Search

To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark–release–recapture (MRR) methods, and with accurate metrics of food consumption by individuals.Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well‐defined 12‐ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed.We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator‐specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non‐biting midges or chironomids) of the four damselfly species.The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410–1,800) g, over 2 months. Each individual consumed 29%–66% (95% CL 9.4–123) of its body weight during its relatively short life span (2.1–4.7 days; 95% CL 0.74–7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species.Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%–1.61%) were consumed.Our synthesis of population sizes, per‐capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities. [ABSTRACT FROM AUTHOR]

Carrier solvents are used frequently in toxicity testing to assist hydrophobic chemicals into solution, but such solvents may have toxic effects on test subjects. Amphibians are model organisms in toxicity studies; however, little is known about the direct effects of solvents on native amphibians. Following modifications to standardized guidelines for native species, we used acute 96‐hour exposures to assess the direct effects of three common solvents on survival, differences in morphology and occurrence of abnormalities of northern leopard frog larvae (Lithobates pipiens). The solvents, dimethyl sulfoxide (DMSO), ethanol (ETOH) and acetone (ACE) were used at nominal concentrations ranging from 1 to 100 μL/L. We also conducted a 30‐day exposure to assess the direct chronic effects of DMSO at 1 and 5 μL/L, on larval growth, development and sex differentiation, but found no effects. Acute exposure to solvents also had no effect on the survival of larvae, but we found significant abnormalities in tadpoles acutely exposed to 100 μL/L ACE. Acute exposure to DMSO and ETOH had further concentration‐dependent effects on larval morphological traits. Our study suggests that DMSO and ETOH at ≤20 μL/L may be used as solvents in amphibian ecotoxicological studies, but ACE should be limited to ≤50 μL/L in ecotoxicity studies and perhaps much less (≤10 μL/L) in studies with other amphibians, based on a review of existing literature. We emphasize pilot studies when using solvents on acute and chronic ecotoxicity tests, using native amphibians. Carrier solvents are commonly used to assist chemicals into solution; however, little is known about their potential toxic effects on amphibians. As amphibians are model organisms in ecotoxicity testing, we assess the effects of three common carrier solvents, dimethyl sulfoxide, ethanol and acetone, on larvae of northern leopard frogs (Lithobates pipiens). Acute exposure to solvents affected differences in morphology and presence of abnormalities. Our results emphasize the importance of undertaking pilot studies when using solvents in native amphibian ecotoxicity tests. [ABSTRACT FROM AUTHOR]

Parasites and pathogens (hereafter parasites) commonly challenge organisms, but the extent to which their infections are physiologically stressful to hosts remains unclear. Importantly, vertebrate hormones, glucocorticoids (GCs), have been reported to increase, decrease or show no alterations stemming from infections, challenging the generality of parasite‐associated GC responses and motivating a search for important moderator variables.We undertook the first meta‐analysis of changes in vertebrate GCs following experimental infection with parasites, extracting 146 effect sizes from 42 studies involving 32 host and 32 parasite species to test for general patterns of GC following infection, as well as the influence of moderators.Overall, infection increased GCs relative to preliminary or control levels when the single largest effect sizes from repeated measures studies were examined, suggesting that parasites of vertebrate hosts can be thought of generally as physiological stressors by elevating GCs.When all effect sizes were included along with the moderator of sampling time post‐infection (tPI), parasite infection still had a positive effect on host GCs. However, the strength of that effect did not relate consistently to tPI, illustrating temporal differences in GC changes during the course of infection among parasite taxa (e.g. arthropod vs. bacterial infections). Other moderator variables examined did not influence GC responses.Studies broadening the range of host and parasite taxa, and sampling during critical time windows, would aid in our understanding of variation in the host stress response and its consequences for fitness of both vertebrate hosts and their parasites. [ABSTRACT FROM AUTHOR]

Neonicotinoids are widely used insecticides that are detectable in agricultural waterways. These insecticides are of concern due to their potential impacts on nontarget organisms. Pesticides can affect development of amphibians and suppress the immune system, which could impact disease susceptibility and tolerance. No previous studies on amphibians have examined the effects of these insecticides on differential blood cell proportions or concentrations of corticosterone (a general stress hormone). We investigated the effects of chronic exposure to 2 neonicotinoids, thiamethoxam and clothianidin, on immunometrics of wood frogs (Lithobates sylvaticus). Frogs were exposed to single, chronic treatments of 2.5 or 250 µg/L of clothianidin or thiamethoxam for 7 wk from Gosner stages 25 to 46. The juvenile frogs were then maintained for 3 wk post metamorphosis without exposure to neonicotinoids. We measured water‐borne corticosterone twice: at 6 d and 8 wk after exposure in larval and juvenile frogs, respectively. We assessed differential blood cell profiles from juvenile frogs. Corticosterone was significantly lower in tadpoles exposed to 250 µg/L of thiamethoxam compared with other tadpole treatments, but no significant differences in corticosterone concentrations were found in treatments using juvenile frogs. Anemia was detected in all treatments compared with controls with the exception of tadpoles exposed to 2.5 µg/L of clothianidin. Neutrophil‐to‐leukocyte and neutrophil‐to‐lymphocyte ratios were elevated in frogs exposed to 250 µg/L of thiamethoxam. Collectively, these results indicate that chronic exposure to neonicotinoids has varied impacts on blood cell profiles and corticosterone concentrations of developing wood frogs, which are indicative of stress. Future studies should investigate whether exposure to neonicotinoids increases susceptibility to infection by parasites in both larval and adult wood frogs. Environ Toxicol Chem 2019;38:1273–1284. © 2019 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Infectious diseases have the potential to spread rapidly and cause high mortality within populations of immunologically naïve hosts. The recent appearance of avian cholera, a highly virulent disease of birds caused by the bacterium Pasteurella multocida, at remote Arctic seabird colonies is an emerging conservation concern. Determining disease risk to population viability requires a quantitative understanding of transmission potential and the factors that regulate epidemic persistence. Estimates of the basic (R0) and real-time (Rt) reproductive number are critical in this regard - enumerating the number of secondary infections caused by each primary infection in a newly invaded host population and the decline in transmission rate as susceptible individuals are removed via mortality or immunized recovery. Here, we use data collected at a closely monitored common eider (Somateria mollissima) breeding colony located in the Canadian Arctic to examine transmission and host population dynamics. Specifically, we infer epidemic curves from daily mortality observations and use a likelihood-based procedure to estimate changes in the reproductive number over a series of annual outbreaks. These data are interpreted in relation to concurrent changes in host numbers to assess local extinction risk. Consistent with expectations for a novel pathogen invasion, case incidence increased exponentially during the initial wave of exposure (R0 = 2-5; generation time = 6-5 days ± 1-1 SD). Disease conditions gradually abated, but only after several years of smouldering infection (Rt ≈ 1). In total, 6194 eider deaths were recorded during outbreaks spanning eight consecutive breeding seasons. Breeding pair abundance declined by 56% from the pre-outbreak peak; however, a robust population of >4000 pairs remained intact upon epidemic fade-out. Overall, outbreak patterns were consistent with herd immunity acting as a mitigating factor governing in the extent and duration of mortality. Disease mortality is frequently modelled as a form of stochastic catastrophe in wildlife population assessments, whereas our approach gives shape to the functional response between transmission and host population dynamics. We conclude that increased emphasis on integrating epidemiological and population processes is essential to predicting the conservation impact of emerging infectious diseases in wildlife. [ABSTRACT FROM AUTHOR]

In this study, we tested which host species' characteristics explain the nature and level of parasitism for host damselfly (Coenagrionidae)-water mite (Arrenuridae) parasite associations. Prevalence and intensity of mite parasites, and mite species richness were examined in relation to geographic range size, regional occurrence, relative local abundance, phenology and body size of host damselfly species. A total of 7107 damselfly individuals were collected representing 16 species from 13 sites in southeastern Ontario and southwestern Quebec, Canada. Using comparative methods, differences in prevalence and intensity of parasitism could be predicted by a host species' geographic range and phenology. Barcoding based on Cytochrome Oxidase I revealed 15 operational taxonomic units (OTUs) for mite species. The number of mite OTUs known to infest a given host species was explained by a host species' regional occurrence. Our findings demonstrate the need to measure factors at several ecological scales in order to understand the breadth of evolutionary interactions with host-parasite associations and the selective 'milieu' for particular species of both hosts and parasites. [ABSTRACT FROM AUTHOR]

ABSTRACT The abundance of Canada geese ( Branta canadensis) nesting in temperate regions of North America has increased dramatically during the past half century. Numbers have reached nuisance levels in many areas and supplementary hunting seasons, which are timed to occur before and after traditional waterfowl hunting periods, are widely employed to limit population growth. We evaluated how changes in hunting regulations have affected population growth, the seasonal age distribution of harvest, and survival rates of temperate-breeding Canada geese banded in Ontario. We found that although the number of geese harvested in the province has increased, population growth has not abated. Annual survival rates [ABSTRACT FROM AUTHOR]

1. This study investigated inter-specific variation in parasitism by gregarines (Eugregarinorida: Actinocephalidae), among sibling species of damselflies (Odonata: Zygoptera), in relation to relative size of geographical ranges of host species. 2. Gregarines are considered generalist parasites, particularly for taxonomically related host species collected at the same sites or area. Prevalence and median intensity of gregarine parasitism was obtained for 1338 adult damselflies, representing 14 species (7 sibling species pairs) across 3 families within the suborder Zygoptera. Damselflies were collected at three local sites in Southeastern Ontario, during the same periods over the season. 3. Five out of seven species pairs had significant differences in parasitism between sibling species. The less widespread host species was the more parasitised for three species pairs with significant differences in gregarine prevalence, and for two species pairs with differences in median intensity. The more widespread host had a higher intensity of infection as expected, in two species pairs. 4. Future studies on ecological determinants of parasitism among related species should examine robust measures of abundance of species and representation of species regionally. [ABSTRACT FROM AUTHOR]

1. Insects commonly resist parasites using melanotic encapsulation. Many studies measuring immune response use the amount of melanin deposited on an artificial object that has been inserted into the animal as a proxy of the amount of resistance that the host is capable of mounting to natural parasites. 2. The relevance of this methodology to immune response in natural insect populations needs further study. Here, we examined two temperate damselfly species to elucidate the relationships among damselfly size, natural resistance to mites, and the immune response mounted by the same damselflies against nylon filaments. 3. The damselfly species that had high rates of melanotic encapsulation of mites in nature deposited more melanin on the nylon inserts than the species with low rates of natural resistance. 4. In females of this species, those that had resisted mites naturally melanised the nylon filament more aggressively than those that did not resist mites. 5. Our results show some support for the use of nylon filaments to assess natural patterns of immune response in these damselflies, but also suggest that caution should be used in interpreting the responses. [ABSTRACT FROM AUTHOR]

Researchers often consider the importance of minimizing holding time during research activities; however, the long-term costs of such handling stress is rarely measured explicitly. As part of an ongoing study of common eiders (Somateria mollissima) at a breeding colony in East Bay, Southampton Island, Nunavut, we recorded duration of restraint for females captured during avian cholera epizootics (2007 and 2008) and monitored female fates (breeding probability, onset of laying, and survival) relative to holding time. Probability of death increased with holding time in 2007 from an estimated 0.05 for females held 20 min to 0.33 for females held for 150 min. In 2008, we responded by limiting holding time to<90 min and mortality was no longer positively correlated with holding time, although total mortality was greater due to increased severity of avian cholera. In both years, longer restraint durations delayed onset of egg-laying after capture by 0.5 days for each 10 min of additional restraint but did not prevent breeding. This delay of nest initiation did not enhance survival probability. Our results show that prolonged holding time can exacerbate mortality during epizootics and emphasize the importance of minimizing restraint time in wild birds, especially in the presence of diseases. [ABSTRACT FROM AUTHOR]

Infectious diseases can have dramatic impacts on animal population dynamics, but how they influence vital rates remains understudied. We took advantage of the appearance of an avian cholera epizootic in an arctic colony of common eiders Somateria mollissima to study variation in juvenile survival and selection on hatch characteristics in relation to this highly infectious disease. Avian cholera is one of the most important infectious diseases affecting wild birds and is thought to primarily affect adult survival. Here, we show that avian cholera was associated with a 90% decline in duckling survival, leading to almost zero recruitment. Before the cholera outbreak, there was significant stabilizing selection on hatching date and significant positive directional selection on hatching mass. During cholera outbreaks, selection on hatch characteristics was no longer significant. These results were based on a low sample of surviving ducklings in cholera years, but suggested that date and mass at hatching did no longer affect duckling survival in the presence of cholera. These effects of avian cholera on post-hatching survival were likely not only the consequence of the disease per se, but also a consequence of an increase in predation rates that followed the emergence of avian cholera. Our results emphasize the dramatic direct and indirect impacts that infectious disease can have on vital rates, and thus population dynamics. [ABSTRACT FROM AUTHOR]

Climatic influences on animal populations, mediated by changes in condition-dependent survival or reproduction, have long intrigued ecologists. We analyzed links between winter North Atlantic Oscillations (NAO), a large scale climatic phenomenon affecting weather conditions over the North Atlantic and the Arctic, and average pre-laying body mass in common eiders. Body mass is a good proxy for condition-dependent reproductive output in this species. Time series links were assessed for two eider populations breeding at high latitudes, over a 10- and a 21-year time series. Winter NAO affected body mass in both populations and these effects were easier to detect when changes in the series rhythm were assessed using a novel method based on data discretization and information theory, rather than detection based on changes in amplitude, assessed using traditional linear models. Winter conditions affected body condition of eiders in both populations. Different mechanisms, however, are likely to be involved in the two populations, one being presumably affected by direct effects of climate and the other by effects through the food chain. Therefore, the same species can respond along different pathways to the same large scale climatic pattern, an important consideration when seeking to understand or manage the response of species to present and future climate change. [ABSTRACT FROM AUTHOR]

Arctic breeding shorebirds travel thousands of kilometres between their wintering and breeding grounds, yet the period over which they arrive and begin to initiate nests spans only several weeks. We investigated the role of local conditions such as weather, snow cover and predator abundance on the timing of arrival and breeding for shorebirds at four sites in the eastern Canadian arctic. Over 11 years, we monitored the arrival of 12 species and found 821 nests. Weather was highly variable over the course of this study, and the date of 50% snow cover varied by up to three weeks between years. In contrast, timing of arrival varied by one week or less at our sites, and was not well predicted by local conditions such as temperature, wind or snow melt. Timing of breeding was related to the date of 50% snow melt, with later snow melt resulting in delayed breeding. Higher predator abundance resulted in earlier nesting than would be predicted by snow cover alone. We hypothesise that when predation risk is high, the value of potential re-nesting exceeds the energetic risks of early breeding. Synchrony of breeding was significantly higher in late breeding years suggesting a relatively fixed date for the termination of nest initiation, after which nesting is no longer profitable. [ABSTRACT FROM AUTHOR]

The effect of artificial habitat in altered landscapes on species interactions and their suite of enemies is largely unknown. Water mites have been associated with reduced fitness of model damselflies. Mite parasitism was variable, but higher for Ischnura verticalis damselflies from natural, than from artificial, wetlands in the same region. There were no differences in timing of sampling, temperature during sampling, or host age or sex composition of samples between wetland types. Landscape structure might constrain mite presence or abundance at wetland sites or wetland type might be a better predictor of mites, based on factors such as prey abundance. Fewer mites on damselflies from numerous artificial wetlands means that the strength of parasite-mediated selection is likely less than would be inferred if only natural wetlands were surveyed. Such effects of human changes in habitats on host species probably occur often. [ABSTRACT FROM AUTHOR]

Intersexes are common in crustaceans. Typically, these intersexes are sterile or function as females, but prior evidence from laboratory experiments suggests that intersexes of a key species of gammaridean amphipod, Corophium volutator, might function as males. We observed that intersexes of C. volutator behaved as males by crawling (mate-searching) on a mudflat during ebb tides and pairing in burrows with female amphipods. In the laboratory, intersexes and males did not differ in aspects of crawling such as movement rate and measures of burrow investigation. I`ntersexuality was costly in that intersexes crawled less often than males on a mudflat, formed fewer pairs with females than males, and remained in tandem less often with receptive females than males. The use of PCR-based identification methods failed to identify the presence of transovarial, feminizing, microsporidian parasites as a major cause of intersexuality in this species in that infected females did not produce broods that contained more intersexes than broods produced by uninfected females. Because intersexes may be mistaken as females, the percentage of functional males in amphipod populations may be underestimated: an important consideration given male limitation in populations of C. volutator. The occurrence of intersexes has significant implications for studies on the evolution and ecology of sex ratios, and the use of crustaceans as indicators of environmental quality. [ABSTRACT FROM AUTHOR]

In vertebrates, males are often more parasitised than conspecific females. This bias in parasitism might result from sex differences in parasite exposure and/or susceptibility to infection. Such information is important for testing hypotheses about allocation of resources to life histories of males and females and for testing hypotheses about factors thought to influence parasite fitness and parasite dynamics. We tested whether double-crested cormorants Phalacrocorax auritus exhibit male-biased parasitism by gut helminths. The prevalence of nematode Contracaecum spp. and trematode Drepanocaphalus spathans infections was ∼90% and 39%, respectively. Cestode, primarily Paradilepis caballeroi and acanthocephalan Andracantha gravida infections were less common (<10%). Male and female cormorants did not differ in prevalence of infection by any helminth species. However, males had twice the abundance and intensity of Contracaecum spp. infections and twice the intensity of D. spathans infections than found in females. For common parasites showing male-biased parasitism, degree of parasitism was also unrelated to body size or mass in either sex. Males and females did not differ in spleen mass and spleen mass was unrelated to abundance of common parasites. Furthermore, abundance of trematodes and nematodes was not correlated. At present, male biases in parasitism by nematodes and trematodes in cormorants are independent patterns that remain unexplained, but are most likely attributable to sex differences in exposure and/or immunological differences not yet assessed. [ABSTRACT FROM AUTHOR]

The importance of multiple enemies from different trophic levels on investment in defence by prey has, with some exceptions, received little attention. Some defences may make the victim more susceptible to other enemies; this latter situation applies to predators and parasites of larval damselflies. Baker and Smith [ Oecologia 109 (1997) 622) showed that larval damselflies were as active in the presence of both mites and fish as they were when only mites were present, an apparently maladaptive behaviour that results in higher fish predation. In this paper, we further examine this maladaptive behavioural response to multiple enemies (fish predators and mite parasites) and test whether their defence responses are a result of the order in which they experience the parasite or predator, and/or if behavioural ‘personalities’ exist, such that some individuals show anti-predator behaviours and other show anti-parasite behaviours. Order of experience did not affect the four main behaviours (groom, crawl, turn and swim) exhibited when larval damselflies were simultaneously exposed to fish and mites. Grooming levels increased in response to mites, decreased in response to fish and when exposed to both mites and fish were similar to when they were exposed to mites alone. Duration of the other three behaviours was lower in the presence of both mites and fish. The crawling ‘personalities’ were evident. The apparently maladaptive response of high grooming levels in the presence of mites and fish is not a result of order of experience or ‘personalities’. It may be a result of relatively high encounter rates with mite parasites, compared with the encounter rates with fish. Lower encounter rates can result in diminishing investment in defence against an enemy. [ABSTRACT FROM AUTHOR]

The effects of contaminants on multispecies interactions can be difficult to predict. The herbicide atrazine is commonly used in North America for corn crops, runs off into wetlands, and has been implicated in the increasing susceptibility of larval frogs to trematode parasites. Using experimental challenges with free-living stages of trematodes (cercariae), it was found that Rana sylvatica tadpoles exposed to 30 μg/L of atrazine had significantly higher intensity of parasitism than did larval frogs either not exposed or exposed to 3 μg/L of atrazine. This result could not be explained by high concentrations of atrazine diminishing antiparasite behavior of tadpoles. Furthermore, when tadpoles and cercariae both were exposed to the same concentration of atrazine, either 3 or 30 μg/L, the abundance of formed cysts was not different from the condition in which both were housed at 0 μg/L of atrazine. Atrazine appears to be debilitating to both free-living cercariae and tadpoles. Studies examining relations between parasitism and contaminant levels must account for such combined effects as well as influences on other interacting species (e.g., first intermediate snail hosts). [ABSTRACT FROM AUTHOR]

Early male arrival at breeding sites, or protandry, is thought to have evolved from intrasexual competition among males for access to mates or breeding resources. Males of polygynous species tend to be larger than females and have exaggerated secondary sexual traits. Additionally, such species show a high degree of protandry, suggesting that timing of arrival is sexually selected. Species showing limited sexual dimorphism and showing sexual monochromatism may be expected to show limited early male arrival. However, there are very few studies of migration timing of the sexes in such species because individuals cannot be readily identified to sex in the hand. In this study, we genetically sexed birds and found no evidence for early male arrival, for a population of migratory Song Sparrows Melospiza melodia. For our study population, males and females display limited sexual size dimorphism and are sexually monochromatic which is characteristic of the species. Fat scores for males were inversely associated with timing of arrival, whereas for females, larger-winged birds arrived sooner – suggesting that early migration timing may be selected for in both sexes. [ABSTRACT FROM AUTHOR]

We studied the relationship between contaminant concentrations in livers, endohelminth prevalence and physiological indices of chronic stress (spleen size, heterophil/lymphocyte ratios) in Northern Fulmars Fulmarus glacialis collected during the breeding season in Nunavut, Canada. No blood parasites were found, similar to reports for other petrel species elsewhere. However, 54% of Fulmars had gastrointestinal helminths, principally cestodes (52% prevalence, mean intensity of 11 worms), nematodes (34% prevalence, 3.6 worms) and acanthocephalans (3%, eight worms). Both prevalence and intensity of helminth infections were lower for Arctic Fulmars than for Fulmars and other petrels found in southern parts of the species’ range. Spleen size was not significantly related to either contaminant concentration or presence of parasites, suggesting that Fulmar health was generally unaffected by contaminant and parasite levels at the colony. However, we cannot rule out the possibility that Fulmars with higher parasitaemias or contaminant loads were in poorer condition and did not attend the breeding colony. [ABSTRACT FROM AUTHOR]

Sex-biased dispersal is well known for birds and mammals, typically by females and males, respectively. Little is known about general patterns of sex-biased dispersal in other animal taxa. We reviewed return rates for a model group of invertebrates (damselflies) and explored putative costs and benefits of dispersal by males and females. We used published capture–mark–recapture data and examined whether a sex bias existed in likelihood of recapture at least once, at both emergence and/or breeding sites. We assessed whether this metric of likelihood of recapture was indicative of dispersal or philopatry, and whether any emerging pattern(s) were consistent across damselfly families. Using a meta-analysis, we found a higher likelihood of recapture at least once for males than for females at both natal sites and breeding sites, which seemed attributable to higher female-biased dispersal, although female-biased mortality cannot be discounted particularly for some species. Sex biases in dispersal among damselflies may be understood based on sex differences in maturation rate and foraging behaviour, both of which should affect the costs and benefits of dispersing. This hypothesis may be useful for explaining patterns of dispersal in other animal taxa. [ABSTRACT FROM AUTHOR]

An important problem in understanding the evolution of parasite host range is determining the extent to which parasite fitness varies among host species and the factors affecting that fitness variation. We present a detailed investigation on the patterns of host use and successful parasitism of two dragonfly species by the ectoparasitic water mite, Limnochares americana Lundblad. In our field surveys, we found both species biases and sex biases in parasitism by mites, which appear explained by differences in exposure. Differential habitat use by dragonflies helped explain male biases in parasitism in both host species, but was not useful in explaining species biases in parasitism. Species biases in parasitism may be explained by more subtle variation in habitat use not explored in this study, or perhaps by differences in timing of emergence, as we found for the two dragonfly species. Despite species differences in parasitism in nature, we found that mites attached equally successfully to both dragonfly species during experimental infestations. However, mites failed to engorge more often on the dragonfly species less often used as a host in nature. This host species also was more likely to have dead mites in natural infestations as compared to the other host species, which was more often and more heavily parasitized. Our results are consistent with previous research suggesting parasites are less successful on less often used hosts. Such research has implications for understanding determinants of host range for animal parasites. [ABSTRACT FROM AUTHOR]

The damselfly, Nehalennia irene (Hagen), has two distinct female colour morphs. Individuals of one morph have male-like colouration and pattern (androchromes), whereas gynochromes are different from males and androchromes in these respects. In several damselflies, such female-limited polychromatism is attributable to a single genetic locus. We developed six polymorphic genetic markers, which were codominant, to test for genetic differentiation in N. irene, collected from two sites located 8 km from one another in eastern Ontario, Canada. Based on three censuses spanning a 10 year period (1992–2001), morph ratios differed consistently and significantly between these two sites. However, subpopulations at these sites were not genetically differentiated with respect to the putatively neutral markers. Our results suggest that site differences in morph ratios of female N. irene cannot be explained by genetic drift, but are consistent with spatially variable selection operating on different morphs, perhaps mediated by male density. Alternatively, morph type may be a plastic trait and cues for induction may differ between sites. [ABSTRACT FROM AUTHOR]

Abstract Variable reporting of results can influence quantitative reviews by limiting the number of studies for analysis, and thereby influencing both the type of analysis and the scope of the review. We performed a Monte Carlo simulation to determine statistical errors for three meta-analytical approaches and related how such errors were affected by numbers of constituent studies. Hedges’d and effect sizes based on item response theory (IRT) had similarly improved error rates with increasing numbers of studies when there was no true effect, but IRT was conservative when there was a true effect. Log response ratio had low precision for detecting null effects as a result of overestimation of effect sizes, but high ability to detect true effects, largely irrespective of number of studies. Traditional meta-analysis based on Hedges’d are preferred; however, quantitative reviews should use various methods in concert to improve representation and inferences from summaries of published data. [ABSTRACT FROM AUTHOR]

Summary 1. Variation in immune responsiveness within and among species is the subject of the emerging field of ecological immunology. The work reported here showed that individuals of Lestes forcipatus Rambur differ in their likelihood of mounting immune responses, and in the magnitude of those responses, against a generalist ectoparasite, the water mite Arrenurus planus Marshall. 2. Immune responses took the form of melanotic encapsulation of mite feeding tubes, occurred in the few days after host emergence, and resulted in mites dying without engorging. Such immune responses were more probable and stronger for hosts sampled later rather than earlier in the season. Such responses may act as selection affecting seasonal patterns of egg hatching and larval abundance of mites. 3. Contrary to expectation, metrics of host size (wing length) and wing cell fluctuating asymmetry were not related to the likelihood of immune responses. 4. The importance of season on immune expression of insects has not been explored in detail. These results suggest possible trade-offs in allocation of melanin (or its precursors) to maturation versus immunity, and indicate the need for studies on the synergistic effects of weather and parasitism on host species that use melanotic encapsulation to combat parasites and pathogens. [ABSTRACT FROM AUTHOR]

Immunosuppressive effects of testosterone lead to a prediction of male-biased parasitism. To test this prediction, prevalences of blood parasites were compared between male and female birds using statistically correct vote counts of data from 33 studies. We found no overall difference in prevalence between males and females, in either breeding or non-breeding birds. However, infections by Haemoproteus (the most common genus of blood parasite found) were significantly more common among breeding females than breeding males. Restricting the analysis to breeding birds of polygynous species, females again were more likely than males to be infected by blood parasites; this result held for an intra-family comparison that controlled for phylogenetic effects. In comparison, measures of sexual size dimorphism did not relate to sex biases in parasitism as predicted, after controlling for phylogeny using independent comparisons. Because testosterone is often implicated in suppressing the immune system, female biases in parasitism are unexpected. Female biases in parasitism by blood parasites could result from differential exposure of the sexes to vectors, or from oestrogen-based effects on immunity. [ABSTRACT FROM AUTHOR]