A TRANSMISSION STUDY OF 2 SYMPATRIC DIGENEANS - SPATIAL CONSTRAINTS AND SOLUTIONS

The distributions of infected molluscan hosts of the digeneans Maritre ma misenensis, a parasite of charadriid birds, and Lepocreadium pegorc his, a parasite of sparid fishes, were examined along a transect spann ing the mediolittoral and upper infralittoral zones at the edge of a p rotected small bay in southeastern France, western Mediterranean. In b oth parasites, the first intermediate host occurs in all area separate d spatially from the definitive host; in each case, only a small fract ion of the potential first intermediate hosts, those nearest the sourc e of eggs, are infected. In both cases, second intermediate hosts over lap in distribution only slightly (or not at all) with the first inter mediate hosts (and, in the case of L. pegorchis, with the definitive h osts). We analyze the strategies evolved to overcome these spatial con straints on transmission.