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Is Being Large More Important for Female Than for Male Parasitic Wasps?

1989; Brill; Volume: 108; Issue: 1-2 Linguagem: Inglês

10.1163/156853989x00114

1568-539X

J. Van Den Assem, J.J.A. Van Iersel, R.L. LOS-DEN HARTOGH,

Insect and Arachnid Ecology and Behavior

We compared the impact of differences in body size on reproductive success of males and females in a species of parasitic wasps (Lariophagus distinguendus; Hym., Chalcidoidea, Pteromalidae), in an effort to obtain an estimate of the consequences of being large or small in terms of classical fitness (the expression of an individual's success of passing on its genes to future generations, DAWKINS, 1982). Body size of male and female Lariophagus may vary over about the same range, but, on average, males are distinctly smaller than females. Sex ratio theory has generated a number of models which predict in what ways a parasite like Lariophagus will treat hosts of variable size (reject, use for a daughter, use for a son) in order to make the most profitable investments (e.g. CHARNOV, 1979, 1982; WERREN, 1984). Assumptions on size and sex-related differential fitness returns underly these models. Our experiments served as a test of CHARNOV'S (1979) hypothesis, that a smaller size may be less of a disadvantage to males than to females. The results give support to this assumption. Large females produced more offspring than small ones because they were more fecund and because they lived longer; large and small differed by a factor 3. Large males lived about twice as long as small ones. Large males were able to inseminate about twice as many females but successful courtship displays of both categories proved to be of equal duration. In competitive situations large males were about 1.2 times more successful to court and copulate first, 1.4 times more successful in stealing a copulation and about twice as successful in obtaining an exclusive copulation without any prior investment in courtship behaviour. Small males were less successful than large ones in avoiding sperm competition; difference were in the order of a factor 2.