The role of climate for the range limits of parapatric European land salamanders

Abrupt range limits of parapatric species may serve as a model system to understand the factors that determine species’ range borders. Theory suggests that parapatric range limits can be caused by abiotic conditions along environmental gradients, biotic interactions or a combination of both. Geographic ranges of the parapatric salamanders, Salamandra salamandra and S. atra, meet in small contact zones in the European Alps and to date, the cause of parapatry and the restricted range of S. atra remain elusive. We combine multivariate approaches and climatic data analysis to explore niche differentiation among the two salamanders with respect to the available climatic environment at their contact zones. Our purpose is to evaluate whether climatic conditions explain the species’ sharp range limits or if biotic interactions may play a role for range delimitation. Analyses were carried out in three contact zones in Switzerland to assess possible geographic variation. Our results indicate that both species occur at localities with different climatic conditions as well as the presence of a strong climatic gradient across the species’ range limits. Although the species’ climatic niches differ moderately (with a wider niche breadth for S. atra), interspecific niche overlap is found. Comparisons among the contact zones confirm geographic variation in the species’ climatic niches as well as in the conditions within the geographically available space. Our results suggest that the change in climatic conditions along the recognized gradient represents a determining factor for species’ range limits within contact zones. However, our analyses of geographic variation in climatic conditions reveal that both salamander species can occur in a much wider range of conditions than observed within contact zones. This finding and the interspecific climatic niche overlap within each contact zone provides indirect evidence that biotic interactions (likely competition) between the two species may also determine their range limits.     

History cleans up messes: The impact of time in driving divergence and introgression in a tropical suture zone

Contact zones provide an excellent arena in which to address questions about how genomic divergence evolves during lineage divergence. They allow us to both infer patterns of genomic divergence in allopatric populations isolated from introgression and to characterize patterns of introgression after lineages meet. Thusly motivated, we analyze genome‐wide introgression data from four contact zones in three genera of lizards endemic to the Australian Wet Tropics. These contact zones all formed between morphologically cryptic lineage‐pairs within morphologically defined species, and the lineage‐pairs meeting in the contact zones diverged anywhere from 3.1 to 5.8 million years ago. By characterizing patterns of molecular divergence across an average of 11K genes and fitting geographic clines to an average of 7.5K variants, we characterize how patterns of genomic differentiation and introgression change through time. Across this range of divergences, we find that genome‐wide differentiation increases but becomes no less heterogeneous. In contrast, we find that introgression heterogeneity decreases dramatically, suggesting that time helps isolated genomes “congeal.” Thus, this work emphasizes the pivotal role that history plays in driving lineage divergence.     

The relative roles of vicariance versus elevational gradients in the genetic differentiation of the high Andean tree frog, Dendropsophus labialis

There are two main competing hypotheses (vicariance and vertical ecotones) that attempt to explain the tremendous diversity of the tropical Andes. We test these hypotheses at the intraspecific level by analyzing mitochondrial and nuclear DNA sequences from 24 populations of the high Andean frog, Dendropsophus labialis (Anura: Hylidae). This species displays geographic variation in a number of phenotypic traits. Most of these traits covary with elevation, while few vary along the horizontal (latitudinal) axis. We found that, both, vicariance and elevation had important effects on the genetic differentiation in this species. We detected two highly divergent clades along the south-north axis using independent information from mitochondrial and nuclear genes, suggesting that this differentiation was the result of long-term barriers to gene flow rather than stochastic processes. We hypothesize mechanisms for D. labialis strong differentiation in light of geological and paleoenvironmental models of evolution in the northern Andean highlands.     

Lack of congruence of genetic and niche divergence in Podarcis hispanicus complex

Niche divergence among closely related lineages can be informative on the ecological and evolutionary processes involved in differentiation, particularly in the case of cryptic species complexes. Here we compared phylogenetic relationships and niche similarity between pairs of lineages included in the Podarcis hispanicus complex to examine patterns of niche divergence and its role in the organization of current diversity patterns, as allopatric, parapatric, and sympatric lineages occur in the Western Mediterranean Basin. First, we used ecological niche models to characterize the realized climatic niche of each Podarcis hispanicus complex lineage based on topographic and climatic variables, to identify important variables, and to test for niche conservatism or divergence between pairs of lineages. Variables related to precipitation generally exhibited the highest contribution to niche models, highlighting the importance of rainfall levels in shaping distributions of Podarcis wall lizards. We found that most forms have significant differences in realized climatic niches that do not follow the pattern of mitochondrial divergence. These results lend support to the hypothesis that genetic divergence across Podarcis hispanicus complex most likely occurred in allopatric conditions, mostly with significant niche divergence. Competition after secondary contact is also suggested by the common occurrence of niche overlap between lineages that exhibit strictly parapatric distribution. The almost continuous distribution of Podarcis lizards in the study area appears to be a result of a combination of complementary suitable niches and competition, which seem two important mechanisms limiting geographic distributions and restricting the existence of extensive contact zones.     

Mountaintop island age determines species richness of boreal mammals in the American Southwest

Models that describe the mechanisms responsible for insular patterns of species richness include the equilibrium theory of island biogeography and the nonequilibrium vicariance model. The relative importance of dispersal or vicariance in structuring insular distribution patterns can be inferred from these models. Predictions of the alternative models were tested for boreal mammals in the American Southwest. Age of mountaintop islands of boreal habitat was determined by constructing a geographic cladogram based on characteristics of intervening valley barriers. Other independent variables included area and isolation of mountaintop islands. Island age was the most important predictor of species richness. In contrast with previous studies of species richness patterns in this system, these results supported the nonequilibrium vicariance model, which indicates that vicariance has been the primary determinant of species distribution patterns in this system.     

Range‐wide analysis of genetic structure in a widespread,highly mobile species (Odocoileus hemionus) reveals the importance of historical biogeography

Highly mobile species that thrive in a wide range of habitats are expected to show little genetic differentiation across their range. A limited but growing number of studies have revealed that patterns of broad‐scale genetic differentiation can and do emerge in vagile, continuously distributed species. However, these patterns are complex and often shaped by both historical and ecological factors. Comprehensive surveys of genetic variation at a broad scale and at high resolution are useful for detecting cryptic spatial genetic structure and for investigating the relative roles of historical and ecological processes in structuring widespread, highly mobile species. In this study, we analysed 10 microsatellite loci from over 1900 samples collected across the full range of mule deer (Odocoileus hemionus), one of the most widely distributed and abundant of all large mammal species in North America. Through both individual‐ and population‐based analyses, we found evidence for three main genetic lineages, one corresponding to the ‘mule deer’ morphological type and two to the ‘black‐tailed deer’ type. Historical biogeographic events likely are the primary drivers of genetic divergence in this species; boundaries of the three lineages correspond well with predictions based on Pleistocene glacial cycles, and substructure within each lineage demonstrates island vicariance. However, across large geographic areas, including the entire mule deer lineage, we found that genetic variation fit an isolation‐by‐distance pattern rather than discrete clusters. A lack of genetic structure across wide geographic areas of the continental west indicates that ecological processes have not resulted in restrictions to gene flow sufficient for spatial genetic structure to emerge. Our results have important implications for our understanding of evolutionary mechanisms of divergence, as well as for taxonomy, conservation and management.     

Barriers to sympatry between avian sibling species (Paridae: Baeolophus) in local secondary contact

Range limits and secondary contact zones often occur at ecotones between major associations of habitat and climate. Therefore, understanding processes that limit sympatry between species in such areas provides an important framework for testing biogeographic and evolutionary hypotheses. Theoretical and empirical work has shown that the evolution of species borders is influenced by a complexity of factors, including gene flow from central to peripheral populations and the ability of species to adapt locally to environmental conditions. However, few studies have used bioclimatic models, combined with molecular and morphological data, to predict geographic range limits in the context of gene flow across a secondary contact zone. In this study, I applied these methods to test specific hypotheses about barriers to sympatry between closely related species where they approach and contact each other. Specifically, I examined the importance of historical isolation, local adaptation, and symmetry of gene flow in limiting sympatry and range expansion of ecologically distinct species across environmental gradients. Molecular (mitochondrial DNA, allozymes), morphological, and bioclimatic data were obtained for two avian sibling species (Baeolophus inornatus and B. ridgwayi) that exist in recent, narrow secondary contact in northern California. These species are broadly allopatric and occupy rangewide associations of oak and pinyon-juniper woodlands, respectively, although B. inornatus also inhabits mixed or juniper woodlands locally. Patterns of molecular variation generally were congruent with morphological and bioclimatic data, and support prior evidence for a history of isolation, adaptation, and divergence in distinctive, species-specific vegetation-climate associations. However, molecular and morphological clines fall east of the limit of oaks, and individuals of B. inornatus in this juniper-associated contact zone experience bioclimates that are more similar to B. ridgwayi than to B. inornatus in oak habitat. Thus, B. inornatus is able to adapt and expand locally into the range of its close relative, but not vice versa. These data support the hypothesis that gene flow is asymmetrical where peripheral populations meet at range boundaries. Physiological differences between species may play an important role in influencing these patterns. Empirical studies that highlight the importance of local adaptation and patterns of gene flow in which closely related species contact across ecotones are central to understanding limits on geographic ranges, sympatry, and introgression-a cornerstone of biogeographic and speciation theory.     

Patterns and causes of morphological population differentiation in the Tenerife skink, Chalcides viridanus

Recent studies indicate that differential selection between mesic and xeric habitats is the most plausible explanation of within-island geographic variation in the Gran Ganarian skink, Chalcides sexlineatus. The island of Tenerife shows mesic/xeric heterogeneity similar to that on Gran Canaria, so we tested the prediction of parallel geographic patterns of morphological population differentiation in the Tenerife skink, Chalcides viridanus. Geographic variation was found to be complex; patterns of differentiation in body dimensions and scalation show evidence of both mosaic and latitudinal facets. Using randomization and regression methods, significant relationships were found between a hypothesized xeric/mesic model of population differentiation and geographic variation in female body dimensions, as well as with substantial proportions of the geographic variation in male and female scalation and, to a lesser extent, body dimensions. Matrix comparisons based on the entire morphological distance matrices show that the patterns of variation are not concordant with an alternative hypothesis of historical secondary contact, or with an isolation-by-distance model. It is argued that a substantial component of the geographic variation in body dimensions and scalation of C. viridanus is due to differential selection along an aridity gradient.     

Phylogeography of white-spotted Charr (Salvelinus leucomaenis) inferred from mitochondrial DNA sequences

The white-spotted charr (Salvelinus leucomaenis) is a coldwater-adapted fish distributed in far-eastern Asia. To assess phylogeographic patterns of this species over most of its range in the Japanese archipelago and Sakhalin Island, Russia, we examined nucleotide sequences of the mitochondrial DNA (mtDNA) cytochrome b region (557 bp) in 141 individuals from 50 populations. A total of 33 (5.5%) nucleotide positions were polymorphic and defined 29 haplotypes. Phylogenetic analysis assigned the observed haplotypes to four main clades, which were characterized by the idiosyncrasies and discontinuity of geographic distributions. The nested clade analyses revealed that the geographical distribution patterns of some haplotypes and clades were explained by historical event such as past fragmentation. Although substantial genetic differentiation was found among the four main clades, their geographic distributions overlapped extensively in several regions. Since white-spotted charr can potentially use both freshwater and marine environments, coexistence among different lineages can be attributed to secondary contact through range expansion by migratory individuals during multiple glacial periods after interglacial isolation. Finally, our data demonstrate that the current subspecies designation does not reflect the phylogeography of this species based on mtDNA analysis. Hierarchical analysis (AMOVA) also showed that genetic variation was far more pronounced within subspecies than among subspecies (i.e., among discrete regions). These results suggest that each population, rather than each subspecies, must be treated as an evolutionarily significant unit.     

Past climatic fluctuations are associated with morphological differentiation in the cloud forest endemic tree <Emphasis Type="Italic">Ocotea psychotrioides</Emphasis> (Lauraceae)

Pleistocene glacial periods have had a major influence on the geographical patterns of genetic structure of species in tropical montane regions. However, their effect on morphological differentiation among populations of cloud forest plants remains virtually unexplored. Here, we address this question by testing whether geographical patterns of morphological variation in Ocotea psychotrioides can be explained by the intensity of climate change occurring during 130,000 years. For this, we measured vegetative and reproductive traits for 96 individuals from 36 localities registered across the species’ distribution range. Species distribution models and multivariate statistics were used to investigate geographical patterns of morphological variation and test their association with current and past climatic conditions. Leaf size and pubescence in O. psychotrioides showed a latitudinal pattern of clinal variation that does not fit the geographical gradient of increasing leaf size towards lower latitudes observed globally among plants. Instead, the observed clinal variation conforms to a pattern of increasing leaf size towards higher latitudes. However, our analyses showed weak to non-significant association between morphology and current climate. Interestingly, our analyses showed that predicted shifts in the distribution range of O. psychotrioides during the last 130,000 years were accompanied by significant changes in climatic conditions, particularly temperature seasonality and precipitation. Accordingly, climatic instability showed a better fit to the observed patterns of leaf size and pubescence variation than current climate conditions. These results suggest that climatic instability during the Pleistocene glacial periods might play a key role in promoting morphological differentiation among populations of cloud forest plants.     

Regulation of gut function varies with life-history traits in chuckwallas (Sauromalus obesus: Iguanidae)

We examined the effects of hibernation and fasting on intestinal glucose and proline uptake rates of chuckwallas (Sauromalus obesus) and on the size of organs directly or indirectly related to digestion. These lizards show geographic variation in body size and growth rate that parallels an elevational gradient in our study area. At low elevation, food is available only for a short time during the spring; at high elevation, food may also be available during summer and autumn, depending on rainfall conditions in a given year. We hypothesized that low-elevation lizards with a short season of food availability would show more pronounced regulation of gut size and function than high-elevation lizards with prolonged or bimodal food availability. Hibernating lizards from both elevations had significantly lower uptake rates per milligram intestine for both nutrients, and lower small intestine mass, than active lizards. The combination of these two effects resulted in significantly lower total nutrient uptake in hibernating animals compared to active ones. The stomach, large intestine, and cecum showed lower masses in hibernators, but these results were not statistically significant. The heart, kidney, and liver showed no difference in mass between hibernating and nonhibernating animals. Lizards from low elevations with a short growing season also showed a greater increase in both uptake rates and small intestine mass from the hibernating to the active state, compared to those from high elevations with longer growing seasons. Thus, compared to those from long growing season areas, lizards from short growing season areas have equal uptake capacity during hibernation but much higher uptake capacity while active and feeding. This pattern of regulation of gut function may or may not be an adaptive response, but it is consistent with variation in life-history characteristics among populations. In areas with a short season, those lizards that can extract nutrients quickly and then reduce the gut will be favored; in areas where food may be available later in the year, those lizards that maintain an active gut would be favored. While other researchers have found much greater magnitudes of gut regulation when making comparisons among species, we find the different patterns of change in gut function between different populations of chuckwallas particularly intriguing because they occur within a single species.     

Differential effects of historical migration,glaciations and human impact on the genetic structure and diversity of the mountain pasture weed Veratrum album L.

Aim Today’s genetic population structure and diversity of species can be understood as the result of range expansion from the area of origin, past climatic oscillations and contemporary processes. We examined the relative importance of these factors in Veratrum album L., a toxic weed of mountain grasslands. Location Continental Europe. Methods Forty populations from the Asian border (Urals and Caucasus) to Portugal were studied using amplified fragment length polymorphisms (AFLPs) combined with selected plant and population measures. The data were analysed with phylogenetic, population genetic and regression methods inferring both genetic structure and diversity from geographic and ecological factors. Results Fragment frequency clines together with genetic distance clustering and principal coordinates analysis indicated an east–west direction in the genetic structure of V. album, suggesting ancient migration into Europe from a proposed Asian origin. However, the strong geographic pattern in the genetic structure, pronounced isolation by distance (R² = 0.74) and moderate overall population differentiation (F_ST = 0.13) suggests high historical gene flow, possibly during glacials, and vicariance into mountainous regions during interglacials. Occurrence of V. album during the last glaciation in several areas along the periphery of the Alps and recolonization of this mountain range from both eastern and central–western areas was indicated. Genetic diversity was highest in central Europe, a pattern that did not agree with the expectations from east–west migration into Europe. Furthermore, managed habitats showed higher levels of genetic diversity compared to unmanaged habitats. Stepwise linear regression determined shoot density and soil phosphorus as the main predictors of within‐population genetic diversity (R² = 0.40). Main conclusions Our results showed that V. album retained genetic imprints of historical range expansion into Europe, although this was alleviated by the influence of climatic oscillations and contemporary processes. For example, genetic population structure was strongly affected by post‐glacial vicariance while patterns of genetic diversity seemed mainly to be influenced by human land use. Our findings highlight the importance of applying a synthetic approach, testing the influence of both historical and contemporary processes on genetic structure and diversity in order to understand complex phylogeographic patterns. This may especially apply to widespread species, such as weeds. Implications of our findings for biological control are briefly discussed.     

Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient

ABSTRACT: BACKGROUND: Four of the five species of Telopea (Proteaceae) are distributed in a latitudinal replacement pattern on the south-eastern Australian mainland. In similar circumstances, a simple allopatric speciation model that identifies the origins of genetic isolation within temporal geographic separation is considered as the default model. However, secondary contact between differentiated lineages can result in similar distributional patterns to those arising from a process of parapatric speciation (where gene flow between lineages remains uninterrupted during differentiation). Our aim was to use the characteristic distributional patterns in Telopea to test whether it reflected the evolutionary models of allopatric or parapatric speciation. Using a combination of genetic evidence and environmental niche modelling, we focused on three main questions: do currently described geographic borders coincide with genetic and environmental boundaries; are there hybrid zones in areas of secondary contact between closely related species; did species distributions contract during the last glacial maximum resulting in distributional gaps even where overlap and hybridisation currently occur? RESULTS: Total genomic DNA was extracted from 619 individuals sampled from 36 populations representing the four species. Seven nuclear microsatellites (nSSR) and six chloroplast microsatellites (cpSSR) were amplified across all populations. Genetic structure and the signature of admixture in overlap zones was described using the Bayesian clustering methods implemented in STUCTURE and NewHybrids respectively. Relationships between chlorotypes were reconstructed as a median-joining network. Environmental niche models were produced for all species using environmental parameters from both the present day and the last glacial maximum (LGM). The nSSR loci amplified a total of 154 alleles, while data for the cpSSR loci produced a network of six chlorotypes. STRUCTURE revealed an optimum number of five clusters corresponding to the four recognised species with the additional division of T. speciosissima into populations north and south of the Shoalhaven River valley. Unexpectedly, the northern disjunct population of T. oreades grouped with T. mongaensis and was identified as a hybrid swarm by the Bayesian assignment test implemented in NewHybrids. Present day and LGM environmental niche models differed dramatically, suggesting that distributions of all species had repeatedly expanded and contracted in response to Pleistocene climatic oscillations and confirming strongly marked historical distributional gaps among taxes. CONCLUSIONS: Genetic structure and bio-climatic modeling results are more consistent with a history of allopatric speciation followed by repeated episodes of secondary contact and localised hybridisation, rather than with parapatric speciation. This study on Telopea shows that the evidence for temporal exclusion of gene flow can be found even outside obvious geographical contexts, and that it is possible to make significant progress towards excluding parapatric speciation as a contributing evolutionary process.     

Diversification of Sulawesi macaque monkeys: decoupled evolution of mitochondrial and autosomal DNA

Abstract. In macaque monkeys, females are philopatric and males are obligate dispersers. This social system is expected to differently affect evolution of genetic elements depending on their mode of inheritance. Because of this, the geographic structure of molecular variation may differ considerably in mitochondrial DNA (mtDNA) and in autosomal DNA (aDNA) in the same individuals, even though these genomes are partially co-inherited. On the Indonesian island of Sulawesi, macaque monkeys underwent an explosive diversification as a result of range fragmentation. Today, barriers to dispersal have receded and fertile hybrid individuals can be found at contact zones between parapatric species. In this study, we examine the impact of range fragmentation on Sulawesi macaque mtDNA and aDNA by comparing evolution, phylogeography, and population subdivision of each genome. Our results suggest that mtDNA is paraphyletic in some species, and that mtDNA phylogeography is largely consistent with a pattern of isolation by distance. Autosomal DNA, however, is suggestive of fragmentation, in that interspecific differentiation across most contact zones is significant but intraspecific differentiation between contact zones is not. Furthermore, in mtDNA, most molecular variation is partitioned between populations within species but in aDNA most variation is partitioned within populations. That mtDNA has a different geographic structure than aDNA (and morphology) in these primates is a probable consequence of (1) a high level of ancestral polymorphism in mtDNA, (2) differences between patterns of ancestral dispersal of matrilines and contemporary dispersal of males, and (3) the fact that female philopatry impedes gene flow of macaque mtDNA.     

Grapes, galls, and geography: the distribution of nuclear and mitochondrial DNA variation across host-plant species and regions in a specialist herbivore

Studies of patterns of molecular variation in natural populations can provide important insights into a number of evolutionary problems. Among these, the question of whether geographic factors are more important than ecological factors in promoting population differentiation and ultimately speciation has been an important and contentious area in evolutionary biology. Systems involving herbivorous insects have played a leading role in this discussion. This study examined the distribution of molecular variation in a highly specialized gall-forming insect, grape phylloxera (Daktulosphaira vitifoliae Fitch), that is found on both sympatric and allopatric host-plant species of the genus Vitis. In addition, the relationship of insects in the introduced range in the United States to ancestral populations in the native range was examined. Evidence for differentiation along host-plant lines from both nuclear (RAPD) and mitochondrial (COI) DNA was confounded with the effect of geography. Differentiation was found where hosts were allopatric or parapatric, but no evidence was found for such differentiation on two hosts, V. vulpina and V. aestivalis, that are broadly sympatric. The question of population differentiation onto these sympatric hosts can be considered to be resolved--it has not occurred in spite of a long history of association. Evidence was equivocal, but suggestive of a period of divergence in allopatry prior to reestablishment of contact, for insects associated with another host plant species, V. cinerea, found in both sympatric and parapatric populations. A low level of diversity and placement of samples collected from the grape species V. riparia at the tip of a phylogenetic tree supports the hypothesis that this host has been recently colonized from populations from the Mississippi Valley. A polyphyletic origin for biotype B grape phylloxera was supported: Although most samples collected from vineyards in the introduced range in California had similar haplotypes, they were closely related to natives on V. vulpina from the Atlantic Coast-Piedmont region. All samples collected from vineyards in Oregon and Washington were closely related to natives on V. riparia in the northern United States.     

Estimating asymptotic body size and testing geographic variation in Agama impalearis

Methods for estimating 'typical' asymptotic- body size in populations of the North African agamid Agma impalearis using individuals of undetermined age were investigated, and the pattern of geographic variation in this characteristic described and tested against simple models based on putative causes. Resampling of a large single-site data set indicated that use of the sample mean led to substantial underestimation of asymptotic size while use of the largest animal per sample led to overestimation, on average. The 80th percentile provided the most accurate estimate of asymptotic size and, compared with the largest individual per sample, had low variance, showed low dependence on sample size and was amenable to bootstrap estimation of confidence intervals. A clear pattern of geographic variation in asymptotic size was evident across Morocco: animals were smallest in the north and east and largest in the southwest. This pattern was discordant with previously-described patterns of variation in scalation and size-free body dimensions and, unlike these characteristics, could not be explained by a model based on secondary contact of previously vicariant populations. Among-site differentiation was strongly associated with a model based on a proxy of current potential gene flow between sites, supporting an alternative in situ differentiation hypothesis based on the combined effects of isolation-by-distance and the dispersal barrier provided by the higher parts of the Atlas mountain range. Possible reasons for the discordance between the pattern of variation in body size and other morphological characteristics are discussed     

Pleistocene climatic fluctuations drive isolation and secondary contact in the red diamond rattlesnake (Crotalus ruber) in Baja California

Aim

Many studies have investigated the phylogeographic history of species on the Baja California Peninsula, and they often show one or more genetic breaks that are spatially concordant among many taxa. These phylogeographic breaks are commonly attributed to vicariance as a result of geological or climatic changes, followed by secondary contact when barriers are no longer present. We use restriction‐site associated DNA sequence data and a phylogeographic model selection approach to explicitly test the secondary contact hypothesis in the red diamond rattlesnake, Crotalus ruber.

Location

Baja California and Southern California.

Methods

We used phylogenetic and population clustering approaches to identify population structure. We then used coalescent methods to simultaneously estimate population parameters and test the fit of phylogeographic models to the data. We used ecological niche models to infer suitable habitat for C. ruber at the Last Glacial Maximum (LGM).

Results

Crotalus ruber is composed of distinct northern and southern populations with a boundary near the town of Loreto in Baja California Sur. A model of isolation followed by secondary contact provides the best fit to the data, with both divergence and contact occurring in the Pleistocene. We also identify a genomic signature of northern range expansion in the northern population, consistent with LGM niche models showing that the northern‐most portion of the range of C. ruber was not suitable habitat during the LGM.

Main conclusions

We provide the first explicitly model‐based test of the secondary contact model in Baja California and show that populations of C. ruber were isolated before coming back into contact near Loreto, a region that shows phylogeographic breaks for other taxa. Given the timing of divergence and contact, we suggest that climatic fluctuations have driven the observed phylogeographic structure observed in C. ruber and that they may have driven similar patterns in other taxa.     

How species longevity, intraspecific morphological variation, and geographic range size are related: a comparison using late Cambrian trilobites

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but it is also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall.     

Cactophilic Drosophila in South America: A Model for Evolutionary Studies

The Drosophila buzzatii cluster is composed of seven cactophilic species and their known geographical distribution encompasses the open vegetation diagonal, which includes the morphoclimatic Domains of the Caatinga, Chaco and Cerrado, which are situated between the Amazon and the Atlantic forests. Besides these areas, these cactophilic species are also found in a narrow strip along the Atlantic coast from northeastern Brazil to the southern tip of the country. The hypothesis of vicariant events, defining the core areas of each species, is proposed to explain the historical diversification for the cluster. The intraspecific analysis for the cluster shows a population structure with gene flow restricted by distance, range expansion with secondary contact resulting in introgression and simpatry, especially in the limits of the species distribution, polytypic populations and assortative mating in inter population experiments. There is a variation related to these events that depends on the species and geographic origin of the population analyzed. These events are, hypothetically, described as the results of expansion and retraction of the population ranges, as a consequence of their association with cacti, which theoretically follow the expansion and retraction of dry areas during the paleoclimatic oscillations in South America, as that promoted by the glacial cycles of the Quaternary. The Drosophila buzzatii cluster is divided into two groups. The first one is composed of D. buzzatii, a species that has a broad geographic distribution and no significant differentiation between its populations. The second is the Drosophila serido sibling set, which encompasses the others species and is characterized by a significant potential for differentiation.