Host Sex Research Articles

Seroprevalence of Toxoplasma gondii among Sylvatic Rodents in Poland.

Simple SummaryToxoplasma gondii is a significant pathogen affecting humans and animals. Rodents are known to be reservoir hosts of T. gondii and therefore play a significant role in the dissemination of this parasite. We conducted seromonitoring for T. gondii in four sylvatic rodent species in Poland. We report an overall seroprevalence of 5.5% (3.6% for Myodes glareolus and 20% for other vole species). Seroprevalence in bank voles varied significantly between host age and sex. Our results, therefore, make a significant contribution to the understanding of the role of wild rodent populations in the maintenance and dissemination of T. gondii and identify key factors that affect the magnitude of seroprevalence in specific host populations.Toxoplasma gondii is an intracellular Apicomplexan parasite with a broad range of intermediate hosts, including humans and rodents. Rodents are considered to be reservoirs of infection for their predators, including cats, felids, pigs, and wild boars. We conducted a multi-site, long-term study on T. gondii in northeastern Poland. The study aimed to monitor the seroprevalence of T. gondii in the four abundant vole species found in the region (Myodes glareolus, Microtus arvalis, Microtus agrestis, and Alexandromys oeconomus) and to assess the influence of both extrinsic (year of study and study site) and intrinsic (host sex and host age) factors on seroprevalence. A bespoke enzyme-linked immunosorbent assay was used to detect antibodies against T. gondii. We examined 577 rodent individuals and detected T. gondii antibodies in the sera of all four rodent species with an overall seroprevalence of 5.5% [4.2–7.3] (3.6% [2.6–4.9] for M. glareolus and 20% [12–30.9] for M. arvalis, M. agrestis, and A. oeconomus). Seroprevalence in bank voles varied significantly between host age and sex. Seroprevalence increased with host age and was higher in females than males. These results contribute to our understanding of the distribution and abundance of T. gondii in voles in Poland and confirm that T. gondii also circulates in M. glareolus and M. arvalis, M. agrestis and A. oeconomus. Therefore, they may potentially play a role as reservoirs of this parasite in the sylvatic environment.

High-elevational occurrence of two tick species, Ixodes ricinus and I. trianguliceps, at their northern distribution range

BackgroundDuring the last decades a northward and upward range shift has been observed among many organisms across different taxa. In the northern hemisphere, ticks have been observed to have increased their latitudinal and altitudinal range limit. However, the elevational expansion at its northern distribution range remains largely unstudied. In this study we investigated the altitudinal distribution of the exophilic Ixodes ricinus and endophilic I. trianguliceps on two mountain slopes in Norway by assessing larval infestation rates on bank voles (Myodes glareolus).MethodsDuring 2017 and 2018, 1325 bank voles were captured during the spring, summer and autumn at ten trapping stations ranging from 100 m to 1000 m.a.s.l. in two study areas in southern Norway. We used generalized logistic regression models to estimate the prevalence of infestation of both tick species along gradients of altitude, considering study area, collection year and season, temperature, humidity and altitude interactions as extrinsic variables, and host body mass and sex as intrinsic predictor variables.ResultsWe found that both I. ricinus and I. trianguliceps infested bank voles at altitudes up to 1000 m.a.s.l., which is a substantial increase in altitude compared to previous findings for I. ricinus in this region. The infestation rates declined more rapidly with increasing altitude for I. ricinus compared to I. trianguliceps, indicating that the endophilic ecology of I. trianguliceps may provide shelter from limiting factors tied to altitude. Seasonal effects limited the occurrence of I. ricinus during autumn, but I. trianguliceps was found to infest rodents at all altitudes during all seasons of both years.ConclusionsThis study provides new insights into the altitudinal distribution of two tick species at their northern distribution range, one with the potential to transmit zoonotic pathogens to both humans and livestock. With warming temperatures predicted to increase, and especially so in the northern regions, the risk of tick-borne infections is likely to become a concern at increasingly higher altitudes in the future.Graphical

Who acquires infection from whom? Estimating herpesvirus transmission rates between wild rodent host groups

To date, few studies of parasite epidemiology have investigated ‘who acquires infection from whom’ in wildlife populations. Nonetheless, identifying routes of disease transmission within a population, and determining the key groups of individuals that drive parasite transmission and maintenance, are fundamental to understanding disease dynamics. Gammaherpesviruses are a widespread group of DNA viruses that infect many vertebrate species, and murine gammaherpesviruses (i.e. MuHV-4) are a standard lab model for studying human herpesviruses, for which much about the pathology and immune response elicited to infection is well understood. However, despite this extensive research effort, primarily in the lab, the transmission route of murine gammaherpesviruses within their natural host populations is not well understood. Here, we aimed to understand wood mouse herpesvirus (WMHV) transmission, by fitting a series of population dynamic models to field data on wood mice naturally infected with WMHV and then estimating transmission parameters within and between demographic groups of the host population. Different models accounted for different combinations of host sex (male/female), age (subadult/adult) and transmission functions (density/frequency-dependent). We found that a density-dependent transmission model incorporating explicit sex groups fitted the data better than all other proposed models. Male-to-male transmission was the highest among all possible combinations of between- and within-sex transmission classes, suggesting that male behaviour is a key factor driving WMHV transmission. Our models also suggest that transmission between sexes, although important, wasn’t symmetrical, with infected males playing a significant role in infecting naïve females but not vice versa. Overall this work shows the power of coupling population dynamic models with long-term field data to elucidate otherwise unobservable transmission processes in wild disease systems.

COMUNIDADES DE PARÁSITOS DE PATAGONOTOTHEN TESSELLATA (RICHARDSON, 1845) (PISCES: NOTOTHENIIDAE) DE CHILE AUSTRAL: ¿QUÉ TAN DETERMINANTE ES EL SEXO DEL HOSPEDERO?

El conocimiento de comunidades de parásitos es muy abundante en peces marinos; sin embargo, hay varias especies que tienen escasa información parasitológica, como es el caso de Patagonotothen tessellata (Richardson, 1845), que posee una amplia distribución y abundancia en la Patagonia. Este estudio tuvo como objetivos determinar la composición comunitaria de parásitos en P. tessellata, y determinar el efecto del sexo de los hospederos en la composición parasítica a través de los descriptores poblacionales y comunitarios de parásitos. En enero de 2018 se recolectaron 118 ejemplares de P. tessellata en dos localidades cercanas entre sí, Muelle Prat y Muelle Remota, Puerto Natales, Chile Austral. En los peces capturados se encontró un total de 13 especies de parásitos, principalmente del Phylum Nematoda y Acanthocephala, de los cuales el nemátodo Pseudodelphis sp. seguido por el acantocéfalo Hypoechinorhynchus magellanicus (Szidat, 1950) fueron los de mayor prevalencia (78,8% y 53,4%, respectivamente) y abundancia (7,18 ± 17,95 y 7,30 ± 15,21, respectivamente). Se determinó que hospederos machos y hembras tenían iguales tamaños corporales y la misma correlación positiva entre peso-longitud, además, no se observaron diferencias significativas en composición y carga parasitaria. Mientras que el género de los peces tampoco afectó la composición parasítica para P. tessellata, pues, no hubo diferencias significativas en la prevalencia ni en la abundancia promedio de las especies de parásitos entre hospederos machos y hembras. Estos resultados indican la semejanza en las comunidades de parásitos entre sexos de P. tessellata y dan a presumir de que las condiciones del hábitat o la dieta de este pez son similares entre machos y hembras. De este modo, ambos grupos estarían expuestos a la infección de las mismas especies parásitas y en similares condiciones ambientales.

Mechanistically comparing reproductive manipulations caused by selfish chromosomes and bacterial symbionts.

Insects naturally harbor a broad range of selfish agents that can manipulate their reproduction and development, often leading to host sex ratio distortion. Such effects directly benefit the spread of the selfish agents. These agents include two broad groups: bacterial symbionts and selfish chromosomes. Recent studies have made steady progress in uncovering the cellular targets of these agents and their effector genes. Here we highlight what is known about the targeted developmental processes, developmental timing, and effector genes expressed by several selfish agents. It is now becoming apparent that: (1) the genetic toolkits used by these agents to induce a given reproductive manipulation are simple, (2) these agents target sex-specific cellular processes very early in development, and (3) in some cases, similar processes are targeted. Knowledge of the molecular underpinnings of these systems will help to solve long-standing puzzles and provide new tools for controlling insect pests.

Horizontal transmission of a murine retrovirus is driven by males within semi‐natural enclosures

Abstract Transmission is a key component of a pathogen's life history, but it is often difficult to obtain reliable ecological estimates of the dominant mode(s) of transmission and how host traits, such as sex, influence transmission dynamics. Here, we have developed a robust system pairing the use of semi‐natural populations of house mice Mus musculus with modern molecular viral titering approaches to evaluate the transmission dynamics of Friend Virus Complex (FVC). Semi‐natural populations were founded with female and male mice that were either ‘index’ (initially infected via intraperitoneal injection) or ‘contact’ (uninfected at the start of experiment). Three experimental population designs were implemented: female index only, male index only and both female and male index. Utilizing these enclosures, we found male–male transmission to be the predominant mode of transmission, with low rates of horizontal female transmission and no evidence of vertical transmission. Additionally, contact males that became infected harbour higher titres than females while suffering a similar amount of spleen enlargement; this, paired with a strong correlation between titre and spleen size in males, and no correlation in females, indicates FVC viral dynamics differ between the sexes. Lastly, natural transmission may be an impediment to FVC replication as infected contact animals have a lower viral titre than index animals. These results illuminate the complex life history of murine leukaemia viruses and demonstrate the important role of host sex on pathogen transmission dynamics. A free Plain Language Summary can be found within the Supporting Information of this article.

Parasitic interactions between bats (Mammalia: Chiroptera) and flies (Insecta: Diptera) in the intersection area of temperate and tropical climates in Brazil

ABSTRACT Bats and ectoparasites, Streblidae and Nycteribiidae, are good models to study ecological interactions due to their specificity. Knowledge about the interactions between these groups is heterogeneous and fragmented throughout Brazilian territory, mainly in the southern region – influenced by the temperate climate with bat fauna presenting elements from both tropical and temperate areas. We evaluated the interaction of parasites and bats in an Atlantic Forest area, southern Brazil. We captured bats and their ectoparasites monthly in 10 campaigns using mist nets. To describe the interactions, we used prevalence and average intensity of infestation, the same indexes we used to compare host sexes. We captured 494 bats, from which 151 had ectoparasites. Artibeus lituratus and Sturnira lilium were the most abundant bat species. We captured 303 ectoparasites, from which Metelasmus wenzeli is a new record to the state of Santa Catarina. Paratrichobius longicrus and Megistopoda proxima were the most abundant ectoparasite species, probably due to the greatest abundances of the host species of bats A. lituratus and S. lilium in this study. Most of the interactions we found are primary associations, which reinforces the specific parasite–host relationship. The data we obtained here are the first for the state of Santa Catarina.

Understanding mosquito host-choice behaviour: a new and low-cost method of identifying the sex of human hosts from mosquito blood meals

BackgroundMosquito-borne diseases are a global health problem, causing hundreds of thousands of deaths per year. Pathogens are transmitted by mosquitoes feeding on the blood of an infected host and then feeding on a new host. Monitoring mosquito host-choice behaviour can help in many aspects of vector-borne disease control. Currently, it is possible to determine the host species and an individual human host from the blood meal of a mosquito by using genotyping to match the blood profile of local inhabitants. Epidemiological models generally assume that mosquito biting behaviour is random; however, numerous studies have shown that certain characteristics, e.g. genetic makeup and skin microbiota, make some individuals more attractive to mosquitoes than others. Analysing blood meals and illuminating host-choice behaviour will help re-evaluate and optimise disease transmission models.MethodsWe describe a new blood meal assay that identifies the sex of the person that a mosquito has bitten. The amelogenin locus (AMEL), a sex marker located on both X and Y chromosomes, was amplified by polymerase chain reaction in DNA extracted from blood-fed Aedes aegypti and Anopheles coluzzii.ResultsAMEL could be successfully amplified up to 24 h after a blood meal in 100% of An. coluzzii and 96.6% of Ae. aegypti, revealing the sex of humans that were fed on by individual mosquitoes.ConclusionsThe method described here, developed using mosquitoes fed on volunteers, can be applied to field-caught mosquitoes to determine the host species and the biological sex of human hosts on which they have blood fed. Two important vector species were tested successfully in our laboratory experiments, demonstrating the potential of this technique to improve epidemiological models of vector-borne diseases. This viable and low-cost approach has the capacity to improve our understanding of vector-borne disease transmission, specifically gender differences in exposure and attractiveness to mosquitoes. The data gathered from field studies using our method can be used to shape new transmission models and aid in the implementation of more effective and targeted vector control strategies by enabling a better understanding of the drivers of vector-host interactions.Graphical

Vector preference and heterogeneity in host sex ratio can affect pathogen spread in natural plant populations.

Vector-borne diseases threaten human and agricultural health and are a critical component of the ecology of plants and animals. While previous studies have shown that pathogen spread can be affected by vector preferences for host infection status, less attention has been paid to vector preference for host sex, despite abundant evidence of sex-specific variation in disease burden. We investigated vector preference for host infection status and sex in the sterilizing "anther-smut" pathogen (Microbotryum) of the alpine carnation, Dianthus pavonius. The pathogen is transferred among hosts by pollinators that visit infected flowers and become contaminated with spores produced by infected anthers. The host plant has a mixed breeding system with hermaphrodites and females. In experimental floral arrays, pollinators strongly preferred healthy hermaphrodites over both females and diseased plants, consistently across different guilds of pollinators and over multiple years. Using an agent-based model, we showed that pollinator preferences for sex can affect pathogen spread in populations with variable sex ratios, even if there is no preference for infection status. Our results demonstrate that vector preferences for host traits other than infection status can play a critical role in pathogen transmission dynamics when there is heterogeneity for those traits in the host population.

Ectoparasitic community of the Mahali mole-rat, Cryptomys hottentotus mahali: potential host for vectors of medical importance in South Africa

BackgroundThe endemic rodent family of Bathyergidae in Africa, particularly South Africa, are understudied as reservoirs of diseases of significant medical importance. Considering the diversity and wide distribution of African mole-rats in South Africa, many of these bathyergids could act as carriers of zoonoses.MethodsThe present study assessed the ectoparasite community of the Mahali mole-rat (Cryptomys hottentotus mahali). We aimed to identify possible parasitic arthropods that may infest this mole-rat species and explore host preference, contributions of seasonality, host sex and body mass as well as social class and colony size on ectoparasite assemblage prevalence and abundance.ResultsA limited number of ectoparasite species were found on C. h. mahali belonging to two significant taxa: mites (Acari) and fleas, with mites being the most prevalent and abundant. We recorded the presence of X. philoxera, a flea well known as the principal reservoir of plague in the southern African region on the Mahali mole-rats. Only three mite species were collected: Androlaelaps scapularis, Androlaelaps capensis and Laelaps liberiensis. Seasonal peaks in prevalence and abundance of X. philoxera and A. scapularis were observed during summer. Xenopsylla philoxera abundance and A. scapularis loads significantly increased on reproductive mole-rat individuals in comparison to non-reproductive individuals.ConclusionDespite the wide distribution of the subterranean African mole-rats, studies investigating their parasitic fauna remain limited and scarce. This dearth in knowledge raises the concern regarding their potential role as an endemic reservoir for zoonotic diseases. Consequently, additional sampling of their ectoparasitic community throughout their distributional range and research addressing their role as a reservoir for zoonotic diseases in southern Africa are urgently needed.

Assessment of the helminth fauna in northern bobwhites (Colinus virginianus) occurring within South Texas.

Populations of northern bobwhites (Colinus virginianus; hereafter bobwhite) have been declining across their geographic range in North America, prompting consideration of the role parasites may play. We conducted this study to learn about the helminth fauna in South Texas, a region that supports a sustainable bobwhite population. Helminths were examined from 356 bobwhites collected during the 2014-2015 (n = 124) and 2015-2016 (n = 232) hunting seasons, when increasing trends in precipitation were observed in comparison with the previous two years. Ten helminth species were found, consisting of 14,127 individuals. Of these, all are heteroxenous parasites and three are pathogenic (Dispharynx nasuta, Tetrameres pattersoni and Oxyspirura petrowi). Aulonocephalus pennula numerically dominated the component community (81% prevalence, 99% of the total helminths found), whereas each of the remaining species occurred rarely (≤9% prevalence) and contributed few individuals (≤0.4%) to the helminth community. Prevalence and abundance of A. pennula were not influenced by host age, sex or body mass, but abundance was higher during the 2014-2015 than the 2015-2016 hunting season. Our findings indicate that the helminth community in bobwhites from South Texas can vary during long-term, highly variable precipitation conditions and these communities are more similar to those found in the Rolling Plains of Texas than those found in the eastern part of the bobwhite's geographic range in the US.

Sex differences in survival: viability selection in nymphal tree crickets from a conopid fly parasitoid

1. Variation in mortality due to parasitoids is expected to be affected by host sex and size.2. We use selection analyses to examine the effects of Stylogaster neglecta (Diptera: Conopidae), a recently discovered parasitoid of nymphal Oecanthus nigricornis (Orthoptera: Gryllidae), on sex and size viability in the host crickets.3. O. nigricornis nymphs were sampled across Ontario and New York State and dissected to determine whether they were parasitised. Logistic regression was used to examine parasitism by host body size and sex.4. There was strong evidence for an effect of sex and body size on parasitism, with males and smaller crickets being more likely to be parasitised and containing more parasitoids in them. There was also weaker evidence of an interaction effect between sex and body size, with body size being a significant predictor of parasitism only in males. Using a selection analysis, we found evidence of positive and disruptive selection on male body size.5. Causes of these viability differences may include sex differences in larval cricket immune function, riskier behaviour of male nymphs as they acquire resources necessary for adult trait development, as well as the effects of S. neglecta flies targeting hosts that maximise fitness.

ROLE OF SEA BREAM FISH P. PAGRUS (FAMILY: SPARIDAE) IN HARBORING SOME LARVAL ASCARIDOIDS (FAMILY: ANISAKIDAE) IN CAIRO GOVERNORATE, EGYPT

The study dealt with anisakid nematode larvae (L3) in a commercially important marine fishPagrus pagrus purchased from different fish markets at 3 localities: El-Matareya, El-Zaitounand, Saray El-Kobba, Cairo. Anisakid nematodes are zoonotic fish-borne parasites that maytransmit to human by consuming raw fish containing the third stage larvae encapsulated in thefish muscles caused a serious disease Anisakidosis. The symptoms of that disease are nausea,diarrhea, vomiting and severe abdominal pain. Four species of L3 larvae were detected;Hysterothylacium sp., Raphidascaris sp., Contracaecum sp. and Terranova sp. Identificationof the larvae depended basically upon the structure of the cephalic region, oesophogus shape,ventricular appendage, tail end and presence or absence of mucron. Two-hundred and thirtythreelarvae were isolated from 80/140 (56.4%) examined fish. The hosts were collected fromNovember 2019 to April 2020. Larvae were measured in relation to host's weight, sex andinfection prevalence. The results statistically showed that larvae prevalence and intensity werevaried significantly in relation to host's sex and weight.

Distinct gut microbiotas between southern elephant seals and Weddell seals of Antarctica.

The gut microbiome provides ecological information about host animals, but we still have limited knowledge of the gut microbiome, particularly for animals inhabiting remote locations, such as Antarctica. Here, we compared fecal microbiota between southern elephant seals (Mirounga leonina) and Weddell seals (Leptonychotes weddelli), that are top predatory marine mammals in the Antarctic ecosystem, using 16S rRNA amplicon sequencing and assessed the relationships of the gut microbial communities to functional profiles using gut metabolite analysis. The bacterial community did not differ significantly by host species or sex at the phylum level, but the distinction at the family level was obvious. The family Ruminococcaceae (Firmicutes) was more abundant in southern elephant seals than in Weddell seals, and the families Acidaminococcaceae (Firmicutes) and Pasteurellaceae (Gammaproteobacteria) were uniquely present in Weddell seals. The fecal bacterial community structure was distinctively clustered by host species, with only 6.7% of amplicon sequence variants (ASVs) shared between host species. This result implies that host phylogeny rather than other factors, such as diet or age, could be the major driver of fecal microbiotic diversification. Interestingly, there was no apparent sex effect on bacterial community structure in Weddell seals, but the effect of sex was pronounced in adult southern elephant seals mainly due to the prevalence of Edwardsiella sp., suggesting that extreme sexual dimorphism may modulate the gut microbiota of southern elephant seals. Unlike the clear distinction in the taxonomic composition of fecal bacterial communities, there were no discernible differences in the profiles of potential microbial functions and gut metabolites between host species or sexes, indicating that functional redundancy dominates the gut microbiota of seals surveyed in this study.

Factors Contributing to Sex Differences in Mice Inhaling Aspergillus fumigatus.

Aspergillus fumigatus is a respiratory fungal pathogen and an allergen, commonly detected in flooded indoor environments and agricultural settings. Previous studies in Balb/c mice showed that repeated inhalation of live and dry A. fumigatus spores, without any adjuvant, elevated allergic immune response and airway remodeling. Sex-specific differences can influence host-pathogen interactions and allergic-asthma related outcomes. However, the effect of host sex on immune response, in the context of A. fumigatus exposure, remains unknown. In this study, we quantified the multivariate and univariate immune response of C57BL/6J mice to live, dry airborne A. fumigatus spores. Our results corroborate previous results in Balb/c mice that repeated inhalation of live A. fumigatus spores is sufficient to induce mucus production and inflammation by day 3 post last challenge, and antibody titers and collagen production by day 28 post-challenge. Principal Component Analysis (PCA) showed that females exhibited significantly higher levels of immune components than males did. Taken together, our data indicate that host-sex is an important factor in shaping the immune response against A. fumigatus, and must be considered when modeling disease in animals, in designing diagnostics and therapeutics for A. fumigatus-associated diseases or while drafting evidence-based guidelines for safe mold levels.

Species, sex and geographic variation in chlamydial prevalence in abundant wild Australian parrots

Chlamydia psittaci (order: Chlamydiales) is a globally distributed zoonotic bacterium that can cause potentially fatal disease in birds and humans. Parrots are a major host, yet prevalence and risk factors for infection in wild parrots are largely unknown. Additionally, recent research suggests there is a diverse range of novel Chlamydiales circulating in wildlife. We therefore sampled seven abundant parrot species in south-eastern Australia, taking cloacal swabs and serum from n = 132 wild adults. We determined C. psittaci and Chlamydiales prevalence and seroprevalence, and tested for host species, sex, geographical and seasonal differences, and temporal changes in individual infection status. Across all species, Chlamydiales prevalence was 39.8% (95% CI 31.6, 48.7), C. psittaci prevalence was 9.8% (95% CI 5.7, 16.3) and C. gallinacea prevalence was 0.8% (95% CI 0.1, 4.5). Other Chlamydiales species were not identified to species level. We identified two C. psittaci strains within the 6BC clade, which is highly virulent in humans. Seroprevalence was 37.0% (95% CI 28.5, 46.4). Host species (including crimson rosellas, galahs, sulphur-crested cockatoos and blue-winged parrots) differed in seroprevalence and Chlamydiales prevalence. Galahs had both highest Chlamydiales prevalence (54.8%) and seroprevalence (74.1%). Seroprevalence differed between sites, with a larger difference in males (range 20–63%) than females (29–44%). We reveal a higher chlamydial prevalence than previously reported in many wild parrots, with implications for potential reservoirs, and transmission risks to humans and other avian hosts.

Ellipsomyxa ariusi sp. nov. (Myxosporea: Ceratomyxidae), a new myxosporean infecting the gallbladder of threadfin sea catfish Arius arius in India.

The present study describes a new species of myxosporean, Ellipsomyxa ariusi sp. nov., infecting the gallbladder of the threadfin sea catfish Arius arius (Hamilton, 1822). E. ariusi sp. nov. is characterized by bivalvular, ellipsoid or elongate-oval myxospores with smooth spore valves and a straight suture, arranged at an angle to the longitudinal spore axis. Mature myxospores measured 10.1 ± 0.8 µm in length, 6.8 ± 0.5 µm in width and 7.7 ± 0.7 µm in thickness. Polar capsules are equal in size and oval to pyriform in shape. They are positioned at an angle to the longitudinal myxospore axis and open in opposite directions. Polar capsules measured 2.8 ± 0.3 µm in length and 2.5 ± 0.4 µm in width; polar filaments formed 4-5 coils, and extended to 32.2 ± 2.1 µm in length. Monosporic and disporic plasmodial stages attached to the wall of gallbladder. Molecular analysis of the type specimen generated a 1703 bp partial SSU rDNA sequence (MN892546), which was identical to the isolates from 3 other locations. In phylogenetic analyses, genus Ellipsomyxa appeared monophyletic and E. ariusi sp. nov. occupied an independent position in maximum likelihood and Bayesian inference trees with high bootstrap values. The overall prevalence of infection was 54.8% and multiway ANOVA revealed that it varied significantly with location, year, season, sex and size of the fish host. Histopathological changes associated with E. ariusi sp. nov. infection included swelling, vacuolation and detachment of epithelial layer, reduced mucus production and altered consistency and colour of bile. Based on the morphologic, morphometric and molecular differences with known species of Ellipsomyxa, and considering differences in host and geographic locations, the present species is treated as new and the name Ellipsomyxa ariusi sp. nov. is proposed.

Pathogen exposure reduces sexual dimorphism in a host's upper thermal limits.

The climate is warming at an unprecedented rate, pushing many species toward and beyond the upper temperatures at which they can survive. Global change is also leading to dramatic shifts in the distribution of pathogens. As a result, upper thermal limits and susceptibility to infection should be key determinants of whether populations continue to persist, or instead go extinct. Within a population, however, individuals vary in both their resistance to both heat stress and infection, and their contributions to vital growth rates. No more so is this true than for males and females. Each sex often varies in their response to pathogen exposure, thermal tolerances, and particularly their influence on population growth, owing to the higher parental investment that females typically make in their offspring. To date, the interplay between host sex, infection, and upper thermal limits has been neglected. Here, we explore the response of male and female Daphnia to bacterial infection and static heat stress. We find that female Daphnia, when uninfected, are much more resistant to static heat stress than males, but that infection negates any advantage that females are afforded. We discuss how the capacity of a population to cope with multiple stressors may be underestimated unless both sexes are considered simultaneously.

Sex- and Age-Specific Effects are Superimposed on Seasonal Variation in Mite Parasitism in Eastern Fence Lizards (Sceloporus undulatus)

The natural histories of parasites and their hosts are intertwined, and intensity of parasitism depends on parasite abundance and host behavior as well as potential effects of sex/age. To characterize potential effects of parasite abundance and host sex/ age on chigger mite (Eutrombicula alfreddugesi) ectoparasitism on Eastern Fence Lizards (Sceloporus undulatus), we measured 1) the abundance of mites in the environment as well as mite load and prevalence on lizards throughout the activity season, 2) sex- and age-specific patterns of ectoparasitism, and 3) week-to-week consistency of mite loads on lizards. Environmental mite abundance varied seasonally in close association with mean monthly temperatures and was the main driver of pronounced seasonal variation in mite loads on lizards. Mite loads were almost always higher on yearlings than on adults and, somewhat unexpectedly, were never higher on adult males than any of the other age-sex classes. As adults, females had higher mite loads than did males in June–July, but as yearlings, males had higher mite loads than did females in July–September. Despite considerable week-to-week variation, rank-ordering of lizard mite loads was highly consistent. These findings indicate that 1) consistent, age-specific sex biases are superimposed on strong seasonal variation in mite loads, and 2) detrimental effects of mites are expected to be consistently stronger in some individuals than in others.

Habitat and host associations of the fish‐burrowing parasite Artystone minima (Cymothoidae: Isopoda) in eastern Amazonia

AbstractCymothoid fish parasites settle on hosts in ways that may impact fish health and energetics. High abundances of Artystone minima observed in Nannostomus beckfordi from the Jeju River in eastern Amazonia were investigated to answer the following questions: (a) What factors are associated with the high prevalence at this locality?; (b) Is high abundance associated with co‐infestation of alternative hosts?; and (c) Is parasite presence associated with host species growth and/or reproduction? Fish assemblages were sampled quarterly (August 2017–May 2018) from five habitats along with environmental data. Parasitic indices were calculated, and parasite presence used to evaluate differences in growth of hosts using analysis of covariance considering host sex and sampling season (wet vs. dry). Parasites were only abundant in one of the habitats, a large, shallow backwater bay with macrophytes. Abiotic environmental factors (flow and depth) likely impact parasite transmission and are, therefore, particularly important in producing these local patterns. Two secondary hosts, Hyphessobrycon cf. rosaceus and Moenkhausia collettii, were found in the wet season. Based on host biology compared to other fish in the habitat, parasite infestation is inferred to be depth associated and long‐term infestation is apparently limited in alternative hosts. Parasite presence was significantly associated with reduced weight (standardized for length) of female Nannostomus beckfordi in the wet season. Furthermore, ovaries of non‐parasitized females from the wet season presented a range of maturation stages, while parasitized females were all immature, indicating a significant association of parasites with host reproductive capacity.Abstract in Portuguese is available with online material