Abstract
We investigated variability between populations of the beetle Timarcha maritima over its geographic range by comparing several variables (size of individuals, fecundity, parasite load, sex ratio, pattern of pairing) in 10 populations along the French Atlantic coast. Populations exhibited significant differences for all variables considered. Our findings also indicate a major influence of the protozoan parasite Gregarina munieri on T. maritima ecology. Beetles paired assortatively according to the parasitic load, a pattern of pairing detected 3 years ago in a highly parasitized population. Size assortative pairing was never significant, even in parasite-free populations. The level of infection by gregarines was also a strong predictor of mean fecundity of females at the inter-population level. Conversely, the role of the external parasite Pseudamansia chrysomelinus (Acari: Canestriniidae) was weak whatever the population considered. This study underlines the need to consider parasites when studying population ecology.