From one to ten in a single stroke--resolving the European Eumidasanguinea (Phyllodocidae, Annelida) species complex

We investigate the genetic structure of European lineages of the polychaete Eumida sanguinea with mitochondrial COI and nuclear ITS, and demonstrate the presence of ten cryptic species. Within the E. sanguinea species complex there are six different white pigmentation patterns but only three of these are unique for a single species. No other consistent morphological differences were observed. We give new species names to seven of the lineages from our study, providing examples of combined morphological and molecular diagnoses, apply the available name E. sanguinea to one species, and leave two lineages with single representatives unnamed. We also include new data and a diagnosis for the poorly known E. notata, which also belongs to the E. sanguinea species complex.     

Marking of Nest Entrances and Vicinity in Two Related Tetramorium Ant Species (Hymenoptera: Formicidae)

Workers of the related ants Tetramorium impurum and T. caespitum mark the vicinity of their nest entrances in a species-specific manner, as seen by similarities between the behavior of nestmates and that of alien conspecifics (e.g., concerning aggregation, locomotion, orientation, tendency to move, and agonistic behavior). Additionally, they mark the inside of their nest entrances in a colony-specific manner, as seen by the following differences in behavior. Nestmates aggregate on these areas, walk rather slowly, but freely and essentially in the middle of the areas, come toward and very near such areas, are not inclined to escape, and are ready to attack possible intruders. Alien conspecifics do not aggregate, walk quickly, and are reluctant to stay on the areas, come neither toward nor very near the areas, are inclined to escape, and often open their mandibles, mainly when in front of a resident. The marking of the nest entrances is performed by T. impurum in 30 min and by T. caespitum in 15 min. If not reinforced, the marking by both species vanishes in 60 and 50 min, respectively. Extracts of hindlegs, metathorax, or metapleural glands produce in unmarked areas the ethological effect of marked entrances. It may be hypothesized that the marking factor is produced by the workers' metapleural glands and deposited onto the ground, via the hindlegs of ants leaving the nest. A worker's head has a species- but not a colony-specific ethological effect. An isolated alien conspecific's head is never attacked, whereas a thorax with abdomen is. This explains why, by opening its mandibles (and then presumably emitting a mandibular gland pheromone), a conspecific ant momentarily inhibits the attack of a nonnestmate. According to Hölldobler and Wilson (1990), the marking of the inside of T. impurum and T. caespitum nest entrances is a territorial and nest-entrance marking, whereas the marking of the close vicinity of the entrances is a home-range marking, as is the marking of the foraging area. These markings are in accordance with the fact that T. impurum foragers deposit their trail pheromone as far as the opening of the nest entrance.     

Genetic Polymorphism of 11 Allozyme Loci in Populations of Wall Lizards (Podarcis sp.) from the Iberian Peninsula and North Africa

The taxonomy of Iberian and North African wall lizards (Podarcis sp.) has been controversial. Recently, morphological and mtDNA sequence data have provided new information on differentiation within these lacertids. To compare these results to those provided by nuclear markers, we investigated variation at 11 polymorphic protein loci using conventional electrophoresis and isoelectric focusing in 11 populations belonging to seven different mtDNA lineages. A total of 62 alleles were found. Populations belonging to the same mtDNA type presented high genetic similarity, whereas strong differentiation was observed between groups. These results are consistent with those previously obtained from morphological and mtDNA analysis and support the idea that Iberian and North African Podarcis are composed of several well-differentiated entities, some of which are already recognized as species, whereas others (belonging to the P. hispanica complex) clearly need taxonomic revision.     

Cryptic diversification in ancient asexuals: evidence from the bdelloid rotifer Philodina flaviceps

Bdelloid rotifers, darwinulid ostracods and some oribatid mites have been called 'ancient asexuals' as they speciated and survived over long-term evolutionary timescale without sexual recombination. Data on their genetic diversification are contrasting: within-species diversification is present mostly at a continental scale in a parthenogenetic oribatid mite, whereas almost no genetic diversification at all seems to occur within darwinulid ostracod species. Strangely enough, no clear data for bdelloid rotifers are available so far. In this paper, we analyse partial COI mtDNA sequences to show that a bdelloid rotifer, Philodina flaviceps, so far considered a single traditional morphological species, has actually been able to diversify into at least nine distinct evolutionary entities, with genetic distances between lineages comparable with those between different traditional species within the same genus. We discovered that local coexistence of such different independent lineages is very common: up to four lineages were found in a same stream, and up to three in a single moss sample of 5 cm(2). In contrast to the large-scale geographic pattern that has recently been reported in the oribatid mite, the spatial distribution of the bdelloid lineages provided evidence of micro-phylogeographic patterns. If the mtDNA diversity indicates that the lineages are independent and represent sympatric cryptic species within P. flaviceps, then the actual bdelloid diversity can be expected to be much greater than that recognized today.     

Fine-scale genetic structure, phylogeny and systematics of threatened crayfish species complex

Systematic uncertainties in the crayfish Austropotamobius pallipes are well grounded by the number of species and subspecies described using different approaches, causing scientists to define this taxon as "complex". However, a key task that conservation programmes are facing regarding the recent and drastic decline of European populations, is the coherent systematic classification of this threatened species. Here we present results obtained by coupling mtDNA and genome analysis suggestive of a novel evolutionary framework to explain the relationships among phylogenetic lineages of A. pallipes. The direct sequencing of mtDNA COI gene fragment revealed a strong geographic structure with four distinct haplogroups separated by a range of 5-25 mutations. However, mitochondrial data were not supported by genomic fingerprinting based on 535 AFLP polymorphisms. Nuclear markers showed an unexpected moderate level of genetic differentiation and the absence of any geographic structure. Consequently, this study proposes that the taxonomic hypothesis of a single species of A. pallipes settling the Italian continental waters, is affected by complex evolutionary events. To solve the paradox, we hypothesized an evolutive scenario in which the separation of ancient mtDNA lineages likely occurred before the latest glacial periods. However, the speciation process remained incomplete due to secondary intensive postglacial contacts that forced the mingling of the genomes, and confounds the phylogeographic signature still detectable within mtDNA. Postglacial dispersion and the following demographic events, such as founder effects, drift and bottlenecks, abruptly depleted the local mtDNA variation, and shaped the current genetic population structure of white-clawed crayfish.     

Two mitochondrial lineages in Korean freshwater Corbicula (Corbiculidae: bivalvia)

The Korean freshwater Corbicula was surveyed genetically by sequencing 614-bp homologous fragment of mitochondrial cytochrome oxidase I subunit. Among a total of 127 individuals collected from 12 Korean freshwater localities we found only two COI haplotypes and these differed by a total of 9 base substitutions. Although the sequence divergence between the two haplotypes is moderate (p = 1.47%), placing the two mitotypic sequences in the context of Asian mtDNA phylogeny reveals that Korean freshwater Corbicula is comprised of two independent freshwater mitochondrial lineages. These results are in serious disagreement with the long-standing conclusions of earlier conchology-based taxonomic work on Korean Corbicula in which a number of species names (a minimum of 10 nominal species) have been used. This indicates that morphological characteristics alone are poor criteria for species-level identification in this group. In addition, our COI dataset shows that there is an extremely low level of genetic variation in Korean freshwater populations, suggesting that these populations have passed through a severe population bottleneck that greatly reduced their genetic variability. Our data also provide new information on the biogeographic distribution of Korean freshwater Corbicula. When haplotypic frequencies were compared, it was evident that the two Korean freshwater mitochondrial lineages have achieved very different distribution ranges: the predominant lineage (FWKR1) is widely distributed in Korean freshwater systems, whereas the minor lineage (FWKR2) is restricted to a relatively narrow range.     

Navigating the mtDNA road map out of the morphological maze: interpreting morphological variation in the diverse Monomorium rothsteini (Forel) complex (Hymenoptera: Formicidae)

Monomorium is a large and diverse ant genus with speciose radiations in both the Afrotropical and Australian regions. According to the most recent taxonomic revision, many Australian species are characterised by very broad distributions and variable morphology, which suggests that some species may be unrecognised species complexes. With a continent‐wide distribution and diverse yet overlapping morphology, M. rothsteini (Forel) is representative of the greater challenge that exists in Australian Monomorium systematics. Here we investigate species boundaries in M. rothsteini using a molecular phylogenetic framework to interpret the complex overlap of nine morphological characters (with 31 states) and examine biogeographic relationships among the lineages. Bayesian inference resolved 38 mtDNA lineages that were morphologically separable, at least from their sister lineage. Although the morphological characters were intermixed across the phylogeny, instances of inseparable morphology among sister clades was rare. Seventeen lineages exhibited complete morphological overlap with one or more other lineages and could not be separated by Principal Component Analysis based on 12 morphometric variables. Two‐thirds of all lineages occurred sympatrically with one or more both genetically and morphologically divergent lineages. The two nuclear markers EF1αF2 and wingless were used to generate haplotype networks which were characterised by a star‐like pattern indicative of a rapid and recent radiation. Several haplotypes for both nuclear gene regions were shared among individuals occurring in separate mtDNA clades which we were also unable to distinguish morphologically or that were occurring in sympatry, indicating possible introgression in both the mtDNA and nuclear genomes. Clear biogeographic affinities among samples within a lineage were detected but there was no overall pattern in the biogeographic relationships among the lineages. We conclude that M. rothsteini is a large species complex that has undergone a complex evolutionary history following aridification of the Australian continent, and discuss the implications of this conclusion for the systematics of Australian Monomorium more generally.     

The wheat curl mite Aceria tosichella (Acari: Eriophyoidea) is a complex of cryptic lineages with divergent host ranges: evidence from molecular and plant bioassay data

Aceria tosichella (the wheat curl mite, WCM) is a global pest of wheat and other cereals, causing losses by direct damage, as well as the transmission of plant viruses. The mite is considered to have an unusually wide host range for an eriophyoid species. The present study tested the commonly held assumption that WCM is a single, highly polyphagous species by assessing the host range of genetically distinct lineages of WCM occurring in Poland on different host plants. Genotyping was performed by analyzing nucleotide sequence data from fragments of the mitochondrial cytochrome c oxidase subunit I (COI) and the nuclear D2 region of 28S rDNA. Mean between‐lineage distance estimated using COI data was found to be one order of magnitude greater than the within‐clade lineage and, in some cases, comparable to distances between WCM lineages and a congeneric outgroup species. Host acceptance was tested by quantifying population growth for different WCM mitochondrial (mt)DNA lineages when transferred from source host plants to test plants. These experiments revealed significant differences in host colonization ability between mtDNA lineages, ranging from highly polyphagous to more host‐specific. The present study reveals that WCM is composed of several discrete genetic lineages with divergent host‐acceptance and specificity traits. Genetic variation for host acceptance within A. tosichella s.l. may act as a reproductive barrier between these lineages, most of which had narrow host ranges. Two lineages appear to have high pest potential on cereals, whereas several others appear to specialize on wild grass species. We conclude that WCM is not a homogeneous species comprising polyphagous panmictic populations rather it is a complex of genetically distinct lineages with variable host ranges and therefore variable pest potential. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 165–180.     

Phylogeny of Triatomine Vectors of Trypanosoma cruzi Suggested by Mitochondrial DNA Sequences

The subfamily Triatominae (Hemiptera: Reduviidae) comprises hematophagous insects, most of which are actual or potential vectors of Trypanosoma cruzi, the protozoan agent of Chagas' disease (American trypanosomiasis). DNA sequence comparisons of mitochondrial DNA (mtDNA) genes were used to infer phylogenetic relationships among 32 species of the subfamily Triatominae, 26 belonging to the genus Triatoma and six species of different genera. We analyzed mtDNA fragments of the 12S and 16S ribosomal RNA genes (totaling 848-851 bp) from each of the 32 species, as well as of the cytochrome oxidase I (COI, 1447 bp) gene from nine. The phylogenetic analyses unambiguously supported several clusters within the genus Triatoma. In the morphological classification, T. costalimai was placed tentatively within the infestans complex while T. guazu was not included in any Triatoma complex. The placement of these species in the molecular phylogeny indicated that both belong to the infestans complex. We confirmed with a strong support the inclusion of T. circummaculata, a member of a different complex based on morphology, within the infestans complex. On the other hand, the present phylogenetics analysis did not support the monophyly of the infestans complex species as it was suggested in our previous studies. While no strong inference of polyphyly of the genus Triatoma was provided by the bootstrap analyses, the other species belonging to Triatomini analyzed could not be distinguished from the species of Triatoma.     

Pleistocene effects on the European freshwater fish fauna: double origin of the cobitid genus Sabanejewia in the Danube basin (Osteichthyes: Cobitidae)

Biogeographical hypotheses of European freshwater fishes were inferred using phylogeographic analysis of the complete cytochrome b and ATP synthase 8 and 6 mitochondrial genes (1982bp). To test the relative importance of drainage origin versus Pleistocene glaciations in the origin of primary freshwater fishes in Europe, we reconstructed the phylogenetic relationships of the genus Sabanejewia which is distributed in European waters. The phylogenetic relationships recovered for the genus Sabanejewia (n=75) provide support for the monophyly of six main evolutionary mtDNA lineages: Sabanejewia larvata, Sabanejewia romanica, Sabanejewia aurata/Sabanejewia caucasica, Sabanejewia kubanica, Sabanejewia baltica, and the Danubian-Balkanian complex. The Caucasian-Caspian mtDNA lineages, S. kubanica, S. aurata/S. caucasica, and the Northern European S. baltica represents the sister group of the Danubian-Balkanian complex mtDNAclade, supporting a Caucasian-Northern European origin of most of mtDNA lineages of the Central European freshwater fish fauna. The mtDNA divergence observed between the Danubian Sabanejewia species is too dissimilar to support their contemporary origin. Rather, the mtDNA data suggest that the Danubian Sabanejewia lineages most likely have a double origin, indicating that the European Sabanejewia lineages have experienced different historical processes for the following reasons. First, the origin of the S. larvata and S. romanica mtDNA clades predates the origin of the Danubian-Balkanian complex, and our results showed that the completion of the Alps and the origin of the Danube drainage seem to have promoted the speciation of the earliest Sabanejewia clades in the Miocene. Second, small genetic distances and the geographical pattern found within the Danubian-Balkanian complex clade indicate that the lineages included in this clade spread recently across the Danube and Greek river drainages. The inclusion of the S. balcanica species within all mtDNA lineages suggests that cyclical cold periods during the Pleistocene glaciations have favoured its rapid expansion and genetic homogenisation across Central European and Greek waters.     

DNA sequence variation at the mitochondrial cytochrome oxidase I subunit among pheromotypes of the sibling taxa Diachrysia chrysitis and D. tutti (Lepidoptera: Noctuidae)

We surveyed variation in the mtDNA cytochrome oxidase subunit I (COI) gene in the noctuid sibling species Diachrysia chrysitis and D. tutti , whose taxonomic status has been queried. Taxonomically, these taxa are separated on the basis of wing pattern and time of flight period. Samples were field-collected from different geographical sites where pheromone traps were baited to attract males containing different mixtures of two blends of pheromone components: (Z)-5-decenyl acetate and (Z)-7-decenyl acetate. Most specimens were sequenced over a 709-bp segment of the COI gene. Single specimens each of D. chrysitis and D. tutti were sequenced over a region of 1.5 kilobases. mtDNA variation within and among D. chrysitis and D. tutti is most simply interpreted as DNA polymorphism within a complex of closely related, but well-differentiated pheromotypes. Maximal nucleotide difference per site among haplotypes was 0.28%, which is at the lower end of the range for interspecific mtDNA nucleotide diversity in Lepidoptera. Coefficient of differentiation G _st was c . 76.3% ± 11.7%, a typical value at the intraspecific level. Sequences revealed stable diagnostic differences between pheromotypes irrespective of geographical origin. Identification of pheromone-trapped males based on morphology remained vague and uncorrelated to mtDNA haplotypes. The survey illustrated the potential utility of direct DNA sequencing in assessing lineage structures or taxon limits among moths that have been previously found to be different using the pheromone mate recognition system, but which have not been subjected to DNA analysis. The results of mtDNA analyses presented here support recognition of chrysitis and tutti lineages as presented in previous allozyme studies.     

High Levels of Diversity Uncovered in a Widespread Nominal Taxon: Continental Phylogeography of the Neotropical Tree Frog Dendropsophus minutus

Species distributed across vast continental areas and across major biomes provide unique model systems for studies of biotic diversification, yet also constitute daunting financial, logistic and political challenges for data collection across such regions. The tree frog Dendropsophus minutus (Anura: Hylidae) is a nominal species, continentally distributed in South America, that may represent a complex of multiple species, each with a more limited distribution. To understand the spatial pattern of molecular diversity throughout the range of this species complex, we obtained DNA sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and the 16S rhibosomal gene (16S) for 407 samples of D. minutus and closely related species distributed across eleven countries, effectively comprising the entire range of the group. We performed phylogenetic and spatially explicit phylogeographic analyses to assess the genetic structure of lineages and infer ancestral areas. We found 43 statistically supported, deep mitochondrial lineages, several of which may represent currently unrecognized distinct species. One major clade, containing 25 divergent lineages, includes samples from the type locality of D. minutus. We defined that clade as the D. minutus complex. The remaining lineages together with the D. minutus complex constitute the D. minutus species group. Historical analyses support an Amazonian origin for the D. minutus species group with a subsequent dispersal to eastern Brazil where the D. minutus complex originated. According to our dataset, a total of eight mtDNA lineages have ranges >100,000 km². One of them occupies an area of almost one million km² encompassing multiple biomes. Our results, at a spatial scale and resolution unprecedented for a Neotropical vertebrate, confirm that widespread amphibian species occur in lowland South America, yet at the same time a large proportion of cryptic diversity still remains to be discovered.     

Glacial cycles as an allopatric speciation pump in north‐eastern American freshwater fishes

Allopatric speciation may be the principal mechanism generating new species. Yet, it remains difficult to judge the generality of this process because few studies have provided evidence that geographic isolation has triggered the development of reproductive isolation over multiple species of a regional fauna. Here, we first combine results from new empirical data sets (7 taxa) and published literature (9 taxa) to show that the eastern Great Lakes drainage represents a multispecies suture zone for glacial lineages of freshwater fishes with variable levels of genetic divergence. Second, we performed amplified fragment length polymorphism analyses among four pairs of lineages. Results indicate that lineages with relatively deep levels of mtDNA 5′ COI (barcode) sequence divergence (>2%) developed strong reproductive barriers, while lineages with lower levels of divergence show weaker reproductive isolation when found in sympatry. This suggests that a threshold of 2% sequence divergence at mtDNA could be used as a first step to flag cryptic species in North American freshwater fishes. By describing different levels of divergence and reproductive isolation in different co‐occurring fishes, we offer strong evidence that allopatric speciation has contributed significantly to the diversification of north‐eastern American freshwater fishes and confirm that Pleistocene glacial cycles can be viewed as a ‘speciation pump’ that played a predominant role in generating biodiversity.     

Microsatellite analysis supports the existence of three cryptic species within the bumble bee <Emphasis Type="Italic">Bombus lucorum sensu lato</Emphasis>

Mitochondrial cytochrome oxidase I (COI) partial sequences are widely used in taxonomy for species identification. Increasingly, these sequence identities are combined with modelling approaches to delineate species. Yet the validity of species delineation based on such DNA ‘barcodes’ is rarely tested and may be called into question by phenomena such as ancestral polymorphisms in DNA sequences, phylogeographic divergence, mitochondrial introgression and hybridization, or distortion of mitochondrial inheritance through such factors as Wolbachia infection. The common and widespread European bumble bee Bombus lucorum s. lato contains three distinct mitochondrial DNA lineages that are assumed to represent three cryptic species, namely Bombus cryptarum, B. lucorum s. str. and B. magnus. To test whether nuclear gene pools of the three putative species were differentiated, we genotyped 304 sympatric members of the lucorum complex (54 B. cryptarum females, 168 B. lucorum s. str. females and 82 B. magnus females, as defined using mtDNA COI haplotypes) from 11 localities spread across the island of Ireland at seven nuclear microsatellite loci. Multilocus genotypes clustered into three discrete groups that largely corresponded to the three mtDNA lineages: B. cryptarum, B. lucorum s. str. and B. magnus. The good fit of mitochondrial haplotype to nuclear (microsatellite) genotypic data supports the view that these three bumble bee taxa are reproductively isolated species, as well as providing a vindication of species identity using so-called DNA barcodes.     

New genus of Cupressaceae from the Upper Cretaceous of Patagonia (Argentina) fills a gap in the evolution of the ovuliferous complex in the family

The conifer family Cupressaceae encompasses seven subfamilies. Five of them were once considered to constitute the family Taxodiaceae, later eliminated because of its paraphyletic nature but remaining as an informal category for early-diverging Cupressaceae lineages. Among the taxodiaceous subfamilies, Athrotaxoideae shows a unique morphology in its ovuliferous complexes (OCs) and a phylogenetically unexplored fossil record. We describe the new genus and species Patagotaxodia lefipanensis, based on OC adpressions associated with leafy branches collected at the Maastrichtian section of the Lefipán Formation (Patagonia, Argentina), and we refer it to Athrotaxoideae. We include Patagotaxodia in total evidence phylogenetic analysis to test its affinity, and we recover it within the subfamilies Athrotaxoideae or Cunninghamioideae. However, we argue that the characters supporting the athrotaxoid affinity are more meaningful in a taxodiaceous systematic context. This placement is also supported by taxon inclusion-exclusion experiments. We discuss the position of other Cretaceous athrotaxoid records. With basis on the morphological insights provided by the OC morphology of extant and extinct Athrotaxoideae, we study the evolution of the OC morphology in the family in a phylogenetic context and discuss the results in the light of the fossil record of the family. We discuss how and when the different morphologies appeared in the family. Based on phylogenetic, temporal, morphological, and ontogenetic evidence, we conclude that the OC morphology shown by the subfamily Athrotaxoideae is intermediate between two of the most common morphologies within extant and extinct Cupressaceae species, one of which would show adaptative advantages over basal morphologies.     

Mitochondrial DNA diversity and taxa delineation in the land snails of the Iberus gualtieranus (Pulmonata,Helicidae) complex

Iberus gualtieranus is a species complex of land snails that is endemic to the Iberian Peninsula. The species taxonomy of the group is based merely on the basis of shell morphology, but validity of the existing taxonomy is uncertain. Using mitochondrial DNA (mtDNA) data (cytochrome oxidase I and 16S rRNA sequences) we were able to validate the observed phylogenetic taxa within the I. gualtieranus s.l. complex by means of the analysis of specimens of the different morphospecies, together with the study of topotypes. Strong incongruences were obtained between morphology and molecular data. The Iberus alonensis morphospecies comprised several genetically divergent but morphologically cryptic lineages. Considering (1) the allopatric distribution of the operational taxonomic units (OTUs), (2) the morphological differentiation, (3) the possible occurrence of hybridization among the different lineages, and (4) the strong differentiation of the mtDNA phylogroups, we suggest the main lineages obtained, for the time being, may be treated as evolutionary species. The robust phylogenetic reconstruction obtained allows us to consider I. alonensis s.s., Iberus campesinus, Iberus carthaginiensis, and Iberus gualtieranus s.s. as valid species. Two additional unnominated taxa of the alonensis shell type have also been identified. Further subdivisions are also considered, including Iberus gualtieranus mariae and Iberus gualtieranus ornatissimus. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 722–737.     

Introgression and selection shaped the evolutionary history of sympatric sister‐species of coral reef fishes (genus: Haemulon)

Closely related marine species with large overlapping ranges provide opportunities to study mechanisms of speciation, particularly when there is evidence of gene flow between such lineages. Here, we focus on a case of hybridization between the sympatric sister‐species Haemulon maculicauda and H. flaviguttatum, using Sanger sequencing of mitochondrial and nuclear loci, as well as 2422 single nucleotide polymorphisms (SNPs) obtained via restriction site‐associated DNA sequencing (RADSeq). Mitochondrial markers revealed a shared haplotype for COI and low divergence for CytB and CR between the sister‐species. On the other hand, complete lineage sorting was observed at the nuclear loci and most of the SNPs. Under neutral expectations, the smaller effective population size of mtDNA should lead to fixation of mutations faster than nDNA. Thus, these results suggest that hybridization in the recent past (0.174–0.263 Ma) led to introgression of the mtDNA, with little effect on the nuclear genome. Analyses of the SNP data revealed 28 loci potentially under divergent selection between the two species. The combination of mtDNA introgression and limited nuclear DNA introgression provides a mechanism for the evolution of independent lineages despite recurrent hybridization events. This study adds to the growing body of research that exemplifies how genetic divergence can be maintained in the presence of gene flow between closely related species.     

A three‐way contact zone between forms of Patella rustica (Mollusca: Patellidae) in the central Mediterranean Sea

Previous studies have reported the occurrence of three differentiated mtDNA lineages within Patella rustica in the Mediterranean Sea. Two hypotheses have been proposed to explain these observations: (1) the maintenance of ancestral polymorphism within a single species; (2) the occurrence of cryptic species not identified previously. To distinguish between these hypotheses, we screened the genetic variability at nine allozyme loci, an intron from the α‐amylase gene and a mitochondrial gene for 187 individuals of P. rustica sampled from seven Mediterranean localities. Eight additional localities were screened for the last two markers to place the differentiated lineages in a clear geographic context. Our results demonstrate that the three mtDNA lineages correspond to three distinct nuclear genotype clusters and provide further details on their distribution: the cluster corresponding to the mtDNA lineage from the Atlantic and western Mediterranean extends as far as the south coast of Italy, whereas the remaining two clusters occur in sympatry in the eastern Mediterranean. One of the eastern Mediterranean clusters is highly differentiated and seems to be reproductively isolated from the codistributed form; we therefore suggest that it corresponds to a new species. The remaining two clusters are less differentiated and form a contact zone across south Italian shores. This three‐way contact zone constitutes an interesting model for the study of speciation in the marine realm. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 154–169.