Ixodes ricinus ticks infected with the causative agent of Lyme disease, Borrelia burgdorferi sensu lato, have higher energy reserves.

Ticks use their energy reserves to maintain their water balance, search for hosts and transmit tick-borne pathogens. However, the influence of tick-borne pathogens on the energy reserves of the tick vector has not been well studied. The relationship between Borrelia burgdorferi sensu lato (s.l.) infection status and fat content in questing Ixodes ricinus nymphs was examined. Nymphs were sampled from the field. Their body mass and fat content were measured, and their Borrelia genospecies infection status (using reverse line blot analysis), and spirochete load (using quantitative PCR) were analysed. Of the 900 nymphs tested, 21.2% were infected with a variety of Borrelia genospecies. Borrelia-infected nymphs had 12.1% higher fat content than uninfected ticks after correcting for body size. For the subset of Borrelia-infected nymphs, no relationship was found between spirochete load and fat content and bioenergetics calculations suggest that Borrelia spirochetes consume a negligible fraction of the tick energy reserves. While the mechanism that causes the association between Borrelia infection and higher fat content in I. ricinus nymphs remains unknown, the present study complements our previous findings that Borrelia-infected nymphs had higher survival times under desiccating conditions and walked less within a humidity gradient.

Paternal inheritance of the primary sex ratio in a copepod.

Uniparentally inherited genetic elements are under strong selection to manipulate sex determination in their host and shift the host sex ratio towards the transmitting sex. For any sex-ratio trait, lineage analysis and quantitative genetics are important tools for characterizing the mode of inheritance (biparental vs. maternal vs. paternal) thereby narrowing the field of possible sex-determining mechanisms (e.g. polygenic, sex chromosomes with meiotic drive, cytoplasmic microorganisms). The primary sex ratio of the harpacticoid copepod, Tigriopus californicus is often male-biased and is highly variable among full sib families. We found that this extra-binomial variation for the primary sex ratio is paternally but not maternally transmitted in T. californicus. Paternal transmission of the primary sex ratio has been well documented in the haplo-diploid hymenoptera but is relatively rare in diplo-diploid organisms. If the sex-ratio trait is paternally transmitted in other closely related harpacticoid copepods it would explain why male biased primary sex ratios are so common in this group.