Sex Ratio in a New Species of Nasonia with Fully-winged Males.

نویسندگان

  • B H King
  • S W Skinner
چکیده

One of the better-studied sex ratio theories is local mate competition (LMC) theory, first developed by Hamilton in 1967 (for reviews see Charnov, 1982; Waage, 1986; King, 1987). LMC models assume a subdivided population structure with emergence and then random mating taking place within local patches followed by female dispersal to new patches to lay offspring. Under these conditions, offspring sex ratio (proportion sons) is expected to increase with increasing num~er of ovipositing mothe.rs in a patch, eventually reaching an asymptote (Hamilton, 1967, 1979). One ofthe best-studied species with regards to LMC theory is the parasitoid wasp Nasonia vitripennis. N. vitripennis's sex ratio as it relates to LMC theory has ~een examined both genetically and behaviorally, both In the laboratory and in the field (e.g., Orzack and Parker, 1986; Werren, 1980, 1983). Although current sex ratio theory cannot completely explain offspring s~x. ratio~ in N. vitripennis (e.g., Orzack, 1986), empirical evidence on N. vitripennis supports LMC model predictions in general. For example, mostN. vitripennis females produce female-biased offspringsex ratios when alone and increase the proportion ofsons they produce when oth~r ovipositing females are present (Walker, 1967; Wylie, 1965; Velthiusetal., 1965; Werren, 1983). Here we examine offspring sex ratios in a newly discovered species of Nasonia, N. giraulti (Darling and Werren, 1990), and compare it to that of N. vitripennis. In N. vitripennis, the explanation for why the species meets the population structure assumed by most LMC models has been that 1) males lack full wings; 2) thus, males cannot disperse to mate, and so mating must take place at the emergence site; and 3) because mating takes place at the site ofemergence, there will be competition for mates among males emerging from the same or nearby hosts (i.e., "local mate competition"). N. giraulti is almost identical morphologically to N. vitripennis, except that N. giraulti males have full wings and can fly. Thus, our expectation was that in N. giraulti, males disperse and so their populations, relative to N. vitripennis, should experience both less competition among brothers for mates and less inbreeding. Either or both ofwhich should have selected for less female-biased sex ratios in N. giraulti than in N. vitripennis (Frank, 1985; Herre, 1985). We present results showing that N. giraulti does manipulate offspring sex ratio in response to the number ofother mothers present, but that N. giraulti produces

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عنوان ژورنال:
  • Evolution; international journal of organic evolution

دوره 45 1  شماره 

صفحات  -

تاریخ انتشار 1991