Under The Pressure Of Different Sperm Competition,Adaptive Relationship Between Sperm Size And Testicular Tissues In 26 Species Of Anura

Sperm competition refers to the situation that females mate with multiple males during the reproductive period.In order to improve the chance of sperm and egg combining,the male produces physiological,morphological and behavioral adaptation.In amphibians,spermatozoa arise in the spermatogenic epithelium of the spermatogenic tubules and are produced gradually through meiosis of spermatogenic cells,finally releasing mature spermatozoa into the lumen of the spermatogenic tubules.However,the relationship between sperm size and testicular internal tissue under different sperm competition pressures has not been well explained.Therefore,this paper took 26 species of Anura as the research object,measured the testicular data of male individuals of 26 species,took photos to measure the testicular internal tissue(spermatogenic tissue,stromal tissue,lumen,capsule)data under the microscope and calculated the proportion.Combined with sperm size data,relative testicular size and mating information were used as indicators of sperm competition intensity.The effects of sperm competition on testicular tissue structure and sperm size,as well as the relationship between spermatogenic tubule size and sperm size were studied by Generalized least squares(GLS)analysis.The results showed that spermatogenic tubule size was not correlated with testicular size(t = 0.574,P = 0.571),but was positively correlated with the relative size of testis(t= 2.348,P = 0.027).The regression results of GLS model showed that there was a significant positive correlation between the size of spermatogenic tubule cross-sectional area and sperm length(t = 4.808,P < 0.001).There was no correlation between the height of spermatogenic epithelium and the cross-sectional area of spermatogenic tubules(P =0.256)nor between the length of spermatozoa(P = 0.5436).The lumen area of spermatogenic tubules was positively correlated with the size of spermatogenic tubules and the length of spermatozoa(t = 13.174,P < 0.001;Sperm length: t = 5.427,P < 0.001).Partial correlation analysis results show that,in addition to the interstitial tissue,the proportions of the capsule membrane organization,sperm production organization,lumen ratio and relative testicular size have significant correlation(| r | < 0.3,P < 0.005).Relative testicular size and mating information were used as risk indicators of sperm competition.The results showed that sperm competition intensity was negatively correlated with the proportion of spermatogenesis tissue in anura(t =-6.464,P < 0.001),was positively correlated with sperm length(t = 5.485,P < 0.001).The present study reveals that there is a significant correlation between testicular structure and sperm length in anura,that is,the longer the sperm length,the larger the spermatogenic tubule.With the increase of sperm competition,the length of anura's sperm and the area of spermatogenic tubules increased.Anura,under the pressure of intense sperm competition,choose to have a larger lumen area and a lower proportion of spermatogenic tissue,and produce higher quality sperm.Our results enrich the theoretical basis of anura sperm competition mechanism.