Climate-driven range expansion and morphological evolution in a marine gastropod

Pushed waves, trailing edges, and extreme events: Eco-evolutionary dynamics of a geographic range shift in the owl limpet, Lottia gigantea

As climatic variation re-shapes global biodiversity, understanding eco-evolutionary feedbacks during species range shifts is of increasing importance. Theory on range expansions distinguishes between two different forms: "pulled" and "pushed" waves. Pulled waves occur when the source of the expansion comes from low-density peripheral populations, while pushed waves occur when recruitment to the expanding edge is supplied by high-density populations closer to the species' core. How extreme events shape pushed/pulled wave expansion events, as well as trailing-edge declines/contractions, remains largely unexplored. We examined eco-evolutionary responses of a marine invertebrate (the owl limpet, Lottia gigantea) that increased in abundance during the 2014-2016 marine heatwaves near the poleward edge of its geographic range in the northeastern Pacific. We used whole-genome sequencing from 19 populations across >11 degrees of latitude to characterize genomic variation, gene flow, and demographic histories across the species' range. We estimated present-day dispersal potential and past climatic stability to identify how contemporary and historical seascape features shape genomic characteristics. Consistent with expectations of a pushed wave, we found little genomic differentiation between core and leading-edge populations, and higher genomic diversity at range edges. A large and well-mixed population in the northern edge of the species' range is likely a result of ocean current anomalies increasing larval settlement and high-dispersal potential across biogeographic boundaries. Trailing-edge populations have higher differentiation from core populations, possibly driven by local selection and limited gene flow, as well as high genomic diversity likely as a result of climatic stability during the Last Glacial Maximum. Our findings suggest that extreme events can drive poleward range expansions that carry the adaptive potential of core populations, while also cautioning that trailing-edge extirpations may threaten unique evolutionary variation. This work highlights the importance of understanding how both trailing and leading edges respond to global change and extreme events.

The nature of science: The fundamental role of natural history in ecology, evolution, conservation, and education

There is a contemporary trend in many major research institutions to de-emphasize the importance of natural history education in favor of theoretical, laboratory, or simulation-based research programs. This may take the form of removing biodiversity and field courses from the curriculum and the sometimes subtle maligning of natural history research as a "lesser" branch of science. Additional threats include massive funding cuts to natural history museums and the maintenance of their collections, the extirpation of taxonomists across disciplines, and a critical under-appreciation of the role that natural history data (and other forms of observational data, including Indigenous knowledge) play in the scientific process. In this paper, we demonstrate that natural history knowledge is integral to any competitive science program through a comprehensive review of the ways in which they continue to shape modern theory and the public perception of science. We do so by reviewing how natural history research has guided the disciplines of ecology, evolution, and conservation and how natural history data are crucial for effective education programs and public policy. We underscore these insights with contemporary case studies, including: how understanding the dynamics of evolutionary radiation relies on natural history data; methods for extracting novel data from museum specimens; insights provided by multi-decade natural history programs; and how natural history is the most logical venue for creating an informed and scientifically literate society. We conclude with recommendations aimed at students, university faculty, and administrators for integrating and supporting natural history in their mandates. Fundamentally, we are all interested in understanding the natural world, but we can often fall into the habit of abstracting our research away from its natural contexts and complexities. Doing so risks losing sight of entire vistas of new questions and insights in favor of an over-emphasis on simulated or overly controlled studies.

Historical biogeography supports Point Conception as the site of turnover between temperate East Pacific ichthyofaunas

The cold temperate and subtropical marine faunas of the Northeastern Pacific meet within California as part of one of the few eastern boundary upwelling ecosystems in the world. Traditionally, it is believed that Point Conception is the precise site of turnover between these two faunas due to sharp changes in oceanographic conditions. However, evidence from intraspecific phylogeography and species range terminals do not support this view, finding stronger biogeographic breaks elsewhere along the coast. Here I develop a new application of historical biogeographic approaches to uncover sites of transition between faunas without needing an a priori hypothesis of where these occur. I used this approach to determine whether the point of transition between northern and southern temperate faunas occurs at Point Conception or elsewhere within California. I also examined expert-vetted latitudinal range data of California fish species from the 1970s and the 2020s to assess how biogeography could change with the backdrop of climate change. The site of turnover was found to occur near Point Conception, in concordance with the traditional view. I suggest that recent species- and population-level processes could be expected to give signals of different events from historical biogeography, possibly explaining the discrepancy across studies. Species richness of California has increased since the 1970s, mostly due to species's ranges expanding northward from Baja California (Mexico). Range shifts under warming conditions seem to be increasing the disparity between northern and southern faunas of California, creating a more divergent biogeography.

Native-alien populations—an apparent oxymoron that requires specific conservation attention

Many countries define nativity at a country-level—taxa are categorised as either alien species or native species. However, there are often substantial within-country biogeographical barriers and so a taxon can be native and alien to different parts of the same country. Here, we use the term ‘native-alien populations’ as a short-hand for populations that result from the human-mediated dispersal of individuals of a species beyond a biogeographical barrier to a point beyond that species’ native range, but that is still within the same political entity as parts of the species’ native range. Based on these criteria, we consider native-alien populations to be biological invasions. However, we argue that, in comparison to other alien populations, native-alien populations: 1) are likely to be closer geographically to their native range; 2) are likely to be phylogenetically and ecologically more similar to native species in their introduced range; and 3) options to control their introduction or manage them will likely be more limited. We argue this means native-alien populations tend to differ from other alien populations in the likelihood of invasion, the types of impacts they have, and in how they can be most effectively managed. We also argue that native-alien populations are similarly a distinct phenomenon from native populations that are increasing in abundance or range extent. And note that native-alien populations are expected to be particularly common in large, ecologically diverse countries with disjunct biomes and ecoregions. Reporting, monitoring, regulating and managing native-alien populations will, we believe, become an increasingly important component of managing global change.

Dynamic species interactions associated with the range-shifting marine gastropod Mexacanthina lugubris

Globally, species are undergoing range shifts in response to climate change. However, the potential impacts of climate-driven range shifts are not well understood. In southern California, the predatory whelk Mexacanthina lugubris has undergone a northward range shift of more than 100 km in the past four decades. We traced the history of the whelk’s range shift and assessed potential effects using an integrated approach, consisting of field surveys, as well as feeding and thermotolerance experiments. We found that at sites where Mexacanthina and native species co-occurred, native whelks distributions peaked lower in the intertidal. In laboratory experiments, we found that the presence of Mexacanthina led to reduced growth in native whelks (Acanthinucella spirata). Additionally, the range-shifting whelk was able to tolerate higher temperatures than common native species (A. spirata and Nucella emarginata), suggesting further impacts as a result of climate warming. Many species are likely to undergo range shifts as a coping mechanism for changing climatic conditions. However, communities are unlikely to shift as a whole due to species-specific responses. By studying the impacts of range-shifting species, like Mexacanthina, we can better understand how climate change will alter existing community structure and composition.

Genealogical structure changes as range expansions transition from pushed to pulled

Range expansions accelerate evolution through multiple mechanisms, including gene surfing and genetic drift. The inference and control of these evolutionary processes ultimately rely on the information contained in genealogical trees. Currently, there are two opposing views on how range expansions shape genealogies. In invasion biology, expansions are typically approximated by a series of population bottlenecks producing genealogies with only pairwise mergers between lineages-a process known as the Kingman coalescent. Conversely, traveling wave models predict a coalescent with multiple mergers, known as the Bolthausen-Sznitman coalescent. Here, we unify these two approaches and show that expansions can generate an entire spectrum of coalescent topologies. Specifically, we show that tree topology is controlled by growth dynamics at the front and exhibits large differences between pulled and pushed expansions. These differences are explained by the fluctuations in the total number of descendants left by the early founders. High growth cooperativity leads to a narrow distribution of reproductive values and the Kingman coalescent. Conversely, low growth cooperativity results in a broad distribution, whose exponent controls the merger sizes in the genealogies. These broad distribution and non-Kingman tree topologies emerge due to the fluctuations in the front shape and position and do not occur in quasi-deterministic simulations. Overall, our results show that range expansions provide a robust mechanism for generating different types of multiple mergers, which could be similar to those observed in populations with strong selection or high fecundity. Thus, caution should be exercised in making inferences about the origin of non-Kingman genealogies.

The impact of prolonged frozen storage on the preparation quality of bird skins and skeletons in zoological collections

Specimens from zoological collections play a pivotal role in improving scientific knowledge in many natural science disciplines. To guarantee an optimum state of conservation and ensure their usefulness, the preparation process employed is crucial. Skins and skeletons are key elements in vertebrate scientific collections and, ideally, are prepared from recently deceased animals; however, specimens are often stored in a frozen state for a long time (years) prior to preparation. Whether the duration of this frozen state has a deleterious effect on preparation quality has rarely been studied. The main objective of this study was thus to contribute towards research into zoological preparation by testing to see whether prolonged frozen storage hinders the preparation of bird skins and skeletons. We used the common buzzard (Buteo buteo) and the barn owl (Tyto alba) as biological models. Our results showed that long-term frozen storage led to weight loss, bone marrow acidification and solidification, and hampered skin preparation. The necropsy affected weight loss and decreased the skin tear resistance, probably due to tissue dehydration. Thus, prolonged frozen storage appears to have a harmful effect on the preparation quality of vertebrate specimens. Since frozen storage could ultimately have an impact on the conservation and scientific use of museum specimens, practices should be implemented to minimise the amount of time specimens are frozen or to mitigate any detrimental effects. More importance should be attached to research on zoological preparation since it is fundamental for optimising the quality, conservation status, and value of museum collections.

Temporal and spatial variation in population structure among brooding sea stars in the genus Leptasterias

Temporal genetic studies of low-dispersing organisms are rare. Marine invertebrates lacking a planktonic larval stage are expected to have lower dispersal, low gene flow, and a higher potential for local adaptation than organisms with planktonic dispersal. Leptasterias is a genus of brooding sea stars containing several cryptic species complexes. Population genetic methods were used to resolve patterns of fine-scale population structure in central California Leptasterias species using three loci from nuclear and mitochondrial genomes. Historic samples (collected between 1897 and 1998) were compared to contemporary samples (collected between 2008 and 2014) to delineate changes in species distributions in space and time. Phylogenetic analysis of contemporary samples confirmed the presence of a bay-localized clade and revealed the presence of an additional bay-localized and previously undescribed clade of Leptasterias. Analysis of contemporary and historic samples indicates two clades are experiencing a constriction in their southern range limit and suggests a decrease in clade-specific abundance at sites at which they were once prevalent. Historic sampling revealed a dramatically different distribution of diversity along the California coastline compared to contemporary sampling and illustrates the importance of temporal genetic sampling in phylogeographic studies. These samples were collected prior to significant impacts of Sea Star Wasting Disease (SSWD) and represent an in-depth analysis of genetic structure over 117 years prior to the SSWD-associated mass die-off of Leptasterias.

Decade-scale stability and change in a marine bivalve microbiome

Predicting how populations and communities of organisms will respond to anthropogenic change is of paramount concern in ecology today. For communities of microorganisms, however, these predictions remain challenging, primarily due to data limitations. Information about long-term dynamics of host-associated microbial communities, in particular, is lacking. In this study, we use well-preserved and freshly collected samples of soft tissue from a marine bivalve host, Donax gouldii, at a single site to quantify the diversity and composition of its microbiome over a decadal timescale. Site-level measurements of temperature, salinity and chlorophyll a allowed us to test how the microbiome of this species responded to two natural experiments: a seasonal increase in temperature and a phytoplankton bloom. Our results show that ethanol-preserved tissue can provide high-resolution information about temporal trends in compositions of host-associated microbial communities. Specifically, we found that the richness of amplicon sequence variants (ASVs) associated with D.gouldii did not change significantly over time despite increases in water temperature (+1.6°C due to seasonal change) and chlorophyll a concentration (more than ninefold). The phylogenetic composition of the communities, on the other hand, varied significantly between all collection years, with only six ASVs persisting over our sampling period. Overall, these results suggest that the diversity of microbial taxa associated with D.gouldii has remained stable over time and in response to seasonal environmental change over the course of more than a decade, but such stability is underlain by substantial turnover in the composition of the microbiome.

Molecular analysis of Spiophanes bombyx complex (Annelida: Spionidae) with description of a new species

Spiophanes bombyx (Claparède, 1870) from the Gulf of Naples, Tyrrhenian Sea, Italy, was the first described Spiophanes with fronto-lateral horns on the prostomium. It was also considered the only horned species occurring in European waters. Our sequence data of five gene fragments suggest the presence of two horned sibling Spiophanes species in northern Europe: S. cf. bombyx in the North and the Norwegian seas, and S. cf. convexus in Brittany, northern France, and Bay of Biscay, northern Spain. Spiophanes cf. bombyx worms are genetically close to a single examined specimen of S. bombyx from Venice Lagoon, Italy but their conspecificity should be verified by further study. Our sequence data show that horned Spiophanes from the North Pacific are genetically distant from horned European species, and that S. uschakowi Zachs, 1933, originally described from the Sea of Japan (East Sea) is a valid species. The data also suggest the presence of two horned sibling Spiophanes species in the North East Pacific: S. hakaiensis Radashevsky & Pankova, n. sp. distributed from Alaska south to about Point Conception, and S. norrisi Meißner & Blank, 2009, distributed from San Francisco Bay south to Baja California Sur, Mexico. Spiophanes from South America, morphologically similar to S. norrisi, are suggested to belong to a new species. Molecular data also suggest the presence of two sibling species among the worms from northern Europe identified by morphology as S. kroyeri Grube, 1860. Worms from the Barents Sea and northern part of the North Sea are tentatively referred to as S. cf. kroyeri; worms from the northern and central parts of the North Sea and from the Bay of Biscay, northern Spain, are tentatively referred to as S. cf. cirrata M. Sars in G.O. Sars, 1872. Sequence data also show that S. duplex from California is genetically different from morphologically similar worms from South America. The South American worms are referred to resurrected S. soederstroemi Hartman, 1953 which was originally described from off Rio Grande do Sul, Brazil, and then considered as a junior synonym of S. duplex. Analysis of divergence times of Spiophanes lineages suggested that the origin of the most recent common ancestor of horned Spiophanes with metameric nuchal organs was around 11.1 mya (95% HPD: 5.1–19.0 mya) and that the divergence of the North Atlantic and North Pacific lineages was around 7.9 mya (95% HPD: 4.1–13.3 mya). The North Atlantic lineage was estimated to have diverged 4.8 mya (95% HPD: 2.2–8.6 mya), resulting in the origin of S. cf. bombyx and S. cf. convexus. The North Pacific lineage was estimated to have diverged first by the isolation and speciation of S. norrisi 1.7 mya (95% HPD: 2.3–1.0 mya), and then by the isolation and speciation of S. uschakowi and S. hakaiensis n. sp. 1.3 mya (95% HPD: 2.0–0.7 mya). The estimates place the divergences soon after maximum glacial period in the North Pacific (2.4–3.0 mya).

Coping with Pleistocene climatic fluctuations: Demographic responses in remote endemic reef fishes

Elucidating demographic history during the settlement of ecological communities is crucial for properly inferring the mechanisms that shape patterns of species diversity and their persistence through time. Here, we used genomic data and coalescent-based approaches to elucidate for the first time the demographic dynamics associated with the settlement by endemic reef fish fauna of one of the most remote peripheral islands of the Pacific Ocean, Rapa Nui (Easter Island). We compared the demographic history of nine endemic species in order to explore their demographic responses to Pleistocene climatic fluctuations. We found that species endemic to Rapa Nui share a common demographic history, as signatures of population expansions were retrieved for almost all of the species studied here, and synchronous demographic expansions initiated during the last glacial period were recovered for more than half of the studied species. These results suggest that eustatic fluctuations associated with Milankovitch cycles have played a central role in species demographic histories and in the final stage of the community assembly of many Rapa Nui reef fishes. Specifically, sea level lowstands resulted in the maximum reef habitat extension for Rapa Nui endemic species; we discuss the potential role of seamounts in allowing endemic species to cope with Pleistocene climatic fluctuations, and we highlight the importance of local historical processes over regional ones. Overall, our results shed light on the mechanisms by which endemism arises and is maintained in peripheral reef fish fauna.

Climate-Driven Shifts in Marine Species Ranges: Scaling from Organisms to Communities

The geographic distributions of marine species are changing rapidly, with leading range edges following climate poleward, deeper, and in other directions and trailing range edges often contracting in similar directions. These shifts have their roots in fine-scale interactions between organisms and their environment-including mosaics and gradients of temperature and oxygen-mediated by physiology, behavior, evolution, dispersal, and species interactions. These shifts reassemble food webs and can have dramatic consequences. Compared with species on land, marine species are more sensitive to changing climate but have a greater capacity for colonization. These differences suggest that species cope with climate change at different spatial scales in the two realms and that range shifts across wide spatial scales are a key mechanism at sea. Additional research is needed to understand how processes interact to promote or constrain range shifts, how the dominant responses vary among species, and how the emergent communities of the future ocean will function.

Genetics, morphology and diet of introduced populations of the ant-eating Texas Horned Lizard (Phrynosoma cornutum)

Introduced species can diverge from their source population when they become established in a new ecosystem. The Texas Horned Lizard (Phrynosoma cornutum) is native to the western United States (US) and was historically introduced to several locations in the southeastern US. We studied three introduced populations in South Carolina, US to determine if they exhibit dietary, morphological and genetic divergence from the native western US populations. We expected little divergence from western populations because P. cornutum is a specialist whose biology is largely shaped by its diet of Pogonomyrmex harvester ants. We show that the introduced populations have mixed ancestry between south Texas and more northern areas and experienced founder effects and genetic bottlenecks resulting in decreased genetic diversity. South Carolina lizards primarily consume ants (94%), but surprisingly, they did not eat harvester ants. Introduced lizards primarily eat Dorymyrmex ants, but each introduced population complements Dorymyrmex with significantly different amounts of other species of ants, insects and plant matter. Introduced populations have smaller body size and have different limb and head shapes compared to western populations. This study demonstrates successful persistence of an introduced vertebrate that may be attributed to phenotypic change, even in the face of reduced genetic diversity.

Genetic and morphological divergence at a biogeographic break in the beach-dwelling brooder Excirolana hirsuticauda Menzies (Crustacea, Peracarida)

BACKGROUND

There is a biogeographic break located at 30°S in the southeast Pacific, in a coastal area of strong environmental discontinuities. Several marine benthic taxa with restricted dispersal have a coincident phylogeographic break at 30°S, indicating that genetic structure is moulded by life history traits that limit gene flow and thereby promote divergence and speciation. In order to evaluate intraspecific divergence at this biogeographic break, we investigated the genetic and morphological variation of the directly developing beach isopod Excirolana hirsuticauda along 1900 km of the southeast Pacific coast, across 30°S.

RESULTS

The COI sequences and microsatellite data both identified a strong discontinuity between populations of E. hirsuticauda to the north and south of 30°S, and a second weaker phylogeographic break at approximately 35°S. The three genetic groups were evidenced by different past demographic and genetic diversity signatures, and were also clearly distinguished with microsatellite data clustering. The COI sequences established that the genetic divergence of E. hirsuticauda at 30°S started earlier than divergence at 35°. Additionally, the three groups have different past demographic signatures, with probable demographic expansion occurring earlier in the southern group (south of 35°S), associated with Pleistocene interglacial periods. Interestingly, body length, multivariate morphometric analyses, and the morphology of a fertilization-related morphological character in males, the appendix masculina, reinforced the three genetic groups detected with genetic data.

CONCLUSIONS

The degree of divergence of COI sequences, microsatellite data, and morphology was concordant and showed two geographic areas in which divergence was promoted at differing historical periods. Variation in the appendix masculina of males has probably promoted reproductive isolation. This variation together with gene flow restrictions promoted by life history traits, small body size, oceanographic discontinuities and sandy-beach habitat continuity, likely influenced species divergence at 30°S in the southeast Pacific coast. The degree of genetic and morphological differentiation of populations to the north and south of 30°S suggests that E. hirsuticauda harbours intraspecific divergence consistent with reproductive isolation and an advanced stage of speciation. The speciation process within E. hirsuticauda has been shaped by both restrictions to gene flow and a prezygotic reproductive barrier.

Disentangling the genetic effects of refugial isolation and range expansion in a trans-continentally distributed species

In wide-ranging taxa with historically dynamic ranges, past allopatric isolation and range expansion can both influence the current structure of genetic diversity. Considering alternate historical scenarios involving expansion from either a single refugium or from multiple refugia can be useful in differentiating the effects of isolation and expansion. Here, we examined patterns of genetic variability in the trans-continentally distributed painted turtle (Chrysemys picta). We utilized an existing phylogeographic dataset for the mitochondrial control region and generated additional data from nine populations for the mitochondrial control region (n = 302) and for eleven nuclear microsatellite loci (n = 247). We created a present-day ecological niche model (ENM) for C. picta and hindcast this model to three reconstructions of historical climate to define three potential scenarios with one, two, or three refugia. Finally, we employed spatially-explicit coalescent simulations and an approximate Bayesian computation (ABC) framework to test which scenario best fit the observed genetic data. Simulations indicated that phylogeographic and multilocus population-level sampling both could differentiate among refugial scenarios, although inferences made using mitochondrial data were less accurate when a longer coalescence time was assumed. Furthermore, all empirical genetic datasets were most consistent with expansion from a single refugium based on ABC. Our results indicate a stronger role for post-glacial range expansion, rather than isolation in allopatric refugia followed by range expansion, in structuring diversity in this species. To distinguish among complex historical scenarios, we recommend explicitly modeling the effects of range expansion and evaluating alternate refugial scenarios for wide-ranging taxa.

Population expansions dominate demographic histories of endemic and widespread Pacific reef fishes

Despite the unique nature of endemic species, their origin and population history remain poorly studied. We investigated the population history of 28 coral reef fish species, close related, from the Gambier and Marquesas Islands, from five families, with range size varying from widespread to small-range endemic. We analyzed both mitochondrial and nuclear sequence data using neutrality test and Bayesian analysis (EBSP and ABC). We found evidence for demographic expansions for most species (24 of 28), irrespective of range size, reproduction strategy or archipelago. The timing of the expansions varied greatly among species, from 8,000 to 2,000,000 years ago. The typical hypothesis for reef fish that links population expansions to the Last Glacial Maximum fit for 14 of the 24 demographic expansions. We propose two evolutionary processes that could lead to expansions older than the LGM: (a) we are retrieving the signature of an old colonization process for widespread, large-range endemic and paleoendemic species or (b) speciation; the expansion reflects the birth of the species for neoendemic species. We show for the first time that the demographic histories of endemic and widespread reef fish are not distinctly different and suggest that a number of processes drive endemism.

Low genetic diversity and recent demographic expansion in the red starfish Echinaster sepositus (Retzius 1816)

Understanding the phylogeography and genetic structure of populations and the processes responsible of patterns therein is crucial for evaluating the vulnerability of marine species and developing management strategies. In this study, we explore how past climatic events and ongoing oceanographic and demographic processes have shaped the genetic structure and diversity of the Atlanto-Mediterranean red starfish Echinaster sepositus. The species is relatively abundant in some areas of the Mediterranean Sea, but some populations have dramatically decreased over recent years due to direct extraction for ornamental aquariums and souvenir industries. Analyses across most of the distribution range of the species based on the mitochondrial cytochrome c oxidase subunit I gene and eight microsatellite loci revealed very low intraspecific genetic diversity. The species showed a weak genetic structure within marine basins despite the a priori low dispersal potential of its lecithotrophic larva. Our results also revealed a very recent demographic expansion across the distribution range of the species. The genetic data presented here indicate that the species might be highly vulnerable, due to its low intraspecific genetic diversity.

Expanding population edges: theories, traits, and trade-offs

Recent patterns of global change have highlighted the importance of understanding the dynamics and mechanisms of species range shifts and expansions. Unique demographic features, spatial processes, and selective pressures can result in the accumulation and evolution of distinctive phenotypic traits at the leading edges of expansions. We review the characteristics of expanding range margins and highlight possible mechanisms for the appearance of phenotypic differences between individuals at the leading edge and core of the range. The development of life history traits that increase dispersal or reproductive ability is predicted by theory and supported with extensive empirical evidence. Many examples of rapid phenotypic change are associated with trade-offs that may influence the persistence of the trait once expansion ends. Accounting for the effects of edge phenotypes and related trade-offs could be critical for predicting the spread of invasive species and population responses to climate change.

Response of top shell assemblages to cyclogenesis disturbances. A case study in the Bay of Biscay

Cyclones and other climate disturbances profoundly affect coastal ecosystems, promoting changes in the benthic communities that require time, sometimes even years, for a complete recovery. In this study we have analysed the morphological and genetic changes occurred in top shell (Gibbula umbilicalis and Phorcus lineatus) assemblages from the Bay of Biscay following explosive cyclogenesis events in 2014. Comparison with previous samples at short (three years before the cyclogenesis) and long (Upper Pleistocene) temporal scales served to better evaluate the extent of change induced by these disturbances in a more global dimension. A significant increase in mean size after the cyclogenesis was found for the two species, suggesting selective sweeping of small individuals weakly adhered to substrata. Loss of haplotype variants at the cytochrome oxidase subunit I gene suggests a population bottleneck, although it was not intense enough to produce significant changes in haplotype frequencies. The high population connectivity and metapopulation structuring of the two species in the area likely help the populations to recover from disturbances. At a wider temporal scale, cyclogenesis effects seemed to compensate the apparent decreasing trends in size for P. lineatus occurred after the Pleistocene-Holocene transition. Considering disturbance regimes for population baselines is recommended when the long-term effects of climate and anthropogenic pressures are evaluated.

Postglacial range shift and demographic expansion of the marine intertidal snail Batillaria attramentaria

To address the impacts of past climate changes, particularly since the last glacial period, on the history of the distribution and demography of marine species, we investigated the evolutionary and demographic responses of the intertidal batillariid gastropod, Batillaria attramentaria, to these changes, using the snail as a model species in the northwest Pacific. We applied phylogeographic and divergence population genetic approaches to mitochondrial COI sequences from B. attramentaria. To cover much of its distributional range, 197 individuals collected throughout Korea and 507 publically available sequences (mostly from Japan) were used. Finally, a Bayesian skyline plot (BSP) method was applied to reconstruct the demographic history of this species. We found four differentiated geographic groups around Korea, confirming the presence of two distinct, geographically subdivided haplogroups on the Japanese coastlines along the bifurcated routes of the warm Tsushima and Kuroshio Currents. These two haplogroups were estimated to have begun to split approximately 400,000 years ago. Population divergence analysis supported the hypothesis that the Yellow Sea was populated by a northward range expansion of a small fraction of founders that split from a southern ancestral population since the last glacial maximum (LGM: 26,000-19,000 years ago), when the southern area became re-submerged. BSP analyses on six geographically and genetically defined groups in Korea and Japan consistently demonstrated that each group has exponentially increased approximately since the LGM. This study resolved the phylogeography of B. attramentaria as a series of events connected over space and time; while paleoceanographic conditions determining the connectivity of neighboring seas in East Asia are responsible for the vicariance of this species, the postglacial sea-level rise and warming temperatures have played a crucial role in rapid range shifts and broad demographic expansions of its populations.

Historical and recent processes shaping the geographic range of a rocky intertidal gastropod: phylogeography, ecology, and habitat availability

Factors shaping the geographic range of a species can be identified when phylogeographic patterns are combined with data on contemporary and historical geographic distribution, range-wide abundance, habitat/food availability, and through comparisons with codistributed taxa. Here, we evaluate range dynamism and phylogeography of the rocky intertidal gastropod Mexacanthina lugubris lugubris across its geographic range – the Pacific coast of the Baja peninsula and southern California. We sequenced mitochondrial DNA (CO1) from ten populations and compliment these data with museum records, habitat availability and range-wide field surveys of the distribution and abundance of M. l. lugubris and its primary prey (the barnacle Chthamalus fissus). The geographic range of M. l. lugubris can be characterized by three different events in its history: an old sundering in the mid-peninsular region of Baja (∼ 417,000 years ago) and more recent northern range expansion and southern range contraction. The mid-peninsular break is shared with many terrestrial and marine species, although M. l. lugubris represents the first mollusc to show it. This common break is often attributed to a hypothesized ancient seaway bisecting the peninsula, but for M. l. lugubris it may result from large habitat gaps in the southern clade. Northern clade populations, particularly near the historical northern limit (prior to the 1970s), have high local abundances and reside in a region with plentiful food and habitat – which makes its northern range conducive to expansion. The observed southern range contraction may result from the opposite scenario, with little food or habitat nearby. Our study highlights the importance of taking an integrative approach to understanding the processes that shape the geographic range of a species via combining range-wide phylogeography data with temporal geographic distributions and spatial patterns of habitat/food availability.

Genetic structuring across marine biogeographic boundaries in rocky shore invertebrates

Biogeography investigates spatial patterns of species distribution. Discontinuities in species distribution are identified as boundaries between biogeographic areas. Do these boundaries affect genetic connectivity? To address this question, a multifactorial hierarchical sampling design, across three of the major marine biogeographic boundaries in the central Mediterranean Sea (Ligurian-Tyrrhenian, Tyrrhenian-Ionian and Ionian-Adriatic) was carried out. Mitochondrial COI sequence polymorphism of seven species of Mediterranean benthic invertebrates was analysed. Two species showed significant genetic structure across the Tyrrhenian-Ionian boundary, as well as two other species across the Ionian Sea, a previously unknown phylogeographic barrier. The hypothesized barrier in the Ligurian-Tyrrhenian cannot be detected in the genetic structure of the investigated species. Connectivity patterns across species at distances up to 800 km apart confirmed that estimates of pelagic larval dispersal were poor predictors of the genetic structure. The detected genetic discontinuities seem more related to the effect of past historical events, though maintained by present day oceanographic processes. Multivariate statistical tools were used to test the consistency of the patterns across species, providing a conceptual framework for across-species barrier locations and strengths. Additional sequences retrieved from public databases supported our findings. Heterogeneity of phylogeographic patterns shown by the 7 investigated species is relevant to the understanding of the genetic diversity, and carry implications for conservation biology.

Impacts of temperature on primary productivity and respiration in naturally structured macroalgal assemblages

Rising global temperatures caused by human-mediated change has already triggered significant responses in organismal physiology, distribution and ecosystem functioning. Although the effects of rising temperature on the physiology of individual organisms are well understood, the effect on community-wide processes has remained elusive. The fixation of carbon via primary productivity is an essential ecosystem function and any shifts in the balance of primary productivity and respiration could alter the carbon balance of ecosystems. Here we show through a series of tests that respiration of naturally structured algal assemblages in southern New Zealand greatly increases with rising temperature, with implications for net primary productivity (NPP). The NPP of in situ macroalgal assemblages was minimally affected by natural temperature variation, possibly through photo-acclimation or temperature acclimation responses, but respiration rates and compensating irradiance were negatively affected. However, laboratory experiments testing the impacts of rising temperature on several photosynthetic parameters showed a decline in NPP, increasing respiration rates and increasing compensating irradiance. The respiration Q10 of laboratory assemblages (the difference in metabolic rates over 10°C) averaged 2.9 compared to a Q10 of 2 often seen in other autotrophs. However, gross primary productivity (GPP) Q10 averaged 2, indicating that respiration was more severely affected by rising temperature. Furthermore, combined high irradiance and high temperature caused photoinhibition in the laboratory, and resulted in 50% lower NPP at high irradiance. Our study shows that communities may be more severely affected by rising global temperatures than would be expected by responses of individual species. In particular, enhanced respiration rates and rising compensation points have the potential to greatly affect the carbon balance of macroalgal assemblages through declines in sub-canopy NPP, the impacts of which may be exacerbated over longer time-scales and could result in declines in sub-canopy species richness and abundance.

Contrasting phylogeography of sandy vs. rocky supralittoral isopods in the megadiverse and geologically dynamic Gulf of California and adjacent areas

Phylogeographic studies of animals with low vagility and restricted to patchy habitats of the supralittoral zone, can uncover unknown diversity and shed light on processes that shaped evolution along a continent's edge. The Pacific coast between southern California and central Mexico, including the megadiverse Gulf of California, offers a remarkable setting to study biological diversification in the supralittoral. A complex geological history coupled with cyclical fluctuations in temperature and sea level provided ample opportunities for diversification of supralittoral organisms. Indeed, a previous phylogeographic study of Ligia, a supralittoral isopod that has limited dispersal abilities and is restricted to rocky patches, revealed high levels of morphologically cryptic diversity. Herein, we examined phylogeographic patterns of Tylos, another supralittoral isopod with limited dispersal potential, but whose habitat (i.e., sandy shores) appears to be more extensive and connected than that of Ligia. We conducted Maximum Likelihood and Bayesian phylogenetic analyses on mitochondrial and nuclear DNA sequences. These analyses revealed multiple highly divergent lineages with discrete regional distributions, despite the recognition of a single valid species for this region. A traditional species-diagnostic morphological trait distinguished several of these lineages. The phylogeographic patterns of Tylos inside the Gulf of California show a deep and complex history. In contrast, patterns along the Pacific region between southern California and the Baja Peninsula indicate a recent range expansion, probably postglacial and related to changes in sea surface temperature (SST). In general, the phylogeographic patterns of Tylos differed from those of Ligia. Differences in the extension and connectivity of the habitats occupied by Tylos and Ligia may account for the different degrees of population isolation experienced by these two isopods and their contrasting phylogeographic patterns. Identification of divergent lineages of Tylos in the study area is important for conservation, as some populations are threatened by human activities.

Dispersal at a snail's pace: historical processes affect contemporary genetic structure in the exploited wavy top snail (Megastraea undosa)

We used population genetics to assess historical and modern demography of the exploited wavy top snail, Megastraea undosa, which has a 5-10 day pelagic larval duration. Foot tissue was sampled from an average of 51 individuals at 17 sites across the range of M. undosa. Genetic structure at the mtDNA locus is strikingly high (ΦST of 0.19 across 1000 km), and a major cline occurs in northern Baja California (ΦCT of 0.29 between northern and southern populations). Genetic data indicate that the northern region is highly connected through larval dispersal, whereas the southern region exhibits low genetic structure. However, additional analyses based on patterns of haplotype diversity and relationships among haplotypes indicate that M. undosa has likely recently expanded into the Southern California Bight or expanded from a small refugial population, and analysis using isolation by distance to calculate dispersal distance indicates surprisingly short estimates of dispersal from 30 m to 3 km. This scenario of a northward expansion and limited larval dispersal is supported by coalescent-based simulations of genetic data. The different patterns of genetic variation between northern and southern populations are likely artifacts of evolutionary history rather than differences in larval dispersal and this may have applications to management of this species. Specifically, these data can help to inform the scale at which this species should be managed, and given the potentially very small dispersal distances, this species should be managed at local scales. Consideration of the evolutionary history of target species allows for a more accurate interpretation of genetic data for management.

The coalescent in boundary-limited range expansions

Habitat ranges of most species shift over time, for instance due to climate change, human intervention, or adaptation. These demographic changes often have drastic population genetic effects, such as a stochastic resampling of the gene pool through the "surfing" phenomenon. Most models assume that the speed of range expansions is only limited by the dispersal ability of the colonizing species and its reproductive potential. While such models of "phenotype-limited" expansions apply to species invasions, it is clear that many range expansions are limited rather by the slow motion of habitat boundaries, as driven for instance by global warming. Here, we develop a coalescent model to study the genetic impact of such "boundary-limited" range expansions. Our simulations and analysis show that the resulting loss of genetic diversity is markedly lower than in species invasions if large carrying capacities can be maintained up to the habitat frontier. Counterintuitively, we find that the total loss of diversity does not depend on the speed of the range expansion: Slower expansions have a smaller rate of loss, but also last longer. Boundary-limited range expansions exhibit a characteristic genetic footprint and should therefore be distinguished from range expansions limited only by intrinsic characteristics of the species.

Examining an outlier: molecular diversity in the cirripedia

Despite the typical assumption in studies of mitochondrial diversity that such data are useful for approximating population size and demography, studies of sequence diversity in mitochondrial DNA across the Metazoa have shown a surprising excess of rare alleles, a pattern associated either with strong selection or population growth. Previous work has shown that this bias toward an excess of rare alleles is typical across the Crustacea, and in particular, in the Cirripedia (barnacles). Here, we directly evaluate sequence data from studies of barnacle populations to ensure that inclusion of cryptic species is not the cause of this pattern. The results shown here reinforce previous studies that suggest caution in interpreting such patterns of allele frequencies, as they are likely to be influenced both by demographic changes and selection.

Environmental and climatic determinants of molecular diversity and genetic population structure in a coenagrionid damselfly

Identifying environmental factors that structure intraspecific genetic diversity is of interest for both habitat preservation and biodiversity conservation. Recent advances in statistical and geographical genetics make it possible to investigate how environmental factors affect geographic organisation and population structure of molecular genetic diversity within species. Here we present a study on a common and wide ranging insect, the blue tailed damselfly Ischnuraelegans, which has been the target of many ecological and evolutionary studies. We addressed the following questions: (i) Is the population structure affected by longitudinal or latitudinal gradients?; (ii) Do geographic boundaries limit gene flow?; (iii) Does geographic distance affect connectivity and is there a signature of past bottlenecks?; (iv) Is there evidence of a recent range expansion and (vi) what is the effect of geography and climatic factors on population structure? We found low to moderate genetic sub-structuring between populations (mean F(ST) = 0.06, D(est) = 0.12), and an effect of longitude, but not latitude, on genetic diversity. No significant effects of geographic boundaries (e.g. water bodies) were found. F(ST)-and D(est)-values increased with geographic distance; however, there was no evidence for recent bottlenecks. Finally, we did not detect any molecular signatures of range expansions or an effect of geographic suitability, although local precipitation had a strong effect on genetic differentiation. The population structure of this small insect has probably been shaped by ecological factors that are correlated with longitudinal gradients, geographic distances, and local precipitation. The relatively weak global population structure and high degree of genetic variation within populations suggest that I. elegans has high dispersal ability, which is consistent with this species being an effective and early coloniser of new habitats.

Genetic population structure of Tectura paleacea: implications for the mechanisms regulating population structure in patchy coastal habitats

The seagrass limpet Tectura paleacea (Gastropoda; Patellogastropoda) belongs to a seagrass obligate lineage that has shifted from the Caribbean in the late Miocene, across the Isthmus of Panama prior to the closing of the Panamanian seaway, and then northward to its modern Baja California - Oregon distribution. To address whether larval entrainment by seagrass beds contributes to population structuring, populations were sampled at six California/Oregon localities approximately 2 degrees latitude apart during two post-settlement periods in July 2002 and June 2003. Partial cytochrome oxidase b (Cytb) sequences were obtained from 20 individuals (10 per year) from each population in order to determine the levels of population subdivision/connectivity. From the 120 individuals sequenced, there were eighty-one unique haplotypes, with the greatest haplotype diversity occurring in southern populations. The only significant genetic break detected was consistent with a peri-Point Conception (PPC) biogeographic boundary while populations north and south of Point Conception were each panmictic. The data further indicate that populations found south of the PPC biogeographic boundary originated from northern populations. This pattern of population structure suggests that seagrass patches are not entraining the larvae of T. paleacea by altering flow regimes within their environment; a process hypothesized to produce extensive genetic subdivision on fine geographic scales. In contrast to the haplotype data, morphological patterns vary significantly over very fine geographic scales that are inconsistent with the observed patterns of genetic population structure, indicating that morphological variation in T. paleacea might be attributed to differential ecophenotypic expression in response to local habitat variability throughout its distribution. These results suggest that highly localized conservation efforts may not be as effective as large-scale conservation efforts in near shore marine environments.

Gene Flow and Isolation among Populations of Marine Animals

Successful dispersal between populations leaves a genetic wake that can reveal historical and contemporary patterns of connectivity. Genetic studies of differentiation in the sea suggest the role of larval dispersal is often tempered by adult ecology, that changes in differentiation with geographic distance are limited by disequilibrium between drift and migration, and that phylogeographic breaks reflect shared barriers to movement in the present more than common historical divisions. Recurring complications include the presence of cryptic species, selection on markers, and a failure to account for differences in heterozygosity among markers and species. A better understanding of effective population sizes is needed. Studies that infer parentage or kinship and coalescent analyses employing more markers are both likely to spur progress, with analyses based on linkage disequilibrium potentially bridging results from these studies and reconciling patterns that vary at ecological and evolutionary timescales.

Biological collections and ecological/environmental research: a review, some observations and a look to the future

Housed worldwide, mostly in museums and herbaria, is a vast collection of biological specimens developed over centuries. These biological collections, and associated taxonomic and systematic research, have received considerable long-term public support. The work remaining in systematics has been expanding as the estimated total number of species of organisms on Earth has risen over recent decades, as have estimated numbers of undescribed species. Despite this increasing task, support for taxonomic and systematic research, and biological collections upon which such research is based, has declined over the last 30-40 years, while other areas of biological research have grown considerably, especially those that focus on environmental issues. Reflecting increases in research that deals with ecological questions (e.g. what determines species distribution and abundance) or environmental issues (e.g. toxic pollution), the level of research attempting to use biological collections in museums or herbaria in an ecological/environmental context has risen dramatically during about the last 20 years. The perceived relevance of biological collections, and hence the support they receive, should be enhanced if this trend continues and they are used prominently regarding such environmental issues as anthropogenic loss of biodiversity and associated ecosystem function, global climate change, and decay of the epidemiological environment. It is unclear, however, how best to use biological collections in the context of such ecological/environmental issues or how best to manage collections to facilitate such use. We demonstrate considerable and increasingly realized potential for research based on biological collections to contribute to ecological/environmental understanding. However, because biological collections were not originally intended for use regarding such issues and have inherent biases and limitations, they are proving more useful in some contexts than in others. Biological collections have, for example, been particularly useful as sources of information regarding variation in attributes of individuals (e.g. morphology, chemical composition) in relation to environmental variables, and provided important information in relation to species' distributions, but less useful in the contexts of habitat associations and population sizes. Changes to policies, strategies and procedures associated with biological collections could mitigate these biases and limitations, and hence make such collections more useful in the context of ecological/environmental issues. Haphazard and opportunistic collecting could be replaced with strategies for adding to existing collections that prioritize projects that use biological collections and include, besides taxonomy and systematics, a focus on significant environmental/ecological issues. Other potential changes include increased recording of the nature and extent of collecting effort and information associated with each specimen such as nearby habitat and other individuals observed but not collected. Such changes have begun to occur within some institutions. Institutions that house biological collections should, we think, pursue a mission of 'understanding the life of the planet to inform its stewardship' (Krishtalka & Humphrey, 2000), as such a mission would facilitate increased use of biological collections in an ecological/environmental context and hence lead to increased appreciation, encouragement and support from the public for these collections, their associated research, and the institutions that house them.

Discordant distribution of populations and genetic variation in a sea star with high dispersal potential

Patiria miniata, a broadcast-spawning sea star species with high dispersal potential, has a geographic range in the intertidal zone of the northeast Pacific Ocean from Alaska to California that is characterized by a large range gap in Washington and Oregon. We analyzed spatial genetic variation across the P. miniata range using multilocus sequence data (mtDNA, nuclear introns) and multilocus genotype data (microsatellites). We found a strong phylogeographic break at Queen Charlotte Sound in British Columbia that was not in the location predicted by the geographical distribution of the populations. However, this population genetic discontinuity does correspond to previously described phylogeographic breaks in other species. Northern populations from Alaska and Haida Gwaii were strongly differentiated from all southern populations from Vancouver Island and California. Populations from Vancouver Island and California were undifferentiated with evidence of high gene flow or very recent separation across the range disjunction between them. The surprising and discordant spatial distribution of populations and alleles suggests that historical vicariance (possibly caused by glaciations) and contemporary dispersal barriers (possibly caused by oceanographic conditions) both shape population genetic structure in this species.

Chapter 3. Effects of climate change and commercial fishing on Atlantic cod Gadus morhua

During the course of the last century, populations of Atlantic cod Gadus morhua L. have undergone dramatic declines in abundance across their biogeographic range, leading to debate about the relative roles of climatic warming and overfishing in driving these changes. In this chapter, we describe the geographic distributions of this important predator of North Atlantic ecosystems and document extensive evidence for limitations of spatial movement and local adaptation from population genetic markers and electronic tagging. Taken together, this evidence demonstrates that knowledge of spatial population ecology is critical for evaluating the effects of climate change and commercial harvesting. To explore the possible effects of climate change on cod, we first describe thermal influences on individual physiology, growth, activity and maturation. We then evaluate evidence that temperature has influenced population-level processes including direct effects on recruitment through enhanced growth and activity, and indirect effects through changes to larval food resources. Although thermal regimes clearly define the biogeographic range of the species, and strongly influence many aspects of cod biology, the evidence that population declines across the North Atlantic are strongly linked to fishing activity is now overwhelming. Although there is considerable concern about low spawning stock biomasses, high levels of fishing activity continues in many areas. Even with reduced fishing effort, the potential for recovery from low abundance may be compromised by unfavourable climate and Allee effects. Current stock assessment and management approaches are reviewed, alongside newly advocated methods for monitoring stock status and recovery. However, it remains uncertain whether the rebuilding of cod to historic population sizes and demographic structures will be possible in a warmer North Atlantic.

Climate-driven diversification in two widespread Galerida larks

BACKGROUND

The major impact of Plio-Pleistocene climatic oscillations on the current genetic structure of many species is widely recognised but their importance in driving speciation remains a matter of controversies. In addition, since most studies focused on Europe and North America, the influence of many other biogeographic barriers such as the Sahara remains poorly understood. In this paper, climate-driven diversification was investigated by using a comparative phylogeographic approach in combination with phenotypic data in two avian species groups distributed on both sides of the deserts belt of Africa and Asia. In particular, we tested whether: 1) vicariance diversification events are concomitant with past climatic events; and 2) current ecological factors (using climate and competition as proxies) contribute to phenotypic divergence between allopatric populations.

RESULTS

Mitochondrial and nuclear sequence data indicated that the crested and Thekla lark species groups diverged in the early Pliocene and that subsequent speciation events were congruent with major late Pliocene and Pleistocene climatic events. In particular, steep increase in aridity in Africa near 2.8 and 1.7 million years ago were coincident with two north-south vicariance speciation events mediated by the Sahara. Subsequent glacial cycles of the last million years seem to have shaped patterns of genetic variation within the two widespread species (G. cristata and G. theklae). The Sahara appears to have allowed dispersal from the tropical areas during climatic optima but to have isolated populations north and south of it during more arid phases. Phenotypic variation did not correlate with the history of populations, but was strongly influenced by current ecological conditions. In particular, our results suggested that (i) desert-adapted plumage evolved at least three times and (ii) variation in body size was mainly driven by interspecific competition, but the response to competition was stronger in more arid areas.

CONCLUSION

Climatic fluctuations of the Plio-Pleistocene strongly impacted diversification patterns in the Galerida larks. Firstly, we found that cladogenesis coincides with major climatic changes, and the Sahara appears to have played a key role in driving speciation events. Secondly, we found that morphology and plumage were strongly determined by ecological factors (interspecific competition, climate) following vicariance.

Molecular ecology of global change

Global environmental change is altering the selection regime for all biota. The key selective factors are altered mean, variance and seasonality of climatic variables and increase in CO(2) concentration itself. We review recent studies that document rapid evolution to global climate change at the phenotypic and genetic level, as a response to shifts in these factors. Among the traits that have changed are photoperiod responses, stress tolerance and traits associated with enhanced dispersal. The genetic basis of two traits with a critical role under climate change, stress tolerance and photoperiod behaviour, is beginning to be understood for model organisms, providing a starting point for candidate gene approaches in targeted nonmodel species. Most studies that have documented evolutionary change are correlative, while selection experiments that manipulate relevant variables are rare. The latter are particularly valuable for prediction because they provide insight into heritable change to simulated future conditions. An important gap is that experimental selection regimes have mostly been testing one variable at a time, while synergistic interactions are likely under global change. The expanding toolbox available to molecular ecologists holds great promise for identifying the genetic basis of many more traits relevant to fitness under global change. Such knowledge, in turn, will significantly advance predictions on global change effects because presence and polymorphism of critical genes can be directly assessed. Moreover, knowledge of the genetic architecture of trait correlations will provide the necessary framework for understanding limits to phenotypic evolution; in particular as lack of critical gene polymorphism or entire pathways, metabolic costs of tolerance and linkage or pleiotropy causing negative trait correlations. Synergism among stressor impacts on organismal function may be causally related to conflict among transcriptomic syndromes specific to stressor types. Because adaptation to changing environment is always contingent upon the spatial distribution of genetic variation, high-resolution estimates of gene flow and hybridization should be used to inform predictions of evolutionary rates.

Traces of ancient range shifts in a mountain plant group (Androsace halleri complex, Primulaceae)

Phylogeographical studies frequently detect range shifts, both expansions (including long-distance dispersal) and contractions (including vicariance), in the studied taxa. These processes are usually inferred from the patterns and distribution of genetic variation, with the potential pitfall that different historical processes may result in similar genetic patterns. Using a combination of DNA sequence data from the plastid genome, AFLP fingerprinting, and rigorous phylogenetic and coalescence-based hypothesis testing, we show that Androsace halleri (currently distributed disjunctly in the northwestern Iberian Cordillera Cantábrica, the eastern Pyrenees, and the French Massif Central and Vosges), or its ancestor, was once more widely distributed in the Pyrenees. While there, it hybridized with Androsace laggeri and Androsace pyrenaica, both of which are currently allopatric with A. halleri. The common ancestor of A. halleri and the north Iberian local endemic Androsace rioxana probably existed in the north Iberian mountain ranges with subsequent range expansion (to the French mountain ranges of the Massif Central and the Vosges) and allopatric speciation (A. rioxana, A. halleri in the eastern Pyrenees, A. halleri elsewhere). We have thus been able to use the reticulate evolution in this species group to help elucidate its phylogeographical history, including evidence of range contraction.

Evolution of blood pressure regulation in humans

The human propensity for hypertension is a product, in part, of our evolutionary history. Adaptation to climate, first in Africa and then throughout the world, has driven our evolution and may have shaped current patterns of hypertension susceptibility. This article reviews human evolution and the impact of climatic adaptation on blood pressure physiology. Evidence suggests that genetic susceptibility to hypertension is ancestral and was magnified during early human evolution. Furthermore, differential susceptibility among human populations is due to differential selection during the out-of-Africa expansion 30,000 to 100,000 years ago. The most important selection pressure was climate, which produced a latitudinal cline in hypertension susceptibility. Therefore, the current epidemic of hypertension is likely due to new exposures of the modern period (e.g.: higher salt intake) interacting with ancestral susceptibility. Worldwide populations may differ in susceptibility to the new exposures, however, such that those from hot, arid environments are more susceptible to hypertension than populations from cold environments.

Mitochondrial DNA variation in space and time in the northeastern Pacific gastropod,Littorina keenae

The present population structure of a species reflects the influence of population history as well as contemporary processes. To examine the relative importance of these factors in shaping the current population structure of Littorina keenae, we sequenced 762 base pairs of the mitochondrial ND6 and cytochrome b genes in 584 snails from 13 sites along the northeastern Pacific coast. Haplotype network analysis revealed a 'star-like' genealogy indicative of a recent population expansion. Nested clade and mismatch analyses also supported the hypothesis of sudden population expansion following a population bottleneck during the Last Glacial Maximum. Analysis of molecular variance and pairwise Phi(ST) showed no significant spatial population differentiation from Mexico to Oregon - not even across the recognized biogeographic boundary at Point Conception. This is probably due to high contemporary gene flow during the free-swimming larval stage of this snail. Surprisingly, we found a highly significant temporal population differentiation between a San Pedro sample from 1996 and one from 2005, which gave an estimate of effective population size (N(e)) of only 135. Nearly statistically significant changes in the frequency of a particular haplotype in three other populations over 2-3 years further support Hedgecock's 'sweepstakes' hypothesis. When by chance nearly all of the progeny from an aggregation of highly fecund sisters that possess a rare haplotype successfully recruit to become the next generation, the rare haplotype can become temporarily common across the entire species' range. This modification of the sweepstakes hypothesis can explain why the temporal variation that we observed was much greater than the spatial variation.