Host and environmental correlates of body size in ticks (Acari: Argasidae and Ixodidae)

Abstract

To evaluate the influence of host mass and environmental temperature on the evolution of body size in ticks, a comparative analysis was performed using data from 193 species. Using the 20 possible phylogenetically independent contrasts among tick species, no relationship was found between body size of female ticks and either host mass or temperature. The statistical power of these analyses was low. Within the two most speciose genera of soft ticks, however, separate cross-species analyses revealed a positive and highly significant relationship between female tick size and host mass. Also, within the two most speciose genera of hard ticks, cross-species analyses showed a positive and highly significant relationship between scutum size of female ticks and host mass. The latter correlation is based on measurements of tick body size that are independent of the level of blood engorgement. No effect of temperature was observed in the within-genera analyses. These within-genera trends may be artefacts of unknown phylogenetic relationships. Another explanation, however, is that host body mass may have influenced the evolution of tick body size.