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1.
    
Adaptive radiation occurs when species diversify rapidly to occupy an array of ecological niches. As opportunities for parasite infection and transmission may greatly vary among these niches, adaptive radiation is expected to be associated with a turnover of the parasite community. As major agents of natural and sexual selection, parasites may play a central role in host diversification. The study of parasite turnover may thus be of general relevance and could significantly improve our understanding of adaptive radiation. In this study, we examined the parasite faunas of eleven species belonging to the tribe Tropheini, one of several adaptive radiations of cichlid fishes in Lake Tanganyika. The most parsimonious ancestral foraging strategy among the Tropheini is relatively unselective substrate browsing of aufwuchs. Several lineages evolved more specialized foraging strategies, such as selective combing of microscopic diatoms or picking of macro‐invertebrates. We found that representatives of these specialized lineages bear reduced infection with food‐web‐transmitted acanthocephalan helminths, but not with parasites with a direct life cycle. Possibly, the evolution of selective foraging strategies entailed reduced ingestion of intermediate invertebrate hosts of acanthocephalans. We conclude that some species belonging to the Tropheini virtually escape acanthocephalan infection as a by‐product of trophic specialization.  相似文献   

2.
    
Genetic differentiation may exist among sympatric populations of a species due to long‐term associations with alternative hosts (i.e. host‐associated differentiation). While host‐associated differentiation has been documented in several phytophagus insects, there are far fewer cases known in animal parasites. The bed bug, Cimex lectularius, a wingless insect, represents a potential model organism for elucidating the processes involved in host‐associated differentiation in animal parasites with relatively limited mobility. In conjunction with the expansion of modern humans from Africa into Eurasia, it has been speculated that bed bugs extended their host range from bats to humans in their shared cave domiciles throughout Eurasia. C. lectularius that associate with humans have a cosmopolitan distribution, whereas those associated with bats occur across Europe, often in human‐built structures. We assessed genetic structure and gene flow within and among populations collected in association with each host using mtDNA, microsatellite loci and knock‐down resistance gene variants. Both nuclear and mitochondrial data support a lack of significant contemporary gene flow between host‐specific populations. Within locations human‐associated bed bug populations exhibit limited genetic diversity and elevated levels of inbreeding, likely due to human‐mediated movement, infrequent additional introduction events per infestation, and pest control. In contrast, populations within bat roosts exhibit higher genetic diversity and lower levels of relatedness, suggesting populations are stable with temporal fluctuations due to host dispersal and bug mortality. In concert with previously published evidence of morphological and behavioural differentiation, the genetic data presented here suggest C. lectularius is currently undergoing lineage divergence through host association.  相似文献   

3.
    
Meristic traits are often treated as distinct phenotypes that can be used to differentiate and delineate recently diverged species. For instance, the number of lateral line scales and vertebrae, two traits that vary substantially among Neotropical Heroine cichlid species, have been previously suggested to co-evolve. These meristic traits could co-evolve due to shared adaptive, developmental, or genetic factors. If they were found to be genetically or developmentally non-independent, this might require a more general re-evaluation of their role in evolutionary or taxonomic studies. We expanded a previous analysis of correlated evolution of meristic traits (lateral line scales and vertebrae counts) in these fishes to include a range of phylogenetic reconstructions as well as the analyses of 13 Nicaraguan Midas cichlid species (Amphilophus spp.). Additionally, we performed qualitative traits locus (QTL) mapping in a F2 laboratory-reared hybrid population from two ecologically divergent Midas cichlid fish species to discover and evaluate whether genomic co-segregation might explain the observed patterns of meristic co-evolution. Meristic values for these traits were found to morphologically differentiate some species of the Midas cichlid adaptive radiation. Our QTL analysis pinpointed several genomic regions associated with divergence in these traits and highlighted the potential for genomic co-segregation of the lateral line and vertebrae numbers on two chromosomes. Further, our phylogenetic comparative analyses consistently recovered a significant positive evolutionary correlation between the counts of lateral line scale and vertebrae numbers in Neotropical cichlids. Hence, the findings of genomic co-segregation could partially explain the co-evolution of these two meristic traits in these species. Continuing to unravel the genetic architecture governing meristic divergence helps to better understand both trait correlations and the utility of meristic traits in taxonomic diagnoses and how traits in phenotypes might be expected to co-evolve.  相似文献   

4.
We propose a new hypothesis for species coexistence by considering behavioral interactions between individuals. The hypothesis states that repulsive behavior between conspecific males (male–male repulsion) creates space for competing species, which promotes their coexistence. This hypothesis can explain the coexistence of two competing species even when their ecological niches completely overlap in spatially homogeneous environments. In addition, the mechanisms underlying such behavior might play a role in enabling the coexistence of two species immediately after speciation, with little or no niche differentiation, as in the case of cichlid fish communities, for example. Although there is limited evidence supporting this hypothesis, it can nevertheless explain the occurrence of species coexistence and biodiversity, which cannot be explained by previous theories.  相似文献   

5.
    
Host specificity has a major influence on a parasite's ability to shift between human and animal host species. Yet there is a dearth of quantitative approaches to explore variation in host specificity across biogeographical scales, particularly in response to the varying community compositions of potential hosts. We built a global dataset of intermediate host associations for nine of the world's most widespread helminth parasites (all of which infect humans). Using hierarchical models, we asked if realised parasite host specificity varied in response to regional variation in the phylogenetic and functional diversities of potential host species. Parasites were recorded in 4–10 zoogeographical regions, with some showing considerable geographical variation in observed versus expected host specificity. Parasites generally exhibited the lowest phylogenetic host specificity in regions with the greatest variation in prospective host phylogenetic diversity, namely the Neotropical, Saharo‐Arabian and Australian regions. Globally, we uncovered notable variation in parasite host shifting potential. Observed host assemblages for Hydatigera taeniaeformis and Hymenolepis diminuta were less phylogenetically diverse than expected, suggesting limited potential to spillover into unrelated hosts. Host assemblages for Echinococcus granulosus, Mesocestoides lineatus and Trichinella spiralis were less functionally diverse than expected, suggesting limited potential to shift across host ecological niches. By contrast, Hyd. taeniaeformis infected a higher functional diversity of hosts than expected, indicating strong potential to shift across hosts with different ecological niches. We show that the realised phylogenetic and functional diversities of infected hosts are determined by biogeographical gradients in prospective host species pools. These findings emphasise the need to account for underlying species diversity when assessing parasite host specificity. Our framework to identify variation in realised host specificity is broadly applicable to other host–parasite systems and will provide key insights into parasite invasion potential at regional and global scales.  相似文献   

6.
    
Geographical isolation, habitat variation and trophic specialization have contributed to a large extent to the astonishing diversity of cichlid fishes in the Great East African lakes. Because parasite communities often vary across space and environments, parasites can accompany and potentially enhance cichlid species diversification. However, host dispersal may reduce opportunities for parasite‐driven evolution by homogenizing parasite communities and allele frequencies of immunity genes. To test for the relationships between parasite community variation, host dispersal and parasite‐induced host evolution, we studied two sympatric cichlid species with contrasting dispersal capacities along the shores of southern Lake Tanganyika. Whereas the philopatric Tropheus moorii evolved into several genetically differentiated colour morphs, Simochromis diagramma is phenotypically rather uniform across its distribution range and shows only weak population structure. Populations of both species were infected with divergent parasite communities and harbour differentiated variant pools of an important set of immune genes, the major histocompatibility complex (MHC). The overall extent of geographical variation of parasites and MHC genes was similar between host species. This indicates that immunogenetic divergence among populations of Lake Tanganyika cichlids can occur even in species that are strongly dispersing. However, because this also includes species that are phenotypically uniform, parasite‐induced evolution may not represent a key factor underlying species diversification in this system.  相似文献   

7.
    
According to the Red Queen hypothesis, hosts and pathogens are engaged in an escalating coevolutionary arms race between resistance and virulence. However, the vast majority of symbionts colonize their hosts' mucosal compartments without triggering any immune response, resulting in durable commensal associations. Here, I propose a simple extension of previous mathematical models for antagonistic coevolution in which the host can mount a delayed immune response; in response, the symbiont can change its virulence following this activation. Even though the levels of virulence in both phases are assumed to be genetically determined, this simple form of plasticity can select for commensal associations. In particular, coevolution can result in hosts that do not activate their immune response, thus preventing phenotypically plastic pathogens from switching to a higher virulence level. I argue that, from the host's point of view, this state is analogous to the mafia behaviour previously described in avian brood parasites. More importantly, this study provides a new hypothesis for the maintenance of a commensal relationship through antagonistic coevolution.  相似文献   

8.
    
Although malaria parasites infecting non‐human primates are important models for human malaria, little is known of the ecology of infection by these parasites in the wild. We extensively sequenced cytochrome b (cytb) of malaria parasites (Apicomplexa: Haemosporida) from free‐living southeast Asian monkeys Macaca nemestrina and Macaca fascicularis. The two most commonly observed taxa were Plasmodium inui and Hepatocystis sp., but certain other sequences did not cluster closely with any previously sequenced species. Most of the major clades of parasites were found in both Macaca species, and the two most commonly occurring parasite infected the two Macaca species at approximately equal levels. However, P. inui showed evidence of genetic differentiation between the populations infecting the two Macaca species, suggesting limited movement of this parasite among hosts. Moreover, coinfection with Plasmodium and Hepatocystis species occurred significantly less frequently than expected on the basis of the rates of infection with either taxon alone, suggesting the possibility of competitive exclusion. The results revealed unexpectedly complex communities of Plasmodium and Hepatocystis taxa infecting wild southeast Asian monkeys. Parasite taxa differed with respect to both the frequency of between‐host movement and their frequency of coinfection.  相似文献   

9.
    
The community of host species that a parasite infects is often explained by functional traits and phylogeny, predicting that closely related hosts or those with particular traits share more parasites with other hosts. Previous research has examined parasite community similarity by regressing pairwise parasite community dissimilarity between two host species against host phylogenetic distance. However, pairwise approaches cannot target specific host species responsible for disproportionate levels of parasite sharing. To better identify why some host species contribute differentially to parasite diversity patterns, we represent parasite sharing using ecological networks consisting of host species connected by instances of shared parasitism. These networks can help identify host species and traits associated with high levels of parasite sharing that may subsequently identify important hosts for parasite maintenance and transmission within communities. We used global‐scale parasite sharing networks of ungulates, carnivores, and primates to determine if host importance – encapsulated by the network measures degree, closeness, betweenness, and eigenvector centrality – was predictable based on host traits. Our findings suggest that host centrality in parasite sharing networks is a function of host population density and range size, with range size reflecting both species geographic range and the home range of those species. In the full network, host taxonomic family became an important predictor of centrality, suggesting a role for evolutionary relationships between host and parasite species. More broadly, these findings show that trait data predict key properties of ecological networks, thus highlighting a role for species traits in understanding network assembly, stability, and structure.  相似文献   

10.
    
Parasites often affect the abundance and life‐history traits of their hosts. We studied the impact of a social parasite – a slavemaking ant – on host ant communities using two complementary field manipulations. In the first experiment, we analysed the effect of social parasite presence on host populations in one habitat. In a second experiment, conducted in two habitats, we used a cross‐fostering design, analysing the effect of sympatric and allopatric social parasites. In the first experiment, host colonies benefited to some extent from residing in parasite‐free areas, showing increased total production. Yet, in the second experiment, host colonies in plots containing social parasites were more productive, and this effect was most evident in response to allopatric social parasites. We propose several explanations for these inconsistent results, which are related to environmental variability. The discrepancies between the two habitats can be explained well by ecological variation as a result of differences in altitudes and climate. For example, ant colonies in the colder habitat were larger and, for one host species, colonies were more often polygynous. In addition, our long‐term documentation – a total of four measurements of community structure in 6 years – showed temporal variation in abundance and life‐history traits of ant colonies, unrelated to the manipulations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 559–570.  相似文献   

11.
    
In the present study, immunologically naive rainbow trout Oncorhynchus mykiss were experimentally exposed to a low‐level Diplostomum spathaceum (Trematoda) infection to stimulate acquired resistance and, along with unexposed controls, were subsequently exposed to natural infection for 8 weeks. The priming of the host resistance, designed to simulate a procedure applicable in aquaculture, decreased the number of establishing parasites compared to untreated controls by the end of the experiment. This effect was slow and did not protect the fish against the parasite‐induced cataracts. The results suggest that this type of priming of host resistance is probably inefficient in preventing the deleterious effects of D. spathaceum infection in aquaculture conditions.  相似文献   

12.
    
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13.
Due to the close association between parasites and their hosts, many ‘generalist’ parasites have a high potential to become specialized on different host species. We investigated this hypothesis for a common ectoparasite of seabirds, the tick Ixodes uriae that is often found in mixed host sites. We examined patterns of neutral genetic variation between ticks collected from Black‐legged kittiwakes (Rissa tridactyla) and Atlantic puffins (Fratercula arctica) in sympatry. To control for a potential distance effect, values were compared to differences among ticks from the same host in nearby monospecific sites. As predicted, there was higher genetic differentiation between ticks from different sympatric host species than between ticks from nearby allopatric populations of the same host species. Patterns suggesting isolation by distance were found among tick populations of each host group, but no such patterns existed between tick populations of different hosts. Overall, results suggest that host‐related selection pressures have led to the specialization of I. uriae and that host race formation may be an important diversifying mechanism in parasites.  相似文献   

14.
  总被引：1，自引：0，他引：1  
Evolution Canyon in Lower Nahal Oren, Mount Carmel, Israel has been identified as a location promoting sympatric speciation. Several previous studies on Drosophila melanogaster populations from the two disparate slopes of the canyon suggest that these two populations are experiencing incipient speciation. However, recent microsatellite data did not reveal the expected level of population differentiation. Given the importance of this system for studying speciation, we set out to test two predictions of the incipient speciation hypothesis--genetic differentiation and sexual isolation. We sequenced six different Acp genes from isofemale lines from the south-facing slope (11 lines) and north-facing slope (nine lines) of Evolution Canyon. We found no evidence of genetic differentiation between the two slopes (F(ST) = -0.03). We also conducted mate choice tests, using intraslope F1 hybrids between different isofemale lines. There was no significant departure from random mating in mixtures of flies from the two slopes. Our results provide further indication that it is unlikely these two populations are experiencing incipient speciation. We discuss our results in light of the discrepancies that have been published on this enigmatic D. melanogaster system from Evolution Canyon.  相似文献   

15.
    
For the past 17 years, scientists have been compiling a list of amphibian species susceptible to infection by the amphibian‐killing chytrid fungus, Batrachochytrium dendrobatidis (Bd), all over the world, with >500 species infected on every continent except Antarctica (Olson et al. 2013 ). Where Bd has been found, the impacts on amphibians has been one of two types: either Bd arrives into a naïve amphibian population followed by a mass die‐off and population declines (e.g. Lips et al. 2006 ), or Bd is present at some moderate prevalence, usually infecting many species but at apparently nonlethal intensities for a long time. In this issue of Molecular Ecology, Rodriguez et al. ( 2014 ) discover that the Atlantic Coastal Forest of Brazil is home to two Bd lineages: the Global Pandemic Lineage (Bd‐GPL) – the strain responsible for mass die‐offs and population declines – and a lineage endemic to Brazil (Bd‐Bz). Even more surprising was that both lineages have been present in this area for the past 100 years, making these the oldest records of Bd infecting amphibians. The team also described a moderate but steady prevalence of ~20% across all sampled anuran families for over 100 years, indicating that Brazil has been in an enzootic disease state for over a century. Most amphibians were infected with Bd‐GPL, suggesting this lineage may be a better competitor than Bd‐Bz or may be replacing the Bd‐Bz lineage. Rodriguez et al. ( 2014 ) also detected likely hybridization of the two Bd lineages, as originally described by Schloegel et al. ( 2012 ).  相似文献   

16.
    
Parasites present a threat for free‐living species and affect several ecological and evolutionary processes. Immune defence is the main physiological barrier against infections, and understanding its evolution is central for predicting disease dynamics. I review theoretical predictions and empirical data on natural selection on quantitative immune defence traits in the wild. Evolutionary theory predicts immune traits to be under stabilizing selection owing to trade‐offs between immune function and life‐history traits. Empirical data, however, support mainly positive directional selection, but also show variation in the form of selection among study systems, immune traits and fitness components. I argue that the differences between theory and empirical data may at least partly arise from methodological difficulties in testing stabilizing selection as well as measuring fitness. I also argue that the commonness of positive directional selection and the variation in selection may be caused by several biological factors. First, selection on immune function may show spatial and temporal variation as epidemics are often local/seasonal. Second, factors affecting the range of phenotypic variation in immune traits could alter potential for selection. Third, different parasites may impose different selective pressures depending on their characteristics. Fourth, condition dependence of immune defence can obscure trade‐offs related to it, thus possibly modifying observed selection gradients. Fifth, nonimmunological defences could affect the form of selection by reducing the benefits of strong immune function. To comprehensively understand the evolution of immune defence, the role of above factors should be considered in future studies.  相似文献   

17.
    
Dispersal is a fundamental component of the life history of most species. Dispersal influences fitness, population dynamics, gene flow, genetic drift and population genetic structure. Even small differences in dispersal can alter ecological interactions and trigger an evolutionary cascade. Linking such ecological processes with evolutionary patterns is difficult, but can be carried out in the proper comparative context. Here, we investigate how differences in phoretic dispersal influence the population genetic structure of two different parasites of the same host species. We focus on two species of host‐specific feather lice (Phthiraptera: Ischnocera) that co‐occur on feral rock pigeons (Columba livia). Although these lice are ecologically very similar, “wing lice” (Columbicola columbae) disperse phoretically by “hitchhiking” on pigeon flies (Diptera: Hippoboscidae), while “body lice” (Campanulotes compar) do not. Differences in the phoretic dispersal of these species are thought to underlie observed differences in host specificity, as well as the degree of host–parasite cospeciation. These ecological and macroevolutionary patterns suggest that body lice should exhibit more genetic differentiation than wing lice. We tested this prediction among lice on individual birds and among lice on birds from three pigeon flocks. We found higher levels of genetic differentiation in body lice compared to wing lice at two spatial scales. Our results indicate that differences in phoretic dispersal can explain microevolutionary differences in population genetic structure and are consistent with macroevolutionary differences in the degree of host–parasite cospeciation.  相似文献   

18.
    
Janzen–Connell effects are negative effects on the survival of a plant's progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density‐dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species‐specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density‐dependent effects and differing preferences of consumer groups.  相似文献   

19.
    
Inequality in male and female numbers may affect population dynamics and extinction probabilities and so has significant conservation implications. We previously demonstrated that Brown‐headed Cowbird Molothrus ater brood parasitism of Song Sparrows Melospiza melodia results in a 50% reduction in the proportion of female host offspring by day 6 post‐hatch and at fledging, which modelling demonstrated is as significant as nest predation in affecting demography. Many avian brood parasites possess special adaptations to parasitize specific hosts so this sex‐ratio effect could be specific to the interaction between these two species. Alternatively, perturbations associated with brood parasitism per se (e.g. the addition of an extra, larger, unrelated nestling), rather than a Cowbird nestling specifically, may be responsible. We experimentally eliminated the effects of Cowbird‐specific traits by parasitizing nests with a conspecific nestling rather than a Cowbird, while otherwise emulating the circumstances of Cowbird parasitism by adding an extra, larger (2‐day‐older), unrelated Song Sparrow nestling to Song Sparrow nests. Our parasitism treatment led to few host offspring deaths and no evidence of male‐biased sex ratios by day 6 post‐hatch. However, after day 6, female nestling mortality rates increased significantly in experimentally parasitized nests, resulting in a 60% reduction in the proportion of females fledging. Cowbird‐specific traits are thus not necessary to cause female‐biased host nestling mortality and far more general features associated with Cowbird parasitism instead appear responsible. Our results suggest, however, that Cowbird‐specific traits may help accelerate the pace of female host deaths. The conservation implications of our results could be wide reaching. Cowbirds are unrelated to all their hosts, are larger than the great majority, and a Cowbird nestling's presence can mean there is an extra mouth to feed. Thus, sex‐biased mortality in parasitized nests could be occurring across a range of host species.  相似文献   

20.
    
Decreasing similarity between ecological communities with increasing geographic distance (i.e. distance‐decay) is a common biogeographical observation in free‐living communities, and a slightly less common observation for parasite communities. Ecological networks of interacting species may adhere to a similar pattern of decreasing interaction similarity with increasing geographic distance, especially if species interactions are maintained across space. We extend this further, examining if host–parasite networks – independent of host and parasite species identities – become more structurally dissimilar with increasing geographic distance. Utilizing a global database of helminth parasite occurrence records, we find evidence for distance‐decay relationships in host and parasite communities at both regional and global scales, but fail to detect similar relationships in network structural similarity. Host and parasite community similarity were strongly related, and both decayed rapidly with increasing geographic distance, typically resulting in complete dissimilarity after approximately 2500 km. Our failure to detect a decay in network structural similarity suggests the possibility that different host and parasite species are filling the same functional roles in interaction networks, or that variation in network similarity may be better explained by other geographic variables or aspects of host and parasite ecology.  相似文献   

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