Does Infection by the Monogenoidean Gill Parasite Aethycteron moorei Affect Reproductive Ecology of the Darter Etheostoma flabellare in Mill Creek, Tennessee?

An increasing body of research shows the ability of parasites to alter the reproductive condition of their hosts, and the hosts' capacity to shift resources allocated to reproduction in response to parasitism. Here we compare host reproductive condition to gill parasite infection load in Fantail Darters ( Etheostoma flabellare ) of Mill Creek, Tennessee, USA, over the course of a year. We sought to determine whether host reproductive season or condition correlated with parasite load, whether parasite load differed between host sexes, and whether parasite load correlated with clutch size in females. We sampled the host population bimonthly and measured host physical and reproductive characteristics and gill parasite load. Infection levels significantly decreased when host reproductive activity ceased. Parasite load did not correlate strongly with body size in either sex. Male hosts were significantly more heavily infected than female hosts. No negative relationship was found between reproductive condition and parasite load in either sex. However, a significant positive correlation was observed between host clutch size and intensity of parasite infection in females, even when controlling for body size. The immunocompetence handicap hypothesis suggests that sex differences in parasite infection levels may be due to an immune defense cost incurred by males as a result of androgen-mediated reproductive effort. Females may have evolved a compensatory response to heavy parasite infection in which they shift androgen-mediated reproductive effort towards larger clutch sizes. Further study is needed to elucidate the relationship between host reproductive timing and seasonal patterns of parasite infection.