The Mating System And Its Evolution Of Emei Moustache Toad(Leptobrachium Boringii)

Mating system refers to the general behavioral strategy employed in obtaining mates in an animal population.It encompasses how mates are acquired,how many mates can be acquired and how parental care is provided by each sex in animals.Sexual selection includes intra-sexual selection and inter-sexual selection.The exploration of sexual selection is pivotal to understand the formation and evolution of animal mating system.The exploration of animal mating system and its evolution mechanism are of great significance to understand the adaptive evolution of animal breeding behavior.However,current researches on the evolution of mating system are far less than systematic and comprehensive.Most researches only take the role of one factor into consideration.In addition,the researches on animal mating system are unbalanced among different animal groups.The evolution mechanisms on many amphibian mating systems are still uncertain.Therefore,it is necessary to carry out a long term and systematic research for animals and combine with species-specific characters as well as all possible factors,to better elucidate the evolution mechanism of animal mating system.In this study,we used a China-endemic amphibian species Emei moustache toad(Leptobrachium boringii)as a model.We combined the methods of field observation as well as genetic analysis and taken the role of ecological factors,sexual selection and parental care into consideration,so as to explore the mating system of L.boringii in natural condition and elucidate the main factors and evolutionary forces in the formation of its mating system.We made a three-year field study of L.boringii in Badagongshan National Nature Reserve in Hunan Province from March to May during 2013-2015.In addition,we used 9 pairs of microsatellite loci to apply the genetic analysis for individuals.We marked a total of 270 male individuals,309 female individuals,89 breeding nests and 397 egg masses during the study period.The following results were obtained:1.The breeding character of L.boringiiThe breeding season of L.boringii can be divided into three periods,including nest occupation period,mating period and parental care period.L.boringii is an explosive breeder.In each breeding season,females arrived at the breeding site asynchronously during the mating period and left once the spawn was finished.Males entered into the breeding site asynchronously since nest occupation period and most individuals left when the mating period was finished.The remaining individuals(2013-2015:25.61%,18.68%and 25.77%)stayed in the breeding site and provided parental care to their offsprings.The adult sex ratio of L.boringii was female biased,and the sex ratios of the three breeding seasons were 1:1.68,1:1.41 and 1:1.35,respectively.The breeding adults of L.boringii exhibited fidelity to the breeding site,and more female individuals(20.91%)moved back to the breeding sites than male individuals(11.55%).The annual growth of the recaptured individuals was very significant in both body weight and SVL(P<0.001).The range of the clutch size was 101?384 for female L.boringii with the average size were 248.The body weight(F1,102=11.786,P=0.001)and SVL(F1,189=14.234,P<0.001)of the gravid females were positively correlated with the clutch size.The understanding of the breeding behavior and characters of L.boringii is the foundation for the research of its mating system and evolution mechanism.2.The sexual selection of L.boringiiL.boringii existed intensely male-male competition not only in occupying nests but also in acquiring mates.In respect of nest competition,there were 17(65.38%)and 19(57.58%)breeding nests existing nest take-over events during 2014-2015.In all nest take-over events(n=121),the winner males were larger than the loser males in both SVL(P=0.012)and body weight(P=0.020).The GLMM results indicated that,males that arriving later(P=0.043)and having a higher attendance(P<0.001)in the breeding site would success more in acquiring breeding nests.In respect of acquiring mates,male body weight(F1,99=15.147,P<0.001),the arriving time(F1,188=4.578,P=0.034)and the attendance(F1,66=26.013,P<0.001)in the breeding site were positively correlated with the number of mates they acquired.Female mate choices of L.boringii were based on both nest quality and male quality.The GLM result indicated that,female preferred polygynous nests(P<0.001)among nest quality factors and larger body weight(P=0.048)among male quality factors.Female's preference for polygynous nests may due to the reason that it may improve male's parental investment.It may also be a mate choice copy strategy for females.Female's preference for higher body weight of males may be a by-product result of male-male competition.In addition,L.boringii displayed male biased sexual size dimorphism.Among all morphological variables,the forearm width and body weight were the most different variables between the two sexes,and the differences were reached to 95.00%and 63.95%,respectively.Intensely male-male competition is likely the main force driving the evolution of male biased sexual size dimorphism.3.Male parental care of L.boringiiMale L.boringii existed parental care behavior.There were totally 63 male individuals(2013-2015:21,17 and 25 male)providing paternal care to their offspring during the three breeding seasons.And the time they spent in parental care lasted from 6 to 62 days.The mainly parental care behavior was attending on the eggs and embryo.Males gain great benefits from providing care to their offsprings.The hatchability(Mann-Whitney U:Z=8.218,P<0.001)and survival rate(Mann-Whitney U:Z=-3.769,P<0.001)of offsprings with paternal care were significantly increased than offsprings without paternal care.In addition,the hatchability(F1,318=34.239,P<0.001)and survival rate(F1,316=45.275,P<0.001)of the offsprings were significantly increased with the number of egg masses within the nests increased.It is likely that male improved their parental investment based on their offspring numbers.It may also due to the dilution effects from predation.Males also suffered costs from providing paternal care.The body weight of the paternal males was significantly decreased(P<0.001),they lost an average of 20.20%initial body weight.And the predation risk was also increased.The main threats of offsprings that had no paternal care were dehydration,fungal infection and predation.The high predation risk of offsprings is likely the main reason driving the evolution of male parental care behavior in L.boringii.4.The mating system and its evolution of L boringiiL.boringii have a mating system of resource defense polygyny.The proportion of polygyny nests is up to 84.27%during the three breeding seasons.The breeding nests(2013-2015:32.00%,22.73%,and 27.59%)contained multiple paternities(2-3 paternities)among different egg masses.The occurrence of multiple paternities within the breeding nests is due to the nest take-over events during mating period.17.69%egg masses contained multiple paternities within the same egg mass.It is likely that males existed alternative breeding strategies.Only an average of 38.74%male individuals could obtain mates each breeding season,and the number of mates they obtained varied from 1 to 11.Males that unable to occupy and defense a nest would have no chances to acquire mates.The distribution pattern of breeding nests and the operational sex ratio during mating period had no effects on the proportion of polygyny.Male individuals could obtain more offsprings through obtaining more mates(F1,65=2524.324,P<0.001).For female individuals,there were no differences in genetic diversity of offsprings between monogamous and polygynous females(P>0.05).However,the hatchability(Mann-Whitney U:Z=-3.798,P<0.001)and survival rate(Mann-Whitney U:Z=-3.769,P<0.001)of offsprings in polygynous nests is significantly higher than those in momogamous nests.Thus,females suffered no cost through choosing polygyny but gained fitness benefits for offsprings.In general,the female and male's common pursuing of higher reproductive success is the main driver leading to the evolution of resource defense polygyny in L.boringii.In conclusion,L.boringii revealed a mating system of resource defense polygyny.Male-male competition was intensely in both defending nests and acquiring mates.Male body weight,arriving time in breeding site and attendance during mating period have important effects on male breeding success.Females L.boringii had mate choice,and they preferred males having a polygynous nest and a higher body weight.Males providing paternal care could improve the hatchability and survival rate of their offsprings.And the hatchability and survival rate of offsprings in polygynous nests were higher than those in monogyous nests.Thus female suffered no cost from choosing polygyny.The female and male's common pursueing of higher reproductive success is the main driver leading to the evolution of resource defense polygyny in L.boringii.Our study provides valuable theoretical significance on revealing the evolutionary meachnism of animal mating system,as well as providing scientific proof on the protection and breeding for L.boringii.