Facultatively ectoparasitic mites as vectors for entomopathogenic bacteria in Drosophila.

Opportunistic bacterial infections are common in insect populations but there is little information on how they are acquired or transmitted. We tested the hypothesis that Macrocheles mites can transmit systemic bacterial infections between Drosophila hosts. We found that 24% of mites acquired detectable levels of bacteria after feeding on infected flies and 87% of infected mites passed bacteria to naïve recipient flies. The probability that a mite could pass Serratia from an infected donor fly to a naïve recipient fly was 27.1%. These data demonstrate that Macrocheles mites are capable of serving as vectors of bacterial infection between insects.

Life history of Macrocheles muscaedomesticae (Parasitiformes: Macrochelidae): new insights on life history and evidence of facultative parasitism on Drosophila.

Macrocheles muscaedomesticae is a cosmopolitan macrochelid mite whose populations have likely diverged considering the many locations they inhabit, but most of the work published on this mite species has been on the basis of their association with the house fly, Musca domestica. Here, we studied several aspects of the biology of M. muscaedomesticae associated with drosophilid flies collected in Alberta, Canada. We assessed the degree of divergence of our populations from others, compared their life history to other published populations and experimentally tested whether M. muscaedomesticae feeds on Drosophila hydei hosts by comparing the body mass of mites that attached to hosts to those that did not. There was no strong phylogenetic differentiation among any of the M. muscaedomesticae specimens, suggesting multiple recent introductions of this species to Canada. Compared to other populations, our mites exhibited lower fecundity, which may have been a result of the temperature or nematode-only diet in which they were maintained. Finally, mites that attached to hosts for 4 h weighed significantly more than those that did not. Without direct evidence for host tissue transfer to the mites, it is difficult to determine whether the mites are indeed feeding on their hosts while attached. However, the existing evidence for the costs fly hosts endure at the expense of these mites makes this relationship antagonistic.

Phenotypic plasticity more essential to maintaining variation in host-attachment behaviour than evolutionary trade-offs in a facultatively parasitic mite.

A prevailing hypothesis for the evolution of parasitism posits that the fitness benefits gained from parasitic activity results in selection for and fixation of parasitic strategies. Despite the potential fitness advantage of parasitism, facultative parasites continue to exhibit genetic variation in parasitic behaviour in nature. We hypothesized that evolutionary trade-offs associated with parasitic host-attachment behaviour maintain natural variation observed in attachment behaviour. In this study, we used replicate lines of a facultatively parasitic mite, previously selected for increased host-attachment behaviour to test whether increased attachment trades off with mite fecundity and longevity, as well as the phenotypic plasticity of attachment. We also tested for potential correlated changes in mite morphology. To test for context-dependent trade-offs, mite fecundity and longevity were assayed in the presence or absence of a host. Our results show that selected and control mites exhibited similar fecundities, longevities, attachment plasticities and morphologies, which did not provide evidence for life history trade-offs associated with increased attachment. Surprisingly, phenotypic plasticity in attachment was maintained despite directional selection on the trait, which suggests that phenotypic plasticity likely plays an important role in maintaining attachment variation in natural populations of this facultative parasite.

Mechanisms underlying parasite infection: influence of host body mass and age on chewing louse distribution among brown-headed cowbirds.

Animal populations exhibit various patterns in ectoparasite distribution across different sexes and age classes, and numerous factors can potentially contribute to ectoparasite abundance and distribution. We examined the influence of host body size and age on the distribution of a chewing louse among brown-headed cowbirds. Differences in louse prevalence (males 62.9 ± 2.8%, females 47.5 ± 4.9%) and intensity (males 15.42 ± 1.51, females 9.04 ± 1.69) were primarily driven by differences in host body mass and not host sex. Larger birds had larger louse infra-populations, which likely translated into a lower risk of local extinction, a possible explanation for higher louse prevalence observed among larger birds. Among males, younger individuals showed higher louse prevalence (70.21 ± 4.72%) compared to older males (59.36 ± 3.59). We speculate that this pattern is likely driven by behavioural difference and not body size, with young males spending relatively more time foraging in large groups, increasing their risk of louse transmission. By examining the mechanisms that underlie the sex- and age-biased infections observed in natural populations, we can better identify the hosts most responsible for parasite transmission.