Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

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Pathological and ecological host consequences of infection by an introduced fish parasite

The infection consequences of the introduced cestode fish parasite Bothriocephalus acheilognathi were studied in a cohort of wild, young-of-the-year common carp Cyprinus carpio that lacked co-evolution with the parasite. Within the cohort, parasite prevalence was 42% and parasite burdens were up to 12% body weight. Pathological changes within the intestinal tract of parasitized carp included distension of the gut wall, epithelial compression and degeneration, pressure necrosis and varied inflammatory changes. These were most pronounced in regions containing the largest proportion of mature proglottids. Although the body lengths of parasitized and non-parasitized fish were not significantly different, parasitized fish were of lower body condition and reduced weight compared to non-parasitized conspecifics. Stable isotope analysis (δ(15)N and δ(13)C) revealed trophic impacts associated with infection, particularly for δ(15)N where values for parasitized fish were significantly reduced as their parasite burden increased. In a controlled aquarium environment where the fish were fed ad libitum on an identical food source, there was no significant difference in values of δ(15)N and δ(13)C between parasitized and non-parasitized fish. The growth consequences remained, however, with parasitized fish growing significantly slower than non-parasitized fish, with their feeding rate (items s(-1)) also significantly lower. Thus, infection by an introduced parasite had multiple pathological, ecological and trophic impacts on a host with no experience of the parasite.     

Resistance of an invasive gastropod to an indigenous trematode parasite in Lake Malawi

Successful establishment and spread of biological invaders may be promoted by the absence of population-regulating enemies such as pathogens, parasites or predators. This may come about when introduced taxa are missing enemies from their native habitats, or through immunity to enemies within invaded habitats. Here we provide field evidence that trematode parasites are absent in a highly invasive morph of the gastropod Melanoides tuberculata in Lake Malawi, and that the invasive morph is resistant to indigenous trematodes that castrate and induce gigantism in native M. tuberculata. Since helminth infections can strongly influence host population abundances in other host-parasite systems, this enemy release may have provided an advantage to the invasive morph in terms of reproductive capacity and survivorship.     

Adaptation of the gypsy moth to an unsuitable host plant

The pattern of adaptation with regard to life history traits and traits thought to be important in feeding habits of caterpillars in two populations of the gypsy moth (Lymantria dispar L.; Lepidoptera: Lymantriidae) originating from the locust tree (Robinia pseudoacacia; Fabaceae) and oak (Quercus petrea; Fagaceae) forests were investigated in the laboratory. The Robinia population has experienced unsuitable locust tree leaves as an exclusive food resource for more than 40 years. Since Quercus species are the principal host plants of the gypsy moth, the specific objectives of this study have been to measure the extent of differentiation between ancestral and derived populations in several life history traits (egg-to-adult viability, duration of larval and pupal stages, and pupal weight) and nutritional indices – relative growth rate (RGR), relative consumption rate (RCR), assimilation efficiency (AD), gross growth efficiency (ECI), and net growth efficiency (ECD). Significant differences between the Quercus and Robinia populations were detected in pupal duration, RGR, RCR, and AD. The presence of a significant population × host interaction in traits such as preadult viability, duration of pupal stage, RGR, and ECI suggests that adaptation of the gypsy moth to the unsuitable host might be ongoing. Using a full-sib design, we screened for genetic variation in life history traits within both populations, and examined the genetic correlations of performance across oak and locust leaves within both populations. The genetic variances for analyzed life history traits were lower under conditions that are commonly encountered in nature. Our data show that positive cross-host genetic correlations preponderate within both populations.     

Adaptation of native and exotic hyperparasites to the introduced primary sawfly parasite,Exenterus amictorius (Panzer) in Wisconsin

In a 10 year period,Exenterus amictorius (Panzer) has become the dominant primary parasite of the introduced pine sawfly,Diprion similis (Hartig), in Wisconsin. During this time (1961–71), eleven secondary parasites have associated themselves withE. amictorius. Nine are endemic to North America and two are exotic but not of recent origin. Of these, four had never been reared previously fromD. similis cocoons; three, previously recorded as primaries, were recorded as hyperparasites; and four, previously recorded as hyperparasites, had broadened their range to includeE. amictorius. All hyperparasites are hymenopterans in the familiesPteromalidae (5),Ichneumonidae (3),Eulophidae (1),Eupelmidae (1), andTorymidae (1).

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Résumé Au cours de la décennie 1961–1971,Exenterus amictorius, est devenu le principal parasite de la TenthrèdeDiprion similis (Hartig), au Wisconsin. Onze parasites secondaires se sont associés àE. amictorius durant la même période: neufs endémiques à l'Amérique du Nord et deux introduits, mais non-récents. De ces parasites, quatre n'avaient jamais été élevés à partir deD. similis auparavant, trois reconnus autrefois comme parasites primaires se sont trouvés être des hyperparasites, et quatre décrits auparavant comme hyperparasites ont étendu leur distribution àE. amictorius. Tous les hyperparasites sont des hyménoptères appartenant aux familles suivantes:Pteromalidae (5),Ichneumonidae (3),Eulophidae (1),Eupelmidae (1), etTorymidae (1).

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Hymenoptera: Ichneumonidae

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Research supported by the College of Agricultural and Life Sciences, and by the Wisconsin Department of Natural Resources through the School of Natural Resources, University of Wisconsin, Madison.     

A native and an introduced parasitoid utilize an exotic gall-maker host

Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is non-native to North America and induces formation of galls on petioles and leaves of all chestnut (Castanea spp., Fagales: Fagaceae). We investigated the interactions between the gall wasp D. kuriphilus, a native parasitoid, Ormyrus labotus (Hymenoptera: Ormyridae), and a non-native parasitoid, Torymus sinensis (Hymenoptera: Torymidae). Galls were collected monthly from May to August and in January from four locations in the United States consisting of orchard-grown hybrid chestnuts (Hiram, OH and Meadowview, VA), suburban-grown ornamental Chinese chestnuts (C. mollissima) (Broadview Heights, OH), or forest-grown American chestnuts (C. dentata) (Bowling Green, KY). Parasitoids were removed from galls and T. sinensis and O. labotus were identified using PCR-markers. The relative abundance of each parasitoid was compared in relation to collection date, habitat, presence of alternative hosts, and gall characteristics. T. sinensis was collected from each location and date, and was dominant in the orchard and suburban locations. However, relatively more O. labotus were collected within the forest, which had significant oak component and alternative cynipid hosts. O. labotus was only collected in spring and early summer, indicating the use of different summer and winter hosts. Observations suggest that in addition to parasitizing D. kuriphilus, O. labotus hyperparasitizes T. sinensis. T. sinensis has a longer ovipositor than O. labotus, and parasitized larger galls. This study improves our understanding of interactions between an invasive gall wasp, an introduced parasitoid, and native parasitoids, and illustrates novel relationships that may form as exotic species expand their geographic range.     

Interactions between an introduced and indigenous coccinellid species at different prey densities

Coccinella septempunctata L. (Coleoptera: Coccinellidae), a Palearctic coccinellid, has established and rapidly spread throughout the United States. This quantitative examination of larval interactions between C. septempunctata and Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), a Nearctic coccinellid, was conducted under controlled prey densities. Larvae of both coccinellid species are affected by a limited diet [one pea aphid per day Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)] compared with an excess diet (>20 aphids per day). Larval survival decreased from 86 to 63% in C. maculata and from 84 to 33% in C. septempunctata; mean preimaginal developmental time increased from 20.6 to 26.7 days in C. maculata, and from 18.1 to 32.0 days in C. septempunctata. Additionally, on one aphid per day, mean adult weight was reduced from 12.39 to 9.79 mg in C. maculata, and from 39.57 to 14.44 mg in C. septempunctata. Interspecific interactions, favoring C. septempunctata over C. maculata at a␣low prey density (one aphid per day), take the form of␣reduced survival of C. maculata compared with C.␣septempunctata (14 versus 66%). Reduced survival of␣C. maculata may be the result of competition for aphids or intraguild predation by C. septempunctata on C.␣maculata. No interspecific interactions (measured as effects on larval survival, preimaginal developmental time, and adult weight) were observed between larvae of these two species at a high prey density (>20 aphids per predator per day). Received: 15 September 1997 / Accepted: 20 May 1998     

Mimetic host shifts in an endangered social parasite of ants

An emerging problem in conservation is whether listed morpho-species with broad distributions, yet specialized lifestyles, consist of more than one cryptic species or functionally distinct forms that have different ecological requirements. We describe extreme regional divergence within an iconic endangered butterfly, whose socially parasitic young stages use non-visual, non-tactile cues to infiltrate and supplant the brood in ant societies. Although indistinguishable morphologically or when using current mitochondrial and nuclear sequence-, or microsatellite data, Maculinea rebeli from Spain and southeast Poland exploit different Myrmica ant species and experience 100 per cent mortality with each other''s hosts. This reflects major differences in the hydrocarbons synthesized from each region by the larvae, which so closely mimic the recognition profiles of their respective hosts that nurse ants afford each parasite a social status above that of their own kin larvae. The two host ants occupy separate niches within grassland; thus, conservation management must differ in each region. Similar cryptic differentiation may be common, yet equally hard to detect, among the approximately 10 000 unstudied morpho-species of social parasite that are estimated to exist, many of which are Red Data Book listed.     

Experimental demonstration of the fitness consequences of an introduced parasite of Darwin's finches

Background

Introduced parasites are a particular threat to small populations of hosts living on islands because extinction can occur before hosts have a chance to evolve effective defenses. An experimental approach in which parasite abundance is manipulated in the field can be the most informative means of assessing a parasite''s impact on the host. The parasitic fly Philornis downsi, recently introduced to the Galápagos Islands, feeds on nestling Darwin''s finches and other land birds. Several correlational studies, and one experimental study of mixed species over several years, reported that the flies reduce host fitness. Here we report the results of a larger scale experimental study of a single species at a single site over a single breeding season.

Methodology/Principal Findings

We manipulated the abundance of flies in the nests of medium ground finches (Geospiza fortis) and quantified the impact of the parasites on nestling growth and fledging success. We used nylon nest liners to reduce the number of parasites in 24 nests, leaving another 24 nests as controls. A significant reduction in mean parasite abundance led to a significant increase in the number of nests that successfully fledged young. Nestlings in parasite-reduced nests also tended to be larger prior to fledging.

Conclusions/Significance

Our results confirm that P. downsi has significant negative effects on the fitness of medium ground finches, and they may pose a serious threat to other species of Darwin''s finches. These data can help in the design of management plans for controlling P. downsi in Darwin''s finch breeding populations.     

Adaptation to an invasive host is driving the loss of a native ecotype

Locally adapted populations are often used as model systems for the early stages of ecological speciation, but most of these young divergent populations will never become complete species. The maintenance of local adaptation relies on the strength of natural selection overwhelming the homogenizing effects of gene flow; however, this balance may be readily upset in changing environments. Here I show that soapberry bugs (Jadera haematoloma) have lost adaptations to their native host plant (Cardiospermum corindum) and are regionally specializing on an invasive host (Koelreuteria elegans), collapsing a classic and well‐documented example of local adaptation. All populations that were adapted to the native host—including those still found on that host today—are now better adapted to the invasive host in multiple phenotypes. Weak differentiation remains in two traits, suggesting that homogenization across the region is incomplete. This study highlights the potential for adaptation to invasive species to disrupt native communities by swamping adaptation to native conditions through maladaptive gene flow.     

Adaptation of HIV-1 to its human host

Human immunodeficiency virus type 1 (HIV-1) originated from three independent cross-species transmissions of simian immunodeficiency virus (SIVcpzPtt) infecting chimpanzees (Pan troglodytes troglodytes) in west central Africa, giving rise to pandemic (group M) and non-pandemic (groups N and O) clades of HIV-1. To identify host-specific adaptations in HIV-1 we compared the inferred ancestral sequences of HIV-1 groups M, N and O to 12 full length genome sequences of SIVcpzPtt and four of the outlying but closely related SIVcpzPts (from P. t. schweinfurthii). This analysis revealed a single site that was completely conserved among SIVcpzPtt strains but different (due to the same change) in all three groups of HIV-1. This site, Gag-30, lies within p17, the gag-encoded matrix protein. It is Met in SIVcpzPtt, underwent a conservative replacement by Leu in one lineage of SIVcpzPts but changed radically to Arg on all three lineages leading to HIV-1. During subsequent diversification this site has been conserved as a basic residue (Arg or Lys) in most lineages of HIV-1. Retrospective analysis revealed that Gag-30 had reverted to Met in a previous experiment in which HIV-1 was passaged through chimpanzees. To examine whether this substitution conferred a species specific growth advantage, we used site-directed mutagenesis to generate variants of these chimpanzee-adapted HIV-1 strains with Lys at Gag-30, and tested their replication in both human and chimpanzee CD4+ T lymphocytes. Remarkably, viruses encoding Met replicated to higher titers than viruses encoding Lys in chimpanzee T cells, but the opposite was found in human T cells. Taken together, these observations provide compelling evidence for host-specific adaptation during the emergence of HIV-1 and identify the viral matrix protein as a modulator of viral fitness following transmission to the new human host.     

Helminthic host defense peptides: using the parasite to defend the host

Parasitic helminths are destined to share niches with a variety of microbiota that inevitably influence their interaction with the host. To modulate the microbiome for their benefit and defend against pathogenic isolates, helminths have developed host defense peptides (HDPs) and proteins as integral elements of their immunity. These often exert a relatively nonspecific membranolytic activity toward bacteria, sometimes with limited or no toxicity toward host cells. With a few exceptions, such as nematode cecropin-like peptides and antibacterial factors (ABFs), helminthic HDPs are largely underexplored. This review scrutinizes current knowledge on the repertoire of such peptides in helminths and promotes their research as potential leads for an anti-infective solution to the burgeoning problem of antibiotic resistance.     

Non-native parasite enhances susceptibility of host to native predators

Parasites often alter host physiology and behavior, which can enhance predation risk for infected hosts. Higher consumption of parasitized prey can in turn lead to a less parasitized prey population (the healthy herd hypothesis). Loxothylacus panopaei is a non-native castrating barnacle parasite on the mud crab Eurypanopeus depressus along the Atlantic coast. Through prey choice mesocosm experiments and a field tethering experiment, we investigated whether the predatory crab Callinectes sapidus and other predators preferentially feed on E. depressus infected with L. panopaei. We found that C. sapidus preferentially consumed infected E. depressus 3 to 1 over visibly uninfected E. depressus in the mesocosm experiments. Similarly, infected E. depressus were consumed 1.2 to 1 over uninfected conspecifics in field tethering trials. We evaluated a mechanism behind this skewed prey choice, specifically whether L. panopaei affects E. depressus movement, making infected prey more vulnerable to predator attack. Counter to our expectations, infected E. depressus ran faster during laboratory trials than uninfected E. depressus, suggesting that quick movement may not decrease predation risk and seems instead to make the prey more vulnerable. Ultimately, the preferential consumption of L. panopaei-infected prey by C. sapidus highlights how interactions between organisms could affect where novel parasites are able to thrive.     

Disentangling the effect of host genetics and gut microbiota on resistance to an intestinal parasite

Resistance to infection is a multifactorial trait, and recent work has suggested that the gut microbiota can also contribute to resistance. Here, we performed a fecal microbiota transplant to disentangle the contribution of the gut microbiota and host genetics as drivers of resistance to the intestinal nematode Heligmosomoides polygyrus. We transplanted the microbiota of a strain of mice (SJL), resistant to H. polygyrus, into a susceptible strain (CBA) and vice-versa. We predicted that if the microbiota shapes resistance to H. polygyrus, the FMT should reverse the pattern of resistance between the two host strains. The two host strains had different microbiota diversities and compositions before the start of the experiment, and the FMT altered the microbiota of recipient mice. One mouse strain (SJL) was more resistant to colonization by the heterologous microbiota, and it maintained its resistance profile to H. polygyrus (lower parasite burden) independently of the FMT. On the contrary, CBA mice harbored parasites with lower fecundity during the early stage of the infection, and had an up-regulated expression of the cytokine IL-4 (a marker of H. polygyrus resistance) after receiving the heterologous microbiota. Therefore, while host genetics remains the main factor shaping the pattern of resistance to H. polygyrus, the composition of the gut microbiota also seems to play a strain-specific role.