Species identity dominates over environment in shaping the microbiota of small mammals.

The mammalian gut microbiota is considered pivotal to host fitness, yet the determinants of community composition remain poorly understood. Laboratory studies show that environmental factors, particularly diet, are important, while comparative work emphasises host genetics. Here, we compare the influence of host genetics and the environment on the microbiota of sympatric small mammal species (mice, voles, shrews) across multiple habitats. While sharing a habitat caused some microbiota convergence, the influence of species identity dominated. In all three host genera examined, an individual's microbiota was more similar to conspecifics living elsewhere than to heterospecifics at the same site. Our results suggest this species-specificity arises in part through host-microbe codiversification. Stomach contents analysis suggested that diet also shapes the microbiota, but where diet is itself influenced by species identity. In this way, we can reconcile the importance of both diet and genetics, while showing that species identity is the strongest predictor of microbiota composition.

What makes a feline fatal in Toxoplasma gondii's fatal feline attraction? Infected rats choose wild cats.

Toxoplasma gondii is an indirectly transmitted protozoan parasite, of which members of the cat family (Felidae) are the only definitive hosts and small mammals such as rats serve as intermediate hosts. The innate aversion of rodents to cat odor provides an obstacle for the parasite against successful predation by the feline definitive host. Previous research has demonstrated that T. gondii appears to alter a rat's perception of the risk of being preyed upon by cats. Although uninfected rats display normal aversion to cat odor, infected rats show no avoidance and in some cases even show attraction to cat odor, which we originally termed the "Fatal Feline Attraction." In this study, we tested for the first time whether the "Fatal Feline Attraction" of T. gondii-infected rats differed according to the type of feline odor used, specifically whether it came from domestic cats (Felis silvestris catus) or wild cats-cheetahs (Acinonyx jubatus) or pumas (Felis concolor). In two-choice odor trials, where wild and domestic cat odors were competed against one another, consistent with previous findings we demonstrated that infected rats spent more time in feline odor zones compared with uninfected rats. However, we further demonstrated that all cat odors are not equal: infected rats had a stronger preference for wild cat odor over that of domestic cats, an effect that did not differ significantly according to the type of wild cat odor used (cheetah or puma). We discuss these results in terms of the potential mechanism of action and their implications for the current and evolutionary role of wild, in addition to domestic, cats in transmission of T. gondii.

Chronic malaria infections increase family inequalities and reduce parental fitness: experimental evidence from a wild bird population.

Avian malaria parasites (Plasmodium) occur commonly in wild birds and are an increasingly popular model system for understanding host-parasite co-evolution. However, whether these parasites have fitness consequences for hosts in endemic areas is much debated, particularly since wild-caught individuals almost always harbour chronic infections of very low parasite density. We used the anti-malarial drug Malarone to test experimentally for fitness effects of chronic malaria infection in a wild population of breeding blue tits (Cyanistes caeruleus). Medication caused a pronounced reduction in Plasmodium infection intensity, usually resulting in complete clearance of these parasites from the blood, as revealed by quantitative PCR. Positive effects of medication on malaria-infected birds were found at multiple stages during breeding, with medicated females showing higher hatching success, provisioning rates and fledging success compared to controls. Most strikingly, we found that treatment of maternal malaria infections strongly altered within-family differences, with reduced inequality in hatching probability and fledging mass within broods reared by medicated females. These within-brood effects appear to explain higher fledging success among medicated females and are consistent with a model of parental optimism in which smaller (marginal) offspring can be successfully raised to independence if additional resources become available during the breeding attempt. Overall, these results demonstrate that chronic avian malaria infections, far from being benign, can have significant effects on host fitness and may thus constitute an important selection pressure in wild bird populations.