HOST SPECIALIZATION DIFFERENTIATES CRYPTIC SPECIES OF FEATHER-FEEDING LICE

Parasite species with differentiated host-specific populations provide a natural opportunity to explore factors involved in parasite diversification. Columbicola macrourae is a species of ectoparasitic feather louse currently recognized from 15 species of New World pigeons and doves. Mitochondrial sequences reveal five divergent haplotype clusters within C. macrourae , suggesting cryptic species. Each cluster is relatively host specific, with only one or a few hosts. We conducted a reciprocal transfer experiment with two of these lineages to test whether host use has an adaptive component. Our results demonstrate that the fitness of each lineage is considerably higher on its native host than on the novel host suggesting that one or more selective agents favor host specialization by the different lineages. In addition, we were able to morphologically separate individual lice from the two experimental lineages using discriminant function analysis. Furthermore, differences in the size of these louse lineages match differences in the size of their respective hosts, paralleling the strong correlation between parasite and host body size across the genus Columbicola . Together, these results suggest that selection in this cryptic species complex reflects selection across the whole genus, and that this selection, in part, contributes to the maintenance of host specialization.     

Geographic variation in the community structure of lice on western scrub-jays

Parasites are incredibly diverse. An important factor in the evolution of this diversity is the fact that many parasite species are restricted to 1, or just a few, host species. In addition, some parasites exhibit geographic specificity that is nested within their specificity to a particular species of host. The environmental factors that restrict parasites to particular regions within the host's range are poorly understood, and it is often difficult to know whether such patterns of geographic specificity are real, or merely artifacts of uneven host sampling. For over a decade, we sampled communities of ectoparasitic lice (Phthiraptera) from western scrub-jays (Aphelocoma californica) throughout their range in the United States, and found 3 common species of lice. Philopterus crassipes was found throughout the host range, whereas the other 2 species of lice had more restricted distributions. Brueelia deficiens was found only on the woodhouseii host subspecies group, and Myrsidea sp. was found largely on the californica host subspecies group. We suggest that differential tolerance to arid conditions and interspecific competition has led to the restricted geographic distributions of these 2 species of lice.     

Host defence mediates interspecific competition in ectoparasites

1. Interspecific competition influences which, how many and where species coexist in biological communities. Interactions between species in different trophic levels can mediate interspecific competition; e.g. predators are known to reduce competition between prey species by suppressing their population sizes. A parallel phenomenon may take place in host-parasite systems, with host defence mediating competition between parasite species. 2. We experimentally investigated the impact of host defence (preening) on competitive interactions between two species of feather-feeding lice: 'wing' lice Columbicola columbae and 'body' lice Campanulotes compar. Both species are host-specific parasites that co-occur on rock pigeons Columba livia. 3. We show that wing lice and body lice compete and that host defence mediates the magnitude of this competitive interaction. 4. Competition is asymmetrical; wing louse populations are negatively impacted by body lice, but not vice versa. This competitive asymmetry is consistent with the fact that body lice predominate in microhabitats on the host's body that offer the most food and the most space. 5. Our results indicate that host-defence-mediated competition can influence the structure of parasite communities and may play a part in the evolution of parasite diversity.     

Differences in straggling rates between two genera of dove lice (Insecta: Phthiraptera) reinforce population genetic and cophylogenetic patterns

Differences in dispersal abilities have been implicated for causing disparate evolutionary patterns between Columbicola and Physconelloides lice (Insecta: Phthiraptera). However, no study has documented straggling (when lice are found on atypical hosts) rates within these lineages. We used the fact that the Galapagos Hawk, Buteo galapagoensis (Gould) (Falconiformes) feeds on the Galapagos Dove Zenaida galapagoensis Gould (Columbiformes) within an ecologically simplified setting. The Galapagos Dove is the only typical host of Columbicola macrourae (Wilson) and Physconelloides galapagensis (Kellogg and Huwana) in Galapagos. We quantitatively sampled and found these lice on both bird species. A DNA barcoding approach confirmed that stragglers were derived from Galapagos doves. We also collected a Bovicola sp. louse, likely originating from a goat (Capra hircus). On hawks, C. macrourae was significantly more prevalent than P. galapagensis. On doves, the two lice were equally prevalent and abundant. Differences in prevalence on hawks was a function of differences in straggling rate between lice, and not a reflection of their relative representation within the dove population. This provides further evidence that differences in dispersal abilities may drive differences in the degree of cospeciation in Columbicola and Phyconelloides lice, which have become model systems in evolutionary biology.     

Evaluating condition-specific and asymmetric competition in a species-distribution context

Mechanisms resulting in parapatric distributions of closely related taxa have long interested ecologists. If two species are distributed across an environmental gradient, and differ in their ability to cope with environmental conditions, the outcome of competitive interactions may be dependent on prevailing abiotic conditions. Two closely related species of poison frogs in north–central Peru were observed to occupy parapatric distributions across an elevation gradient. Ameerega bassleri is a highland endemic restricted to a small region of Peru, and A. trivittata is distributed throughout lowland Amazonia. The goal of this study was to examine the effect of an abiotic factor (elevation) on two biotic factors (intraspecific and interspecific competition), by measuring growth and survival in the larvae of A. trivittata and A. bassleri . Using mesocosm experiments arranged in a fractional factorial design, we found that (1) A. bassleri had a strong negative effect on the growth and survival of A. trivittata regardless of elevation, (2) A. trivittata had no effect on the growth of A. bassleri at either elevation, but did appear to reduce the survival of A. bassleri more strongly in the lowlands than highlands, (3) lowland conditions uniformly reduced survival in all treatments and in both species, and (4) competition was strongly asymmetric between A. bassleri and A. trivittata . We conclude that the perceived low density of A. trivittata in highland sites may be influenced by the presence of A. bassleri, but the lower limit to the distribution of A. bassleri cannot be explained by competition with A. trivittata and may be due to physiological constraints imposed by lowland conditions.     

Condition-specific competition allows coexistence of competitively superior exotic oysters with native oysters

1. Trade-offs between competitive ability and tolerance of abiotic stress are widespread in the literature. Thus, condition-specific competition may explain spatial variability in the success of some biological invaders and why, in environments where there is small-scale environmental variability, competitively inferior and superior species can coexist. 2. We tested the hypothesis that differences in abiotic stress alter the outcome of competitive interactions between the native Sydney rock oysters Saccostrea glomerata and exotic Pacific oysters Crassostrea gigas by experimentally testing patterns of intra- and interspecific competition across a tidal elevation gradient of abiotic stress at three sites on the east coast of Australia. 3. At low and mid-intertidal heights, exotic C. gigas were able to rapidly overgrow and smother native S. glomerata, which grew at c. 60% of the exotic's rate. In high intertidal areas, where C. gigas displayed about 80% mortality but similar growth rates to S. glomerata, the native oyster was not affected by the presence of the exotic species. 4. Asymmetrical effects of the exotic species on the native could not be replicated by manipulating densities of conspecifics, confirming that effects at low and mid-intertidal heights were due to interspecific competition. 5. Our results suggest that the more rapid growth of C. gigas than S. glomerata comes at the cost of higher mortality under conditions of abiotic stress. Thus, although C. gigas may rapidly overgrow S. glomerata at low and mid tidal heights, the native oyster will not be competitively excluded by the exotic due to release from competition at high intertidal elevations. 6. The success of trade-offs in explaining spatial variation in the outcome of competitive interactions between C. gigas and S. glomerata strengthen the claim that these may be a useful tool in the quest to produce general predictive models of invasion success.     

Diet quality determines interspecific parasite interactions in host populations

The widespread occurrence of multiple infections and the often vast range of nutritional resources for their hosts allow that interspecific parasite interactions in natural host populations might be determined by host diet quality. Nevertheless, the role of diet quality with respect to multispecies parasite interactions on host population level is not clear. We here tested the effect of host population diet quality on the parasite community in an experimental study using Daphnia populations. We studied the effect of diet quality on Daphnia population demography and the interactions in multispecies parasite infections of this freshwater crustacean host. The results of our experiment show that the fitness of a low‐virulent microsporidian parasite decreased in low, but not in high‐host‐diet quality conditions. Interestingly, infections with the microsporidium protected Daphnia populations against a more virulent bacterial parasite. The observed interspecific parasite interactions are discussed with respect to the role of diet quality‐dependent changes in host fecundity. This study reflects that exploitation competition in multispecies parasite infections is environmentally dependent, more in particular it shows that diet quality affects interspecific parasite competition within a single host and that this can be mediated by host population‐level effects.     

The role of abiotic and biotic factors in determining coexistence of multiple pollinators in the yucca–yucca moth mutualism

The determinants of a species' geographic distribution are a combination of both abiotic and biotic factors. Environmental niche modeling of climatic factors has been instrumental in documenting the role of abiotic factors in a species' niche. Integrating this approach with data from species interactions provides a means to assess the relative roles of abiotic and biotic components. Here, we examine whether the high host specificity typically exhibited in the active pollination mutualism between yuccas and yucca moths is the result of differences in climatic niche requirements that limit yucca moth distributions or the result of competition among mutualistic moths that would co‐occur on the same yucca species. We compared the species distribution models of two Tegeticula pollinator moths that use the geographically widespread plant Yucca filamentosa. Tegeticula yuccasella occurs throughout eastern North America whereas T. cassandra is restricted to the southeastern portion of the range, primarily occurring in Florida. Species distribution models demonstrate that T. cassandra is restricted climatically to the southeastern United States and T. yuccasella is predicted to be able to live across all of eastern North America. Data on moth abundances in Florida demonstrate that both moth species are present on Y. filamentosa; however, T. cassandra is numerically dominant. Taken together, the results suggest that moth geographic distributions are heavily influenced by climate, but competition among pollinating congeners will act to restrict populations of moth species that co‐occur.     

Biogeography,macroecology and species' traits mediate competitive interactions in the order Lagomorpha

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Detecting the influence of climatic variables on species distributions: a test using GIS niche-based models along a steep longitudinal environmental gradient

Aim  To investigate the influence of climate variables in shaping species distributions across a steep longitudinal environmental gradient.
Location  The state of Oklahoma, south-central United States.
Methods  We used Geographical Information Systems (GIS) niche-based models to predict the geographic distributions of six pairs of closely related amphibian and reptile species across a steep longitudinal environmental gradient. We compared results from modelling with actual distributions to determine whether species distributions were primarily limited by environmental factors, and to assess the potential roles of competition and historical factors in influencing distributions.
Results  For all species pairs, GIS models predicted an overlap zone in which both species should occur, although in reality in some cases this area was occupied by only one of the species. We found that environmental factors clearly influence the distributions of most species pairs. We also found evidence suggesting that competition and evolutionary history play a role in determining the distributions of some species pairs.
Main conclusions  Niche-based GIS modelling is a useful tool for investigating species distribution patterns and the factors affecting them. Our results showed that environmental factors strongly influenced species distributions, and that competition and historical factors may also be involved in some cases. Furthermore, results suggested additional lines of research, such as ecological comparisons among populations occurring inside and outside predicted overlap zones, which may provide more direct insight into the roles of competitive interactions and historical factors in shaping species distributions.     

Co-Occurrence and Occupancy of Mourning Doves and Eurasian Collared-Doves

Understanding how land cover and potential competition with invasive species shape patterns of occupancy, extirpation, and colonization of native species across a landscape can help target management for declining native populations. Mourning dove (Zenaida macroura) populations have declined throughout the United States from 1965–2015. The expansion of the Eurasian collared-dove (Streptopelia decaocto), an introduced species with similar food preferences, may further threaten mourning dove populations. We analyzed data from 2009–2016 from a large-scale monitoring program in the Western Great Plains of the United States in a 2-species occupancy model to assess the effects of collared-doves on mourning dove distributions, while accounting for imperfect detection and variation in land cover across the landscape. Mourning dove occupancy was stable or increasing across our study area, and despite overlap in resource use and co-occurrence between mourning doves and Eurasian collared-doves, we found no evidence that collared-doves are extirpating mourning doves from preferred habitat during the breeding season. © 2020 The Wildlife Society.     

Can infection by eugregarine parasites mediate species coexistence in Calopteryx damselflies?

1. Parasitism may be an important factor determining the coexistence of closely related species. Although host–parasite interactions can affect the ecology and distribution of the host species, virtually nothing is known about how other interspecific interactions affecting the host, such as competition or predation, relate to the parasite burden of the host. 2. We studied parasite‐mediated competition between two closely related Calopteryx damselflies, C. virgo L. and C. splendens Harris. We investigated a total of 31 populations, including 18 allopatric and 13 sympatric populations. We measured the occurrence of gut parasites, eugregarines. 3. We found that the prevalence of gregarines was higher in C. virgo than in C. splendens. On average, more than half of the C. virgo individuals were infected by eugregarines both in allopatric and sympatric populations. However, hardly any allopatric C. splendens populations had gregarines, but most of sympatric populations had infected individuals. 4. According to our results, co‐existence of the host species affects the likelihood of the subordinate species showing higher levels of parasitism. Interspecific aggression, lower species genetic heterozygosity, and the difference in host species immunity are proposed as possible explanations for greater parasite burdens in the inferior species at sympatric sites.     

相互作用的集合种群研究动态

在集合种群水平上,两个或更多物种可以生活在同一个斑块网络中而没有相互作用.但在很多情况下,种间的相互作用会影响种群的迁移率、灭绝率和侵占率,从而调节相应物种的集合种群动态.这方面的研究主要有集合种群水平上物种之间的竞争、捕食以及在没有任何环境异质性的条件下物种在空间上聚集分布的产生和维持等.综述了近年来关于集合种群水平上的竞争,捕食者和猎物系统以及捕食与复杂空间动态的最新研究成果.     

Competition, predation and species responses to environmental change

Despite much effort over the past decade on the ecological consequences of global warming, ecologists still have little understanding of the importance of interspecific interactions in species responses to environmental change. Models predict that predation should mitigate species responses to environmental change, and that interspecific competition should aggravate species responses to environmental change. To test this prediction, we studied how predation and competition affected the responses of two ciliates, Colpidium striatum and Paramecium tetraurelia , to temperature change in laboratory microcosms. We found that neither predation nor competition altered the responses of Colpidium striatum to temperature change, and that competition but not predation altered the responses of Paramecium tetraurelia to temperature change. Asymmetric interactions and temperature-dependent interactions may have contributed to the disparity between model predictions and experimental results. Our results suggest that models ignoring inherent complexities in ecological communities may be inadequate in forecasting species responses to environmental change.     

Save your host,save yourself? Caste‐ratio adjustment in a parasite with division of labor and snail host survival following shell damage

Shell damage and parasitic infections are frequent in gastropods, influencing key snail host life‐history traits such as survival, growth, and reproduction. However, their interactions and potential effects on hosts and parasites have never been tested. Host–parasite interactions are particularly interesting in the context of the recently discovered division of labor in trematodes infecting marine snails. Some species have colonies consisting of two different castes present at varying ratios; reproductive members and nonreproductive soldiers specialized in defending the colony. We assessed snail host survival, growth, and shell regeneration in interaction with infections by two trematode species, Philophthalmus sp. and Maritrema novaezealandense, following damage to the shell in the New Zealand mud snail Zeacumantus subcarinatus. We concomitantly assessed caste‐ratio adjustment between nonreproductive soldiers and reproductive members in colonies of the trematode Philophthalmus sp. in response to interspecific competition and shell damage to its snail host. Shell damage, but not parasitic infection, significantly increased snail mortality, likely due to secondary infections by pathogens. However, trematode infection and shell damage did not negatively affect shell regeneration or growth in Z. subcarinatus; infected snails actually produced more new shell than their uninfected counterparts. Both interspecific competition and shell damage to the snail host induced caste‐ratio adjustment in Philophthalmus sp. colonies. The proportion of nonreproductive soldiers increased in response to interspecific competition and host shell damage, likely to defend the parasite colony and potentially the snail host against increasing threats. These results indicate that secondary infections by pathogens following shell damage to snails both significantly increased snail mortality and induced caste‐ratio adjustments in parasites. This is the first evidence that parasites with a division of labor may be able to produce nonreproductive soldiers according to environmental factors other than interspecific competition with other parasites.     

Intra- and interspecific competition among helminth parasites: effects on Coitocaecum parvum life history strategy, size and fecundity

Larval helminths often share intermediate hosts with other individuals of the same or different species. Competition for resources and/or conflicts over transmission routes are likely to influence both the association patterns between species and the life history strategies of each individual. Parasites sharing common intermediate hosts may have evolved ways to avoid or associate with other species depending on their definitive host. If not, individual parasites could develop alternative life history strategies in response to association with particular species. Three sympatric species of helminths exploit the amphipod Paracalliope fluviatilis as an intermediate host in New Zealand: the acanthocephalan Acanthocephalus galaxii, the trematode Microphallus sp. and the progenetic trematode Coitocaecum parvum. Adult A. galaxii and C. parvum are both fish parasites whereas Microphallus sp. infects birds. We found no association, either positive or negative, among the three parasite species. The effects of intra- and interspecific interactions were also measured in the trematode C. parvum. Both intra- and interspecific competition seemed to affect both the life history strategy and the size and fecundity of C. parvum. Firstly, the proportion of progenesis was higher in metacercariae sharing their host with Microphallus sp., the bird parasite, than in any other situation. Second, the intensity of intraspecific competition apparently constrained the ability of metacercariae to adopt progenesis and limited both the growth and egg production of progenetic individuals. These results show that the life history strategy adopted by a parasite may be influenced by other parasites sharing the same host.     

Does timing matter? How priority effects influence the outcome of parasite interactions within hosts

In nature, hosts are exposed to an assemblage of parasite species that collectively form a complex community within the host. To date, however, our understanding of how within-host–parasite communities assemble and interact remains limited. Using a larval amphibian host (Pacific chorus frog, Pseudacris regilla) and two common trematode parasites (Ribeiroia ondatrae and Echinostoma trivolvis), we experimentally examined how the sequence of host exposure influenced parasite interactions within hosts. While there was no evidence that the parasites interacted when hosts were exposed to both parasites simultaneously, we detected evidence of both intraspecific and interspecific competition when exposures were temporally staggered. However, the strength and outcome of these priority effects depended on the sequence of addition, even after accounting for the fact that parasites added early in host development were more likely to encyst compared to parasites added later. Ribeiroia infection success was reduced by 14 % when Echinostoma was added prior to Ribeiroia, whereas no such effect was noted for Echinostoma when Ribeiroia was added first. Using a novel fluorescent-labeling technique that allowed us to track Ribeiroia infections from different exposure events, we also discovered that, similar to the interspecific interactions, early encysting parasites reduced the encystment success of later arriving parasites by 41 %, which could be mediated by host immune responses and/or competition for space. These results suggest that parasite identity interacts with host immune responses to mediate parasite interactions within the host, such that priority effects may play an important role in structuring parasite communities within hosts. This knowledge can be used to assess host–parasite interactions within natural communities in which environmental conditions can lead to heterogeneity in the timing and composition of host exposure to parasites.     

Temperature and multiple parasites combine to alter host community structure

Predicting the effects of climate change requires understanding complex interactions among multiple abiotic and biotic factors. By influencing key interactions among host species, parasites can affect community and ecosystem structuring. Yet, our understanding of how multiple parasites and abiotic factors interact to alter ecosystem structure remains limited. To empirically test the role of temperature variation and parasites in shaping communities, we used a multigenerational mesocosm experiment composed of four sympatric freshwater crustacean species (isopods and amphipods) that share up to four parasite species. Mesocosms were assigned to one of four different treatments with contrasting seasonal temperatures (normal and elevated) and parasite exposure levels (continuous and arrested (presence or absence of parasite larvae in mesocosm)). We found that parasite exposure and water temperature had interactive effects on the host community. Continuous exposure to parasites altered the community structure and differences in water temperature altered species abundance. The abundance of the amphipod Paracalliope fluviatilis decreased substantially when experiencing continuous parasite exposure and elevated water temperatures. Elevated temperatures also led to parasite-induced mortality in another amphipod host, Paracorophium excavatum. Contrastingly, isopod hosts were affected much less, suggesting increasing temperatures in conjunction with higher parasite exposure might increase their relative abundance in the community. Changes in invertebrate host populations have implications for other species such as fish and birds that consume crustaceans as well as having impacts on ecosystem processes, such as aquatic primary production and nutrient cycling. In light of climate change predictions, parasite exposure and rise in average temperatures may have substantial impacts on communities and ecosystems, altering ecosystem structure and dynamics.     

The population genetics of host specificity: genetic differentiation in dove lice (Insecta: Phthiraptera)

Some species of parasites occur on a wide range of hosts while others are restricted to one or a few host species. The host specificity of a parasite species is determined, in part, by its ability to disperse between host species. Dispersal limitations can be studied by exploring the genetic structure of parasite populations both within a single species of host and across multiple host species. In this study we examined the genetic structure in the mitochondrial cytochrome oxidase I (COI) gene of two genera of lice (Insecta: Phthiraptera) occurring on multiple sympatric species of doves in southern North and Central America. One genus, Columbicola, is generally less host-specific than the other, Physconelloides. For both genera we identified substantial genetic differentiation between populations of conspecific lice on different host species, generally 10-20% sequence divergence. This level of divergence is in the range of that often observed between species of these two genera. We used nested clade analysis to explore fine scale genetic structure within species of these feather lice. We found that species of Physconelloides exhibited more genetic structure, both among hosts and among geographical localities, than did species of Columbicola. In many cases, single haplotypes within species of Columbicola are distributed on multiple host species. Thus, the population genetic structure of species of Physconelloides reveals evidence of geographical differentiation on top of high host species specificity. Underlying differences in dispersal biology probably explain the differences in population genetic structure that we observed between Columbicola and Physconelloides.     

Interspecific and intraspecific interactions between salt marsh plants: integrating the effects of environmental factors and density on plant performance

There has been much debate about the role of plant interactions in the structure and function of vegetation communities. Here the results of a pot experiment with controlled environments are described where three environmental variables (nutrients, sediment type and waterlogging) were manipulated factorially to identify their effects on the growth and intensity of interactions occurring between Spartina anglica and Puccinellia maritima. The two species were grown in split-plot planting treatments, representing intraspecific and interspecific addition series experiments, to determine individual and interactive effects of environmental factors and plant interactions on plant biomass.
Above-ground growth of both species involved interactions between the environmental and planting treatments, while below-ground, environmental factors affected the biomass irrespective of planting treatments. It was suggested that this difference in growth response is evidence that in our experiment plant interactions between the two species occur primarily at the above-ground level.
The intensity of plant interactions varied in a number of ways. First, interactions between Spartina and Puccinellia were distinctly asymmetrical, Puccinellia exerting a competitive effect on Spartina, with no reciprocal effect, and with a facilitative effect of Spartina on Puccinellia in low nutrient conditions. Second, the interactions varied in intensity in different environmental conditions. Interspecific competitive effects of Puccinellia on Spartina were more intense in conditions favourable to growth of Puccinellia and reduced or non-existent in environments with more abiotic stress. Third, intraspecific competition was found to be less intense for both species than interspecific interactions. Finally, the intensity of plant interactions involving both species was more intense above ground than below ground, with a disproportionate reduction in the intensity of interspecific competition below relative to above ground in treatments with less productive sediments and greater immersion. This is interpreted as reflecting a potential mechanism by which Spartina may be able to evade competitive neighbours.