Complex fine‐scale phylogeographical patterns in a putative refugial region for Fagus sylvatica (Fagaceae)

Broad‐scale plastid (chloroplast) DNA studies of beech (Fagus sylvatica) populations suggest the existence of glacial refugia and introgression zones in south‐eastern Europe. We choose a possible refugium of beech in northern Greece, Mt. Paggeo, which hosts a private plastid haplotype for beech, to conduct a fine‐scale genetic study. We attempt to confirm or reject the hypothesis of the existence of a small‐scale refugium and to gain an understanding of the ecological and topographical factors affecting the spatial distribution of plastid haplotypes in the area. Our results reveal a high haplotype diversity on Mt. Paggeo, but the overall distribution of haplotypes shows no significant correlation with the ecological characteristics of the beech forests. However, the private haplotype is found at high frequencies in beech forests located in or near ravines, having a high spatial overlap with a relict vegetation type occurring in ecological conditions found mainly in ravines. This result emphasizes the importance of topography in the existence of glacial refugia in the wider area. Furthermore, haplotypes originating from two more widespread beech lineages in Greece are found on Mt. Paggeo, indicating a possible mixing of populations originating from a local refugium with populations from remote refugia that possibly migrated into the area after the last glaciation. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 516–528.     

Population history of the terrestrial orchid Cremastra appendiculata var. variabilis from Korea,inferred from levels and distribution of genetic diversity

Cremastra appendiculata var. variabilis is a self‐compatible, insect‐pollinated, terrestrial orchid that is a typical member of the warm‐temperate vegetation in the Korean Peninsula. Here we examine levels and partitioning of allozyme diversity (22 loci) in 12 populations of this orchid to gain insight into its genetic structure and post‐glacial colonization history in Korea. It harboured considerably higher levels of genetic variation within populations (%P = 48.1, A = 1.70 and H_e = 0.217) and lower degree of differentiation among populations (F_ST = 0.068) than those typical of allozyme‐based studies in other terrestrial orchid species. These patterns suggest that extant populations were derived from multiple source populations (i.e. from multiple glacial refugia), although further studies are needed to confirm this scenario. In addition to population history, traits such as high potential of seed dispersal, a mixed mating system and its occurrence in large and continuous populations would have contributed to the current levels and distribution of genetic diversity in Korean populations of C. appendiculata var. variabilis. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 721–732.     

Relationships between lake ecology and morphological characters in Icelandic Arctic charr,Salvelinus alpinus

The common occurrence of parallel phenotypic patterns suggests that a strong relationship exists between ecological dynamics and micro‐evolution. Comparative studies from a large number of populations under varying sets of ecological drivers could contribute to a better understanding of this relationship. We used data on morphology of arctic charr (Salvelinus alpinus) and ecological factors from 35 Icelandic lakes to test the hypothesis that morphological patterns among monomorphic charr populations from different lakes are related to interlake variation in ecological characteristics. There is extensive phenotypic diversity among populations of Icelandic charr, and populations are easily distinguished based on overall body morphology. The results obtained in the present study showed that the morphological diversity of charr was related to large‐scale diversity in lake ecology. Variation in charr morphology was related to water origin (e.g. spring fed versus run‐off), bedrock age, and fish community structure. The present study shows how various ecological factors can shape the biological diversity that we observe. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 761–771.     

Phytogeographical evidence for post‐glacial dispersal limitation of European beech forest species

The post‐glacial migration of European beech Fagus sylvatica has been addressed by many studies using either genetic or fossil data or a combination of both. In contrast to this, only little is known about the migration history of beech forest understorey species. In a review of phytosociological literature, we identified 110 plant species which are closely associated with beech forest. We divided the distribution range of European beech forests into 40 geographical regions, and the presence or absence of each species was recorded for each region. We compared overall species numbers per region and numbers of narrow‐range species (species present in <10 regions). A multiple regression model was used to test for the explanatory value of three potential diversity controls: range in elevation, soil type diversity, and distance to the nearest potential refuge area. A hierarchical cluster analysis of the narrow‐range species was performed. The frequency of range sizes shows a U‐shaped distribution, with 42 species occurring in <10 regions. The highest number of beech forest species is found in the southern Alps and adjacent regions, and species numbers decrease with increasing distance from these regions. With only narrow‐range species taken into consideration, secondary maxima are found in Spain, the southern Apennines, the Carpathians, and Greece. Distance to the nearest potential refuge area is the strongest predictor of beech forest species richness, while altitudinal range and soil type diversity had little or no predictive value. The clusters of narrow‐range species are in good concordance with the glacial refuge areas of beech and other temperate tree species as estimated in recent studies. These findings support the hypothesis that the distribution of many beech forest species is limited by post‐glacial dispersal rather than by their environmental requirements.     

Patterns of allozyme variation in western Eurasian Fagus

Fagus sylvatica L. is one of the most widespread broad‐leaved trees in the temperate forests of the northern hemisphere. In addition to two subspecies, F. sylvatica ssp. sylvatica in Europe and F. sylvatica ssp. orientalis in south‐western Asia, two further taxa were described: F. moesiaca (Maly) Czeczott in the south‐western Balkans and F. taurica Popl. in Crimea. The opinions about the number and ranks of taxa within this complex are highly controversial. To assess the degree of genetic differentiation among them, and to reveal geographical patterns of genetic diversity and their relationships to history and biogeography of beech populations, genetic variation at 12 allozyme loci was studied in 279 populations in western Eurasia. A Bayesian analysis of population structure revealed the existence of two clusters, which fairly well coincided with F. sylvatica ssp. sylvatica and F. sylvatica ssp. orientalis, whereby the populations from the south‐western Balkans and Crimea contained a mixture of these two gene pools. On the other hand, a neighbour‐joining tree based on pairwise F_ST failed to separate the subspecies into well‐defined distinct clades. Populations of F. sylvatica ssp. orientalis proved to be incomparably more differentiated than ssp. sylvatica (F_ST = 0.157 and 0.032, respectively). Asian populations also showed higher levels of allelic richness both on population and taxon levels than the European ones (the number of alleles after rarefaction was 3.40 and 4.27 in F. sylvatica ssp. sylvatica and ssp. orientalis, respectively). This indicates that the gene pool of F. sylvatica ssp. orientalis has not been depleted by reduced population sizes during the Pleistocene glaciations, as is the case of F. sylvatica ssp. sylvatica. Genetic similarities between isolated regional populations are explained by shared ancestral polymorphisms and/or range overlaps with subsequent hybridization in the past. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154 , 165–174.     

Patterns of divergence in the olive sunbird Cyanomitra olivacea (Aves: Nectariniidae) across the African rainforest–savanna ecotone

In the debate over modes of vertebrate diversification in tropical rainforests, two competing hypotheses of speciation predominate: those that emphasize the role of geographical isolation during glacial periods and those that stress the role of ecology and diversifying selection across ecotones or environmental gradients. To investigate the relative roles of selection versus isolation in refugia, we contrasted genetic and morphologic divergence of the olive sunbird (Cyanomitra olivacea) at 18 sites (approximately 200 individuals) across the forest–savanna ecotone of Central Africa in a region considered to have harboured three hypothesized refugia during glacial periods. Habitats were characterized using bioclimatic and satellite remote‐sensing data. We found relatively high levels of gene flow between ecotone and forest populations and between refugia. Consistent with a pattern of divergence‐with‐gene‐flow, we found morphological characters to be significantly divergent across the gradient [forest versus ecotone (mean ± SD): wing length 60.47 ± 1.81 mm versus 62.18 ± 1.35 mm; tarsus length 15.51 ± 0.82 mm versus 16.00 ± 0.57 mm; upper mandible length 21.77 ± 1.09 mm versus 23.19 ± 0.98 mm, respectively]. Within‐habitat comparisons across forest and ecotone sites showed no significant differences in morphology. The results show that divergence in morphological traits is tied to environmental variables across the gradient and is occurring despite gene flow. The pattern of divergence‐with‐gene‐flow found is similar to that described for other rainforest species across the gradient. These results suggest that neither refugia, nor isolation‐by‐distance have played a major role in divergence in the olive sunbird, although ecological differences along the forest and savanna ecotone may impose significant selection pressures on the phenotype and potentially be important in diversification. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 821–835.     

Rhytidium rugosum (Bryophyta) colonized Scandinavia from at least two glacial refugial source populations

The Scandinavian post‐glacial history of the moss Rhytidium rugosum is traced on the basis of information from the nuclear markers ITS and gpd for 229 Scandinavian and 81 other specimens. Some haplotypes, groups or lineages identified in a NeighborNet split network are predominantly northern Scandinavian, whereas others are southern. With the distributions of individual haplotypes and the timing of the deglaciation in different parts of Scandinavia, this implies colonization from the south and from the north or north‐east. High haplotype and nucleotide diversity and the occurrence of certain private haplotypes in the north suggest that the species may have survived the Last Glacial Maximum in local refugia. Slightly higher numbers of private haplotypes in Scandinavia than in central or north‐eastern Europe also favour an explanation with at least some local glacial survival. Low diversity in the southernmost contiguous region of the Scandinavian mountain range is probably a result of recent land uplift and late colonization. The Scandinavian lowland regional populations probably represent remains of an earlier widespread population that became increasingly restricted to small and isolated areas when the vegetation closed during the post‐glacial period. Some of the lowland populations require extensive management to survive. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 635–657.     

Phylogeography and genetic structure of the orchid Himantoglossum hircinum (L.) Spreng. across its European central–marginal gradient

Aim This study aims to link demographic traits and post‐glacial recolonization processes with genetic traits in Himantoglossum hircinum (L.) Spreng (Orchidaceae), and to test the implications of the central–marginal concept (CMC) in Europe. Location Twenty sites covering the entire European distribution range of this species. Methods We employed amplified fragment length polymorphism (AFLP) markers and performed a plastid microsatellite survey to assess genetic variation in 20 populations of H. hircinum located along central–marginal gradients. We measured demographic traits to assess population fitness along geographical gradients and to test for correlations between demographic traits and genetic diversity. We used genetic diversity indices and analyses of molecular variance (AMOVA) to test hypotheses of reduced genetic diversity and increased genetic differentiation and isolation from central to peripheral sites. We used Bayesian simulations to analyse genetic relationships among populations. Results Genetic diversity decreased significantly with increasing latitudinal and longitudinal distance from the distribution centre when excluding outlying populations. The AMOVA revealed significant genetic differentiation among populations (F_ST = 0.146) and an increase in genetic differentiation from the centre of the geographical range to the margins (except for the Atlantic group). Population fitness, expressed as the ratio N_R/N, decreased significantly with increasing latitudinal distance from the distribution centre. Flower production was lower in most eastern peripheral sites. The geographical distribution of microsatellite haplotypes suggests post‐glacial range expansion along three major migratory pathways, as also supported by individual membership fractions in six ancestral genetic clusters (C1–C6). No correlations between genetic diversity (e.g. diversity indices, haplotype frequency) and population demographic traits were detected. Main conclusions Reduced genetic diversity and haplotype frequency in H. hircinum at marginal sites reflect historical range expansions. Spatial variation in demographic traits could not explain genetic diversity patterns. For those sites that did not fit into the CMC, the genetic pattern is probably masked by other factors directly affecting either demography or population genetic structure. These include post‐glacial recolonization patterns and changes in habitat suitability due to climate change at the northern periphery. Our findings emphasize the importance of distinguishing historical effects from those caused by geographical variation in population demography of species when studying evolutionary and ecological processes at the range margins under global change.     

Determining patterns of genetic diversity and post‐glacial recolonization of western Canada in the Iowa golden saxifrage,Chrysosplenium iowense (Saxifragaceae), using inter‐simple sequence repeats

Chrysosplenium iowense Rydb. (Saxifragaceae) is a southern Canadian boreal forest species with a small number of disjunct populations occurring in the Driftless Area of northeastern Iowa and southeastern Minnesota. This disjunction is attributed to the actions of glacial movement and climate change during the Pleistocene. Populations within each of these distributions may have been isolated for 115 000 years or more and, although levels of genetic divergence between these regions may be significant, there is no morphological or cytological variation associated with this geographic break. We employed inter‐simple sequence repeat (ISSR) markers to determine patterns of genetic diversity within 12 populations (six Canadian; six Iowan) of C. iowense and elucidate the routes of post‐glacial recolonization for the species. Despite finding relatively high levels of genetic divergence (θ^II = 0.383, θ^II = 0.299) between Driftless Area and Canadian populations, there is no conclusive evidence of a speciation event within C. iowense. Analyses show moderate levels of genetic diversity within the species (H_T = 0.188), the majority of which is partitioned among individuals within populations (68.18%), which were similar across the northern (H_T = 0.234, H_T = 0.28) and southern (H_T = 0.189) ranges. Finally, the patterns of genetic diversity within C. iowense suggest that the Canadian range was established by migrants originating in now extinct refugial populations that existed outside the Driftless Area. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 815–823.     

In situ marker‐based assessment of leaf trait evolutionary potential in a marginal European beech population

Evolutionary processes are expected to be crucial for the adaptation of natural populations to environmental changes. In particular, the capacity of rear edge populations to evolve in response to the species limiting conditions remains a major issue that requires to address their evolutionary potential. In situ quantitative genetic studies based on molecular markers offer the possibility to estimate evolutionary potentials manipulating neither the environment nor the individuals on which phenotypes are measured. The goal of this study was to estimate heritability and genetic correlations of a suite of leaf functional traits involved in climate adaptation for a natural population of the tree Fagus sylvatica, growing at the rear edge of the species range. Using two marker‐based quantitative genetics approaches, we obtained consistent and significant estimates of heritability for leaf phenological (phenology of leaf flush), morphological (mass, area, ratio mass/area) and physiological (δ¹³C, nitrogen content) traits. Moreover, we found only one significant positive genetic correlation between leaf area and leaf mass, which likely reflected mechanical constraints. We conclude first that the studied population has considerable genetic diversity for important ecophysiological traits regarding drought adaptation and, second, that genetic correlations are not likely to impose strong genetic constraints to future population evolution. Our results bring important insights into the question of the capacity of rear edge populations to evolve.     

Geographical variation in reproductive traits and trade‐offs between size and number of eggs in the king ratsnake,Elaphe carinata

We collected gravid king ratsnakes (Elaphe carinata) from three geographically separated populations in Chenzhou (CZ), Lishui (LS) and Dinghai (DH) of China to study the geographical variation in female reproductive traits and trade‐offs between the size and number of eggs. Not all reproductive traits varied among the three populations. Of the traits examined, five (egg‐laying date, post‐oviposition body mass, clutch size, egg mass and egg width) differed among the three populations. The egg‐laying date, ranging from late June to early August, varied among populations in a geographically continuous trend, with females at the most northern latitude (DH) laying eggs latest, and females at the most southern latitude (CZ) laying eggs earliest. Such a trend was less evident or even absent in the other traits that differed among the three populations. CZ and DH females, although separated by a distance of approximately 1100 km as the crow flies, were similar to each other in most traits examined. LS females were distinguished from CZ and DH females by the fact that they laid a greater number of eggs, but these were smaller. The egg size–number trade‐off was evident in each of the three populations and, at a given level of relative fecundity, egg mass was significantly greater in the DH population than in the LS population. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 701–709.     

Allometry of the baculum and sexual size dimorphism in American martens and fishers (Mammalia: Mustelidae)

Genitalia are among the most variable of morphological traits, and recent research suggests that this variability may be the result of sexual selection. For example, large bacula may undergo post‐copulatory selection by females as a signal of male size and age. This should lead to positive allometry in baculum size. In addition to hyperallometry, sexually selected traits that undergo strong directional selection should exhibit high phenotypic variation. Nonetheless, in species in which pre‐copulatory selection predominates over post‐copulatory selection (such as those with male‐biased sexual size dimorphism), baculum allometry may be isometric or exhibit negative allometry. We tested this hypothesis using data collected from two highly dimorphic species of the Mustelidae, the American marten (Martes americana) and the fisher (Martes pennanti). Allometric relationships were weak, with only 4.5–10.1% of the variation in baculum length explained by body length. Because of this weak relationship, there was a large discrepancy in slope estimates derived from ordinary least squares and reduced major axis regression models. We conclude that stabilizing selection rather than sexual selection is the evolutionary force shaping variation in baculum length because allometric slopes were less than one (using the ordinary least squares regression model), a very low proportion of variance in baculum length was explained by body length, and there was low phenotypic variability in baculum length relative to other traits. We hypothesize that this pattern occurs because post‐copulatory selection plays a smaller role than pre‐copulatory selection (manifested as male‐biased sexual size dimorphism). We suggest a broader analysis of baculum allometry and sexual size dimorphism in the Mustelidae, and other taxonomic groups, coupled with a comparative analysis and with phylogenetic contrasts to test our hypothesis. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 955–963.     

Salicornia L. (Amaranthaceae) in South Africa and Namibia: rapid spread and ecological diversification of cryptic species

In Salicornia, morphology does not provide reliable diagnostic characters supporting the true extent of evolutionary divergence in the genus, and species concepts have been challenged by molecular analyses. Here, we report the results of an analysis of 91 accessions of the S. meyeriana complex from South Africa and Namibia using the measurements of 38 morphological traits and external transcribed spacer (ETS) sequence data. Morphological data were analysed using discriminant analysis, principal coordinate analysis and nonmetric multidimensional scaling. Phylogenetic divergence was compared with the geographical and ecological diversity of the sampled populations. Tree topology corresponds to geography and ecology, but not to morphology. Most clades have distinct distribution areas and ecological profiles related to tidal, supratidal or inland saline habitats. Salicornia probably diversified in habitats that have experienced regular fragmentation by marine transgression/regression cycles during the Pleistocene. We suggest that this radiation produced young, but genetically, geographically and ecologically well‐defined lineages. The lack of morphological signal reveals the existence of cryptic species in Salicornia and demonstrates the necessity of using molecular data to define taxa in this genus. We propose the recognition of two subspecies in the S. meyeriana complex: S. meyeriana subsp. meyeriana and S. meyeriana subsp. knysnaensis. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 175–186.     

Genetic and morphological differentiation in Populus nigra L.: isolation by colonization or isolation by adaptation?

Identifying processes underlying the genetic and morphological differences among populations is a central question of evolutionary biology. Forest trees typically contain high levels of neutral genetic variation, and genetic differences are often correlated with geographic distance between populations [isolation by distance (IBD)] or are due to historic vicariance events [isolation by colonization (IBC)]. In contrast, morphological differences are largely due to local adaptation. Here, we examined genetic (microsatellite) and morphological (from a common garden experiment) variation in Populus nigra L., European black poplar, collected from 13 sites across western Europe and grown in a common garden in Belgium. Significant genetic differentiation was observed, with populations from France displaying greater admixture than the distinct Spanish and central European gene pools, consistent with previously described glacial refugia (IBC). Many quantitative traits displayed a bimodal distribution, approximately corresponding to small‐leaf and large‐leaf ecotypes. Examination of nine climatic variables revealed the sampling locations to have diverse climates, and although the correlation between morphological and climatic differences was significant, the pattern was not consistent with strict local adaptation. Partial Mantel tests based on multivariate summary statistics identified significant residual correlation in comparisons of small‐leaf to large‐leaf ecotypes, and within the small‐leaf samples, but not within large‐leaf ecotypes, indicating that variation within the small‐leaf morphotype in particular may be adaptive. Some small‐leaf populations experience climates very similar to those in large‐leaf sites. We conclude that adaptive differentiation and persistent IBC acted in combination to produce the genetic and morphological patterns observed in P. nigra.     

Northern richness and southern poverty: contrasting genetic footprints of glacial refugia in the relictual tree Sciadopitys verticillata (Coniferales: Sciadopityaceae)

Sciadopitys verticillata is amongst the most relictual of all plants, being the last living member of an ancient conifer lineage, the Sciadopityaceae, and is distributed in small and disjunct populations in high rainfall regions of Japan. Although mega‐fossils indicate the persistence of the species within Japan through the Pleistocene glacial–interglacial cycles, how the species withstood the colder and drier climates of the glacials is not well known. The present study utilized phylogeography and palaeodistribution modelling to test whether the species survived within pollen‐based coastal temperate forest glacial refugia or within previously unidentified refugia close to its current range. Sixteen chloroplast haplotypes were found that displayed significant geographical structuring. Unexpectedly, northern populations in central Honshu most distant from coastal refugia had the highest chloroplast diversity and were differentiated from the south, a legacy of glacial populations possibly in inland river valleys close to its current northern range. By contrast, populations near putative coastal refugia in southern Japan, harboured the lower chloroplast diversity and were dominated by a single haplotype. Fragment size polymorphism at a highly variable and homoplasious mononucleotide repeat region in the trnT‐trnL intergenic spacer reinforced the contrasting patterns of diversity observed between northern and southern populations. The divergent histories of northern and southern populations revealed in the present study will inform the management of this globally significant conifer. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108 , 263–277.     

Geographic structure in the searching behaviour of a specialist parasitoid: combining molecular and behavioural approaches

An increasing number of studies have shown that the traits important to species interactions may differ geographically among populations or groups of populations within a single interacting species. We examined geographic structure in the searching behaviour of a recently discovered parasitoid in the genus Agathis (Hymenoptera: Braconidae) by examining the pattern of population structure obtained from sequence data of mitochondrial DNA cytochrome oxidase I and the pattern of population differentiation in female searching behaviour. Analyses of population structure showed no isolation by distance and suggested long distance dispersal among populations. This pattern is consistent with recent post‐glacial expansion of Agathis n. sp. Observations of searching behaviour demonstrated that populations of Agathis n. sp. differed in a subset of the behavioural traits examined and also one morphological trait. These population differences appear to be driven in part by local host plant characteristics, and based on the population structure of Agathis n. sp., have arisen relatively quickly in evolutionary time. This study suggests that the interaction between parasitoids and their host insects may exhibit substantial geographic variation, and studies that focus at the level of single populations or the species‐level may be missing much of the evolutionary dynamics of parasitoid–host interactions.     

Composition of Leaf n‐Alkanes in Three Satureja montana L. Subspecies from the Balkan Peninsula: Ecological and Taxonomic Aspects

The composition of the epicuticular leaf n‐alkanes of eight populations of three Satureja montana subspecies (S. montana L. subsp. pisidica (Wettst.) ?ili? , S. montana L. subsp. montana, and S. montana L. subsp. variegata (Host ) P. W. Ball ), from central and western areas of the Balkan Peninsula was characterized by GC‐FID and GC/MS analyses. In the leaf waxes, 15 n‐alkane homologs with chain‐lengths ranging from C₂₁ to C₃₅ were identified. The main n‐alkane in almost all samples was n‐nonacosane (C₂₉), but differences in the contents of three other dominant n‐alkanes allowed separating the coastal from the continental populations. The diversity and variability of the epicuticular‐leaf‐n‐alkane patterns and their relation to different geographic and bioclimatic parameters were analyzed by several statistical methods (principal component, discriminant, and cluster analyses as well as the Mantel test). All tests showed a high correlation between the leaf n‐alkane pattern and the geographical distribution of the investigated populations, confirming the differentiation between S. montana subsp. pisidica and the other two subspecies. The S. montana subsp. variegata and S. montana subsp. montana populations are geographically closer and their differentiation according to the leaf‐n‐alkane patterns was not clear, even though there was some indication of discrimination between them. Moreover, most of the bioclimatic parameters related to temperature were highly correlated with the differentiation of the coastal and the continental populations.     

Ecological character displacement in competing common green lacewings in Europe: a route to speciation?

Competitive interactions among the three common green lacewing species of the Chrysoperla complex in Europe are presented. Four morphological characters were registered as semi‐quantitative traits to assess variation between populations. Data were obtained from 325 adults originating from 14 locations. A statistical approach was performed in conjunction with observations of ecological traits and a survey of genetic relationships assessed by mitochondrial DNA cytochrome b analysis. The results indicate character displacement in Chrysoperla affinis when living in sympatry with Chrysoperla carnea. The morphological traits of Ch. affinis sympatric with Ch. carnea differ from those of allopatric Ch. affinis, although the genetic distance between those strains was weak. This was associated with a large difference in microhabitats and premating behaviour. Variation in courtship songs manifests a process of speciation within related populations. Thus, that ecological switching can also promote character displacement is supported. This suggests that character displacement acts through phenotypic variability and mediates negative interactions among species. These findings suggest that the highest rate of speciation occurs in groups of species in which competition is the strongest. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 292–300.     

Leaf diversity influences in-stream litter decomposition through effects on shredders

1. The functioning of many aquatic ecosystems is controlled by surrounding terrestrial ecosystems. In a view of growing interest in linking biodiversity to ecosystem‐level processes, we examined whether and how leaf diversity influences litter decomposition and consumers in streams. 2. We tested experimentally the hypothesis that the effects of leaf diversity on decomposition are determined by the responses of leaf consumers to resource–habitat heterogeneity. Leaves from three common riparian trees, beech (Fagus sylvatica), hazel (Corylus avellana) and ash (Fraxinus excelsior), were exposed alone and in all possible mixtures of two and three species in a stream. We analysed individual leaf species for decomposition rate, microbial respiration and mycelial biomass, and we determined the species composition, abundance and biomass of shredders in leaf bags. 3. We found that the decomposition of the fastest decomposing leaves (hazel and ash) was substantially stimulated (up to twofold higher than single species leaf packs) in mixtures containing beech leaves, which are refractory. In contrast, the decomposition of beech leaves was not affected by leaf mixing. Such species‐specific behaviour of leaves in species mixtures has been overlooked in previous studies that examined the overall decomposition of litter mixtures. 4. The effects of leaf diversity on decomposition varied with the abundance and biomass of shredders but not with microbial parameters. Beech leaves alone were less attractive to shredders than leaf packs made of hazel, ash or any mixture of species. Moreover, the presence of beech leaves in mixtures led to higher shredder abundance and biomass than we had expected from data from single species exposed alone. Lastly, we found that early instars of the caddisfly Potamophylax (the dominant shredder in terms of biomass) almost exclusively used the toughest material (i.e. beech leaves) to construct their cases. 5. Leaf pack heterogeneity may have altered shredder‐mediated decomposition. Shredders colonising diverse leaf packs benefited from the stable substratum provided by beech leaves, whereas ash and hazel leaves were primarily used as food. Thus, our findings provide strong evidence for an intimate linkage between the diversity of riparian vegetation and aquatic communities.     

Reticulate evolution patterns in western-Eurasian beeches

Reticulate evolution resulting from gene flow among diverged taxa was studied on the example of the Fagus sylvatica species complex in Europe and western Asia. F. sylvatica L. is one of the most widespread woody species of the Northern Hemisphere with two commonly recognized subspecies (namely, F. sylvatica subsp. sylvatica and F. sylvatica subsp. orientalis) and two putatively hybridogenous or intermediate taxa (F. moesiaca and F. taurica). Whereas the distribution of F. sylvatica subsp. sylvatica in Europe is almost continuous, the Asian range of F. sylvatica subsp. orientalis is fragmented into several larger regional populations. We studied genetic variation at 12 allozyme loci in 279 local subpopulations to assess whether previous contacts of regional populations left traces in their gene pools. Two approaches were used to infer potential reticulations: the reticulate network (Makarenkov and Legendre in J Comp Biol 11:195–212, 2004) and the neighbor-net network (Bryant and Moulton in Mol Biol Evol 21:255–265, 2004). A UPGMA dendrogram based on genetic distances between local populations revealed a high differentiation level within subsp. orientalis, whereby populations from Asia Minor, the Caucasus and the Alborz mts. were placed in different clusters. The reticulated network showed possible connections among adjacent populations, putatively resulting from previous contacts. The neighbor-net network also consisted of two major groups corresponding to F. sylvatica s. str. + F. moesiaca and F. orientalis including F. taurica. Regional populations of F. moesiaca are placed close to the basis of the European branch and are highly networked, indicating ambiguity in the phylogenetic signal. Similarly, three subgroups can be distinguished within the F. orientalis group and correspond well with broad regions of Asia Minor, the Caucasus and the Alborz. The Amanus regional population is intermediary between the subgroup of Asia Minor and the Caucasian subgroup. Crimean populations (i.e., putative hybrids) are placed near the basis of the subgraph. Two explanations of the observed reticulations are discussed: expansions and retreats of the range of beech associated with Pliocene and Pleistocene climatic fluctuations, resulting in contacts and exchanges of gene pools among regional populations, and sharing ancestral polymorphisms due to incomplete lineage sorting.