Association Analysis Of Abdominal Muscle Content And The Related Phenotypes With SSR Markers In Red Swamp Crayfish (Procambarus Clarkii)

Red swamp crayfish(Procambarus clarkii)is a kind of freshwater crayfish,which has the highest yield compared with other culturing crayfish in China.However,the ways of breeding the offspring mainly depended on the self-propagation.It resulted in germplasm degradation,showing a phenomenon of big head while abdomen small,which means there is lower muscle content.Therefore,more inedible parts will be produced,such as shell and chelae.However,the great majority of them will be wasted directly because of the low utilization,in that case,it will result in serious environmental pollution and economic loss.In order to improve the cultivation income,the method of breeding and culturing separation have become more and more popular in China,it leads the increasing demand of the offspring.Therefore,the aim of this study is to uncover the phenotype variation of abdomen muscle content,and identify the related traits as the selection target for breeding,which is of great theoretical significance to raise resource utilization,protect environment and improve economic value.In this study,1327 red swamp crayfish including 692 females and 635 males were collected.The following phenotypes were measured including chelae length,chelae weight,body length and body weight,muscle weight,carapace length and carapace width,and then calculating abdominal muscle content.The eight traits were grouped and analyzed by gender and body weight,the results showed that the abdominal muscle content in females was higher than that in males under the same specification,and it gradually decreased with the increase of body weight.The regression and path analysis of muscle content and the phenotypes were performed by gender in both medium individuals(body weight: 25-35 g)and large individuals(body weight: 40-45 g).The results showed that it is necessary to reduce chelae weight to improve abdominal muscle content because chelae weight is the decision variable and body weight is the main limiting variable.Therefore,it’s efficient to improve the abdominal muscle content by breeding the varieties with smaller chelae under the conditions of keeping body weight invariant.Two associated populations were cultured as experimental materials in this study by monoculture technology.The first population(pop1)was a natural population,cultured from the similar sizes,including 167 individuals.The second population(pop2)was cultured from the same life stages including 72 half sib individuals.The individual phenotypes in two populations,including chelae length,chelae weight,chelae width,body length,body weight,carapace length and carapace width,were measured and then calculating proportion of chelae weight and body weight after chelae removal.The muscle tissue of red swamp crayfish was collected for DNA extraction.The genetic diversity of two populations were analyzed by 600 SSR markers.At the same time,the association analysis was carried out between the chelae related traits(chelae length,chelae width,chelae weight,proportion of chelae weight,proportion of chelae length and weight after chelae removal)and the SSR marker loci.The results are as follow:In pop1,344 SSR markers were detected to be polymorphic and achieve 929 alleles totally,with an average of 2.70 alleles per marker.The polymorphism information content(PIC)ranged from 0.05 to 0.76,with an average of 0.38.288 SSR markers were amplified and polymorphic in pop2,achieving 713 alleles totally,with an average of 1.86 alleles per maker.The PIC varied from 0.06 to 0.70,with an average of 0.33.The genetic diversity of pop2 was lower than that of the pop1.A total of 20 SSR markers were found to be associated with chelae related traits in pop1(P < 0.05),of which 8 in females and 14 in males,and 2marker loci were repeatedly detected in different genders 23 SSR loci were found significantly related to chelae related traits in pop2(P < 0.05),9 in females,14 in males.Both of the PCM1966 and PCM2209 were detected repeatedly in populations with different gender,and the explaining the variation of chelae was 11.96%-26.44%;The PCM987 marker locus was respectively detected in the females of pop1 and the males of pop2,and the explaining the variation of chelae was 5.85%-23.45%.By analyzing phenotypic values under different alleles of these three markers,major dominant alleles have not been found.Therefore,in order to use PCM987,PCM1966 and PCM2209 makers to breeding the red swamp crayfish with smaller chelae,more associated populations have to be used to prove it.All in all,the results of this study not only lay a foundation for analyzing the variation pattern and the genetic regulation basis of abdominal muscle of red swamp crayfish,but also play an important role in breeding to improve the abdominal muscle content of red swamp crayfish.