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.     

The Postponed Agenda: Archaeology and Human Biogeography in the Twenty-First Century

Scholarly views on the prehistory of the Pacific Islanders are currently undergoing a major shift in perspective and underlying assumptions. This shift is driven by new research data and a need for new theoretical perspectives on space, time, and causal process. A new research agenda is coming to the fore, replacing the agenda guiding Pacific studies since the 1950s. Instead of looking at these islands as remote, undeveloped human colonies scattered across a vast and empty expanse of sea, we are finding that the Pacific was a notably early sphere of human accomplishments, on land and sea, where the ocean was more an avenue than a barrier for cultural interchange. The roots of this new perspective can be traced back, in part, to the Wenner-Gren/Smithsonian conference on human biogeography held in Washington, D.C., in 1974.     

Phylogeography of the chestnut‐tailed antbird (Myrmeciza hemimelaena) clarifies the role of rivers in Amazonian biogeography

Aim We examined patterns of spatial and temporal diversification of the Amazonian endemic chestnut‐tailed antbird, Mymeciza hemimelaena (Thamnophilidae), to evaluate the diversification of a widespread avian taxon across rivers that potentially represent major natural barriers. Location Lowland Amazonia. Methods Sequences of the mitochondrial ND2 and cytochrome b genes were investigated from 65 individuals distributed throughout the entire range of M. hemimelaena, and including the two currently valid subspecies M. h. hemimelaena and M. h. pallens. Based on a combination of phylogeographic tools, molecular dating, and population genetic methods, we reconstructed a spatio‐temporal scenario of diversification of M. hemimelaena in the Amazon. Results The data revealed three genetically divergent and monophyletic groups in M. hemimelaena, which can also be distinguished by a combination of morphological and vocal characters. Two of these clades correspond to the previously described taxa M. h. hemimelaena and M. h. pallens, which are separated by the upper Madeira River, a main Amazonian tributary. The third clade is distributed between the middle reaches of the Madeira River and the much smaller tributaries Jiparaná and Aripuanã, and, although currently treated as M. h. pallens, clearly constitutes an independent evolutionary lineage probably deserving separate species status. Molecular clock and population genetic analyses indicate that diversification in this group occurred throughout the Pleistocene, with demographic fluctuations assumed for M. h. hemimelaena and M. h. pallens. Main conclusions The findings implicate rivers as barriers driving diversification in the M. hemimelaena complex. Levels of mitochondrial DNA divergence and associated morphological and vocal traits support its division into at least three separate species with comparatively small ranges. The existence of a previously unrecognized lineage in the M. hemimelaena complex, and the high degree of population structuring found in M. h. hemimelaena underscore the pervasiveness of cryptic endemism throughout Amazonia and the importance of DNA‐based taxonomic and phylogeographic studies in providing the accurate estimates of diversity that are essential for conservation planning.     

Review Oribatid mites of the Galápagos Islands – faunistics, ecology and speciation

The results from investigations on oribatid mites of the Galápagos archipelago during 10 years are presented. Samples were taken on all larger and most smaller islands of the archipelago, as well as in all vegetation zones and some special habitats such as grass or cactus litter and fumaroles. A total of 202 oribatid species belonging to 64 families were encountered; among them 81 species are new to science. The Oribatida occur from the littoral zone to the summit of the volcanoes. Diversity and abundance increases from the arid to the moister zones at higher elevations. Most species prefer moist habitats at medium to higher elevations of the islands, in some parts reaching remarkably high abundances (in the Scalesia zone of Santa Cruz approximately 18 000 individuals m–2). The species richness of an island depends on the altitude and number of available habitats rather than the area of the island. Many oribatid species on the Galápagos Islands have a wide biogeographical distribution. The majority originate from the Central and South American mainland, but several Pacific and even Holarctic elements were also found. In comparison with the species composition of the adjacent mainland, the oribatid mite fauna of the Galápagos Islands can be regarded as disharmonic. Sea surface transportation has been proved at least between the islands, which also applies to oribatid species living at higher elevations. Long distance dispersal can be assumed to be mainly hydrochorous. The oribatid fauna of the littoral and arid vegetation zones is presented in detail. Some species even inhabit such extreme habitats as warm fern litter in fumaroles or hot volcanic soils. Others were mainly found in or near agricultural areas, suggesting human introduction. Striking distribution patterns within the archipelago are discussed. The distribution of endemic forms in the genera Aeroppia, Scapheremaeus, Scheloribates and Cultrobates indicates both speciation on different islands, as well as speciation on the same island by occupying different habitats.     

Avian mitochondrial DNA sequence divergence across a headwater stream of the Rio Tapajós, a major Amazonian river

Populations of ten Amazonian bird species were sampled on opposite banks of the Rio Teles Pires, a headwater stream of the Rio Tapajós, in the Alta Floresta region, northern Mato Grosso, Brazil. The river is 100–300 m wide in this region. We found a range of genetic differentiation from none to relatively high levels; six of the ten species studied exhibit what appear to be genetic breaks at the river. With one exception, the antbird Hylophylax poecilinota, there is no morphologically recognized differentiation correlating with genetic differentiation. From the perspective of traditional morphology-based taxonomy, the Rio Teles Pires is not a faunal barrier. Rather, contact zones between members of species and subspecies pairs appear more or less randomly distributed in this region, some being located at varying distances to the east, others at varying distances to the west of the Rio Teles Pires, with few following the course of this river itself.

Islands and evolution: theory and opinion in Darwin's earlier years

Islands were not of special interest to evolutionists before Darwin. It was he who first appreciated their importance for demonstrating evolution in miniature. They were not of special interest because: (a) their peculiar products seemed no more peculiar than those of continents; (b) there was no special category of oceanic islands, but a continuum from such groups as the Canaries, Madeiras and Galápagos through New Zealand and Madagascar to Australia, Britain, and true continents; and (c) the concept of adaptive radiation, if known at all, was applied only to the higher levels of classification, and then very feebly.
When Darwin was young, classification at the lower levels hardly recognized convergence, and at the higher levels was subject to great changes, while only slowly separating out the major groups. In consequence, many of the facts of geographical distribution were misinterpreted, and numerous theories of the origination of species, groups, and biogeographical provinces were still plausible. It was largely the need for a historical, not ecological, explanation of the distribution of some mammals and plants, plus what he saw for himself in the Galápagos Islands, that convinced Darwin that evolution had occurred. His was a remarkable achievement in recognizing through all this 'noise' the meaning of adaptive radiation.     

Distributional patterning of terrestrial herpetofauna on the Wessel and English Company Island groups,northeastern Arnhem Land,Northern Territory,Australia

Forty-four species of terrestrial reptiles and eight species of frogs were recorded from 60 continental islands of the Wessel and English Company groups off northeastern Arnhem Land, Northern Territory. Two gecko species, Oedura rhombifer and Heteronotia binoei, were present on the most islands (34 and 31, respectively), and occurred on islands < 5 ha. In contrast, agamids, pygopodids and varanids were absent from islands < 18 ha, and snakes and frogs were not reported from islands < 240 ha. Island size explained 82% of the variation in species richness for terrestrial reptiles, and 84% of that for lizards. The relationship was less good for (i) groups with generally uncommon species (notably snakes), for which sampling effort explained more variation, and (ii) groups with species which had relatively specific habitat requirements (notably frogs), for which island size and isolation factors were not especially relevant. For most taxonomic groups considered, isolation factors added little to the relationship between species richness and island size. Across all reptiles, larger species were found on fewer islands, and had larger island size thresholds. This relationship broke down with analysis restricted to the single most species-rich family, Scincidae. Only 6 of the 20 most frequently recorded species showed significant variation in abundance among 8 vegetation types sampled by 226 quadrats across 40 islands. The number of species (alpha-diversity) and total abundance of herpetofauna within quadrats was generally unrelated to island size; however, (with analysis restricted to islands on which they occurred) six individual species were significantly more abundant on smaller islands than on larger islands, with no species showing the opposite pattern. The islands’ herpetofauna is largely a relatively depauperate subset of that of the far more complex sandstone massif and escarpment of western Arnhem Land, especially missing species associated with rugged sandstone gorges, riparian areas, open forests, swamps and clay soils. Patterns in species richness and composition are explained by greater range of environments on larger islands allowing better retention of species since isolation and/or richer tallies at the time of isolation. The evidence suggests that there has been relatively little colonization, although at least two gecko species and one varanid may have moved reasonably frequently.     

A PHYLOGENETIC PERSPECTIVE ON ELEVATIONAL SPECIES RICHNESS PATTERNS IN MIDDLE AMERICAN TREEFROGS: WHY SO FEW SPECIES IN LOWLAND TROPICAL RAINFORESTS?

Differences in species richness at different elevations are widespread and important for conservation, but the causes of these patterns remain poorly understood. Here, we use a phylogenetic perspective to address the evolutionary and biogeographic processes that underlie elevational diversity patterns within a region. We focus on a diverse but well-studied fauna of tropical amphibians, the hylid frogs of Middle America. Middle American treefrogs show a \"hump-shaped\" pattern of species richness (common in many organisms and regions), with the highest regional diversity at intermediate elevations. We reconstructed phylogenetic relationships among 138 species by combining new and published sequence data from 10 genes and then used this phylogeny to infer evolutionary rates and patterns. The high species richness of intermediate elevations seems to result from two factors. First, a tendency for montane clades to have higher rates of diversification. Second, the early colonization of montane regions, leaving less time for speciation to build up species richness in lowland regions (including tropical rainforests) that have been colonized more recently. This \"time-for-speciation\" effect may explain many diversity patterns and has important implications for conservation. The results also imply that local-scale environmental factors alone may be insufficient to explain the high species richness of lowland tropical rainforests, and that diversification rates are lower in earth's most species-rich biome.     

Allopatric speciation of Meteterakis (Heterakoidea: Heterakidae), a highly dispersible parasitic nematode,in the East Asian islands

To clarify how the species diversity of highly dispersible parasites has developed, molecular phylogenetic analyses of Meteterakis spp., multi-host endoparasitic nematodes of reptiles and amphibians from the East Asian islands, were conducted. The results demonstrated the existence of two major clades, the J- and A-groups, with exclusive geographic ranges that are discordant with the host faunal province. However, diversification within the J-group was concordant with the host biogeography and suggested co-divergence of this group with vicariance of the host fauna. In contrast, the phylogenetic pattern within the A-group was discordant with host biogeography and implied diversification by repeated colonization. In addition, the mosaic distribution pattern of a J-group and an A-group species in the Japanese Archipelago, along with comparison of population genetic parameters and the genetic distance from their closest relatives, suggested the initial occurrence of a J-group lineage followed by exclusion in the western part of this region caused by invasion of an A-group lineage. Thus, the present study suggested that the species diversity of highly dispersible parasites including Meteterakis is formed not only by co-divergence with host faunal vicariance but also by peripatric speciation and exclusive interactions between species.     

Dispersal and speciation of skinks among archipelagos in the tropical Pacific Ocean

Summary We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific archipelagos. The entire tropical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found within more than one archipelago) and endemic (found within only one archipelago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 archipelagos in the study area. Nine geographic variables reflecting archipelago size, isolation and elevation were estimated for each archipelago. Principal components analysis was used to reduce the nine variables to three uncorrelated composite variables that were interpreted as representing archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an archipelago were related to the composite geographic variables using multiple linear regression analysis. Archipelago size and isolation were important predictors of both skink diversity and endemism. Results were then compared to diversity and endemism of birds within the study area. Skinks showed an archipelago-wide level of endemism similar to that of birds. On an archipelago by archipelago basis, however, large differences between birds and skinks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Marquesas were nearly completely endemic, while no endemic skinks occurred in these two archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rates of colonization and speciation. Differences may also be due partly to morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as separate species. The discovery of such cryptic species, however, is unlikely to increase the endemic skink fauna of Hawaii and other distant archipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ecological interactions.