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.