extant members of the genus Fukomys being distributed west of the main Rift Valley. However, a small number of isolated populations are known to occur east of the African Rift Valley in Tanzania, where Heliophobius is the most common bathyergid rodent. We conducted morphological, craniometric and phylogenetic analysis of mitochondrial cytochrome b (cyt b) sequences of two allopatric populations of Tanzanian mole-rats (genus Fukomys) at Ujiji and around Mount Hanang, in comparison with both geographically adjacent and more distant populations of Fukomys. Our results reveal two distinct evolutionary lineages, forming clades that constitute previously unnamed species. Here, we formally describe and designate these new species F. livingstoni and F. hanangensis respectively. Molecular clock-based estimates of divergence times, together with maximum likelihood inference of biogeographic range evolution, offers strong support for the hypothesis that vicariance in the Western Rift Valley and the drainage patterns of major river systems has subdivided populations of mole-rats. More recent climatic changes and tectonic activity in the “Mbeya triple junction” and Rungwe volcanic province between Lakes Rukwa and Nyasa have played a role in further isolation of these extra-limital populations of Fukomys in Tanzania.

Phylogeography of a Morphologically Cryptic Golden Mole Assemblage from South-Eastern Africa

The Greater Maputaland-Pondoland-Albany (GMPA) region of southern Africa was recently designated as a centre of vertebrate endemism. The phylogeography of the vertebrate taxa occupying this region may provide insights into the evolution of faunal endemism in south-eastern Africa. Here we investigate the phylogeographic patterns of an understudied small mammal species assemblage (Amblysomus) endemic to the GMPA, to test for cryptic diversity within the genus, and to better understand diversification across the region. We sampled specimens from 50 sites across the distributional range of Amblysomus, with emphasis on the widespread A. hottentotus, to analyse geographic patterns of genetic diversity using mitochondrial DNA (mtDNA) and nuclear intron data. Molecular dating was used to elucidate the evolutionary and phylogeographic history of Amblysomus. Our phylogenetic reconstructions show that A. hottentotus comprises several distinct lineages, or evolutionarily significant units (ESUs), some with restricted geographic ranges and thus worthy of conservation attention. Divergence of the major lineages dated to the early Pliocene, with later radiations in the GMPA during the late-Pliocene to early-Pleistocene. Evolutionary diversification within Amblysomus may have been driven by uplift of the Great Escarpment c. 5-3 million years ago (Ma), habitat changes associated with intensification of the east-west rainfall gradient across South Africa and the influence of subsequent global climatic cycles. These drivers possibly facilitated geographic spread of ancestral lineages, local adaptation and vicariant isolation. Our study adds to growing empirical evidence identifying East and southern Africa as cradles of vertebrate diversity.

Infrageneric phylogeny and temporal divergence of Sorghum (Andropogoneae, Poaceae) based on low-copy nuclear and plastid sequences

The infrageneric phylogeny and temporal divergence of Sorghum were explored in the present study. Sequence data of two low-copy nuclear (LCN) genes, phosphoenolpyruvate carboxylase 4 (Pepc4) and granule-bound starch synthase I (GBSSI), from 79 accessions of Sorghum plus Cleistachne sorghoides together with those from outgroups were used for maximum likelihood (ML) and Bayesian inference (BI) analyses. Bayesian dating based on three plastid DNA markers (ndhA intron, rpl32-trnL, and rps16 intron) was used to estimate the ages of major diversification events in Sorghum. The monophyly of Sorghum plus Cleistachne sorghoides (with the latter nested within Sorghum) was strongly supported by the Pepc4 data using BI analysis, and the monophyly of Sorghum was strongly supported by GBSSI data using both ML and BI analyses. Sorghum was divided into three clades in the Pepc4, GBSSI, and plastid phylograms: the subg. Sorghum lineage; the subg. Parasorghum and Stiposorghum lineage; and the subg. Chaetosorghum and Heterosorghum lineage. Two LCN homoeologous loci of Cleistachne sorghoides were first discovered in the same accession. Sorghum arundinaceum, S. bicolor, S. x drummondii, S. propinquum, and S. virgatum were closely related to S. x almum in the Pepc4, GBSSI, and plastid phylograms, suggesting that they may be potential genome donors to S. almum. Multiple LCN and plastid allelic variants have been identified in S. halepense of subg. Sorghum. The crown ages of Sorghum plus Cleistachne sorghoides and subg. Sorghum are estimated to be 12.7 million years ago (Mya) and 8.6 Mya, respectively. Molecular results support the recognition of three distinct subgenera in Sorghum: subg. Chaetosorghum with two sections, each with a single species, subg. Parasorghum with 17 species, and subg. Sorghum with nine species and we also provide a new nomenclatural combination, Sorghum sorghoides.

Niche divergence promotes rapid diversification of East African sky island white-eyes (Aves: Zosteropidae)

The Eastern Afromontane biodiversity hotspot composed of highly fragmented forested highlands (sky islands) harbours exceptional diversity and endemicity, particularly within birds. To explain their elevated diversity within this region, models founded on niche conservatism have been offered, although detailed phylogeographic studies are limited to a few avian lineages. Here, we focus on the recent songbird genus Zosterops, represented by montane and lowland members, to test the roles of niche conservatism versus niche divergence in the diversification and colonization of East Africa's sky islands. The species-rich white-eyes are a typically homogeneous family with an exceptional colonizing ability, but in contrast to their diversity on oceanic islands, continental diversity is considered depauperate and has been largely neglected. Molecular phylogenetic analysis of ~140 taxa reveals extensive polyphyly among different montane populations of Z. poliogastrus. These larger endemic birds are shown to be more closely related to taxa with divergent habitat types, altitudinal distributions and dispersal abilities than they are to populations of restricted endemics that occur in neighbouring montane forest fragments. This repeated transition between lowland and highland habitats over time demonstrate that diversification of the focal group is explained by niche divergence. Our results also highlight an underestimation of diversity compared to morphological studies that has implications for their taxonomy and conservation. Molecular dating suggests that the spatially extensive African radiation arose exceptionally rapidly (1-2.5 Ma) during the fluctuating Plio-Pleistocene climate, which may have provided the primary driver for lineage diversification.

An improved approximate-Bayesian model-choice method for estimating shared evolutionary history

Background

To understand biological diversification, it is important to account for large-scale processes that affect the evolutionary history of groups of co-distributed populations of organisms. Such events predict temporally clustered divergences times, a pattern that can be estimated using genetic data from co-distributed species. I introduce a new approximate-Bayesian method for comparative phylogeographical model-choice that estimates the temporal distribution of divergences across taxa from multi-locus DNA sequence data. The model is an extension of that implemented in msBayes.

Results

By reparameterizing the model, introducing more flexible priors on demographic and divergence-time parameters, and implementing a non-parametric Dirichlet-process prior over divergence models, I improved the robustness, accuracy, and power of the method for estimating shared evolutionary history across taxa.

Conclusions

The results demonstrate the improved performance of the new method is due to (1) more appropriate priors on divergence-time and demographic parameters that avoid prohibitively small marginal likelihoods for models with more divergence events, and (2) the Dirichlet-process providing a flexible prior on divergence histories that does not strongly disfavor models with intermediate numbers of divergence events. The new method yields more robust estimates of posterior uncertainty, and thus greatly reduces the tendency to incorrectly estimate models of shared evolutionary history with strong support.

Inferring the demographic history of European Ficedula flycatcher populations

Background

Inference of population and species histories and population stratification using genetic data is important for discriminating between different speciation scenarios and for correct interpretation of genome scans for signs of adaptive evolution and trait association. Here we use data from 24 intronic loci re-sequenced in population samples of two closely related species, the pied flycatcher and the collared flycatcher.

Results

We applied Isolation-Migration models, assignment analyses and estimated the genetic differentiation and diversity between species and between populations within species. The data indicate a divergence time between the species of <1 million years, significantly shorter than previous estimates using mtDNA, point to a scenario with unidirectional gene-flow from the pied flycatcher into the collared flycatcher and imply that barriers to hybridisation are still permeable in a recently established hybrid zone. Furthermore, we detect significant population stratification, predominantly between the Spanish population and other pied flycatcher populations.

Conclusions

Our results provide further evidence for a divergence process where different genomic regions may be at different stages of speciation. We also conclude that forthcoming analyses of genotype-phenotype relations in these ecological model species should be designed to take population stratification into account.

Sequential fragmentation of Pleistocene forests in an East Africa biodiversity hotspot: chameleons as a model to track forest history

BACKGROUND

The Eastern Arc Mountains (EAM) is an example of naturally fragmented tropical forests, which contain one of the highest known concentrations of endemic plants and vertebrates. Numerous paleo-climatic studies have not provided direct evidence for ancient presence of Pleistocene forests, particularly in the regions in which savannah presently occurs. Knowledge of the last period when forests connected EAM would provide a sound basis for hypothesis testing of vicariance and dispersal models of speciation. Dated phylogenies have revealed complex patterns throughout EAM, so we investigated divergence times of forest fauna on four montane isolates in close proximity to determine whether forest break-up was most likely to have been simultaneous or sequential, using population genetics of a forest restricted arboreal chameleon, Kinyongia boehmei.

METHODOLOGY/PRINCIPAL FINDINGS

We used mitochondrial and nuclear genetic sequence data and mutation rates from a fossil-calibrated phylogeny to estimate divergence times between montane isolates using a coalescent approach. We found that chameleons on all mountains are most likely to have diverged sequentially within the Pleistocene from 0.93-0.59 Ma (95% HPD 0.22-1.84 Ma). In addition, post-hoc tests on chameleons on the largest montane isolate suggest a population expansion ∼182 Ka.

CONCLUSIONS/SIGNIFICANCE

Sequential divergence is most likely to have occurred after the last of three wet periods within the arid Plio-Pleistocene era, but was not correlated with inter-montane distance. We speculate that forest connection persisted due to riparian corridors regardless of proximity, highlighting their importance in the region's historic dispersal events. The population expansion coincides with nearby volcanic activity, which may also explain the relative paucity of the Taita's endemic fauna. Our study shows that forest chameleons are an apposite group to track forest fragmentation, with the inference that forest extended between some EAM during the Pleistocene 1.1-0.9 Ma.