The Male Strategy Adjustment And Its Effects Associate With Sperm Competition In Galerucella Birmanica Jacoby(Coleoptera:Chrysomelidae)

Males respond to the underlying sperm competition threat adaptively in changeable environment by altering their behavior.Recent studies showed that males could extent mating duration when they encounter rivals before mating,causing increased ejaculate,thereby more offspring.Most similar studies were conducted in the fruit fly.Here,we investigated males‘ response to the potential sperm competition in a leaf beetle Galerucella birmanica when rival males appear before and at mating.In addition,we discuss how the changeable behavior of males influences the fitness on male and female.Multiple mating is widespread across Insecta,either mating repeatedly with the same male(monandry)or mating multiply with different males(polyandry).The evolutionary maintenance of female polyandry is traditionally attributed to the material(direct)and genetic(indirect)benefits of using the mating resources and sperm of different males.This fails to explain the coexistence of female monandry and polyandry in insects.In addition,the model of sperm precedence has not yet been reported.(1)Our results indicated that the effect on males and females of exposure length before mating was more intense than exposure rivals.The longer the length of exposure,the shorter the latency to mate and female longevity,and the longer the mating duration.The number of offspring was first decreased until exposure length of 24 hours and then increased.Accordingly,we conclude that the males needs some time to prepare for the physiology,and there was a ?time window? of 24 h to evoke males mightily in response to the potential sperm competition threat.Two kinds of sexual interference both significantly influenced the number of effective eggs and hatch rate.Additionally,we found that males lag their plastic response when spouse and female-interference appeared simultaneously.(2)We compared the fitness consequences of monandrous and polyandrous multiple mating(MM and PM)to female G.birmanica.We found that the longevity of PM females was significantly shorter than that of MM females.The egg producing duration of PM females was significantly shorter than that of MM females,but the duration of fertilized egg production did not differ significantly.PM females produced significantly more eggs but significantly less fertilized eggs than MM females;this resulted from the decreased hatch rate of eggs produced by PM females.When housed with the same male and new males,females expressed reluctance to new males‘ courtship and most of them mated with the previous males.In addition,those PM females who were always mated with virgin males had shorter longevity and lifetime fecundity compared with those PM females.These results indicated that females of G.birmanica gained more fitness by living longer and producing more offspring from monandrous multiple mating than from polyandrous multiple mating.(3)Using the technology of SSR Paternity Identification and analyzing P2 of offspring of G.birmanica,we found that sperm bias would be influenced if we change mating times and mating interval.When the female mated for multiple times in a short time,the proportion of offspring inherited in the first male decreased and that inherited in the last male increased,therefore sperm precedence presents the last male advantage.When the mating interval was long enough(more than two days),occupying the advantages of insemination by the sperm of the first mating male leading to the offspring inheriting from the first male in the beginning,but the proportion of offspring of the last male increased gradually over time,therefore the last male precedence was postponed.In conclusion,we found that males of G.birmanica produces a series of adaptive responses when potential sperm competition appears;in the comparison of monandrous and polyandrous multiple mating,we found that the former obtained more direct benefits than the latter;through the microsatellite patriarchal identification technique,we found that the model of sperm bias showed the last male precedence advantage.