Energetic benefits of sociality offset the costs of parasitism in a cooperative mammal

Helminth and protozoan parasites of subterranean rodents (Chordata, Mammalia, Rodentia) of the world

Published studies and ten new unpublished records included herein reveal that approximately 174 species of endoparasites (helminths and protozoans) are known from 65 of 163 species of rodents that occupy the subterranean ecotope globally. Of those, 94 endoparasite species were originally described from these rodents. A total of 282 host-parasite associations are summarized from four major zoogeographic regions including Ethiopian, Palearctic/Oriental, Nearctic, and Neotropical. Thirty-four parasite records from the literature have been identified to only the level of the genus. In this summary, ten new records have been added, and the most current taxonomic status of each parasite species is noted. Interestingly, there are no data on endoparasites from more than 68% of described subterranean rodents, which indicates that discovery and documentation are at an early stage and must continue.

The social evolution of individual differences: Future directions for a comparative science of personality in social behavior

Personality is essential for understanding the evolution of cooperation and conflict in behavior. However, personality science remains disconnected from the field of social evolution, limiting our ability to explain how personality and plasticity shape phenotypic adaptation in social behavior. Researchers also lack an integrative framework for comparing personality in the contextualized and multifaceted behaviors central to social interactions among humans and other animals. Here we address these challenges by developing a social evolutionary approach to personality, synthesizing theory, methods, and organizing questions in the study of individuality and sociality in behavior. We critically review current measurement practices and introduce social reaction norm models for comparative research on the evolution of personality in social environments. These models demonstrate that social plasticity affects the heritable variance of personality, and that individual differences in social plasticity can further modify the rate and direction of adaptive social evolution. Future empirical studies of frequency- and density-dependent social selection on personality are crucial for further developing this framework and testing adaptive theory of social niche specialization.

Association patterns and community structure among female bottlenose dolphins: environmental, genetic and cultural factors

Social structuring from assortative associations may affect individual fitness, as well as population-level processes. Gaining a broader understanding of social structure can improve our knowledge of social evolution and inform wildlife conservation. We investigated association patterns and community structure of female Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia, assessing the role of kinship, shared culturally transmitted foraging techniques, and habitat similarity based on water depth. Our results indicated that associations are influenced by a combination of uni- and biparental relatedness, cultural behaviour and habitat similarity, as these were positively correlated with a measure of dyadic association. These findings were matched in a community level analysis. Members of the same communities overwhelmingly shared the same habitat and foraging techniques, demonstrating a strong homophilic tendency. Both uni- and biparental relatedness between dyads were higher within than between communities. Our results illustrate that intraspecific variation in sociality in bottlenose dolphins is influenced by a complex combination of genetic, cultural, and environmental aspects.

The energetic costs of sub-lethal helminth parasites in mammals: a meta-analysis

Parasites, by definition, have a negative effect on their host. However, in wild mammal health and conservation research, sub-lethal infections are commonly assumed to have negligible health effects unless parasites are present in overwhelming numbers. Here, we propose a definition for host health in mammals that includes sub-lethal effects of parasites on the host's capacity to adapt to the environment and maintain homeostasis. We synthesized the growing number of studies on helminth parasites in mammals to assess evidence for the relative magnitude of sub-lethal effects of infection across mammal taxa based on this expanded definition. Specifically, we develop and apply a framework for organizing disparate metrics of parasite effects on host health and body condition according to their impact on an animal's energetic condition, defined as the energetic burden of pathogens on host physiological and behavioural functions that relate directly to fitness. Applying this framework within a global meta-analysis of helminth parasites in wild, laboratory and domestic mammal hosts produced 142 peer-reviewed studies documenting 599 infection-condition effects. Analysing these data within a multiple working hypotheses framework allowed us to evaluate the relative weighted contribution of methodological (study design, sampling protocol, parasite quantification methods) and biological (phylogenetic relationships and host/parasite life history) moderators to variation in the magnitude of health effects. We found consistently strong negative effects of infection on host energetic condition across taxonomic groups, with unusually low heterogeneity in effect sizes when compared with other ecological meta-analyses. Observed effect size was significantly lower within cross-sectional studies (i.e. observational studies that investigated a sub-set of a population at a single point in time), the most prevalent methodology. Furthermore, opportunistic sampling led to a weaker negative effect compared to proactive sampling. In the model of host taxonomic group, the effect of infection on energetic condition in carnivores was not significant. However, when sampling method was included, it explained substantial inter-study variance; proactive sampling showing a strongly significant negative effect while opportunistic sampling detected only a weak, non-significant effect. This may partly underlie previous assumptions that sub-lethal parasites do not have significant effects on host health. We recommend future studies adopt energetic condition as the framework for assessing parasite effects on wildlife health and provide guidelines for the selection of research protocols, health proxies, and relating infection to fitness.

Energetics and Water Flux in the Subterranean Rodent Family Bathyergidae

The doubly labeled water (DLW) technique and indirect calorimetry enable measurement of an animal’s daily energy expenditure (DEE, kJ/day), resting metabolic rate (RMR, kJ/d), sustained metabolic scope (SusMS), body fat content (BF, %) as well as water turnover (WTO, ml/day), and water economy index (ml/kJ). Small mammals have been the primary focus of many of the DLW studies to date. From large multi-species analyses of the energetics and water flux of aboveground small mammals, well-defined trends have been observed. These trends mainly refer to an adaptive advantage for lower RMR, DEE, SusMS, WTO and WEI in more ariddwelling animals to increase water and energy savings under low and unpredictable resource availability. The study of the subterranean rodent family Bathyergidae (African mole-rats) has been of particular interest with regards to field metabolic rate and metabolic studies. Although a great deal of research has been conducted on the Bathyergidae, a complete overview and multi-species analysis of the energetics and water flux of this family is lacking. Consequently, we assessed DEE, RMR, SusMS, BF, WTO and WEI across several different species of bathyergids from various climatic regions, and compared these to the established patterns of energetics and water flux for aboveground rodents. There was notable variation across the Bathyergidae inhabiting areas with different aridities, often contrary to the variations observed in above-ground species. These include increased DEE and WEI in arid-dwelling bathyergid species. While the climate was not a clear factor when predicting the SusMS of a bathyergid species, rather the degree of group living was a strong driver of SusMS, with solitary species possessing the highest SusMS compared to the socially living species. We conclude that the constraints of the underground lifestyle and the consequent spectrum of social behaviors possessed by the family Bathyergidae are most likely to be more crucial to their energetics and water flux than their habitat; however other important unstudied factors may still be at play. More so, this study provides evidence that often unreported parameters, measured through use of the DLW technique (such as BF and WEI) can enable species to be identified that might be at particular risk to climate change.

Socializing in an Infectious World: The Role of Parasites in Social Evolution of a Unique Rodent Family

Transmission of parasites between hosts is facilitated by close contact of hosts. Consequently, parasites have been proposed as an important constraint to the evolution of sociality accounting for its rarity. Despite the presumed costs associated with parasitism, the majority of species of African mole-rats (Family: Bathyergidae) are social. In fact, only the extremes of sociality (i.e., solitary and singular breeding) are represented in this subterranean rodent family. But how did bathyergids overcome the costs of parasitism? Parasite burden is a function of the exposure and susceptibility of a host to parasites. In this review I explore how living in sealed burrow systems and the group defenses that can be employed by closely related group members can effectively reduce the exposure and susceptibility of social bathyergids to parasites. Evidence suggests that this can be achieved largely by investment in relatively cheap and flexible behavioral rather than physiological defense mechanisms. This also shifts the selection pressure for parasites on successful transmission between group members rather than transmission between groups. In turn, this constrains the evolution of virulence and favors socially transmitted parasites (e.g., mites and lice) further reducing the costs of parasitism for social Bathyergidae. I conclude by highlighting directions for future research to evaluate the mechanisms proposed and to consider parasites as facilitators of social evolution not only in this rodent family but also other singular breeders.

Parasite-Mediated Mate Preferences in a Cooperatively Breeding Rodent

Females of many species discriminate among males when choosing a mate and this can bear indirect and direct benefits including the avoidance of parasite transmission from infested males. In rodents, this may be mediated by androgen hormones that affect the expression of urinary odors. Female choosiness may also vary with a female’s infestation status, with infested females being less choosy. In the current study we tested the preference of cooperatively breeding highveld mole-rat (Cryptomys hottentotus hottentotus) females for male urinary odors from healthy males and those naturally infested with a cestode (Mathevotaenia sp.). Thirty females (15 healthy, 15 infested) were allowed to explore a Y-maze with urine samples from healthy and infested males and the frequency of entering choice arms and chambers as well as the duration spend with each odor sample was recorded. Infestation status did neither affect male body mass, urinary testosterone, nor cortisol levels or the body condition of females. Although overall female activity was not affected by infestation status, infested females entered choice arms and chambers significantly less frequently than healthy females. Surprisingly, healthy females preferred odors from infested males while the opposite was true for infested females, independent of male hormone levels. As the study species lives in groups that tend to share the same infestation status, we suggest that highveld mole-rat females may exhibit a preference for unfamiliar odors, possibly as an indicator of genetic diversity, rather than discriminate between infestation status of males. Similar mechanisms may also play a role in other social species.

Prevalence and intensity of avian malaria in a quail hybrid zone

Hybrid zones have been described as natural laboratories by researchers who study speciation and the various mechanisms that may affect gene flow. The evolutionary consequences of hybridization depend not only on reproductive compatibility between sympatric species, but also on factors like vulnerability to each other's predators and parasites. We examined infection patterns of the blood parasite Haemoproteus lophortyx, a causative agent of avian malaria, at a site in the contact zone between California quail (Callipepla californica) and Gambel's quail (C. gambelii). Controlling for the potential influence of sex and year, we tested whether species identity predicted infection status and intensity. We found that infection prevalence was lower in California and hybrid quail compared with Gambel's quail. However, infected California and hybrid quail had higher infection intensities than Gambel's quail. California and hybrid quail exhibited no significant differences in prevalence or intensity of infection. These findings suggest that infection by H. lophortyx has the potential to influence species barrier dynamics in this system; however, more work is necessary to determine the exact evolutionary consequences of this blood parasite on hybridization.

Social interaction and the thermogenic response of chicken hatchlings

The aggregation of two or more individuals of the same species (huddling) is common in mammals and birds, especially in the cold. The physical contact reduces the weight-specific body surface exposed to the environment, thus lowering heat loss and the thermogenic needs. This study investigated the possibility that the mere presence of a conspecific, in absence of physical contact, may by itself influence metabolic rate during cold. The oxygen consumption (Vo₂) of pairs of chicken hatchlings was measured when the hatchlings were in isolation (individuals), together in the respirometer but kept separated by a grid (separated) or together in the respirometer free to huddle (together), in random order, in warm (ambient normothermia, 37.5 °C) and cold conditions (26 °C, 1 h). In warm, Vo₂ did not differ significantly among individuals, separated and together (~ 1.03 ± 0.04 ml O₂/min). During the whole cold period, Vo₂ of individuals exceeded the value by 23.3 ± 3.1 ml of O₂, significantly more than in separated (15.3 ± 2.0 ml O₂, P<0.01) and together (13.9 ± 3.3 ml O₂; P<0.001). Separated and together did not differ significantly. Vo₂ in the cold averaged 149 ± 7% of the value measured in normothermia in isolated, 132 ± 5% in separated and 128 ± 7% in together. By the end of the cold-exposure, Vo₂ averaged 166 ± 8% of normothermia in isolated, 146 ± 8% in separated and 140 ± 9% in together. In all cases, values of isolated significantly exceeded those of separated (P<0.01) and together (P<0.0001), while separated and together did not differ from each other (P>0.05; Two-way RM ANOVA). Hence, in this experimental model, social interaction without physical contact decreased the thermogenic response to cold as much as huddling did. Presumably, during the cold exposure, social interaction lowered the additional energetic cost of the stress of isolation.

First Report of Gastrointestinal Parasites from Ansell's Mole-Rat ( Fukomys anselli) in Zambia

The endoparasite fauna of Ansell's mole-rat, Fukomys anselli (Burda, Zima, Scharff, Macholán and Kawalika) (Rodentia, Bathyergidae), was studied for the first time near Lusaka, Zambia. We recovered 7 endoparasite taxa including 5 nematodes ( Hexametra sp.; Protospirura numidica Seurat, 1914; Protospirura muricola Gedoelst, 1916; Protospirura sp.; and Mammalakis zambiensis Junker, Lutermann and Mutafchiev, 2017 ); and 2 cestodes ( Inermicapsifer sp. and Rodentolepis cf. microstoma Dujardin, 1845) from 272 individuals sampled between February 2009 and February 2010. Species richness (0-2), prevalence (14.7%), and abundance (0.44 ± 0.10) were low, probably as a result of the subterranean lifestyle of the study species. Although effect of host sex on helminth burden was largely absent, helminth burden varied with season and breeding status of the host. This may be a result of seasonal variation in burrow size in response to rainfall, but also the division of labor present in the study species.

The Distribution of Gastrointestinal Parasites in Two Populations of Common Mole-Rats ( Cryptomys hottentotus hottentotus)

The spread of parasites through a host population is based on the variation in behavior and immune function between individuals and is rarely uniform. We studied the gastrointestinal parasites of common mole-rats ( Cryptomys hottentotus hottentotus, Lesson 1826) from 2 sites and assessed the levels of infection based on host sex, breeding status, and season. Only nematode species were found: Neoheligmonella sp. and Mammalakis macrospiculum (Ortlepp, 1939) and a single specimen of Trichuris sp., all of which have direct life cycles. Parasite burden and species richness was greater in the mesic habitat. The abundance of Neoheligmonella sp. differed significantly between seasons, and the season of peak abundance differed between sites, perhaps due to differences in host densities between sites. In addition, parasite burden did not differ between the sexes, but breeding animals had higher infections of Neoheligmonella sp. and M. macrospiculum than non-breeding animals. This and previous studies thus suggest that the subterranean environment is beneficial in reducing parasite diversity, although the restrictions on movement may lead to certain individuals suffering higher parasite burdens.

Temporal and demographic blood parasite dynamics in two free-ranging neotropical primates

Parasite-host relationships are influenced by several factors intrinsic to hosts, such as social standing, group membership, sex, and age. However, in wild populations, temporal variation in parasite distributions and concomitant infections can alter these patterns. We used microscropy and molecular methods to screen for naturally occurring haemoparasitic infections in two Neotropical primate host populations, the saddleback (Leontocebus weddelli) and emperor (Saguinus imperator) tamarin, in the lowland tropical rainforests of southeastern Peru. Repeat sampling was conducted from known individuals over a three-year period to test for parasite-host and parasite-parasite associations. Three parasites were detected in L. weddelli including Trypanosoma minasense, Mansonella mariae, and Dipetalonema spp., while S. imperator only hosted the latter two. Temporal variation in prevalence was observed in T. minasense and Dipetalonema spp., confirming the necessity of a multi-year study to evaluate parasite-host relationships in this system. Although callitrichids display a distinct reproductive dominance hierarchy, characterized by single breeding females that typically mate polyandrously and can suppress the reproduction of subdominant females, logistic models did not identify sex or breeding status as determining factors in the presence of these parasites. However, age class had a positive effect on infection with M. mariae and T. minasense, and adults demonstrated higher parasite species richness than juveniles or sub-adults across both species. Body weight had a positive effect on the presence of Dipetalonema spp. The inclusion of co-infection variables in statistical models of parasite presence/absence data improved model fit for two of three parasites. This study verifies the importance and need for broad spectrum and long-term screening of parasite assemblages of natural host populations.

A Potential Role for mu-Opioids in Mediating the Positive Effects of Gratitude

Gratitude is a complex emotional feeling associated with universally desirable positive effects in personal, social, and physiological domains. Why or how gratitude achieves these functional outcomes is not clear. Toward the goal of identifying its' underlying physiological processes, we recently investigated the neural correlates of gratitude. In our study, participants were exposed to gratitude-inducing stimuli, and rated each according to how much gratitude it provoked. As expected, self-reported gratitude intensity correlated with brain activity in distinct regions of the medial pre-frontal cortex associated with social reward and moral cognition. Here we draw from our data and existing literature to offer a theoretical foundation for the physiological correlates of gratitude. We propose that mu-opioid signaling (1) accompanies the mental experience of gratitude, and (2) may account for the positive effects of gratitude on social relationships, subjective wellbeing, and physiological health.

Variability of whipworm infection and humoral immune response in a wild population of mole voles (Ellobius talpinus Pall.)

Restricted mobility and spatial isolation of social units in gregarious subterranean mammals ensure good defence mechanisms against parasites, which in turn allows for a reduction of immunity components. In contrast, a parasite invasion may cause an increased adaptive immune response. Therefore, it can be expected that spatial and temporal distribution of parasites within a population will correlate with the local variability in the host's immunocompetence. To test this hypothesis, the intra-population variability of a whipworm infestation and the humoral immune response to non-replicated antigens in mole voles (Ellobius talpinus Pall.), social subterranean rodents, was estimated. Whipworm prevalence in mole voles increased from spring to autumn, and this tendency was more pronounced in settlements living in natural meadows compared to settlements in man-made meadows. However, humoral immune response was lowest in animals from natural meadows trapped in autumn. Since whipworm infestation does not directly affect the immunity of mole voles, the reciprocal tendencies in seasonal dynamics and spatial distribution of whipworm abundance and host immunocompetence may be explained by local deterioration of habitat conditions, which increases the probability of an infestation.

Immunocompetence of breeding females is sensitive to cortisol levels but not to communal rearing in the degu (Octodon degus)

One hypothesis largely examined in social insects is that cooperation in the context of breeding benefits individuals through decreasing the burden of immunocompetence and provide passive immunity through social contact. Similarly, communal rearing in social mammals may benefit adult female members of social groups by reducing the cost of immunocompetence, and through the transfer of immunological compounds during allonursing. Yet, these benefits may come at a cost to breeders in terms of a need to increase investment in individual immunocompetence. We examined how these potential immunocompetence costs and benefits relate to reproductive success and survival in a natural population of the communally rearing rodent, Octodon degus. We related immunocompetence (based on ratios of white blood cell counts, total and specific immunoglobulins of G isotype titers) and fecal glucocorticoid metabolite (FGC) levels of adults immunized with hemocyanin from the mollusk Concholepas concholepas to measures of sociality (group size) and communal rearing (number of breeding females). Offspring immunocompetence was quantified based on circulating levels of the same immune parameters. Neither female nor offspring immunocompetence was influenced by communal rearing or sociality. These findings did not support that communal rearing and sociality enhance the ability of females to respond to immunological challenges during lactation, or contribute to enhance offspring condition (based on immunocompetence) or early survival (i.e., to 3months of age). Instead, levels of humoral and cellular components of immunocompetence were associated with variation in glucorcorticoid levels of females. We hypothesize that this covariation is driven by physiological (life-history) adjustments needed to sustain breeding.