Morphological Characteristics Affect Individual Mate Choice Decisions In Female And Male Western Mosquitofish (Gambusia Affinis)

Sexual selection through mate choice plays a central role in driving evolutionary processes,including speciation.Individual mate choice decisions are based on multiple sources of information about potential mating partners.Morphological characteristic is one of the major factors to affect male and female's mate choice.The western mosquitofish?Gambusia affinis?is a small,hard boned,warm-blooded ovoviviparous fish native to the central Atlantic coast of North America and member of the family Poeciliidae and the genus Gambusia.As one of the top 100 invasive species in the world,G.affinis is widely distributed and has the characteristics of rapid growth,high reproductive rate and long breeding season.The western mosquitofish has a coercive mating system and females often suffer from sexually harassment by males.Male sexual activity includes approaching a female,touching the female's genital pore and gonopodial thrusting.Western mosquitofish has a typical sexual dimorphism in body size and secondary sexual characteristics.Some studies have shown that both male and female show obvious mate choice preference.So,Gambusia affinis is an ideal model animal to study mating selection.In order to explore the influence of morphological characteristics of mate choice in male and female western mosquitofish,we constructed the morphological parameters and made computer animations to study mate choice with both sex.The main results were as follows:1.Female mate choice for male with erect gonopidium in Gambusia affinisIn dichotomous mating preference tests,females avoid males with erect gonopodium(t₃₂=-2.23,P=0.03,mean SOP=-0.13),and this result indicates that females reject sexual coercion and sexual harassment in coercive copulation system.2.Female age affects male mating preference in Gambusia affinisIn dichotomous mating preference tests,males have obvious preference for young females(t₃₅=2.54,P=0.016,mean SOP=0.17),and the strength of preference?SOP?was positively correlated with male body size?R²=0.13?.It suggests male sensitivity on sperm competition and may be related to male's social status.By quantifying relative gravid spot size and analyzing landscape morphometric of young and old females,we made a series of computer animation pairs and conducted dichotomous mating preference tests.Male prefer virtual female with relative large gravid spot regardless female age(Young:t₂₂=-2.95,P=0.007,mean SOP=-0.24;Old:t₂₃=-2.49,P=0.021,mean SOP=-0.21).Gravid spot size may work as an important/sensitive predictor of male mating.The results may suggest an innate male mating preference for high fecundity.Compared with virtual old female?with a curved spinal shape and large abdominal shape?,males showed stronger preference for virtual young female?with a straight spinal shape and small abdominal shape?(t₃₅=2.14,P=0.04,mean SOP=0.15).Male preference for young female morphological trait was only observed in one set,together with our morph manipulation only covered 69.36%variance.Maybe other traits play an additional role in affecting males'evaluation of female age,such as yellow spot.There were no or weak mating preferences of males related to female body size(Young:t₄₇=-0.80,P=0.43,mean SOP=-0.05;Old:t₄₇=-1.59,P=0.12,mean SOP=-0.10).Large-bodied male showed a tendency towards avoiding large-bodied females when animation derived from old females(t₂₆=-1.66,P=0.11,mean SOP=-0.15).Because large male's social status is higher than small male,and large male has more mating opportunities than smaller male.It suggests they can afford to be choosier than small males.In summary,I found that male and female western mosquitofish have different reproductive strategies in mate choice.In female mate choice,male's sexual harassment is one of the main indicators.In male mate choice,male explores potential mates comprehensively and a single morphological treat may not lead their preference.Here,all results reflect synthesis trade-off in different morphological treats of the opposite sex in G.affinis mate choice.