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APPLICATION OF HEMICLONAL ANALYSIS TO INTER-LOCUS ANTAGONISTIC COEVOLUTION

To use hemiclonal analysis to assess the potential for inter-locus sexual conflict to drive genetic divergence among allopatric populations, we review results from two recent studies in our laboratory. In the first study, a random set of 35 genomic haplotypes was sampled from the LHM base population and used to construct five replicated sets of the 35 female hemiclones (Linder and Rice, 2005). The number of females in each replicate was 20 per hemiclone. The females were collected as virgins and then mass mated by brief (90 min) exposure to a 3:1 ratio of males to females from the LMM base population. Once mated, the females were randomly divided into two experimental treatments during the 2-day adult competition phase of their 2-week generation cycle. The treatments were (i) a “male-protected” environment in which the 10 hemiclonal females competed with 6 unrelated females for the resource that limited their lifetime fecundity (10 mg of live yeast, applied to the surface of the killed-yeast medium) in the absence of persistent courtship from males (no males present), and (ii) a “male-exposed” environment that was identical to the former treatment except that females competed in the presence of males at a 1:1: sex ratio of males to female, i.e., they competed under the social environment experienced during the normal propagation of the LHM base population. The environmental conditions under which the flies were assayed (for example, timing of events, food levels, and densities and ages of flies) closely matched those to which the LHM base population had adapted for >300 generations. Finally, the lifetime fecundity of the females was compared between the two treatments by measuring egg production during the last 18 h of their 2-week generation cycle (which is equivalent to egg production in the oviposition vials during the normal propagation of the LHM base population). Any reduction in fecundity in the male-exposed compared with the male-protected treatments estimated the total cost of interacting with males, that is, the reduction in fecundity owing to resources spent by females when they decamped, kicked, and otherwise responded to persistent interactions with males. Control experiments demonstrated that males did not compete with females for their limiting resource (live yeast) and that differences in fly density did not contribute to the difference in fecundity between treatments (Linder and Rice, 2005).

All 35 hemiclones experienced a decline in lifetime fecundity due to their interactions with males (Fig. 3.4, modified from Linder and Rice, 2005). On average, lifetime fecundity was reduced by 15.4% in the male-exposed treatment relative to the male-protected treatment. However, some hemiclones were harmed more than others (Fig. 3.4), and this het-



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