Parasitized mates increase infection risk for partners

Maximizing horizontal transmission through mating: increased mating frequency and mating competitiveness associated with Microsporidia MB-infected Anopheles arabiensis males

BACKGROUND

Microsporidia MB is a naturally occurring symbiont in Anopheles arabiensis mosquitoes that inhibits the development of Plasmodium. It is transmitted both vertically and horizontally, enabling its spread within mosquito populations. Currently, mating is the only known mechanism for horizontal transmission. Understanding the factors that influence Microsporidia MB transmission during mating is crucial for developing a malaria transmission-blocking strategy based on this symbiont.

METHODS

The effect of mosquito age on Microsporidia MB transmission was determined through mating bioassays between infected and uninfected Anopheles arabiensis males and females in three age groups: 3-4 days, 7-8 days, and 10-11 days. Mating bioassays were also conducted to determine if Microsporidia MB infection affects the individual male mating frequencies and mating competitiveness of male mosquitoes. To assess the effect of Microsporidia MB-infection on swarming under field conditions, swarming and non-swarming An. arabiensis male mosquitoes were collected and compared for Microsporidia MB prevalence.

RESULTS

The age of mosquitoes does not affect the transmission of Microsporidia MB from males to females (χ2 = 11.6, df = 12, p = 0.47). However, transmission of the Microsporidia MB from female mosquitoes to males was not observed in the 3-4 days old age group. Although heterogeneous, there is higher overall transmission from male to female (41.5%) compared to female to male (22.4%). When individual males (Microsporidia MB infected or uninfected) were mated with females, Microsporidia MB-infected males on average mated two times more than the Microsporidia MB-uninfected F1 male mates from the age of 3-4 days to death (t = 2.2, df = 56.8, p = 0.03). Also, Microsporidia MB-infected males when combined in a cage with Microsporidia MB uninfected males were twice as competitive (χ2 = 4.74, df = 1, p = 0.02) to the uninfected males in mating with uninfected females. In natural swarms, the proportion of Microsporidia MB-infected males was significantly higher compared to the non-swarming male mosquitoes (χ2 = 685.5, df = 1, p < 0.0001).

CONCLUSION

There is a moderate, although heterogenous, horizontal transmission of Microsporidia MB across all age groups, except from 3-4 days old, infected females to males. Microsporidia MB-infected male mosquitoes were almost twice as competitive in mating as their uninfected counterparts. Therefore, Microsporidia MB infected males can potentially disseminate Microsporidia MB in the natural mosquito populations, thus, contributing to malaria control. However, semi-field studies are required to validate these results in a natural environment.

Low evolutionary potential for blue-green egg colouration in a wild bird population

Exploring the evolutionary architecture of female sexual traits and their potential evolvability is important to understand their possible role as postmating sexual signals. Egg colouration has been proposed to be one of these postmating sexual signals, honestly advertising female quality in birds, especially in blue-green laying species. In this study, we used an animal model in a Bayesian framework to estimate the evolvability of multiple descriptors of blue-green egg colouration and egg size in a wild long-term monitored population of spotless starlings (Sturnus unicolor). Our results show low to moderate heritability (h2 = 0.31-0.44) for 3 egg colour descriptors (blue-green chroma, chroma, and lightness) and egg size. Using the coefficient of additive genetic variance (CVA) and the evolvability (IA) as proxies of evolutionary potential of all components of this trait, we found low values of CVA for all these variables, suggesting a small evolutionary potential of these phenotypic traits, contrasting to previous results reported in another blue-green egg laying species. Our results indicate a modest raw genetic material of this trait on which sexual selection can act upon and, therefore, a small probability for these traits to respond easily to selection.

Female post-copulatory behavior in a group of olive baboons (Papio anubis) infected by Treponema pallidum

Pathogens exert a profound and pervasive cost on various aspects of primate sociality and reproduction. In olive baboons (Papio anubis) at Lake Manyara National Park, Tanzania, genital skin ulcers, caused by the bacterium Treponema pallidum subsp. pertenue, are associated with increased female mating avoidance and altered male mating patterns at a pre-copulatory and copulatory level. Beyond this, mating is also comprised of post-copulatory interactions among sexual partners (i.e., copulation calls, darting [post-copulatory sprint away from the male], and post-copulatory grooming). In baboons, female post-copulatory behavior is hypothesized to incite male-male competition, promote subsequent copulations, and/or strengthen the bonds between the mating pairs. Due to a higher reproductive burden (i.e. pregnancy, lactation, infant rearing), females should avoid proceptive behavior after mating to decrease further exposure to potential pathogens. To investigate whether the presence of genital skin ulcers has an impact at the post-copulatory level, we analyzed 517 copulation events of 33 cycling females and 29 males with and without genital skin ulcers. The occurrence of female post-copulatory behaviors was not altered by genital skin ulcerations in males. Similar to other baboon populations, females in our study group were more likely to utter copulation calls after an ejaculatory copulation. The likelihood of darting was higher after ejaculatory copulations and with the presence of copulation calls. Post-copulatory grooming (i.e., occurring within 15 seconds after a copulation) was not frequently observed. Our results indicate that despite the presence of conspicuous signs of disease, female post-copulatory behavior was not affected by the genital health status of the males. This indicates that in our study group, infection cues caused by T. pallidum subsp. pertenue play a major role before and during mating, but not after mating. The post-copulatory behavior of females is most likely affected by physiological or evolutionary constraints other than sexually transmitted infections.

Host Genetic Diversity and Infectious Diseases. Focus on Wild Boar, Red Deer and Tuberculosis

Host genetic diversity tends to limit disease spread in nature and buffers populations against epidemics. Genetic diversity in wildlife is expected to receive increasing attention in contexts related to disease transmission and human health. Ungulates such as wild boar (Sus scrofa) and red deer (Cervus elaphus) are important zoonotic hosts that can be precursors to disease emergence and spread in humans. Tuberculosis is a zoonotic disease with relevant consequences and can present high prevalence in wild boar and red deer populations. Here, we review studies on the genetic diversity of ungulates and determine to what extent these studies consider its importance on the spread of disease. This assessment also focused on wild boar, red deer, and tuberculosis. We found a disconnection between studies treating genetic diversity and those dealing with infectious diseases. Contrarily, genetic diversity studies in ungulates are mainly concerned with conservation. Despite the existing disconnection between studies on genetic diversity and studies on disease emergence and spread, the knowledge gathered in each discipline can be applied to the other. The bidirectional applications are illustrated in wild boar and red deer populations from Spain, where TB is an important threat for wildlife, livestock, and humans.

Temporal and spatial dynamics of gastrointestinal parasite infection in Père David's deer

Background

The Père David's deer (Elaphurus davidianus) population was established from only a small number of individuals. Their genetic diversity is therefore relatively low and transmissible (parasitic) diseases affecting them merit further attention. Parasitic infections can affect the health, survival, and population development of the host. However, few reports have been published on the gastrointestinal parasites of Père David's deer. The aims of this study were: (1) to identify the intestinal parasites groups in Père David's deer; (2) to determine their prevalence and burden and clarify the effects of different seasons and regions on various indicators of Père David's deer intestinal parasites; (3) to evaluate the effects of the Père David's deer reproductive period on these parasites; (4) to reveal the regularity of the parasites in space and time.

Methods

In total, 1,345 Père David's deer faecal samples from four regions during four seasons were tested using the flotation (saturated sodium nitrate solution) to identify parasites of different genus or group, and the McMaster technique to count the number of eggs or oocysts.

Results

Four groups of gastrointestinal parasites were found, of which strongyles were dominant; their prevalence and burden were significantly higher than other groups. Significant temporal and spatial effects on gastrointestinal parasitic infection were found. Parasite diversity, prevalence, parasite burden, and aggregation were the highest in summer. Among the four regions, parasite diversity, prevalence, and burden were the highest in the Dongting Lake area. In addition, parasite diversity and burden during the reproductive period of Père David's deer was significantly higher than during the post-reproductive period.

Conclusions

The summer season and the reproductive period of Père David's deer had great potential for parasite transmission, and there is a high risk of parasite outbreaks in the Dongting Lake area.

Immune-challenged vampire bats produce fewer contact calls

Vocalizations are an important means to facilitate social interactions, but vocal communication may be affected by infections. While such effects have been shown for mate-attraction calls, other vocalizations that facilitate social contact have received less attention. When isolated, vampire bats produce contact calls that attract highly associated groupmates. Here, we test the effect of an immune challenge on contact calling rates of individually isolated vampire bats. Sickness behaviour did not appear to change call structure, but it decreased the number of contact calls produced. This effect could decrease contact with groupmates and augment other established mechanisms by which sickness reduces social encounters (e.g. mortality, lethargy and social withdrawal or disinterest).

Conspecific infection threat rapidly biases the social responses of female mice: Involvement of oxytocin

Pathogen threat affects social preferences and responses across species. Here we examined the effects of social context and the infection status of conspecific females and males on the social and mate responses of female mice. The responses of female mice to males were rapidly affected by the presence of infected female conspecifics and infected males. In mice odor cues drive appetitive and aversive social and mate responses. Brief (1 min) exposure to the fresh urinary odors of females infected with the murine nematode parasite, Heligmosomoides polygyrus, attenuated the responses of other uninfected females to the odors of naturally preferred unfamiliar males and enhanced their preferences for familiar males. Likewise exposure to the odors of a male either infected with H. polygyrus or treated with the bacterial endotoxin, lipopolysaccharide, reduced the responses of females to the odors of unfamiliar males. In addition, females displayed an avoidance of, and discrimination against, male mice whose odors had been associated with that of an infected female ("guilt by association") and a preference for the odors associated with an uninfected female ("mate copying"). These shifts in preferences for female associated male odors were attenuated in a dose-related manner by pre-treatment with the oxytocin receptor antagonist, L-368,899. These findings show that social information associated with the infection status of conspecifics can rapidly bias the mate preferences of female mice in an oxytocin receptor dependent manner.

Seasonal differences of corticosterone metabolite concentrations and parasite burden in northern bald ibis (Geronticus eremita): The role of affiliative interactions

The reproductive season is energetically costly as revealed by elevated glucocorticoid concentrations, constrained immune functions and an increased risk of infections. Social allies and affiliative interactions may buffer physiological stress responses and thereby alleviate associated effects. In the present study, we investigated the seasonal differences of immune reactive corticosterone metabolite concentrations, endoparasite burden (nematode eggs and coccidian oocysts) and affiliative interactions in northern bald ibis (Geronticus eremita), a critically endangered bird. In total, 43 individually marked focal animals from a free-ranging colony were investigated. The analyses included a description of initiated and received affiliative interactions, pair bond status as well as seasonal patterns of hormone and endoparasite levels. During the reproductive season, droppings contained parasite eggs more often and corticosterone metabolite levels were higher as compared to the period after reproduction. The excretion rate of endoparasite products was lower in paired individuals than in unpaired ones, but paired animals exhibited higher corticosterone metabolite concentrations than unpaired individuals. Furthermore, paired individuals initiated affiliative behaviour more frequently than unpaired ones. This suggests that the reproductive season influences the excretion patterns of endoparasite products and corticosterone metabolites and that affiliative interactions between pair partners may positively affect endoparasite burden during periods of elevated glucocorticoid levels. Being embedded in a pair bond may have a positive impact on individual immune system and parasite resistance.

The sociality-health-fitness nexus: synthesis, conclusions and future directions

This theme issue has highlighted the links between sociality, health and fitness in a broad range of organisms, and with approaches that include field and captive studies of animals, comparative and meta-analyses, theoretical modelling and clinical and psychological studies of humans. In this concluding chapter, we synthesize the results of these diverse studies into some of the key concepts discussed in this issue, focusing on risks of infectious disease through social contact, the effects of competition in groups on susceptibility to disease, and the integration of sociality into research on life-history trade-offs. Interestingly, the studies in this issue both support pre-existing hypotheses, and in other ways challenge those hypotheses. We focus on unexpected results, including a lack of association between ectoparasites and fitness and weak results from a meta-analysis of the links between dominance rank and immune function, and place these results in a broader context. We also review relevant topics that were not covered fully in this theme issue, including self-medication and sickness behaviours, society-level defences against infectious disease, sexual selection, evolutionary medicine, implications for conservation biology and selective pressures on parasite traits. We conclude by identifying general open questions to stimulate and guide future research on the links between sociality, health and fitness.

Evidence of long-term structured cuckoo parasitism on individual magpie hosts

Brood parasites usually reduce their host's breeding success, resulting in strong selection for the evolution of host defences. Intriguingly, some host individuals/populations show no defence against parasitism, which has been explained within the frame of three different evolutionary hypotheses. One of these hypotheses posits that intermediate levels of defence at the population level may result from nonrandom distribution of parasitism among host individuals (i.e. structured parasitism). Empirical evidence for structured brood parasitism is, however, lacking for hosts of European cuckoos due to the absence of long-term studies. Here, we seek to identify the patterns of structured parasitism by studying great spotted cuckoo parasitism on individual magpie hosts over five breeding seasons. We also aim to identify whether individual characteristics of female magpies and/or their territories were related to the status of repeated parasitism. We found that 28·3% of the females in our population consistently escaped from cuckoo parasitism. Only 11·3% of females were always parasitized, and the remaining 60·4% changed their parasitism status. The percentage of females that maintained their status of parasitism (i.e. either parasitized or nonparasitized) between consecutive years varied over the study. Females that never suffered cuckoo parasitism built bigger nests than parasitized females at the beginning of the breeding season and smaller nests than those of parasitized females later in the season. Nonparasitized females also moved little from year to year and preferred areas with different characteristics over the course of the breeding season than parasitized females. Overall, females escaping from cuckoo parasitism reared twice as many chicks per year than those that were parasitized. In conclusion, our study reveals for first time the existence of a structured pattern of cuckoo parasitism based on phenotypic characteristics of individual hosts and of their territories.