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Host Shifts (host + shift)
Selected AbstractsRAPID SPECIATION FOLLOWING RECENT HOST SHIFTS IN THE PLANT PATHOGENIC FUNGUS RHYNCHOSPORIUMEVOLUTION, Issue 6 2008Pascal L. Zaffarano Agriculture played a significant role in increasing the number of pathogen species and in expanding their geographic range during the last 10,000 years. We tested the hypothesis that a fungal pathogen of cereals and grasses emerged at the time of domestication of cereals in the Fertile Crescent and subsequently speciated after adaptation to its hosts. Rhynchosporium secalis, originally described from rye, causes an important disease on barley called scald, although it also infects other species of Hordeum and Agropyron. Phylogenetic analyses based on four DNA sequence loci identified three host-associated lineages that were confirmed by cross-pathogenicity tests. Bayesian analyses of divergence time suggested that the three lineages emerged between ,1200 to 3600 years before present (B.P.) with a 95% highest posterior density ranging from 100 to 12,000 years B.P. depending on the implemented clock models. The coalescent inference of demographic history revealed a very recent population expansion for all three pathogens. We propose that Rhynchosporium on barley, rye, and Agropyron host species represent three cryptic pathogen species that underwent independent evolution and ecological divergence by host-specialization. We postulate that the recent emergence of these pathogens followed host shifts. The subsequent population expansions followed the expansion of the cultivated host populations and accompanying expansion of the weedy Agropyron spp. found in fields of cultivated cereals. Hence, agriculture played a major role in the emergence of the scald diseases, the adaptation of the pathogens to new hosts and their worldwide dissemination. [source] HOST SHIFTS AND THE BEGINNING OF SIGNAL DIVERGENCEEVOLUTION, Issue 1 2008Rafael L. Rodríguez Divergence between populations adapting to different environments may be facilitated when the populations differ in their sexual traits. We tested whether colonizing a novel environment may, through phenotypic plasticity, change sexual traits in a way that could alter the dynamics of sexual selection. This hypothesis has two components: changes in mean phenotypes across environments, and changes in the genetic background of the phenotypes that are produced,or genotype × environment interaction (G × E). We simulated colonization of a novel environment and tested its effect on the mating signals of a member of the Enchenopa binotata species complex of treehoppers (Hemiptera: Membracidae), a clade that has diverged in a process involving host plant shifts and signal diversification. We found substantial genetic variation and G × E in most signal traits measured, with little or no change in mean signal phenotypes. We suggest that the expression of extant genetic variation across old and novel environments can initiate signal divergence. [source] Sequential radiation of unrelated organisms: the gall fly Eurosta solidaginis and the tumbling flower beetle Mordellistena convictaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2003W. G. Abrahamson Abstract Host shifts and the formation of insect-host races are likely common processes in the speciation of herbivorous insects. The interactions of goldenrods Solidago (Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae) and the beetle Mordellistena convicta (Coleoptera: Mordellidae) provide behavioural, ecological and genetic evidence of host races that may represent incipient species forming via sympatric speciation. We summarize evidence for Eurosta host races and show that M. convicta has radiated from goldenrod stems to Eurosta galls to form host-part races and, having exploited the galler's host shift, has begun to differentiate into host races within galls. Thus, host-race formation has occurred in two interacting, but unrelated organisms representing two trophic levels, resulting in ,sequential radiation' (escalation of biodiversity up the trophic system). Distributions of host races and their behavioural isolating mechanisms suggest sympatric differentiation. Such differentiation suggests host-race formation and subsequent speciation may be an important source of biodiversity. [source] Do parasitoids diversify in response to host-plant shifts by herbivorous insects?ECOLOGICAL ENTOMOLOGY, Issue 4 2001James T. Cronin Summary 1. For herbivorous insects, the incorporation of a novel host into the diet, and subsequent formation of distinct host associations (races), is thought to be a significant early step in the speciation process. While many studies have addressed this issue, virtually nothing is known about the evolutionary response of natural enemies to herbivore host-race formation. 2. The hypothesis that the parasitoid wasp Eurytoma gigantea (Hymenoptera: Eurytomidae) has formed host races in direct response to the host shift and subsequent host-race formation by its host, the gallmaker Eurosta solidaginis (Diptera: Tephritidae) was tested. Emergence time, mating preference, and female oviposition preference were determined for parasitoids derived from galls of each Eurosta host race. 3. Male and female E. gigantea overlap broadly in their emergence times from each Eurosta host race, suggesting that there is no phenological barrier to gene flow. 4. In choice experiments, female parasitoids did not mate assortatively: females that emerged from one Eurosta host race were equally likely to mate with males from either Eurosta host race. 5. Oviposition behaviour experiments revealed that female parasitoids do not prefer to oviposit on their host race of origin and that there is no overall preference for one host race, even though fitness is higher when parasitoids are reared from Eurosta galls of the Solidago gigantea host race than when reared from Eurosta galls of the Solidago altissima host race. 6. These results suggest that E. gigantea has not diverged in parallel with its host in response to the herbivore host-plant shift. Further studies are needed before the ubiquity of this diversification mechanism can be evaluated fully. [source] A novel host shift and invaded range of a seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), of an invasive weed, Leucaena leucocephalaENTOMOLOGICAL SCIENCE, Issue 1 2009Midori TUDA Abstract An endophagous seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), utilizes Neotropical Leucaena (Fabaceae: Mimosoideae). One of its hosts, Leucaena leucocephala, is a fast-growing nitrogen-fixing tree that serves as a multipurpose beneficial plant but eventually becomes an aggressive invader where it was introduced. Herein, we report A. macrophthalmus invasion of the Far East, South Asian tropics and subtropics (Japanese Pacific Islands, Taiwan, Southern China, Northern Thailand and Southern India). Of other field-collected mimosoid legumes, an introduced tree, Falcataria moluccana, in Taiwan was found to be used by the seed predator. Conversely, our published work review revealed that the seed predator had retained high host specificity to Leucaena species in its native and introduced regions. Acanthoscelides macrophthalmus was able to utilize aphagously postharvest mature seeds for oviposition and larval development, which is a trait of post-dispersal seed predators. We confirmed that A. macrophthalmus that was reared on L. leucocephala was able to utilize F. moluccana as well. Although the relatively high host specificity of the oligophagous beetle is suitable for controlling the weedy L. leucocephala, the potential host range expansion confirmed by this study must be cautioned. [source] A NOVEL PREFERENCE FOR AN INVASIVE PLANT AS A MECHANISM FOR ANIMAL HYBRID SPECIATIONEVOLUTION, Issue 2 2007Dietmar Schwarz Homoploid hybrid speciation,speciation via hybridization without a change in chromosome number,is rarely documented and poorly understood in animals. In particular, the mechanisms by which animal homoploid hybrid species become ecologically and reproductively isolated from their parents are hypothetical and remain largely untested by experiments. For the many host-specific parasites that mate on their host, choosing the right host is the most important ecological and reproductive barrier between these species. One example of a host-specific parasite is the Lonicera fly, a population of tephritid fruit flies that evolved within the last 250 years likely by hybridization between two native Rhagoletis species following a host shift to invasive honeysuckle. We studied the host preference of the Lonicera fly and its putative parent species in laboratory experiments. The Lonicera fly prefers its new host, introduced honeysuckle, over the hosts of both parental species, demonstrating the rapid acquisition of preference for a new host as a means of behavioral isolation from the parent species. The parent taxa discriminate against each other's native hosts, but both accept honeysuckle fruit, leaving the potential for asymmetric gene flow from the parent species. Importantly, this pattern allows us to formulate hypotheses about the initial formation of the Lonicera fly. As mating partners from the two parent taxa are more likely to meet on invasive honeysuckle than on their respective native hosts, independent acceptance of honeysuckle by both parents likely preceded hybridization. We propose that invasive honeysuckle served as a catalyst for the local breakdown of reproductive isolation between the native parent species, a novel consequence of the introduction of an exotic weed. We describe behavioral mechanisms that explain the initial hybridization and subsequent reproductive isolation of the hybrid Lonicera fly. These results provide experimental support for a combination of host shift and hybridization as a model for hybrid speciation in parasitic animals. [source] Genetic and morphological differentiation in Tephritis bardanae (Diptera: Tephritidae): evidence for host-race formationJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004T. Diegisser Abstract The fruit fly Tephritis bardanae infests flower heads of two burdock hosts, Arctium tomentosum and A. minus. Observations suggest host-associated mating and behavioural differences at oviposition indicating host-race status. Previously, flies from each host plant were found to differ slightly in allozyme allele frequencies, but these differences could as well be explained by geographical separation of host plants. In the present study, we explicitly test whether genetic and morphological variance among T. bardanae are explained best by host-plant association or by geographical location, and if this pattern is stable over a 10-year period. Populations of A. tomentosum flies differed significantly from those of A. minus flies in (i) allozyme allele frequencies at the loci Pep-A and Pgd, (ii) mtDNA haplotype frequencies and (iii) wing size. In contrast, geographical location had no significant influence on the variance estimates. While it remains uncertain whether morphometric differentiation reflects genotypic variability or phenotypic plasticity, allozyme and mtDNA differentiation is genetically determined. This provides strong evidence for host-race formation in T. bardanae. However, the levels of differentiation are relatively low indicating that the system is in an early stage of divergence. This might be due to a lack of time (i.e. the host shift occurred recently) or due to relatively high gene flow preventing much differentiation at loci not experiencing selection. [source] Sequential radiation of unrelated organisms: the gall fly Eurosta solidaginis and the tumbling flower beetle Mordellistena convictaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2003W. G. Abrahamson Abstract Host shifts and the formation of insect-host races are likely common processes in the speciation of herbivorous insects. The interactions of goldenrods Solidago (Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae) and the beetle Mordellistena convicta (Coleoptera: Mordellidae) provide behavioural, ecological and genetic evidence of host races that may represent incipient species forming via sympatric speciation. We summarize evidence for Eurosta host races and show that M. convicta has radiated from goldenrod stems to Eurosta galls to form host-part races and, having exploited the galler's host shift, has begun to differentiate into host races within galls. Thus, host-race formation has occurred in two interacting, but unrelated organisms representing two trophic levels, resulting in ,sequential radiation' (escalation of biodiversity up the trophic system). Distributions of host races and their behavioural isolating mechanisms suggest sympatric differentiation. Such differentiation suggests host-race formation and subsequent speciation may be an important source of biodiversity. [source] Significance of a new field oviposition record for Graphium eurypylus (L.) (Lepidoptera: Papilionidae) on Michelia champaca (Magnoliaceae)AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 1 2008Michelle L Larsen Abstract, Phytochemical similarities among ancient Angiosperms presumably played a role in the ecological and evolutionary diversification of the swallowtail butterflies (Papilionidae). Host family feeding specialisation is typical of most Papilionidae species, but field records of oviposition are rare for most swallowtail butterflies. It is even more uncommon to witness oviposition and larval feeding on new host plant species, especially in plant families not previously reported for the butterfly species. Oviposition by a female on a new host, or even on a toxic plant, may represent ancestral behaviour (with a loss of larval acceptance, detoxification or processing abilities) or novel behaviour (providing genetic variation for a potential expansion of host range, or host shift). We document the oviposition, larval use and pupation of the Annonaceae specialised and geographically widespread Graphium eurypylus on a Magnoliaceae species, all under field conditions in Queensland, Australia. This is the first time such field observations of oviposition and larval feeding on Michelia champaca (Magnoliaceae) have been documented anywhere for this species. [source] RAPID SPECIATION FOLLOWING RECENT HOST SHIFTS IN THE PLANT PATHOGENIC FUNGUS RHYNCHOSPORIUMEVOLUTION, Issue 6 2008Pascal L. Zaffarano Agriculture played a significant role in increasing the number of pathogen species and in expanding their geographic range during the last 10,000 years. We tested the hypothesis that a fungal pathogen of cereals and grasses emerged at the time of domestication of cereals in the Fertile Crescent and subsequently speciated after adaptation to its hosts. Rhynchosporium secalis, originally described from rye, causes an important disease on barley called scald, although it also infects other species of Hordeum and Agropyron. Phylogenetic analyses based on four DNA sequence loci identified three host-associated lineages that were confirmed by cross-pathogenicity tests. Bayesian analyses of divergence time suggested that the three lineages emerged between ,1200 to 3600 years before present (B.P.) with a 95% highest posterior density ranging from 100 to 12,000 years B.P. depending on the implemented clock models. The coalescent inference of demographic history revealed a very recent population expansion for all three pathogens. We propose that Rhynchosporium on barley, rye, and Agropyron host species represent three cryptic pathogen species that underwent independent evolution and ecological divergence by host-specialization. We postulate that the recent emergence of these pathogens followed host shifts. The subsequent population expansions followed the expansion of the cultivated host populations and accompanying expansion of the weedy Agropyron spp. found in fields of cultivated cereals. Hence, agriculture played a major role in the emergence of the scald diseases, the adaptation of the pathogens to new hosts and their worldwide dissemination. [source] PHYTOPHAGOUS INSECT,MICROBE MUTUALISMS AND ADAPTIVE EVOLUTIONARY DIVERSIFICATIONEVOLUTION, Issue 5 2008Eric M. Janson Adaptive diversification is a process intrinsically tied to species interactions. Yet, the influence of most types of interspecific interactions on adaptive evolutionary diversification remains poorly understood. In particular, the role of mutualistic interactions in shaping adaptive radiations has been largely unexplored, despite the ubiquity of mutualisms and increasing evidence of their ecological and evolutionary importance. Our aim here is to encourage empirical inquiry into the relationship between mutualism and evolutionary diversification, using herbivorous insects and their microbial mutualists as exemplars. Phytophagous insects have long been used to test theories of evolutionary diversification; moreover, the diversification of a number of phytophagous insect lineages has been linked to mutualisms with microbes. In this perspective, we examine microbial mutualist mediation of ecological opportunity and ecologically based divergent natural selection for their insect hosts. We also explore the conditions and mechanisms by which microbial mutualists may either facilitate or impede adaptive evolutionary diversification. These include effects on the availability of novel host plants or adaptive zones, modifying host-associated fitness trade-offs during host shifts, creating or reducing enemy-free space, and, overall, shaping the evolution of ecological (host plant) specialization. Although the conceptual framework presented here is built on phytophagous insect,microbe mutualisms, many of the processes and predictions are broadly applicable to other mutualisms in which host ecology is altered by mutualistic interactions. [source] MUSEUM SPECIMENS AND PHYLOGENIES ELUCIDATE ECOLOGY'S ROLE IN COEVOLUTIONARY ASSOCIATIONS BETWEEN MITES AND THEIR BEE HOSTSEVOLUTION, Issue 6 2007Pavel B. Klimov Coevolutionary associations between hosts and symbionts (or parasites) are often reflected in correlated patterns of divergence as a consequence of limitations on dispersal and establishment on new hosts. Here we show that a phylogenetic correlation is observed between chaetodactylid mites and their hosts, the long-tongued bees; however, this association manifests itself in an atypical fashion. Recently derived mites tend to be associated with basal bee lineages, and vice versa, ruling out a process of cospeciation, and the existence of mites on multiple hosts also suggests ample opportunity for host shifts. An extensive survey of museum collections reveals a pattern of infrequent host shifts at a higher taxonomic level, and yet, frequent shifts at a lower level, which suggests that ecological constraints structure the coevolutionary history of the mites and bees. Certain bee traits, particularly aspects of their nesting behavior, provide a highly predictive framework for the observed pattern of host use, with 82.1% of taxa correctly classified. Thus, the museum survey and phylogenetic analyses provide a unique window into the central role ecology plays in this coevolutionary association. This role is apparent from two different perspectives,as (a) a constraining force evident in the historical processes underlying the significant correlation between the mite and bee phylogenies, as well as (b) by the highly nonrandom composition of bee taxa that serve as hosts to chaetodactylid mites. [source] Molecular mechanisms of pathogenicity: how do pathogenic microorganisms develop cross-kingdom host jumps?FEMS MICROBIOLOGY REVIEWS, Issue 3 2007Peter Van Baarlen Abstract It is common knowledge that pathogenic viruses can change hosts, with avian influenza, the HIV, and the causal agent of variant Creutzfeldt,Jacob encephalitis as well-known examples. Less well known, however, is that host jumps also occur with more complex pathogenic microorganisms such as bacteria and fungi. In extreme cases, these host jumps even cross kingdom of life barriers. A number of requirements need to be met to enable a microorganism to cross such kingdom barriers. Potential cross-kingdom pathogenic microorganisms must be able to come into close and frequent contact with potential hosts, and must be able to overcome or evade host defences. Reproduction on, in, or near the new host will ensure the transmission or release of successful genotypes. An unexpectedly high number of cross-kingdom host shifts of bacterial and fungal pathogens are described in the literature. Interestingly, the molecular mechanisms underlying these shifts show commonalities. The evolution of pathogenicity towards novel hosts may be based on traits that were originally developed to ensure survival in the microorganism's original habitat, including former hosts. [source] Adaptations of an insect to a novel host plant: a phylogenetic approachFUNCTIONAL ECOLOGY, Issue 3 2006A. J. GASSMANN Summary 1The importance of behavioural vs physiological adaptations in the evolution of host associations by herbivorous insects is largely unknown. 2We compared sister species of beetles, one of which, Ophraella slobodkini, feeds on the lineage's ancestral host, Ambrosia artemisiifolia, while O. notulata has shifted to a novel host, Iva frutescens. Assuming O. slobodkini represents the features of the Ambrosia -feeding ancestor, we asked if behavioural and physiological barriers to utilizing Iva existed and if adaptation to these barriers occurred. We also tested for trade-offs between use of novel and ancestral hosts by O. notulata. 3We found evidence that the ancestor of O. notulata would have been deterred from feeding on Iva and suffered lower conversion efficiency. 4Ophraella notulata appears to have adapted behaviourally by increasing consumption of Iva, but we did not detect a significant increase in its physiological capacity to use Iva. Additionally, the switch to Iva by O. notulata did not reduce its physiological capacity to use the ancestral host, Ambrosia. 5Our results suggest that novel host associations may arise from behavioural adaptations, with physiological adaptations a secondary result of behavioural changes. We discuss implications for hypotheses of host shifts and the evolution of specialization. [source] Genetic structure and gene flow in French populations of two Ostrinia taxa: host races or sibling species?MOLECULAR ECOLOGY, Issue 20 2007T. MALAUSA Abstract Most models of ecological speciation concern phytophagous insects in which speciation is thought to be driven by host shifts and subsequent adaptations of populations. Despite the ever-increasing number of studies, the current evolutionary status of most models remains incompletely resolved, as estimates of gene flow between taxa remain extremely rare. We studied the population genetics of two taxa of the Ostrinia genus , one feeding mainly on maize and the other on mugwort and hop , occurring in sympatry throughout France. The actual level of divergence of these taxa was unknown because the genetic structure of populations had been investigated over a limited geographical area and the magnitude of gene flow between populations had not been estimated. We used 11 microsatellite markers to investigate the genetic structure of populations throughout France and the extent of gene flow between the two Ostrinia taxa at several sites at which they are sympatric. We observed clear genetic differentiation between most populations collected on the typical respective hosts of each taxon. However, populations displaying intermediate allelic frequencies were found on hop plants in southern France. Individual assignments revealed that this result could be accounted for by the presence of both taxa on the same host. Gene flow, estimated by determining the proportion of hybrids detected, was low: probably < 1% per generation, regardless of site. This indicates that the two Ostrinia taxa have reached a high level of genetic divergence and should be considered sibling species rather than host races. [source] Ecology of Leptocoris Hahn (Hemiptera: Rhopalidae) soapberry bugs in AustraliaAUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 4 2005Scott P Carroll Abstract, Soapberry bugs are worldwide seed predators of plants in the family Sapindaceae. Australian sapinds are diverse and widespread, consisting of about 200 native trees and shrubs. This flora also includes two introduced environmental weeds, plus cultivated lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.) and rambutan (Nephelium lappaceum L.). Accordingly, Australian soapberry bugs may be significant in ecology, conservation and agriculture. Here we provide the first account of their ecology. We find five species of Leptocoris Hahn in Australia, and list sapinds that do and do not serve as reproductive hosts. From museum and field records we map the continental distributions of the insects and primary hosts. Frequency of occupation varies among host species, and the number of hosts varies among the insects. In addition, differences in body size and beak length are related to host use. For example, the long-beaked Leptocoris tagalicus Burmeister is highly polyphagous in eastern rainforests, where it occurs on at least 10 native and non-native hosts. It aggregates on hosts with immature fruit and commences feeding before fruits dehisce. Most of its continental range, however, matches that of a single dryland tree, Atalaya hemiglauca F. Muell., which has comparatively unprotected seeds. The taxon includes a smaller and shorter-beaked form that is closely associated with Atalaya, and appears to be taxonomically distinct. The other widespread soapberry bug is the endemic Leptocoris mitellatus Bergroth. It too is short-beaked, and colonises hosts phenologically later than L. tagalicus, as seeds become more accessible in open capsules. Continentally its distribution is more southerly and corresponds mainly to that of Alectryon oleifolius Desf. Among all host species, the non-native environmental weeds Cardiospermum L. and Koelreuteria Laxm. are most consistently attacked, principally by L. tagalicus. These recent host shifts have biocontrol implications. In contrast, the sapinds planted as fruit crops appear to be less frequently used at present and mainly by the longer-beaked species. [source] | |||||||||||||||||||