Physiological responses of insular wild black rat (Rattus rattus) to natural infection by the digenean trematode Fasciola hepatica

The Connection between Immunocompetence and Reproduction in Wildlife

Reproduction rate is important for the survival of animal populations. During gravidity, a trade-off occurs between the individual well-being of gravid females and investment in offspring. Due to the high synthesis and energy requirements for the growing fetus, other physiological activities are downregulated in pregnant females. This causes changes in the composition of the reproductive microbiome and a decreased immune response to presented antigens and pathogens. As a result, the immunocompetence of gravid wild animals declines. In general, therefore, increased infection rates during pregnancy can be observed in all wildlife species studied. In the course of evolution, however, this has apparently evolved as a suitable strategy to ensure the survival of the population as a whole.

Cryptosporidium spp. in wild murids (Rodentia) from Corsica, France

Cryptosporidium spp. are worldwide protozoan parasites that can affect to a broad range of vertebrate hosts, including rodents. In the island of Corsica (France), there are no previous data about these protozoa infecting wild rodents. To estimate the distribution and occurrence, a total of 117 wild murine rodents of the species Rattus rattus (84), Mus musculus domesticus (21), Apodemus sylvaticus (11), and Rattus norvegicus (1) were captured in 24 different biotopes. Fecal samples were screened for Cryptosporidium spp. by nested PCR to amplify an 830 bp fragment of the 18S rRNA gene. As general occurrence, 15.4% of the rodents analyzed were positive for Cryptosporidium spp., being detected widely distributed along the island in R. rattus (17.6%) and M. m. domesticus (14.3%). Cryptosporidium viatorum, Cryptosporidium sp. rat genotype II, and Cryptosporidium sp. rat genotype III were successfully identified in R. rattus. The results herein reported provide the first data on Cryptosporidium spp. in wild murine species from a Mediterranean island and constitute the first report of the zoonotic species C. viatorum in R. rattus. Although a low occurrence of Cryptosporidium spp. in murids was obtained and only in one animal the zoonotic species C. viatorum was identified, our results highlight that wild murine rodents from Corsica could mediate in the maintenance and transmission of this protozoan to the environment and other hosts including humans and animals. Further studies are required to better understand the epidemiology of Cryptosporidium spp. in wild rodents from Corsica and their possible public health repercussions.

Life History Transitions at the Origins of Agriculture: A Model for Understanding How Niche Construction Impacts Human Growth, Demography and Health

Over recent millennia, human populations have regularly reconstructed their subsistence niches, changing both how they obtain food and the conditions in which they live. For example, over the last 12,000 years the vast majority of human populations shifted from foraging to practicing different forms of agriculture. The shift to farming is widely understood to have impacted several aspects of human demography and biology, including mortality risk, population growth, adult body size, and physical markers of health. However, these trends have not been integrated within an over-arching conceptual framework, and there is poor understanding of why populations tended to increase in population size during periods when markers of health deteriorated. Here, we offer a novel conceptual approach based on evolutionary life history theory. This theory assumes that energy availability is finite and must be allocated in competition between the functions of maintenance, growth, reproduction, and defence. In any given environment, and at any given stage during the life-course, natural selection favours energy allocation strategies that maximise fitness. We argue that the origins of agriculture involved profound transformations in human life history strategies, impacting both the availability of energy and the way that it was allocated between life history functions in the body. Although overall energy supply increased, the diet composition changed, while sedentary populations were challenged by new infectious burdens. We propose that this composite new ecological niche favoured increased energy allocation to defence (immune function) and reproduction, thus reducing the allocation to growth and maintenance. We review evidence in support of this hypothesis and highlight how further work could address both heterogeneity and specific aspects of the origins of agriculture in more detail. Our approach can be applied to many other transformations of the human subsistence niche, and can shed new light on the way that health, height, life expectancy, and fertility patterns are changing in association with globalization and nutrition transition.

Comparative analyses of basal rate of metabolism in mammals: data selection does matter

Basal rate of metabolism (BMR) is a physiological parameter that should be measured under strictly defined experimental conditions. In comparative analyses among mammals BMR is widely used as an index of the intensity of the metabolic machinery or as a proxy for energy expenditure. Many databases with BMR values for mammals are available, but the criteria used to select metabolic data as BMR estimates have often varied and the potential effect of this variability has rarely been questioned. We provide a new, expanded BMR database reflecting compliance with standard criteria (resting, postabsorptive state; thermal neutrality; adult, non-reproductive status for females) and examine potential effects of differential selectivity on the results of comparative analyses. The database includes 1739 different entries for 817 species of mammals, compiled from the original sources. It provides information permitting assessment of the validity of each estimate and presents the value closest to a proper BMR for each entry. Using different selection criteria, several alternative data sets were extracted and used in comparative analyses of (i) the scaling of BMR to body mass and (ii) the relationship between brain mass and BMR. It was expected that results would be especially dependent on selection criteria with small sample sizes and with relatively weak relationships. Phylogenetically informed regression (phylogenetic generalized least squares, PGLS) was applied to the alternative data sets for several different clades (Mammalia, Eutheria, Metatheria, or individual orders). For Mammalia, a 'subsampling procedure' was also applied, in which random subsamples of different sample sizes were taken from each original data set and successively analysed. In each case, two data sets with identical sample size and species, but comprising BMR data with different degrees of reliability, were compared. Selection criteria had minor effects on scaling equations computed for large clades (Mammalia, Eutheria, Metatheria), although less-reliable estimates of BMR were generally about 12-20% larger than more-reliable ones. Larger effects were found with more-limited clades, such as sciuromorph rodents. For the relationship between BMR and brain mass the results of comparative analyses were found to depend strongly on the data set used, especially with more-limited, order-level clades. In fact, with small sample sizes (e.g. <100) results often appeared erratic. Subsampling revealed that sample size has a non-linear effect on the probability of a zero slope for a given relationship. Depending on the species included, results could differ dramatically, especially with small sample sizes. Overall, our findings indicate a need for due diligence when selecting BMR estimates and caution regarding results (even if seemingly significant) with small sample sizes.

Fasciola hepatica Infection in an Indigenous Community of the Peruvian Jungle

Fasciola hepatica is a zoonotic infection with a worldwide distribution. Autochthonous cases have not been reported in the Amazon region of Peru. Operculated eggs resembling F. hepatica were identified in the stools of five out of 215 subjects in a remote indigenous community of the Peruvian jungle. Polymerase chain reaction targeting Fasciola hepatica cytochrome oxidase subunit 1 (COI) gene and sequencing of the products confirmed Fasciola infection.

Host density and competency determine the effects of host diversity on trematode parasite infection

Variation in host species composition can dramatically alter parasite transmission in natural communities. Whether diverse host communities dilute or amplify parasite transmission is thought to depend critically on species traits, particularly on how hosts affect each other’s densities, and their relative competency as hosts. Here we studied a community of potential hosts and/or decoys (i.e. non-competent hosts) for two trematode parasite species, Echinostoma trivolvis and Ribeiroia ondatrae, which commonly infect wildlife across North America. We manipulated the density of a focal host (green frog tadpoles, Rana clamitans), in concert with manipulating the diversity of alternative species, to simulate communities where alternative species either (1) replace the focal host species so that the total number of individuals remains constant (substitution) or (2) add to total host density (addition). For E. trivolvis, we found that total parasite transmission remained roughly equal (or perhaps decreased slightly) when alternative species replaced focal host individuals, but parasite transmission was higher when alternative species were added to a community without replacing focal host individuals. Given the alternative species were roughly equal in competency, these results are consistent with current theory. Remarkably, both total tadpole and per-capita tadpole infection intensity by E. trivolvis increased with increasing intraspecific host density. For R. ondatrae, alternative species did not function as effective decoys or hosts for parasite infective stages, and the diversity and density treatments did not produce clear changes in parasite transmission, although high tank to tank variation in R. ondatrae infection could have obscured patterns.

Effects of parasites on host energy expenditure: the resting metabolic rate stalemate

Detrimental effects of parasitism on host fitness are frequently attributed to parasite-associated perturbations to host energy budgets. It has therefore been widely hypothesized that energetic costs of infection may be manifest as changes in host resting metabolic rate (RMR). Attempts to quantify these effects have yielded contradictory results across host–parasite systems. We used a meta-analysis of the literature to test the effects of parasites on mass-specific (n = 22) and whole-body (n = 15) host RMR. Parasites resulted in a qualitative increase in host RMR in the majority of studies; however, the overall effect of parasites on host RMR was small and statistically nonsignificant. Additionally, substantial among-study variation in host RMR could not be explained by any of the tested covariates. We conclude that the lack of an overall effect of parasites on host metabolism reflects inconsistent directionality and varying magnitudes of parasite-associated effects across studies, rather than an absence of system-specific effects. We contend that a general understanding of parasite effects on host energetics may be best achieved through identifying mechanisms underlying among-system variance in parasite effects on host RMR and relating parasite-associated perturbations of host energy budgets to robust estimates of host fitness.

The impact of multiple infections on wild animal hosts: a review

Field parasitological studies consistently demonstrate the reality of polyparasitism in natural systems. However, only recently, studies from ecological and evolutionary fields have emphasised a broad spectrum of potential multiple infections-related impacts. The main goal of our review is to reunify the different approaches on the impacts of polyparasitism, not only from laboratory or human medical studies but also from field or theoretical studies. We put forward that ecological and epidemiological determinants to explain the level of polyparasitism, which regularly affects not only host body condition, survival or reproduction but also host metabolism, genetics or immune investment. Despite inherent limitations of all these studies, multiple infections should be considered more systematically in wildlife to better appreciate the importance of parasite diversity in wildlife, cumulative effects of parasitism on the ecology and evolution of their hosts.

Energetic costs of parasitism in the Cape ground squirrel Xerus inauris

Parasites have been suggested to influence many aspects of host behaviour. Some of these effects may be mediated via their impact on host energy budgets. This impact may include effects on both energy intake and absorption as well as components of expenditure, including resting metabolic rate (RMR) and activity (e.g. grooming). Despite their potential importance, the energy costs of parasitism have seldom been directly quantified in a field setting. Here we pharmacologically treated female Cape ground squirrels (Xerus inauris) with anti-parasite drugs and measured the change in body composition, the daily energy expenditure (DEE) using doubly labelled water, the RMR by respirometry and the proportions of time spent looking for food, feeding, moving and grooming. Post-treatment animals gained an average 19g of fat or approximately 25kJd-1. DEE averaged 382kJd-1 prior to and 375kJd-1 post treatment (p>0.05). RMR averaged 174kJd-1 prior to and 217kJd-1 post treatment (p<0.009). Post-treatment animals spent less time looking for food and grooming, but more time on feeding. A primary impact of infection by parasites could be suppression of feeding behaviour and, hence, total available energy resources. The significant elevation of RMR after treatment was unexpected. One explanation might be that parasites produce metabolic by-products that suppress RMR. Overall, these findings suggest that impacts of parasites on host energy budgets are complex and are not easily explained by simple effects such as stimulation of a costly immune response. There is currently no broadly generalizable framework available for predicting the energetic consequences of parasitic infection.

The intestinal nematode Trichuris arvicolae affects the fecundity of its host, the common vole Microtus arvalis

Parasites have detrimental effects on host fitness. Consequently, they play a major role for host population dynamics. In this study, we investigated experimentally the impact of the nematode Trichuris arvicolae on the reproduction of its host, the common vole Microtus arvalis. Wild common voles were trapped in east of France and reared in standardized conditions before being experimentally infected. Infection with Trichuris arvicolae did not affect host consumption of food or water. Parasitized females gave birth to slightly less pups (mean 3.36 +/- 0.38) than unparasitized females (mean 3.60 +/- 0.40). Controlling for natal litter size using analysis of covariance (ANCOVA), T. arvicolae infection had a significant effect on the individual mass at birth, with pups from parasitized females having significantly lower mass (2.11 g +/- 0.01) than pups from unparasitized females (2.20 g +/- 0.01). Other measures of host reproductive outputs (time to first reproduction, mass of pups at weaning, litter survival) were not affected by maternal parasite infection. We discuss how these changes in M. arvalis reproductive investments associated with T. arvicolae infection must now be investigated in the context of physiological trade-offs.