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Sexual dimorphism in Gammarus pulex: the effect of current flow on pre‐copula pair formation
Author(s) -
GREENWOOD PAUL J.,
ADAMS JONATHAN
Publication year - 1984
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1984.tb00035.x
Subject(s) - gammarus pulex , biology , sexual dimorphism , assortative mating , copula (linguistics) , zoology , mating , mathematics , amphipoda , crustacean , econometrics
SUMMARY. 1. Male Gammarus pulex (L.) are typically twice as heavy as females in field caught pre‐copula pairs and mating is positively size assortative. Earlier work had shown that relatively large males can swim in pre‐copula at higher current speeds than males that are relatively small compared with their mates. We describe experiments on pair formation in the laboratory, in static water and in an artificial stream. 2. Pairs formed in the artificial stream had a significantly higher weight ratio than either those formed in static water or those caught in the field. In both experimental conditions, males in pairs were significantly larger than singles. In the stream, the weight ratio of pairs increased with formation sequence due to a significant decrease in the size of selected females. 3. It is concluded that these results are consistent with the hypothesis that the relatively large size of paired male G. pulex is a product of mechanical constraints rather than male–male competition.