Geography is more important than host plant use for the population genetic structure of a generalist insect herbivore

Population divergence can occur due to mechanisms associated with geographic isolation and/or due to selection associated with different ecological niches. Much of the evidence for selection‐driven speciation has come from studies of specialist insect herbivores that use different host plant species; however, the influence of host plant use on population divergence of generalist herbivores remains poorly understood. We tested how diet breadth, host plant species and geographic distance influence population divergence of the fall webworm (Hyphantria cunea; FW). FW is a broadly distributed, extreme generalist herbivore consisting of two morphotypes that have been argued to represent two different species: black‐headed and red‐headed. We characterized the differentiation of FW populations at two geographic scales. We first analysed the influence of host plant and geographic distance on genetic divergence across a broad continental scale for both colour types. We further analysed the influence of host plant, diet breadth and geographic distance on divergence at a finer geographic scale focusing on red‐headed FW in Colorado. We found clear genetic and morphological distinction between red‐ and black‐headed FW, and Colorado FW formed a genetic cluster distinct from other locations. Although both geographic distance and host plant use were correlated with genetic distance, geographic distance accounted for up to 3× more variation in genetic distance than did host plant use. As a rare study investigating the genetic structure of a widespread generalist herbivore over a broad geographic range (up to 3,000 km), our study supports a strong role for geographic isolation in divergence in this system.     

Patterns of ecomorphological convergence among mainland and island Anolis lizards

Differing selective pressures on islands versus the mainland may produce alternative evolutionary outcomes among closely related lineages. Conversely, lineages may be constrained to produce similar outcomes in different mainland and island environments, or mainland and island environments may not differ significantly. Among the best‐studied island radiations are Caribbean Anolis lizards. Distinct morphotypes, or ‘ecomorphs’, have been described, and the same ecomorphs have evolved independently on each Greater Antillean island. The mainland Anolis radiation has received much less attention. We use a large morphological data set and a novel phylogenetic hypothesis to show that mainland Anolis did not evolve the same morphotypes as island Anolis, despite some island species being more closely related to mainland species than to island species that share their morphotype. A maximum of four of the six Caribbean ecomorphs were found to exist on the mainland, and just 15 of 123 mainland species are assignable to a Caribbean ecomorph. This result was insensitive to differing taxon samples and alternative phylogenetic hypotheses. Mainland convergence to a Caribbean ecomorph occurs only among species assigned to the grass‐bush ecomorph. Thus, the ecomorphs that have evolved convergently multiple times in the Caribbean have not evolved in parallel on the mainland. These results are consistent with the hypothesis that mainland and island environments offer different selective pressures. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 852–859.     

Host shifts and signal divergence: mating signals covary with host use in a complex of specialized plant‐feeding insects

A combination of divergent natural and sexual selection is a powerful cause of speciation. This conjunction of evolutionary forces may often occur when divergence is initiated by ecological differences between populations because local adaptation to new resources can lead to changes in sexual selection. The hypothesis that differences in resource use contribute to the evolution of reproductive isolation by altering the nature of sexual selection predicts that: (1) differences in sexual traits, such as signals and preferences, are an important source of reproductive isolation between species using different resources; (2) there are identifiable sources of selection on sexual traits that differ between species using different resources; and (3) signals vary between populations using different resources to a larger extent than between populations using the same resource at different localities. Testing these predictions requires a group of closely‐related species or populations that specialize on different resources and for which the traits involved in mate choice are known. The Enchenopa binotata species complex of treehoppers (Hemiptera: Membracidae) are host plant specialists in which speciation is associated with shifts to novel host plants. Mating in this complex is preceded by an exchange of vibrational signals transmitted through host plant stems, and the signal traits important for mate choice have been identified. In the E. binotata complex, previous work has supported the first two predictions: (1) signal differences between species are important in mate recognition and (2) host shifts can alter both the trait values favoured by sexual selection and the evolutionary response to that selection. In the present study, we tested the last prediction by conducting a large‐scale study of mating signal variation within and between the 11 species in the complex. We find that differences in host use are strongly associated with differences in signal traits important for mate recognition. This result supports the hypothesis that hosts shifts have led to speciation in this group in part through their influence on divergence in mate communication systems. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 60–72.     

Landscape and oceanic barriers shape dispersal and population structure in the island nematode Pristionchus pacificus

In this study evolutionary host plant patterns at ranks from order to species were analysed using spatial evolutionary and ecological vicariance analysis (SEEVA), based on a multigene phylogeny of 45 ascomycete fungal species. The objective was to understand speciation events and host associations in Ophiognomonia (Gnomoniaceae). Species of this genus are perithecial fungi that occur as endophytes, pathogens, and latent saprobes on plants in the families of Betulaceae, Fagaceae, Juglandaceae, Lauraceae, Malvaceae, Platanaceae, Rosaceae, Salicaceae, and Sapindaceae. A second objective was to determine whether speciation events are influenced by host conservatism, host specialization, or host switching at different taxonomic host ranks. Host differences between sister clades were interpreted using the divergence index (D) from the SEEVA analysis, ranging from 0 for no divergence to 1 for maximum possible divergence. Several fungal subclades showed clear patterns of host order/family conservatism (D = 1.00) for hosts in Betulaceae, Fagaceae, Juglandaceae, and Rosaceae. Clear trends of host specialization at host genus and species ranks (D = 1.00) were suggested within these host families. Independent host jumps were observed for two species at the family rank and three at the order rank. As a result of this study, host specificity and specialization is hypothesized as a mechanism that can strongly contribute to speciation patterns in fungal pathogens. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 1–16.     

Three new species, Lamellodiscus tubulicornis n. sp., L. magnicornis n. sp. and L. parvicornis n. sp. (Monogenea: Diplectanidae) from Gymnocranius spp. (Lethrinidae: Monotaxinae) off New Caledonia, with the proposal of the new morphological group ‘tubulicornis’ within Lamellodiscus Johnston & Tiegs, 1922

Three new species of Lamellodiscus are described from four (including two undescribed) species of Gymnocranius off New Caledonia, South Pacific. All three species have a similar body anatomy and morphology of the haptoral hard parts and are distinguished on the basis of the male copulatory organ (MCO). Lamellodiscus tubulicornis n. sp. (type-host: G. grandoculis; other host: Gymnocranius sp. B) has an MCO with a tube and horn; L. magnicornis n. sp. (type-host: G. grandoculis; other hosts: G. euanus, Gymnocranius sp. A and Gymnocranius sp. B) has an MCO with a long horn and a membrane; L. parvicornis n. sp. (type-host: G. euanus; other hosts: G. grandoculis and Gymnocranius sp. B) has an MCO with a small horn and a membrane. Lamellodiscus epsilon Yamaguti, 1968 is redescribed based on the type-specimens (from Monotaxis grandoculis off Hawaii). Lamellodiscus sp. is recorded from Gnathodentex aureolineatus off New Caledonia. All these five species have lamellodiscs that exhibit a unique characteristic: the second lamella forms an almost closed circle, in contrast to all other described species of Lamellodiscus in which the second lamella has the form of one or two crescents. Lamellodiscus spp. are usually classified in two groups, the ‘ignoratus’ and ‘elegans’ groups, according to the structure of the lamellodisc; we propose a new ‘tubulicornis’ group for these five species. In addition to their lamellodisc structure, species of the tubulicornis group are also characterised by their egg (elongate in contrast to tetrahedral in the two other groups) and their hosts (monotaxine lethrinids as opposed to mainly sparids). The generic diagnosis of Lamellodiscus given by Amine & Euzet (2005) is amended to include species with elongate eggs.     

Lack of association between winter coat colour and genetic population structure in the Japanese hare,Lepus brachyurus (Lagomorpha: Leporidae)

Seasonal changes in fur colour in some mammalian species have long attracted the attention of biologists, especially in species showing population variation in these seasonal changes. Genetic differences among populations that show differences in seasonal changes in coat colour have been poorly studied. Because the Japanese hare (Lepus brachyurus) has two allopatric morphotypes that show remarkably different coat colours in winter, we examined the population genetic structure of the species using partial sequences of the SRY gene and six autosomal genes: three coat colour‐related genes (ASIP, TYR, and MC1R) and three putatively neutral genes (TSHB, APOB, and SPTBN1). The phylogenetic tree of SRY sequences exhibited two distinct lineages that diverged approsimately 1 Mya. Although the two lineages exhibited a clear allopatric distribution, it was not consistent with the distribution of morphotypes. In addition, six nuclear gene sequences failed to reveal genetic differences between morphotypes. Population network trees for 11 expedient populations divided the populations into four groups. Genetic structure analysis revealed an admixture of four genetic clusters in L. brachyurus, two of which showed large genetic differences. Our results suggest ancient vicariance in L. brachyurus, and we detected no genetic differences between the two morphotypes. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 761–776.     

Phylogeny and floral hosts of a predominantly pollen generalist group of mason bees (Megachilidae: Osmiini)

Within the genus Osmia, the three subgenera Osmia, Monosmia, and Orientosmia form a closely‐related group of predominantly pollen generalist (‘polylectic’) mason bees. Despite the great scientific and economic interest in several species of this clade, which are promoted commercially for orchard pollination, their phylogenetic relationships remain poorly understood. We inferred the phylogeny of 21 Osmia species belonging to this clade by applying Bayesian and maximum likelihood methods based on five genes and morphology. Because our results revealed paraphyly of the largest subgenus (Osmia s.s.), we synonymized Monosmia and Orientosmia under Osmia s.s. Microscopical analysis of female pollen loads revealed that five species are specialized (‘oligolectic’) on Fabaceae or Boraginaceae, whereas the remaining species are polylectic, harvesting pollen from up to 19 plant families. Polylecty appears to be the ancestral state, with oligolectic lineages having evolved twice independently. Among the polylectic species, several intriguing patterns of host plant use were found, suggesting that host plant choice of these bees is constrained to different degrees and governed by flower morphology, pollen chemistry or nectar availability, thus supporting previous findings on predominantly oligolectic clades of bees. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 78–91.     

Testing for host‐associated differentiation in two egg parasitoids of a forest herbivore

Several studies underline the importance of ecological barriers and differential selection in driving sympatric speciation. Host‐associated differentiation (HAD) has been proposed as one of the mechanisms leading to sympatric speciation. However, it is still unclear how common HAD is or which are the factors that could promote it. In particular, not much is known about HAD in predators and parasitoids of herbivorous insects. One of the characteristics postulated to pre‐dispose insects to HAD is parthenogenesis as it may favour adaptive responses to particular environments, amplifying selected gene complexes. In this study, we used amplified fragment length polymorphism (AFLP) markers to determine whether HAD is present in two parthenogenetic egg parasitoids attacking the same herbivore species – the pine processionary moth, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) – on two host Pinus species. A total of 100 loci for 59 individuals sampled in four populations of Baryscapus servadeii (Domenichini) (Hymenoptera: Eulophidae), a specialist parasitoid, and 106 loci for 117 individuals sampled in six populations of Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae), a generalist parasitoid, were analysed. Levels of genetic differentiation were also assessed with an outlier analysis, checking for alleles associated to host plants. No evidence of HAD was detected in any of the two parasitoid species. We hypothesize that both the lack of strict parthenogenetic reproduction and the ectophagous nature of the insect host could explain the absence of HAD. The genetic variation observed in the generalist parasitoid responded to a pattern of local adaptation, whereas no relationship with either host or geography was found in the specialist parasitoid.     

Danaea (Marattiaceae) revisited: biodiversity,a new classification and ten new species of a neotropical fern genus

Revision of the Neotropical fern genus Danaea (Marattiaceae) has resulted in the recognition of ten new species, which are here for the first time presented to the scientific audience. Morphological and molecular data suggest that the genus consists of three monophyletic subgenera that are circumscribed here. A key is provided to aid species identification. The geographical ranges of the species are summarized and discussed with regard to speciation. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 360–385.     

Host plant preference and performance of the sibling species of butterflies <Emphasis Type="Italic">Leptidea sinapis</Emphasis> and <Emphasis Type="Italic">Leptidea reali</Emphasis>: a test of the trade-off hypothesis for food specialisation

A large proportion of phytophagous insect species are specialised on one or a few host plants, and female host plant preference is predicted to be tightly linked to high larval survival and performance on the preferred plant(s). Specialisation is likely favoured by selection under stable circumstances, since different host plant species are likely to differ in suitability—a pattern usually explained by the “trade-off hypothesis”, which posits that increased performance on a given plant comes at a cost of decreased performance on other plants. Host plant specialisation is also ascribed an important role in host shift speciation, where different incipient species specialise on different host plants. Hence, it is important to determine the role of host plants when studying species divergence and niche partitioning between closely related species, such as the butterfly species pair Leptidea sinapis and Leptidea reali. In Sweden, Leptidea sinapis is a habitat generalist, appearing in both forests and meadows, whereas Leptidea reali is specialised on meadows. Here, we study the female preference and larval survival and performance in terms of growth rate, pupal weight and development time on the seven most-utilised host plants. Both species showed similar host plant rank orders, and larvae survived and performed equally well on most plants with the exceptions of two rarely utilised forest plants. We therefore conclude that differences in preference or performance on plants from the two habitats do not drive, or maintain, niche separation, and we argue that the results of this study do not support the trade-off hypothesis for host plant specialisation, since the host plant generalist Leptidea sinapis survived and performed as well on the most preferred meadow host plant Lathyrus pratensis as did Leptidea reali although the generalist species also includes other plants in its host range. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The evolution of sex pheromones in an ecologically diverse genus of flies

In theory, pheromones important in specific mate recognition should evolve via large shifts in composition (saltational changes) at speciation events. However, where other mechanisms exist to ensure reproductive isolation, no such selection for rapid divergence is expected. In Bactrocera fruit flies (Diptera: Tephritidae), males produce volatile chemicals to attract females for mating. Bactrocera species exhibit great ecological diversity, with a wide range of geographical locations and host plants used. They also have other mechanisms, including temporal and behavioural differences, which ensure reproductive isolation. Therefore, we predicted that their sex pheromones would not exhibit rapid divergence at speciation events. In the present study, we tested this idea by combining data on male sex pheromone composition for 19 species of Bactrocera with a phylogeny constructed from DNA sequence data. Analyses of the combined data revealed positive correlations between pheromone differences and nucleotide divergence between species, and between the number of pheromone changes along the phylogeny and the branch lengths associated with these changes. These results suggest a gradual rather than saltational mode of evolution. However, remarkable differences in sex pheromones composition exist, even between closely-related species. It appears therefore that the mode of evolution of sex pheromones in Bactrocera is best described by rapid saltational changes associated with speciation, followed by gradual divergence thereafter. Furthermore, species that do not overlap ecologically are just as different pheromonally as species that do. Thus, large changes in pheromone composition appear to be achieved, even in cases where other mechanisms to ensure reproductive isolation exist. We suggest that these differences are closely associated with rapid changes in host plant use, which is a characteristic feature of Bactrocera speciation. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97 , 594–603.     

Divergent host plant adaptation drives the evolution of sexual isolation in the grasshopper Hesperotettix viridis (Orthoptera: Acrididae) in the absence of reinforcement

Early stages of lineage divergence in insect herbivores are often related to shifts in host plant use and divergence in mating capabilities, which may lead to sexual isolation of populations of herbivorous insects. We examined host preferences, degree of differentiation in mate choice, and divergence in cuticular morphology using near‐infrared spectroscopy in the grasshopper Hesperotettix viridis aiming to understand lineage divergence. In Kansas (USA), H. viridis is an oligophagous species feeding on Gutierrezia and Solidago host species. To identify incipient mechanisms of lineage divergence and isolation, we compared host choice, mate choice, and phenotypic divergence among natural grasshopper populations in zones of contact with populations encountering only one of the host species. A significant host‐based preference from the two host groups was detected in host‐paired feeding preference studies. No‐choice mate selection experiments revealed a preference for individuals collected from the same host species independent of geographic location, and little mating was observed between individuals collected from different host species. Female mate choice tests between males from the two host species resulted in 100% fidelity with respect to host use. Significant differentiation in colour and cuticular composition of individuals from different host plants was observed, which correlated positively with host choice and mate choice. No evidence for reinforcement in the zone of contact was detected, suggesting that divergent selection for host plant use promotes sexual isolation in this species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 866–878.     

Partitioning of herbivore hosts across time and food plants promotes diversification in the Megastigmus dorsalis oak gall parasitoid complex

Communities of insect herbivores and their natural enemies are rich and ecologically crucial components of terrestrial biodiversity. Understanding the processes that promote their origin and maintenance is thus of considerable interest. One major proposed mechanism is ecological speciation through host‐associated differentiation (HAD), the divergence of a polyphagous species first into ecological host races and eventually into more specialized daughter species. The rich chalcid parasitoid communities attacking cynipid oak gall wasp hosts are structured by multiple host traits, including food plant taxon, host gall phenology, and gall structure. Here, we ask whether the same traits structure genetic diversity within supposedly generalist parasitoid morphospecies. We use mitochondrial DNA sequences and microsatellite genotypes to quantify HAD for Megastigmus (Bootanomyia) dorsalis, a complex of two apparently generalist cryptic parasitoid species attacking oak galls. Ancient Balkan refugial populations showed phenological separation between the cryptic species, one primarily attacking spring galls, and the other mainly attacking autumn galls. The spring species also contained host races specializing on galls developing on different host‐plant lineages (sections Cerris vs. Quercus) within the oak genus Quercus. These results indicate more significant host‐associated structuring within oak gall parasitoid communities than previously thought and support ecological theory predicting the evolution of specialist lineages within generalist parasitoids. In contrast, UK populations of the autumn cryptic species associated with both native and recently invading oak gall wasps showed no evidence of population differentiation, implying rapid recruitment of native parasitoid populations onto invading hosts, and hence potential for natural biological control. This is of significance given recent rapid range expansion of the economically damaging chestnut gall wasp, Dryocosmus kuriphilus, in Europe.     

Growth and development of a generalist insect herbivore, Operophtera brumata, on original and alternative host plants

A generalist feeding strategy is common among eruptive insect herbivores but the ultimate reasons for a generalist strategy are not clear. Although generalist insect herbivores are able to complete their life cycle on several species of host plants, there is wide variation in the performance of individuals grown on different hosts. We examined whether different populations of Operophtera brumata are adapted to use the host species which is locally most abundant, and how the host plant affects growth and development of the insect. We reared two allopatric populations (eastern Finland, Prunus padus; south-west Finland, Quercus robur) on four species of host plants (Pr. padus, Populus tremula, Q. robur, Salix phylicifolia) from neonate larvae to the adult stage and measured the growth and development of individuals and the timing of adult hatching. The performance of both populations was best on Pr. padus, and the south-western population, originally on Q. robur, was well adapted to this host. The host affected the growth of females more than that of males. The host plant had an unexpected effect on hatching times of the adults. Individuals grown on the original host hatched in normal synchrony, i.e. males 6–7 days before females; but on alternative hosts this synchrony was disturbed. As is common in eruptive, capital-breeding generalist moths where female fecundity is linked to weight, host quality is critical for the flightless females of O. brumata. We suggest that in a heterogeneous environment the disturbing effect of alternative host plants on adult emergence may decrease the population density and growth rate compared to the potential maximum in a homogeneous environment. Received: 8 July 1999 / Accepted: 29 October 1999     

Discordant mitochondrial and nuclear gene phylogenies in emydid turtles: implications for speciation and conservation

Do phylogenies and branch lengths based on mitochondrial DNA (mtDNA) provide a reasonable approximation to those based on multiple nuclear loci? In the present study, we show widespread discordance between phylogenies based on mtDNA (two genes) and nuclear DNA (nucDNA; six loci) in a phylogenetic analysis of the turtle family Emydidae. We also find an unusual type of discordance involving the unexpected homogeneity of mtDNA sequences across species within genera. Of the 36 clades in the combined nucDNA phylogeny, 24 are contradicted by the mtDNA phylogeny, and six are strongly contested by each data set. Two genera (Graptemys, Pseudemys) show remarkably low mtDNA divergence among species, whereas the combined nuclear data show deep divergences and (for Pseudemys) strongly supported clades. These latter results suggest that the mitochondrial data alone are highly misleading about the rate of speciation in these genera and also about the species status of endangered Graptemys and Pseudemys species. In addition, despite a strongly supported phylogeny from the combined nuclear genes, we find extensive discordance between this tree and individual nuclear gene trees. Overall, the results obtained illustrate the potential dangers of making inferences about phylogeny, speciation, divergence times, and conservation from mtDNA data alone (or even from single nuclear genes), and suggest the benefits of using large numbers of unlinked nuclear loci. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 445–461.     

A molecular study of hybridization and homoploid hybrid speciation in Argyranthemum (Asteraceae) on Tenerife,the Canary Islands

Examples of recurrent homoploid hybrid speciation are few. One often‐cited example is Argyranthemum sundingii. This example includes two described species, A. lemsii and A. sundingii, resulting from reciprocal hybridization between A. broussonetii and A. frutescens on Tenerife. The four species and artificial F₁ and F₂ hybrids have previously been investigated morphologically and cytologically. Here, we examine population differentiation based on amplified fragment length polymorphism to get a better understanding of the genetic relationships among the species and the extent of hybridization. We aim to investigate if there is molecular support for treating the hybrid species as one taxon. Seven parental and four hybrid species populations (149 individuals) were analysed and we scored 85 polymorphic markers. A few (2–5) were private to each species but variably present and mostly rare. Our principal coordinate, STRUCTURE and BAPS analyses and AMOVA resulted in a clear separation of the parental species. The hybrid species were genetically less divergent but not identical. Our data indicate that hybridization and introgression are common in all these species on Tenerife and support the hypothesis that homoploid hybrid speciation has occurred repeatedly. Intrinsic post‐zygotic barriers are notoriously weak in Argyranthemum and reproductive isolation and speciation result primarily from strong ecological selection. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 19–31.     

HOST SWITCHING PROMOTES DIVERSITY IN HOST‐SPECIALIZED MYCOPARASITIC FUNGI: UNCOUPLED EVOLUTION IN THE BIATOROPSIS‐USNEA SYSTEM

Fungal mycoparasitism—fungi parasitizing other fungi—is a common lifestyle in some basal lineages of the basidiomycetes, particularly within the Tremellales. Relatively nonaggressive mycoparasitic fungi of this group are in general highly host specific, suggesting cospeciation as a plausible speciation mode in these associations. Species delimitation in the Tremellales is often challenging because morphological characters are scant. Host specificity is therefore a great aid to discriminate between species but appropriate species delimitation methods that account for actual diversity are needed to identify both specialist and generalist taxa and avoid inflating or underestimating diversity. We use the Biatoropsis‐Usnea system to study factors inducing parasite diversification. We employ morphological, ecological, and molecular data—methods including genealogical concordance phylogenetic species recognition (GCPSR) and the general mixed Yule‐coalescent (GMYC) model—to assess the diversity of fungi currently assigned to Biatoropsis usnearum. The degree of cospeciation in this association is assessed with two cophylogeny analysis tools (ParaFit and Jane 4.0). Biatoropsis constitutes a species complex formed by at least seven different independent lineages and host switching is a prominent force driving speciation, particularly in host specialists. Combining ITS and nLSU is recommended as barcode system in tremellalean fungi.     

When rare species become endangered: cryptic speciation in myrmecophilous hoverflies

The myrmecophilous hoverfly, Microdon mutabilis, is listed as a ‘Rare’ or ‘Nationally Notable Species’ in UK Red Data Books. As an obligate social parasite, feeding only from ant colonies, its life‐style satisfies theoretical conditions under which cryptic speciation is predicted to evolve; namely, strong selection for nonmorphological adaptations that enhance its exploitation of a local subspecies or populations of its host. Samples of larvae and pupae in Ireland, Scotland and England showed that M. mutabilis exploits a single and different host ant species on different sites across its range. In nine southern English colonies, 95.6% of infested nests were of Myrmica scabrinodis whereas in six Irish and two Scottish colonies 100% and 94.2%, respectively, of the infested nests were of Formica lemani, despite M. scabrinodis being common at all sites. Although the adults from ‘scabrinodis’ (and lemani) populations are cryptic, morphometric measurements of pupae showed consistent diagnostic characters that were sufficiently distinct for these ecotypes to be classed as separate species. We conclude that M. mutabilis is the ‘lemani‐type’ and designate the ‘scabrinodis‐type’ as a new species, Microdon myrmicae spec. nov. Thus, one of the listed threatened species of the British Isles becomes two species, each possessing about half the number of populations and occupying half the range of the original ‘species’. Each also inhabits a different serai stage within grassland or heathland, and will require a different management regime if its declining populations are to be conserved. ‘M. mutabilis’ is reported with other host ant species on the European continent. In the light of our results, these may prove to be additional cryptic species. We suggest that cryptic speciation is apt to evolve in species, such as myrmecophiles, endoparasites and koinobiont parasitoids, whose life‐styles result in strong selection on their physiological or behavioural characters. The implications for Red Data Book classifications and for practical conservation are discussed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75 , 291–300.     

Distribution,host plant affiliation,phenology, and phylogeny of walnut‐infesting Rhagoletis flies (Diptera: Tephritidae) in Mexico

Many taxa of Nearctic origin have diversified in the subtropical highlands of Mexico. In particular, flies in the genus Rhagoletis have undergone episodes of isolation and gene flow during Pleistocene glaciations and post‐glacial times that have produced lineage differentiation and reproductive isolation. To reach a better understanding of the phylogeography of the genus Rhagoletis, a host plant survey of the walnut‐infesting Rhagoletis suavis species group was conducted across sixteen states comprising 34 different collecting sites in Mexico over a 9‐year period. Five species of Juglans were found to be infested by three species of walnut‐attacking Rhagoletis flies. Several species of parasitoids were also recovered from collections, but in contrast to their walnut fly hosts, they revealed little evidence for host or geographic subdivision. There was no consistent difference in mean eclosion time between walnut fly species or populations associated with different host walnuts in Mexico, unlike the case for other Rhagoletis species, in which allochronic isolation arising from variation in diapause timing is a major ecological adaptation, reproductively isolating flies. We compare the distribution of R. suavis flies in Mexico with those of other Rhagoletis species attacking hawthorns and cherries, and discuss its implications for population divergence and speciation. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 765–779.