Investigating early hominin dispersal patterns: developing a framework for climate data integration

An investigation using the Stepping Out model of early hominin dispersal out of Africa is presented here. The late arrival of early hominins into Europe, as deduced from the fossil record, is shown to be consistent with poor ability of these hominins to survive in the Eurasian landscape. The present study also extends the understanding of modelling results from the original study by Mithen and Reed (2002. Stepping out: a computer simulation of hominid dispersal from Africa. J. Hum. Evol. 43, 433-462). The representation of climate and vegetation patterns has been improved through the use of climate model output. This study demonstrates that interpretative confidence may be strengthened, and new insights gained when climate models and hominin dispersal models are integrated.     

Dispersal and colonisation, long and short chronologies: how continuous is the Early Pleistocene record for hominids outside East Africa?

This paper examines the evidence for hominids outside East Africa during the Early Pleistocene. Most attention has focused recently on the evidence for or against a late Pliocene dispersal, ca. 1.8 Ma., of hominids out of Africa into Asia and possibly southern Europe. Here, the focus is widened to include North Africa as well as southern Asia and Europe, as well as the evidence in these regions for hominids after their first putative appearance ca. 1.8 Ma. It suggests that overall there is very little evidence for hominids in most of these regions before the Middle Pleistocene. Consequently, it concludes that the colonising capabilities of Homo erectus may have been seriously over-rated, and that even if hominids did occupy parts of North Africa, southern Europe and southern Asia shortly after 2 Ma, there is little evidence of colonisation. Whilst further fieldwork will doubtless slowly fill many gaps in a poorly documented Lower Pleistocene hominid record, it appears premature to conclude that the appearance of hominids in North Africa, Europe and Asia was automatically followed by permanent settlement. Rather, current data are more consistent with the view that Lower Pleistocene hominid populations outside East Africa were often spatially and temporally discontinuous, that hominid expansion was strongly constrained by latitude, and that occupation of temperate latitudes north of latitude 40 degrees was largely confined to interglacial periods.     

Mechanisms of hominoid dispersal in Miocene East Africa

The thesis of this essay is that the ecological changes which occurred during the Miocene in East Africa, created both the need and the conditions for the development of dispersal behaviour and other adaptations. The major ecological change in East Africa during the Miocene was the break-up of the relatively homogenous, lowland, tropical rainforest. The forest break-up was due to the combined effects of climatic change and rifting. The result of the fragmentation for species adapted to the forest, was increasing resource limitation. Species responded either by retreating with the forests, becoming extinct, or by evolving or developing new behaviours to cope with the new environment. The focus of this paper is upon the development of dispersal as a behaviour pattern for locating patchy resources. An ecological model is advanced to explain the development of dispersal and to place it in the context of other competing evolutionary responses to the ecological changes of the Miocene. The anatomical evolution of the Old World monkeys and apes during the Miocene is looked at in terms of the model. Bovid evolution over the same period is also looked at as evidence of a broad, episodic turnover in response to the ecological changes. It is suggested that hominid bipedalism may also fit the model and may have evolved as an adaptation for dispersion.     

The diversity and distribution of diatoms: from cosmopolitanism to narrow endemism

It has been claimed that microbial taxa will not exhibit endemism because their enormous populations remove dispersal as an effective constraint on geographical range. Here we review evidence that challenges this ubiquity hypothesis for the most speciose group of microbial eukaryotes, the diatoms. Detailed taxonomic inventories using fine-grained morphological characteristics, molecular markers, and crossing experiments have revealed that the geographic distribution of diatoms ranges from global to narrow endemic. Records of human-mediated introductions of exotic species further provide a strong indication that geographic dispersal was limiting in the past. Finally, recent studies have revealed that diatom community structure and diversity are influenced by geographical factors independent of environmental conditions. Diatom communities are thus regulated by the same processes that operate in macro-organisms, although possibly to a different degree, implying that dispersal limitation is significant and the endemism observed in isolated areas is real. These results underscore the pressing need to (1) continue research into diatom biology, ecology and the factors driving diatom species diversity and geographic distributions, and (2) protect relatively isolated areas against further introductions of exotic species. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.     

The Dispersal Ecology of Rhodesian Sleeping Sickness Following Its Introduction to a New Area

Tsetse-transmitted human and animal trypanosomiasis are constraints to both human and animal health in sub-Saharan Africa, and although these diseases have been known for over a century, there is little recent evidence demonstrating how the parasites circulate in natural hosts and ecosystems. The spread of Rhodesian sleeping sickness (caused by Trypanosoma brucei rhodesiense) within Uganda over the past 15 years has been linked to the movement of infected, untreated livestock (the predominant reservoir) from endemic areas. However, despite an understanding of the environmental dependencies of sleeping sickness, little research has focused on the environmental factors controlling transmission establishment or the spatially heterogeneous dispersal of disease following a new introduction. In the current study, an annually stratified case-control study of Rhodesian sleeping sickness cases from Serere District, Uganda was used to allow the temporal assessment of correlations between the spatial distribution of sleeping sickness and landscape factors. Significant relationships were detected between Rhodesian sleeping sickness and selected factors, including elevation and the proportion of land which was “seasonally flooding grassland” or “woodlands and dense savannah.” Temporal trends in these relationships were detected, illustrating the dispersal of Rhodesian sleeping sickness into more ‘suitable’ areas over time, with diminishing dependence on the point of introduction in concurrence with an increasing dependence on environmental and landscape factors. These results provide a novel insight into the ecology of Rhodesian sleeping sickness dispersal and may contribute towards the implementation of evidence-based control measures to prevent its further spread.     

History,environment and social behaviour: experimentally induced cooperative breeding in the carrion crow

Kin-based cooperative breeding, where grown offspring delay natal dispersal and help their parents to rear new young, has a long history in some avian lineages. Family formation and helping behaviour in extant populations may therefore simply represent the retention of ancestral features, tolerated under current conditions, rather than a current adaptive process driven by environmental factors. Separating these two possibilities challenges evolutionary biologists because of the tight coupling that normally exists between phylogeny and the environmental distribution of species and populations. The carrion crow Corvus corone corone, which exhibits extreme interpopulational variation in the extent of cooperative breeding, with populations showing no delayed dispersal and helping at all, provides a unique opportunity for an experimental approach. Here we show that offspring of non-cooperative carrion crows from Switzerland will remain on the natal territory and express helping behaviour when raised in a cooperative population in Spain. When we transferred carrion crow eggs from Switzerland to Spain, five out of six transplanted juveniles delayed dispersal, and two of those became helpers in the following breeding season. Our results provide compelling experimental evidence of the causal relationship between current environmental conditions and expression of cooperative behaviour.     

Ranking the ecological causes of dispersal in a butterfly

Dispersal, i.e. movements potentially leading to gene flow, is central in evolutionary ecology. Many factors can trigger dispersal, all linked to the social and/or the environmental context. Moreover, it is now widely demonstrated that phenotypes with contrasted dispersal abilities coexist within populations of a same species. The current challenge is to elucidate how social and environmental factors will influence the dispersal decision of individuals with distinct phenotypes. We have used the Metatron, a unique experimental mesocosm dedicated to the study of dispersal within fragmented landscapes, to analyze the relative and interactive roles played by ten potential dispersal triggers in experimental two‐patch metapopulations of butterflies. We demonstrate in our model species that some factors (flight performance and wing length) have direct effects on emigration decision, others act only through interactive effects (sex ratio), while a third class of factors presents both direct and interactive effects (weather conditions, habitat quality and sex). We also show that disperser and resident individuals have distinct behavioral and morphological attributes, revealing the existence of a dispersal syndrome. Finally, our results also suggest that the environmental context, and especially weather conditions and habitat quality, prevails over social factors and individual phenotypes in butterflies' decision to disperse. Our approach is applicable to many species facing medium to strong environmental fluctuations, and constitutes a new way to master the idiosyncrasy of the dispersal process. Our framework should also help prioritize the factors responsible for populations' spatial distribution, which is obviously crucial in the current era of global changes.     

Fore- and hindlimb proportions in Plio-Pleistocene hominids.

Associated fore- and hindlimb parts of five individuals are known from the hominid Plio-Pleistocene fossil collections in Africa. Four of these have been classified as Australopithecus and show definite evidence that in comparison with humans, forelimbs were relatively large and hindlimbs were relatively small. The fourth individual, placed in the genus Homo, has human proportions. These findings do not necessarily imply locomotor differences: the forelimbs may have been relatively long in Australopithecus simply because they were as yet not completely reduced from their generalized hominoid ancestral state.     

Where am I and why? Synthesizing range biology and the eco‐evolutionary dynamics of dispersal

Although generations of researchers have studied the factors that limit the distributions of species, we still do not seem to understand this phenomenon comprehensively. Traditionally, species’ ranges have been seen as the consequence of abiotic conditions and local adaptation to the environment. However, during the last years it has become more and more evident that biotic factors – such as intra‐ and interspecific interactions or the dispersal capacity of species – and even rapidly occurring evolutionary processes can strongly influence the range of a species and its potential to spread to new habitats. Relevant eco‐evolutionary forces can be found at all hierarchical levels: from landscapes to communities via populations, individuals and genes. We here use the metapopulation concept to develop a framework that allows us to synthesize this broad spectrum of different factors. Since species’ ranges are the result of a dynamic equilibrium of colonization and local extinction events, the importance of dispersal is immediately clear. We highlight the complex interrelations and feedbacks between ecological and evolutionary forces that shape dispersal and result in non‐trivial and partially counter‐intuitive range dynamics. Our concept synthesizes current knowledge on range biology and the eco‐evolutionary dynamics of dispersal. Synthesis What factors are responsible for the dynamics of species' ranges? Answering this question has never been more important than today, in the light of rapid environmental changes. Surprisingly, the ecological and evolutionary dynamics of dispersal – which represent the driving forces behind range formation – have rarely been considered in this context. We here present a framework that closes this gap. Dispersal evolution may be responsible for highly complex and non‐trivial range dynamics. In order to understand these, and possibly provide projections of future range positions, it is crucial to take the ecological and evolutionary dynamics of dispersal into account.     

Ecological and demographic correlates of cooperation from individual to budding dispersal

Identifying the ecological and demographic factors that promote the evolution of cooperation is a major challenge for evolutionary biologists. Explanations for the adaptive evolution of cooperation seek to determine which factors make reproduction in cooperative groups more favourable than independent breeding or other selfish strategies. A vast majority of the hypotheses posit that cooperative groups emerge in the context of philopatry, high costs of dispersal, high population density and environmental stability. This route to cooperation, however, fails to explain a growing body of empirical evidence in which cooperation is not associated with one or more of these predictors. We propose an alternative evolutionary path towards the emergence of cooperation that accounts for the disparities observed in the current literature. We find that when dispersal is mediated by a group mode of dispersal, commonly termed budding dispersal, our mathematical model reveals an association between cooperation and immigration, lower costs of dispersal, low population density and environmental variability. Furthermore, by studying the continuum from the individual to the partial and full budding mode of dispersal, we can explicitly explain why the correlates of cooperation change under budding. This enables us to outline a general model for the evolution of cooperation that accounts for a substantial amount of empirical evidence. Our results suggest that natural selection may have favoured two major contrasting pathways for the evolution of cooperation depending on a set of key ecological and demographic factors.     

Climate change and evolving human diversity in Europe during the last glacial

A link between climate change and human evolution during the Pleistocene has often been assumed but rarely tested. At the macro-evolutionary level Foley showed for hominids that extinction, rather than speciation, correlates with environmental change as recorded in the deep sea record. Our aim is to examine this finding at a smaller scale and with high-resolution environmental and archaeological archives. Our interest is in changing patterns of human dispersal under shifting Pleistocene climates during the last glacial period in Europe. Selecting this time frame and region allows us to observe how two hominid taxa, Neanderthals and Crô-Magnons, adapted to climatic conditions during oxygen isotope stage 3. These taxa are representative of two hominid adaptive radiations, termed terrestrial and aquatic, which exhibited different habitat preferences but similar tolerances to climatic factors. Their response to changing ecological conditions was predicated upon their ability to extend their societies in space and time. We examine this difference further using a database of all available radiocarbon determinations from western Europe in the late glacial. These data act as proxies for population history, and in particular the expansion and contraction of regional populations as climate changed rapidly. Independent assessment of these processes is obtained from the genetic history of Europeans. The results indicate that climate affects population contraction rather than expansion. We discuss the consequences for genetic and cultural diversity which led to the legacy of the Ice Age: a single hominid species, globally distributed.     

An ecomorphological model of the initial hominid dispersal from Africa

We use new data on the timing and extent of the early Pleistocene dispersal of Homo erectus to estimate diffusion coefficients of early Homo from Africa. These diffusion coefficients indicate more rapid and efficient dispersals than those calculated for fossil Macaca sp., Theropithecus darti, and Mesopithecus pentelicus. Increases in home range size associated with changes in ecology, hominid body size, and possibly foraging strategy may underlay these differences in dispersal efficiency. Ecological data for extant primates and human foragers indicate a close relationship between body size, home range size, and diet quality. These data predict that evolutionary changes in body size and foraging behavior would have produced a 10-fold increase in the home range size of H. erectus compared with that of the australopithecines. These two independent datasets provide a means of quantifying aspects of the dispersal of early Homo and suggest that rapid rates of dispersal appear to have been promoted by changes in foraging strategy and body size in H. erectus facilitated by changes in ecosystem structure during the Plio-Pleistocene.     

海草床种子扩散过程及种子库形成机制研究进展

海草是唯一一类可以完全生活在海水中的高等被子植物，具有重要的生态服务功能和巨大的经济价值。但受气候变化和人类活动的双重影响，海草床退化趋势日益严峻。海草床生态系统受到外界胁迫后的稳定性和恢复能力很大程度上依赖于有性繁殖即种子繁殖，当胁迫造成海草死亡等不可逆转的伤害时，通过沉积物种子库能够进行种群维持和自我更新，因此研究海草种子扩散过程及种子库形成机制对海草生态系统稳定性的维持具有重要意义。综述了海草生活史类型、种子繁殖特征、种子扩散过程及影响因素、种子库形成机制等。在此基础上总结了目前研究存在的几方面不足和未来展望：1)不同环境胁迫条件对海草有性繁殖努力的影响研究；2)海草种子二次扩散的影响因素和扩散机制研究；3)沉积物沉降和再悬浮对种子扩散和截留的影响研究；4)环境因素变化下种子库的潜在分布和海草适宜生境预测与模拟。本研究以期为海草床生态系统的保护恢复研究提供理论参考。     

Using phylogeographic approaches to analyse the dispersal history,velocity and direction of viral lineages — Application to rabies virus spread in Iran

Recent years have seen the extensive use of phylogeographic approaches to unveil the dispersal history of virus epidemics. Spatially explicit reconstructions of viral spread represent valuable sources of lineage movement data that can be exploited to investigate the impact of underlying environmental layers on the dispersal of pathogens. Here, we performed phylogeographic inference and applied different post hoc approaches to analyse a new and comprehensive data set of viral genomes to elucidate the dispersal history and dynamics of rabies virus (RABV) in Iran, which have remained largely unknown. We first analysed the association between environmental factors and variations in dispersal velocity among lineages. Second, we present, test and apply a new approach to study the link between environmental conditions and the dispersal direction of lineages. The statistical performance (power of detection, false‐positive rate) of this new method was assessed using simulations. We performed phylogeographic analyses of RABV genomes, allowing us to describe the large diversity of RABV in Iran and to confirm the cocirculation of several clades in the country. Overall, we estimate a relatively high lineage dispersal velocity, similar to previous estimates for dog rabies virus spread in northern Africa. Finally, we highlight a tendency for RABV lineages to spread in accessible areas associated with high human population density. Our analytical workflow illustrates how phylogeographic approaches can be used to investigate the impact of environmental factors on several aspects of viral dispersal dynamics.     

Environmental distribution and population biology of Candidatus Accumulibacter, a primary agent of biological phosphorus removal

Members of the uncultured bacterial genus Candidatus Accumulibacter are capable of intracellular accumulation of inorganic phosphate in activated sludge wastewater treatment plants (WWTPs) performing enhanced biological phosphorus removal, but were also recently shown to inhabit freshwater and estuarine sediments. Additionally, metagenomic sequencing of two bioreactor cultures enriched in Candidatus Accumulibacter, but housed on separate continents, revealed the potential for global dispersal of particular Candidatus Accumulibacter strains, which we hypothesize is facilitated by the ability of Candidatus Accumulibacter to persist in environmental habitats. In the current study, we used sequencing of a phylogenetic marker, the ppk1 gene, to characterize Candidatus Accumulibacter populations in diverse environments, at varying distances from WWTPs. We discovered several new lineages of Candidatus Accumulibacter which had not previously been detected in WWTPs, and also uncovered new diversity and structure within previously detected lineages. Habitat characteristics were found to be a key determinant of Candidatus Accumulibacter lineage distribution while, as predicted, geographic distance played little role in limiting dispersal on a regional scale. However, on a local scale, enrichment of particular Candidatus Accumulibacter lineages in WWTP appeared to impact local environmental populations. These results provide evidence of ecological differences among Candidatus Accumulibacter lineages.     

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics

Many species exhibit widespread spatial synchrony in population fluctuations. This pattern is of great ecological interest and can be a source of concern when the species is rare or endangered. Both dispersal and spatial correlations in the environment have been implicated as possible causes of this pattern, but these two factors have rarely been studied in combination. We develop a spatially structured population model, simple enough to obtain analytic solutions for the population correlation, that incorporates both dispersal and environmental correlation. We ask whether these two synchronizing factors contribute additively to the total spatial population covariance. We find that there is always an interaction between these two factors and that this interaction is small only when one or both of the environmental correlation and the dispersal rate are small. The interaction is opposite in sign to the environmental correlation; so, in the normal case of positive environmental correlation across sites, the population synchrony will be lower than predicted by simply adding the effects of dispersal and environmental correlation. We also find that population synchrony declines as the strength of population regulation increases. These results indicate that dispersal and environmental correlation need to be considered in combination as explanations for observed patterns of population synchrony.     

Mid-ocean isolation and the evolution of Hawaiian reef fishes

The Hawaiian fish fauna has close affinities with the fauna of the Indo-west Pacific from which it is derived, but is depauperate. It is characterized by a large number of endemic species (30% of inshore fishes), which are often the most abundant species in their families in Hawaii. Although there is evidence of local adaptation, there has been no radiation of species within the island chain, as occurs in the terrestrial biota of isolated islands. Three major factors have contributed to these trends: (1) the geographic isolation of the islands, and oceanographic features, especially current patterns; (2) the life history characteristics of the fishes, especially their dispersal capabilities; and (3) the extent of adaptive differentiation to environmental conditions after they reached Hawaii.     

There Is No Evidence for a Temporal Link between Pathogen Arrival and Frog Extinctions in North-Eastern Australia

Pathogen spread can cause population declines and even species extinctions. Nonetheless, in the absence of tailored monitoring schemes, documenting pathogen spread can be difficult. In the case of worldwide amphibian declines the best present understanding is that the chytrid fungus Batrachochytrium dendrobatidis (Bd) has recently spread, causing amphibian declines and extinction in the process. However, good evidence demonstrating pathogen arrival followed by amphibian decline is rare, and analysis of putative evidence is often inadequate. Here we attempt to examine the relationship between Bd arrival and amphibian decline across north-eastern Australia, using sites where a wave-like pattern of amphibian decline was first noticed and at which intensive research has since been conducted. We develop an analytical framework that allows rigorous estimation of pathogen arrival date, which can then be used to test for a correlation between the time of pathogen arrival and amphibian decline across sites. Our results show that, with the current dataset, the earliest possible arrival date of Bd in north-eastern Australia is completely unresolved; Bd could have arrived immediately before sampling commenced or may have arrived thousands of years earlier, the present data simply cannot say. The currently available data are thus insufficient to assess the link between timing of pathogen arrival and population decline in this part of the world. This data insufficiency is surprising given that there have been decades of research on chytridiomycosis in Australia and that there is a general belief that the link between Bd arrival and population decline is well resolved in this region. The lack of data on Bd arrival currently acts as a major impediment to determining the role of environmental factors in driving the global amphibian declines, and should be a major focus of future research.     

Dispersal and spatial scale affect synchrony in spatial population dynamics

A large body of theoretical studies has shown that synchrony among populations is critical for the long-term persistence of species in fragmented habitats. Although the effects of dispersal and environmental factors on synchrony have been investigated theoretically, empirical studies of these relationships have been lacking. We explored the interplay between environmental and demographic factors (fecundity, survival, dispersal) on population synchrony for 53 species of birds. We show that the interspecific differences in mean synchrony were determined by global environmental factors whose action was probably mediated by the abundance of each species. After removing the effect of these global factors on synchrony, the residual synchrony was strongly correlated with dispersal distance. The relationship between dispersal and synchrony was stronger for the species nesting in wet habitats than for those nesting in dry habitats. Our results indicate that different factors synchronize bird populations at different spatial scales, thus highlighting the role of scale in understanding spatial population dynamics and extinction risks.