Intraspecific variation of body size in a gamasid mite Laelaps clethrionomydis: environment, geography and host dependence.

We investigated intraspecific variation in body size of an ectoparasitic gamasid mite, Laelaps clethrionomydis, across 12 localities in the Palearctic. We asked whether mites collected from the same host species in different localities or from different host species in the same locality vary in body size. Within host species, mites collected in different localities differed significantly in body size, tending to be larger in northern than in southern localities. In addition, mite body size correlated negatively with mean annual temperature in a locality. Mites collected from different hosts in the same locality differed significantly in body size when hosts belonged to different genera but did not differ when collected from congeneric hosts. We conclude that intraspecific variation in mite body size is caused by interplay of environmental and host-related factors.