Contrasting patterns of diversification in a bird family (Aves: Gruiformes: Rallidae) are revealed by analysis of geospatial distribution of species and phylogenetic diversity

Geospatial patterns in the distribution of regional biodiversity reflect the composite processes that underpin evolution: speciation, dispersal and extinction. The spatial distribution and phylogeny of a globally widespread and species rich bird family (Rallidae) were used to help assess the role of large‐scale biogeographical processes in diversity and diversification. Here, we examine how different geostatistical diversity metrics enhance our understanding of species distribution by linking occurrence records of rail species to corresponding species level phylogeny. Tropical regions and temperate zones contained a large proportion of rail species richness and phylogenetic diversity whilst small islands in Australian, Oceanian and Oriental regions held the highest weighted and phylogenetic endemism. Our results suggest that habitat connectivity and dispersal were important ecological features in rail evolution and distribution. Spatial isolation was a significant driver of diversification where islands in Oceania were centres of neo‐endemism with recent multiple and independent speciation events and could be considered as nurseries of biodiversity. Palaeo‐endemism was mostly associated with older stable regions, so despite extensive long distance range shifting these areas retain their own ancient and distinct character. Madagascar was the major area of palaeo‐endemism associated with the oldest rail lineages and could be considered a museum of rail diversity. This implies a mixture of processes determine the current distribution and diversity of rail clades with some areas dominated by recent ‘in situ’ speciation while others harbour old diversity with ecological traits that have stood the test of time.     

Areas of endemism and spatial diversification of the Muscidae (Insecta: Diptera) in the Andean and Neotropical regions

Aim We present a biogeographical analysis of the areas of endemism and areas of diversification in the Muscidae. This analysis searched for geographical patterns in the Muscidae to reconstruct elements of the evolutionary biogeographical history of this insect family. Location Andean and Neotropical regions. Method We constructed a geographic database of 728 species from the literature and museum specimens. Areas of endemism were established by parsimony analysis of endemicity (PAE) based on grids of two different sizes: 5° (550 × 550 km) and 2° (220 × 220 km). Areas of diversification were delimited by track analysis that also included phylogenetic information. This process was independently applied to 11 genera. For each genus, we plotted generalized tracks generated by sister species on a map. When these generalized tracks supported inter‐generic nodes they were manually contoured and inferred to be areas of diversification for the Muscidae. Results Thirteen endemic areas were found using the 5° grid, and eight endemic areas resulted from the 2° grid. Ten areas were in agreement with previous studies, and 11 were new. Amazonian and Atlantic areas of diversification agreed with previous areas for the genus Polietina, and new areas of diversification were found in Panama and in central Chile. Main conclusions Six spatial patterns in the Muscidae were identified: (1) areas of endemism in both Pampa and Puna provinces were established with species whose distributions had not previously been analysed; (2) a new area of endemism was established in extreme southern South America, in Tierra del Fuego; (3) two new areas of diversification, which include Panama and central Chile, were identified; (4) a spatial association was identified between the separation of Chiloe Island from the continent and the diversification in Andean species; (5) a north–south track axis and latitudinal node intervals were identified, interpreted as spatial responses to glaciation or glacial retreat in the Andes; and (6) a spatial coincidence of areas of endemism, of diversification and high species richness in the Muscidae was discovered. The analysis of a complete database and the recognition of areas of diversification are extremely important in elucidating novel biogeographical patterns, which will in turn contribute to a better understanding of the geographical patterns of evolution in the Muscidae.     

西南地区壳斗科物种丰富度和特有性分布格局模拟及其环境解释

如何准确地模拟物种宏观丰富度格局和特有性中心是生物多样性保护工作的重点,也是生物地理学的热点话题。西南地区是我国壳斗科植物最丰富的地区之一,但物种多样性格局及环境驱动机制尚不清楚。本研究基于西南地区161种壳斗科植物7258个分布点位数据,利用点格局法和物种分布模型两种方式构建了物种丰富度、加权特有性指数和校正加权特有性指数的分布格局,并采用空间自回归模型(SAR)分析上述3个多样性指数与环境因子间的关系。总体上看,物种分布模型模拟的3个指数在空间上比点格局法更为连续,但数值高低分布情况具有相似性: 两种方式模拟的物种丰富度高值区主要分布在滇南边缘、桂北部和桂西南部地区(62～89种);加权特有性指数最大值集中在滇南和桂西地区(1.77～5.02);藏东南、秦岭-大巴山、桂西南部和滇东南地区具有最高的校正加权特有性指数(0.07～0.17)。SAR模型结果显示:最干月降雨量、温度季节性变化标准差、海拔变幅和土壤有机碳含量对物种丰富度的影响均显著,最干月降雨量、温度季节性变化标准差、潜在蒸散量和海拔变幅对加权特有性有着显著影响,温度季节性变化标准差、最干月降雨量、历史温度变化、增强型植被指数变异系数和海拔变幅对校正加权特有性的影响显著;SAR模型对物种丰富度、特有性指数和加权特有性指数的拟合效果(R²=0.857、0.733、0.593)分别优于普通线性模型(R²=0.689、0.425、0.422)。综上,水分可获得性、气候季节性、生境异质性、历史气候变化和土壤状况是制约西南地区壳斗科丰富度和特有性分布的最重要因素。滇南、滇东南、桂西南、桂西、秦岭-大巴山以及藏东南地区是壳斗科物种丰富度中心或特有性中心,应受到重点关注和保护。     

The coincidence of rarity and richness and the potential signature of history in centres of endemism

We investigate the relative importance of stochastic and environmental/topographic effects on the occurrence of avian centres of endemism, evaluating their potential historical importance for broad‐scale patterns in species richness across Sub‐Saharan Africa. Because species‐rich areas are more likely to be centres of endemism by chance alone, we test two null models: Model 1 calculates expected patterns of endemism using a random draw from the occurrence records of the continental assemblage, whereas Model 2 additionally implements the potential role of geometric constraints. Since Model 1 yields better quantitative predictions we use it to identify centres of endemism controlled for richness. Altitudinal range and low seasonality emerge as core environmental predictors for these areas, which contain unusually high species richness compared to other parts of sub‐Saharan Africa, even when controlled for environmental differences. This result supports the idea that centres of endemism may represent areas of special evolutionary history, probably as centres of diversification.     

Defining spatial and temporal patterns of phylogeographic structure in Madagascar's iguanid lizards (genus Oplurus)

Understanding the remarkably high species diversity and levels of endemism found among Madagascar’s flora and fauna has been the focus of many studies. One hypothesis that has received much attention proposes that Quaternary climate fluctuations spurred diversification. While spatial patterns of distribution and phylogenetic relationships can provide support for biogeographic predictions, temporal estimates of divergence are required to determine the fit of these geospatial patterns to climatic or biogeographic mechanisms. We use multilocus DNA sequence data to test whether divergence times among Malagasy iguanid lizards of the subfamily Oplurinae are compatible with a hypotheses of Pliocene–Pleistocene diversification. We estimate the oplurine species tree and associated divergence times under a relaxed‐clock model. In addition, we examine the phylogeographic structure and population divergence times within two sister species of Oplurus primarily distributed in the north‐west and south‐west of Madagascar (Oplurus cuvieri and Oplurus cyclurus, respectively). We find that divergence events among oplurine lineages occurred in the Oligocene and Miocene and are thus far older and incompatible with the hypothesis that recent climate fluctuations are related to current species diversity. However, the timing of intraspecific divergences and spatial patterns of population genetic structure within O. cuvieri and O. cyclurus suggest a role for both intrinsic barriers and recent climate fluctuations at population‐level divergences. Integrating information across spatial and temporal scales allows us to identify and better understand the mechanisms generating patterns diversity.     

A palaeobiogeographic model for biotic diversification within Amazonia over the past three million years

Many hypotheses have been proposed to explain high species diversity in Amazonia, but few generalizations have emerged. In part, this has arisen from the scarcity of rigorous tests for mechanisms promoting speciation, and from major uncertainties about palaeogeographic events and their spatial and temporal associations with diversification. Here, we investigate the environmental history of Amazonia using a phylogenetic and biogeographic analysis of trumpeters (Aves: Psophia), which are represented by species in each of the vertebrate areas of endemism. Their relationships reveal an unforeseen 'complete' time-slice of Amazonian diversification over the past 3.0 Myr. We employ this temporally calibrated phylogeny to test competing palaeogeographic hypotheses. Our results are consistent with the establishment of the current Amazonian drainage system at approximately 3.0-2.0 Ma and predict the temporal pattern of major river formation over Plio-Pleistocene times. We propose a palaeobiogeographic model for the last 3.0 Myr of Amazonian history that has implications for understanding patterns of endemism, the temporal history of Amazonian diversification and mechanisms promoting speciation. The history of Psophia, in combination with new geological evidence, provides the strongest direct evidence supporting a role for river dynamics in Amazonian diversification, and the absence of such a role for glacial climate cycles and refugia.     

Patterns and processes of global riverine fish endemism

Aim To explore global patterns of riverine fish endemism by applying an island biogeography framework to river drainage basins and highlight evolutionary mechanisms producing two kinds of endemism: neo‐endemism, arising from within‐drainage cladogenetic speciation, and palaeo‐endemism, arising from species range contraction or anagenetic speciation. Location World‐wide. Methods We use a uniquely comprehensive data set of riverine fish species distributions to map global fish endemism patterns. We then use the relationships between (1) total species richness and proportions of endemic species and (2) total species richness and a measure of in situ (i.e. within‐drainage basin) probability of speciation by cladogenesis, to identify the two distinct forms of endemism. After separating drainage basins into two different sets according to dominance of one of these two forms, we apply a model averaging procedure to highlight, for both datasets, the environmental and historical variables that better explain endemism patterns. We finally analyse the effect of biotic components related to dispersal ability on the percentages of both kinds of endemism among lineages. Results Our results indicate that the two types of endemism are distributed differently across space and taxonomic lineages: (1) neo‐endemism, positively related to the overall richness of the drainage basin, is essentially linked to in situ cladogenetic speciation and is positively related to drainage basin area, negatively related to climate variability since glacial periods and negatively related to all proxies of dispersal ability; and (2) palaeo‐endemism, not directly contributing to drainage basin richness, is a pure process of extinction through range contraction and/or isolation through time and is mostly related to geographic isolation, glacial history and positively related to marine‐derived origin of families. Main conclusions The non‐random spatial and taxonomic distribution of neo‐endemism and palaeo‐endemism sharply reflects the role of evolutionary processes and provides a way to identify areas of high conservation interest based on their high present and future diversification potential.     

Molecular evolution and radiation of dung beetles in Madagascar

Madagascar is the world's fourth largest island and has a wide range of climates and ecosystems. Environmental diversity combined with long history of isolation (160 Myr) has generated a high level of endemism at different taxonomic levels, making Madagascar one of the hotspots of global biodiversity. Dung beetles, represented by the two tribes of Canthonini and Helictopleurini, exemplify a large insect taxon. Helictopleurini are completely endemic to Madagascar while Canthonini are endemic at generic level. Using data from mitochondrial and nuclear genes, phylogenetic relationships were investigated in a sample of 44 species. The phylogeny for Canthonini consists of several distinct clades, possibly reflecting multiple colonization of Madagascar. The phylogeny does not support the current taxonomy for all genera. The phylogeny for Helictopleurini lacks statistical support at supra‐specific level, and genetic divergence among the Helictopleurini species is comparable with that among species within genera in Canthonini. These results suggest that Helictopleurini has undergone rapid speciation and most likely more recently than Canthonini, consistent with the estimated radiation time based on mtDNA mutation rates in insects and with knowledge about the systematics and geographic distribution of dung beetles worldwide. A detailed analysis of sequence composition identified common patterns in Malagasy dung beetles and other insects. © The Willi Hennig Society 2007.     

THE EVOLUTION OF LOCAL ENDEMISM IN MADAGASCAR: WATERSHED VERSUS CLIMATIC GRADIENT HYPOTHESES EVALUATED BY NULL BIOGEOGRAPHIC MODELS

Substantial insular speciation has resulted in exceptionally high levels of endemism in Madagascar, creating locally restricted species' ranges that remain poorly understood. The contributions of alternative processes that could influence patterns of local endemism—including speciation by geographic isolation or adaptation to environmental gradients—are widely debated, both for Madagascar and elsewhere. A recently proposed hypothesis (the "watershed hypothesis") suggests that allopatric speciation driven by isolation in watersheds during Quaternary climate shifts provides a general explanation for patterns of local endemism across taxa in Madagascar. Here we tested coincidence between species' distributions and areas of endemism predicted by two contrasting biogeographic hypotheses: (1) the watershed hypothesis, and (2) an alternative hypothesis driven by climatic gradients (the "current climate hypothesis"). Statistical significance of coincidence was assessed by comparing against a null model. Surprisingly, we found that extant distributions of lemurs, geckos, and chameleons reveal species patterns that are significantly coincident with the watershed and current climate hypotheses. These results strongly support local endemism developing from multiple processes, even among closely related species. Our findings thus indicate that pluralistic approaches will offer the best option both for understanding processes that generate local endemism, and for incorporating endemism within conservation priority setting.     

Spatial Biodiversity Patterns of Madagascar's Amphibians and Reptiles

Madagascar has become a model region for testing hypotheses of species diversification and biogeography, and many studies have focused on its diverse and highly endemic herpetofauna. Here we combine species distribution models of a near-complete set of species of reptiles and amphibians known from the island with body size data and a tabulation of herpetofaunal communities from field surveys, compiled up to 2008. Though taxonomic revisions and novel distributional records arose since compilation, we are confident that the data are appropriate for inferring and comparing biogeographic patterns among these groups of organisms. We observed species richness of both amphibians and reptiles was highest in the humid rainforest biome of eastern Madagascar, but reptiles also show areas of high richness in the dry and subarid western biomes. In several amphibian subclades, especially within the Mantellidae, species richness peaks in the central eastern geographic regions while in reptiles different subclades differ distinctly in their richness centers. A high proportion of clades and subclades of both amphibians and reptiles have a peak of local endemism in the topographically and bioclimatically diverse northern geographic regions. This northern area is roughly delimited by a diagonal spanning from 15.5°S on the east coast to ca. 15.0°S on the west coast. Amphibian diversity is highest at altitudes between 800–1200 m above sea-level whereas reptiles have their highest richness at low elevations, probably reflecting the comparatively large number of species specialized to the extended low-elevation areas in the dry and subarid biomes. We found that the range sizes of both amphibians and reptiles strongly correlated with body size, and differences between the two groups are explained by the larger body sizes of reptiles. However, snakes have larger range sizes than lizards which cannot be readily explained by their larger body sizes alone. Range filling, i.e., the amount of suitable habitat occupied by a species, is less expressed in amphibians than in reptiles, possibly reflecting their lower dispersal capacity. Taxonomic composition of communities assessed by field surveys is largely explained by bioclimatic regions, with communities from the dry and especially subarid biomes distinctly differing from humid and subhumid biomes.