Parasite transmission in complex communities: predators and alternative hosts alter pathogenic infections in amphibians

While often studied in isolation, host-parasite interactions are typically embedded within complex communities. Other community members, including predators and alternative hosts, can therefore alter parasite transmission (e.g., the dilution effect), yet few studies have experimentally evaluated more than one such mechanism. Here, we used data from natural wetlands to design experiments investigating how alternative hosts and predators of parasites mediate trematode (Ribeiroia ondatrae) infection in a focal amphibian host (Pseudacris regilla). In short-term predation bioassays involving mollusks, zooplankton, fish, larval insects, or newts, four of seven tested species removed 62-93% of infectious stages. In transmission experiments, damselfly nymphs (predators) and newt larvae (alternative hosts) reduced infection in P. regilla tadpoles by -50%, whereas mosquitofish (potential predators and alternative hosts) did not significantly influence transmission. Additional bioassays indicated that predators consumed parasites even in the presence of alternative prey. In natural wetlands, newts had similar infection intensities as P. regilla, suggesting that they commonly function as alternative hosts despite their unpalatability to downstream hosts, whereas mosquitofish had substantially lower infection intensities and are unlikely to function as hosts. These results underscore the importance of studying host-parasite interactions in complex communities and of broadly linking research on predation, biodiversity loss, and infectious diseases.     

Adding infection to injury: synergistic effects of predation and parasitism on amphibian malformations

We explored the importance of interactions between parasite infection and predation in driving an emerging phenomenon of conservation importance: amphibian limb malformations. We suggest that injury resulting from intraspecific predation in combination with trematode infection contributes to the frequency and severity of malformations in salamanders. By integrating field surveys and experiments, we evaluated the individual and combined effects of conspecific attack and parasite (Ribeiroia ondatrae) infection on limb development of long-toed salamanders (Ambystoma macrodactylum). In the absence of Ribeiroia, abnormalities involved missing digits, feet, or limbs and were similar to those produced by cannibalistic attack in experimental trials. At field sites that supported Ribeiroia, malformations were dominated by extra limbs and digits. Correspondingly, laboratory exposure of larval salamanders to Ribeiroia cercariae over a 30-day period induced high frequencies of malformations, including extra digits, extra limbs, cutaneous fusion, and micromelia. However, salamander limbs exposed to both injury and infection exhibited 3-5 times more abnormalities than those exposed to either factor alone. Infection also caused significant delays in limb regeneration and time-to-metamorphosis. Taken together, these results help to explain malformation patterns observed in natural salamander populations while emphasizing the importance of interactions between parasitism and predation in driving disease.     

Endangered light-footed clapper rail affects parasite community structure in coastal wetlands.

An extinction necessarily affects community members that have obligate relationships with the extinct species. Indirect or cascading effects can lead to even broader changes at the community or ecosystem level. However, it is not clear whether generalist parasites should be affected by the extinction of one of their hosts. We tested the prediction that loss of a host species could affect the structure of a generalist parasite community by investigating the role of endangered Light-footed Clapper Rails (Rallus longirostris levipes) in structuring trematode communities in four tidal wetlands in southern California, U.S.A. (Carpinteria Salt Marsh, Mugu Lagoon) and Mexico (Estero de Punta Banda, Bahia Falsa-San Quintin). We used larval trematode parasites in first intermediate host snails (Cerithidea californica) as windows into the adult trematodes that parasitize Clapper Rails. Within and among wetlands, we found positive associations between Clapper Rails and four trematode species, particularly in the vegetated marsh habitat where Clapper Rails typically occur. This suggests that further loss of Clapper Rails is likely to affect the abundance of several competitively dominant trematode species in wetlands with California horn snails, with possible indirect effects on the trematode community and changes in the impacts of these parasites on fishes and invertebrates.     

Species diversity reduces parasite infection through cross-generational effects on host abundance

With growing interest in the effects of biodiversity on disease, there is a critical need for studies that empirically identify the mechanisms underlying the diversity-disease relationship. Here, we combined wetland surveys of host community structure with mechanistic experiments involving a multi-host parasite to evaluate competing explanations for the dilution effect. Sampling of 320 wetlands in California indicated that snail host communities were strongly nested, with competent hosts for the trematode Ribeiroia ondatrae predominating in low-richness assemblages and unsuitable hosts increasingly present in more diverse communities. Moreover, competent host density was negatively associated with increases in snail species richness. These patterns in host community assembly support a key prerequisite underlying the dilution effect. Results of multigenerational mesocosm experiments designed to mimic field-observed community assemblages allowed us to evaluate the relative importance of host density and diversity in influencing parasite infection success. Increases in snail species richness (from one to four species) had sharply negative effects on the density of infected hosts (-90% reduction). However, this effect was indirect; competition associated with non-host species led to a 95% reduction in host density (susceptible host regulation), owing primarily to a reduction in host reproduction. Among susceptible hosts, there were no differences in infection prevalence as a function of community structure, indicating a lack of support for a direct effect of diversity on infection (encounter reduction). In monospecific conditions, higher initial host densities increased infection among adult hosts; however, compensatory reproduction in the low-density treatments equalized the final number of infected hosts by the next generation, underscoring the relevance of multigenerational studies in understanding the dilution effect. These findings highlight the role of interspecific competition in mediating the relationship between species richness and parasite infection and emphasize the importance of field-informed experimental research in understanding mechanisms underlying the diversity-disease relationship.     

Cuckoo wasps manipulate foraging and resting activities in their hosts

Parasite-induced alterations in host behaviour have been reported in a large number of taxa. However, some parasites are better than others to exploit the resources offered by their hosts. To date, our understanding of the extent to which some obligate parasites exploit social insect colonies is still limited. In this study, we examined parasite-mediated behavioural alterations of Polistes biglumis wasps parasitized by the obligate social parasite Polistes atrimandibularis by comparing host female-activity in parasitized and non-parasitized colonies. Host foundresses foraged more and rested less in parasitized than in non-parasitized colonies (controlling for the number of larvae in the nest, the time of day, and the day in the season). Next, we used short-term parasite removal experiments to investigate how social parasites manipulate their hosts. We found that parasitized hosts foraged more and rested less when social parasites were on the nest rather than after their removal, and we tested which kind of interactions occurred between parasites and hosts. P. atrimandibularis parasites may use mainly non-aggressive interactions (such as antennation and trophallaxis) to manipulate host activities, rather than visual, acoustic or chemical signals as other parasites do.     

Coevolution,communication, and host chick mimicry in parasitic finches: who mimics whom?

Why do brood parasitic Vidua nestlings mimic the intricate gape patterns of their hosts’ young so precisely? The classic explanation is that mimicry is the outcome of a coevolutionary arms race, driven by host rejection of odd-looking offspring. Selection favors parasitic nestlings that converge on the host young’s mouth markings, and simultaneously benefits hosts whose mouth markings diverge from those of the parasite. The outcome is highly elaborate mouth markings in host young that are accurately mimicked by parasite nestlings. Our review of recent work provides mixed support for this traditional view and, instead suggest that complex mouth markings function to stimulate adequate provisioning, rather than to signal species identity. Thus, similarly elaborate gape morphologies in hosts and parasites could have evolved through nestling competition for parental care. According to this view, and in contrast with existing hypotheses, it is host young that mimic parasitic offspring, in order to compete effectively for food.     

Parasite facilitates plant species coexistence in a coastal wetland

Outbreaks of infectious agents in natural ecosystems are on the rise. Understanding host-pathogen interactions and their impact on community composition may be central to the conservation of biological diversity. Infectious agents can convey both exploitive and facilitative effects that regulate host populations and community structure. Parasitic angiosperms are highly conspicuous in many plant communities, and they provide a tractable model for understanding parasite effects in multispecies communities. I examined host identity and variation in host infectivity of a holoparasitic vine (Cuscuta salina) within a California salt marsh. In a two-year parasite removal experiment, I measured the effect of C. salina on its most frequent host, a rare hemiparasite, and the plant community. C. salina clearly suppressed the dominant host, but rare plant fitness and plant species diversity were enhanced through indirect effects. Priority effects played a role in the strength of the outcome due to the timing of life history characteristics. The differential influence of parasites on the fecundity of multiple hosts can change population dynamics, benefit rare species, and alter community structure. The continuum of negative to positive consequences of parasitic interactions deserves more attention if we are to understand community dynamics and successfully restore tidal wetlands.     

Why are larvae of the social parasite wasp <Emphasis Type="Italic">Polistes sulcifer</Emphasis> not removed from the host nest?

A challenge for parasites is how to evade the sophisticated detection and rejection abilities of potential hosts. Many studies have shown how insect social parasites overcome host recognition systems and successfully enter host colonies. However, once a social parasite has successfully usurped an alien nest, its brood still face the challenge of avoiding host recognition. How immature stages of parasites fool the hosts has been little studied in social insects, though this has been deeply investigated in birds. We look at how larvae of the paper wasp obligate social parasite Polistes sulcifer fool their hosts. We focus on cuticular hydrocarbons (CHCs), which are keys for adult recognition, and use behavioral recognition assays. Parasite larvae might camouflage themselves either by underproducing CHCs (odorless hypothesis) or by acquiring a chemical profile that matches that of their hosts. GC/MS analyses show that parasite larvae do not have lower levels of CHCs and that their CHCs profile is similar to the host larval profile but shows a reduced colony specificity. Behavioral tests show that the hosts discriminate against alien conspecific larvae from different colonies but are more tolerant towards parasite larvae. Our results demonstrate that parasite larvae have evolved a host larval profile, which overcomes the host colony recognition system probably because of the lower proportion of branched compounds compared to host larvae. In some ways, this is a similar hypothesis to the odorless hypothesis, but it assumes that the parasite larvae are covered by a chemical blend that is not meaningful to the host.     

Eggshell spotting in brood parasitic shiny cowbirds (<Emphasis Type="Italic">Molothrus bonariensis</Emphasis>) is not linked to the female sex chromosome

For avian brood parasites in which individual females are host-specialists, the arms race between hosts and parasites has favored egg color polymorphism in the parasite, with female lineages laying mimetic eggs that resemble those of the host species they parasitize. Female sex-linked inheritance of egg color fosters evolutionary stability of egg polymorphism if female lineages show both consistent eggshell color and host use. This co-evolutionary relationship is unlikely to occur if individual brood parasites use different hosts or if egg color is not maternally inherited. The shiny cowbird (Molothrus bonariensis) is an extreme generalist brood parasite that shows a very high degree of egg polymorphism. We tested whether egg spotting in this species has female sex-linked inheritance. If genetic factors controlling the expression of egg spotting were present on the female-specific W chromosome, we expected co-segregation between spotting patterns and mtDNA haplotypes, as both W and mtDNA are maternally inherited. In contrast to the known maternal inheritance of spotting patterns in great tits, we found no associations between eggshell spotting and mtDNA haplotypes, which suggests that eggshell spotting is not maternally inherited in this cowbird species.     

Genetic relatedness and eusociality: parasite-mediated selection on the genetic composition of groups

Summary Contrary to the expectations of kin selection theory, intracolony relatedness in eusocial insects is often low. We examined the idea that associations of low relatedness (high genetic variability) may be advantageous because of negative frequency-dependent selection on common host phenotypes by rapidly evolving parasites and pathogens. Using the natural host-parasite system of the bumble bee Bombus terrestris and its intestinal trypanosome Crithidia bombi, we investigated the transmission properties of parasites in host groups. Within naturally infested nests and in artificially constructed groups of workers, prevalence of infestation increased with time of exposure (Table 1). The susceptibility of isolated groups of workers to the parasites to which they were exposed differed with identity and natural infestation of their nest of origin (Table 2). In addition, those workers that were related to the individual introducing an infection to their group were more likely to become infested than were unrelated workers (Table 3). Although the bumble bee workers in experimental boxes appeared to differ in behavior toward kin and non-kin, making more physical contacts with kin, we found no discernible relationship between number of physical contacts and prevalence of infestation in a group. Therefore, we conclude that differences in parasite transmission reflected interactions among different host and parasite phenotypes. This system thus demonstrates the factors necessary for negative frequency-dependent selection by parasites on common host phenotypes - variability for susceptibility and infectiousness in host and parasite populations and similarity for these traits among related individuals. If, as we show here, high genetic relatedness within groups enhances parasite transmission, kin directed altruism may increase the risk of contracting parasites and infectious diseases. Therefore, parasites and pathogens may be an important force moderating the genetic structure of social groups. Offprint requests to: J.A. Shykoff at the present address     

Effects of salinity on multiplication and transmission of an intertidal trematode parasite

Salinity levels vary spatially in coastal areas, depending on proximity to freshwater sources, and may also be slowly decreasing as a result of anthropogenic climatic changes. The impact of salinity on host–parasite interactions is potentially a key regulator of transmission processes in intertidal areas, where trematodes are extremely common parasites of invertebrates and vertebrates. We investigated experimentally the effects of long-term exposure to decreased salinity levels on output of infective stages (cercariae) and their transmission success in the trematode Philophthalmus sp. This parasite uses the snail Zeacumantus subcarinatus as intermediate host, in which it asexually produces cercariae. After leaving the snail, cercariae encyst externally on hard substrates to await accidental ingestion by shorebirds, which serve as definitive hosts. We found that at reduced salinities (25 or 30 psu), the cercarial output of the parasite was lower, the time taken by cercariae to encyst was longer, fewer cercariae successfully encysted and encysted parasites had lower long-term survival than at normal seawater salinity (35 psu). The strong effect of salinity on the replication and transmission of this parasite suggests that there may be sources and sinks of transmission to birds along coastal areas, depending on local salinity conditions. Also, unless it evolves to adapt to changing conditions, the predicted reduction in salinity as a consequence of climate change may have negative impact on the parasite’s abundance.     

House sparrows selectively eject parasitic conspecific eggs and incur very low rejection costs

Most host species of obligate interspecific brood parasites are under strong selection because such parasitism, e.g., that involving evictor nestmates, is highly costly. Egg rejection is one of the most efficient host defences against avian brood parasites. Many hosts have thus evolved egg-recognition ability and rejection behaviour. However, this defensive mechanism has not evolved in most species where only intraspecific brood parasitism occurs, probably because (1) the eggs of conspecific females are very similar in appearance, making egg rejection less likely to emerge, and (2) such parasitism is frequently less costly than interspecific parasitism. Using a captive population of house sparrows (Passer domesticus) with a low breeding density, we here provide new evidence showing that this species actually has a fine capacity to discriminate conspecific eggs and to eject them (44.2% of foreign eggs ejected) while incurring very low rejection costs (4.2% of own eggs ejected). This result contradicts those previously found in high-density house sparrow populations in which very high rejection costs and very high clutch desertion rates were reported, probably as a consequence of intraspecific competition and infanticide provoked by the high breeding density. The house sparrow has only rarely been reported as the host of an interspecific brood parasite, which implies that it is a newly described example of an altricial species in which egg ejection has evolved and is maintained in response to intraspecific brood parasitism.     

Temporal, spatial, and between-host comparisons of patterns of parasitism in lake zooplankton

In nature, multiple parasite species infect multiple host species and are influenced by processes operating across different spatial and temporal scales. Data sets incorporating these complexities offer exciting opportunities to examine factors that shape epidemics. We present a method using generalized linear mixed models in a multilevel modeling framework to analyze patterns of variances and correlations in binomially distributed prevalence data. We then apply it to a multi-lake, multiyear data set involving two Daphnia host species and nine microparasite species. We found that the largest source of variation in parasite prevalence was the species identities of host-parasite pairs, indicating strong host-parasite specificity. Within host-parasite combinations, spatial variation (among lakes) exceeded interannual variation. This suggests that factors promoting differences among lakes (e.g., habitat characteristics and species interactions) better explain variation in peak infection prevalence in our data set than factors driving differences among years (e.g., climate). Prevalences of parasites in D. dentifera were more positively correlated than those for D. pulicaria, suggesting that similar factors influenced epidemic size among parasites in D. dentifera. Overall, this study demonstrates a method for parsing patterns of variation and covariation in infection prevalence data, providing greater insight into the relative importance of different underlying drivers of parasitism.     

Tactics of parasitic American coots: host choice and the pattern of egg dispersion among host nests

Summary I examined the tactics adopted by a conspecific brood parasite, the American coot (Fulica americana), and the degree to which these tactics reflect sources of mortality for parasitic eggs. Only 8% of parasitic eggs produced independent offspring, compared to a 35% success rate for non-parasitic eggs, and most mortality was due to egg-rejection by hosts or the consequences of laying eggs too late in the host's nesting cycle. Parasites usually laid parasitically before initiating their own nests and usually parasitized immediate neighbours. Parasites did not remove host eggs before laying their own egg, and egg disappearance in general was not more common at parasitized nests. I found no evidence for non-random host choice, either on the basis of stage of the host's nesting cycle or the host's brood size. The absence of adaptive host choice is likely a consequence of the fact that, due to host limitation, only a small proportion of parasites had meaningful variation among potential hosts to choose from. The pattern of egg dispersion among host nests by individual parasites appears to be a compromise between constraints imposed by host limitation and the increased success obtained from spreading eggs among nests. Most females laying fewer than five parasitic eggs laid them in a single host nest while females laying five or more eggs normally parasitized two or more hosts. An examination of egg rejection and survival rates showed that parasites would maximize success by laying a single egg per host nest, and the pattern of laying several eggs per host nest is likely a consequence of host limitation. However, no egg that was the fifth laid, or later, parasitic egg in a host nest was ever successful and this probably explains why most females laying five or more eggs parasitized more than one host.     

Infectious Diseases and Extinction Risk in Wild Mammals

Abstract:  Parasite-driven declines in wildlife have become increasingly common and can pose significant risks to natural populations. We used the IUCN Red List of Threatened and Endangered Species and compiled data on hosts threatened by infectious disease and their parasites to better understand the role of infectious disease in contemporary host extinctions. The majority of mammal species considered threatened by parasites were either carnivores or artiodactyls, two clades that include the majority of domesticated animals. Parasites affecting host threat status were predominantly viruses and bacteria that infect a wide range of host species, including domesticated animals. Counter to our predictions, parasites transmitted by close contact were more likely to cause extinction risk than those transmitted by other routes. Mammal species threatened by parasites were not better studied for infectious diseases than other threatened mammals and did not have more parasites or differ in four key traits demonstrated to affect parasite species richness in other comparative studies. Our findings underscore the need for better information concerning the distribution and impacts of infectious diseases in populations of endangered mammals. In addition, our results suggest that evolutionary similarity to domesticated animals may be a key factor associated with parasite-mediated declines; thus, efforts to limit contact between domesticated hosts and wildlife could reduce extinction risk.     

Do these eggs smell funny to you?: an experimental study of egg discrimination by hosts of the social parasite Polyergus breviceps (Hymenoptera: Formicidae)

Social parasites exploit the behaviours of other social species. Infiltration of host systems involves a variety of mechanisms depending on the conditions within the host society and the needs of the social parasite. For many species of socially parasitic ants, colony establishment entails the usurpation of colonies of other species. This frequently involves the eviction or death of the host colony queen and the subsequent adoption of the invading queen. The social parasite queen achieves host worker acceptance by either manipulating the nest-mate recognition processes of the host or undergoing chemical modification. Little is known, however, about how host workers respond to social parasite eggs or whether host species defend against brood parasitism during parasite invasions. Host species are believed to adopt social parasite offspring because the recent common ancestry between many social parasites and their hosts may grant the sharing of certain characteristics such as chemical cues. Use of multiple host species, however, suggests other processes are needed for the social bond between host and parasite young to form. This study reports the findings of adoption bioassays in which eggs from a slave-maker ant, Polyergus breviceps, were offered to workers of two of its host species from unparasitised or newly parasitised nests to determine whether P. breviceps eggs generally elicit rearing behaviours from multiple host species. Comparisons of parasite egg survival until adulthood with conspecific egg survival reveal that workers of both host species, free-living or newly enslaved, do not typically accept slave-maker eggs. Both host species thus have sufficient discriminatory power to reject social parasite eggs although our hydrocarbon analysis indicates parasite eggs may be adapted to their local host species. Combined these results suggest that host rearing of P. breviceps eggs may reflect an evolutionary equilibrium that is maintained by probability and cost of recognition errors.Communicated by L. Sundström     

Interactions between macroparasites and microparasites drive infection patterns in free-ranging African buffalo

Epidemiological studies typically focus on single-parasite systems, although most hosts harbor multiple parasite species; thus, the potential impacts of co-infection on disease dynamics are only beginning to be recognized. Interactions between macroparasites, such as gastrointestinal nematodes, and microparasites causing diseases like TB, AIDS, and malaria are particularly interesting because co-infection may favor transmission and progression of these important diseases. Here we present evidence for strong interactions between gastrointestinal worms and bovine tuberculosis (TB) in free-ranging African buffalo (Syncerus caffer). TB and worms are negatively associated at the population, among-herd, and within-herd scales, and this association is not solely the result of demographic heterogeneities in infection. Combining data from 1362 buffalo with simple mechanistic models, we find that both accelerated mortality of co-infected individuals and TB transmission heterogeneity caused by trade-offs in immunity to the two types of parasites likely contribute to observed infection patterns. This study is one of the first to examine the relevance of within-host immunological trade-offs for understanding parasite distribution patterns in natural populations.     

Interannual dynamics of antibody levels in naturally infected long-lived colonial birds

Little is known about the long-term persistence of specific antibodies (Ab) in natural host-parasite systems despite its potential epidemiological and ecological importance. In long-lived species, knowledge of the dynamics of individual immunological profiles can be important not only for interpreting serology results, but also for assessing transmission dynamics and the potential selective pressures acting on parasites. The aim of this paper was to investigate temporal variation in levels of specific Ab against the bacterium Borrelia burgdorferi sensu lato in adults of a long-lived colonial seabird, the Black-legged Kittiwake Rissa tridactyla. In wild populations, adults are naturally exposed each breeding season to a Borrelia vector, the tick Ixodes uriae. Breeding birds were captured during four consecutive breeding seasons, and parasite infestation quantified. Using enzyme-linked immunosorbent assay (ELISA) and immunoblots, we found that the immunological profiles of anti-Borrelia Ab were highly repeatable among years, reflecting the interannual persistence of Ab levels. We nevertheless also observed that year-to-year changes of Ab levels were related to exposure to ticks in the previous year. The long-term persistence of Ab levels may be an important mechanism of individual protection against future exposure to the microparasite. It will also affect the availability of susceptible hosts, and thus the transmission dynamics of the bacterium. These results illustrate the need to consider the dynamics of the immune response in order to better understand the evolutionary ecology of host-parasite interactions in natural populations.     

Understanding the net effects of pesticides on amphibian trematode infections

Anthropogenic factors can have simultaneous positive and negative effects on parasite transmission, and thus it is important to quantify their net effects on disease risk. Net effects will be a product of changes in the survival and traits (e.g., susceptibility, infectivity) of both hosts and parasites. In separate laboratory experiments, we exposed cercariae of the trematode Echinostoma trivolvis, and its first and second intermediate hosts, snails (Planorbella trivolvis) and green frog tadpoles (Rana clamitans), respectively, to one of four common pesticides (atrazine, glyphosate, carbaryl, and malathion) at standardized, ecologically relevant concentrations (201.0, 3700.0, 33.5, and 9.6 microg/L, respectively). We measured effects of pesticide exposure on six mechanisms important to this host-parasite interaction: (1) survival of E. trivolvis cercariae over 26 hours, (2) tadpole survival over two weeks, (3) snail survival over four weeks, (4) snail growth and fecundity, (5) cercarial infectivity, and (6) tadpole susceptibility to a fixed number of cercariae. Pesticides, in general, caused significantly greater mortality of E. trivolvis cercariae than did control treatments, but atrazine was the lone chemical to significantly reduce cercarial survival (LC50 value = 267 mg/L) and then only at concentrations greater than commonly found in aquatic ecosystems (> or =200 microg/L). None of the pesticides significantly enhanced E. trivolvis virulence, decreased tadpole survival, or reduced snail survival, growth, or fecundity. Sublethal exposure of the cercariae to the pesticides (4 h) did not significantly affect trematode encystment in R. clamitans. In contrast, sublethal exposure of R. clamitans to each of the four pesticides increased their susceptibility as measured by the percentage of cercariae that encysted. The reduction in exposure to trematodes due to pesticide-induced cercarial mortality (a density-mediated effect) was smaller than the pesticide-induced increase in amphibian susceptibility (a trait-mediated effect), suggesting that the net effect of exposure to environmentally realistic levels of pesticides will be to elevate amphibian trematode infections. These findings highlight the importance of elucidating the lethal and sublethal effects of anthropogenic factors on both hosts and parasites to understand the mechanisms underlying changes in parasite transmission and virulence, an approach that is especially needed for amphibians, a taxon experiencing global disease-related declines.     

Parasites as conservation tools

Parasite success typically depends on a close relationship with one or more hosts; therefore, attributes of parasitic infection have the potential to provide indirect details of host natural history and are biologically relevant to animal conservation. Characterization of parasite infections has been useful in delineating host populations and has served as a proxy for assessment of environmental quality. In other cases, the utility of parasites is just being explored, for example, as indicators of host connectivity. Innovative studies of parasite biology can provide information to manage major conservation threats by using parasite assemblage, prevalence, or genetic data to provide insights into the host. Overexploitation, habitat loss and fragmentation, invasive species, and climate change are major threats to animal conservation, and all of these can be informed by parasites.