Predictors of individual performance and evolutionary potential of life-history traits in a hematophagous ectoparasite

Little is known about the intraspecific variation of parasite life-history traits and on how this variation may affect parasite fitness and evolution. We investigated how life-history traits predict success of individual tree-hole ticks Ixodes arboricola and estimated their evolutionary potential, as well as genetic correlations within stages and phenotypic correlations within and across stages. Ticks were followed individually over two generations while allowed to feed on great tits Parus major. After accounting for host and tick maternal effects, we found that short feeding times and high engorgement weights strongly increased moulting success. Also, moulting time was positively correlated with feeding success in adults. In larvae and nymphs we found negative phenotypic correlations between engorgement weight and both feeding and moulting time, the latter supported by a negative genetic correlation. We found sex-related differences in feeding time (longer in male nymphs) and moulting time (longer in male larvae but shorter in male nymphs). Also, time since the last feeding event (set experimentally) reduced larval and nymphal fitness while it increased adult female fitness. Furthermore, we found significant heritability and evolvability, i.e. the potential to respond to selection, for engorgement weight and moulting time across all stages but no significant heritability for feeding time. Our findings suggest that variation in tick fitness is shaped by consistent individual differences in tick quality, for which engorgement weight is a good proxy, rather than by life-history trade-offs.