Different female mating rates in different populations do not reflect the benefits the females gain from polyandry in the adzuki bean beetle
The question why females in many species mate with several males (polyandry) has engaged the interest of evolutionary biologists for many years, and many studies have been conducted on the nature of the benefits that the females gain from polyandry. To understand the variation of female mating rates among species and populations it is indispensable to test the prediction that females of more polyandrous populations experience larger fitness benefit than those of less polyandrous populations. We compared the fitness components of two strains of the adzuki bean beetle Callosobruchus chinensis that have genetically different female mating rates. We measured the number of hatched eggs of once-copulated females and twice-copulated females in each strain. The statistical interaction for the number of hatched eggs between the number of matings and strains was determined. The increase in the number of hatched eggs is larger for the lower mating-rate strain than for the higher mating rate strain. This means that females of the lower mating-rate strain would have larger fitness gain from polyandry than those of the higher mating-rate strain. The actual mating rates of females did not reflect female interests in adzuki bean beetles, suggesting they are affected by sexual conflict.
KeywordsSexual conflict Mating rate Polyandry Multiple mating Population Adzuki been beetle
Professor Tetsukazu Yahara provided valuable advice and criticism throughout the study. Professor Takahisa Miyatake and Doctor Tomohiro Harano provided laboratory strains of the adzuki bean beetle for this study, and valuable advice. Takashi Kuriwada made comments on the manuscript. This study was in part supported by a Grant-in-Aid of Scientific Research from the Japan Society for the Promotion of Science (Nos. 16370013 and 16370045) to Eiiti Kasuya. We would like to thank our colleagues at the Laboratory of Ecology, Kyushu University for help and encouragement.
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