Studies On The Mating Mode And Sexual Selection Of Rapana Venosa

Sexual selection refer to the choice of increasing the reproductive success of animal traits in the sexual reproduction environment. It is a special form of natural selection. The success of sexual selection directly determine the reproductive success of animals and have a significant impact on the genetic of biological characteristics. It is also the most important animal behavior in the sexual reproduction environment and has the great significance for the evolution of species. Gastropods are the most widely distributed and rebundant species in the mollusca, second only to the number of insects. Gastropods have complicated courtship and mating ways. The phenomenon of multiple mating and sperm storage are more prevalent. In recent years, it becomes the hotspot group of the sexual selection study in aquatic invertebrates. Rapana venosa belongs to Mollusca, Gastropoda, Muricoidea, Rapana. It is widely distributed in the bohai sea and yellow sea of the coastal area of China. R. venosa which have delicious taste and rich nutritional value, is the important economic snails of China. The object of the study is to develop microsatellite markers in R. venosa, and explore the mating pattern and the behavior of sexual selection by combining paternity identification based on microsatellites and mating behavior observation.. This study will provide guidelines for captive breeding and conservation managements in Rapana venosa, and also provide basic data and information for studies on the evolution of sexual selection, species evolution, and so on, in gastropods.1. Characterization of microsatellite loci for R, venosaA total of 203,364 reads with an average read length of 307 bp were obtained through 454 sequencing, and 84,493 reads contained microsatellite loci. According to the selection principle of microsatellite,538 beads were selected. Among the 275 candidate loci tested,220 loci were successfully amplified and 57 loci showed polymorphic in 30 wild individuals. The microsatellite sequences could be categorized structurally as follows:perfect (57.9%), imperfect (29.8%), and compound (12.3%). The number of alleles per locus varied from 2 to 14. The observed and expected heterozygosities ranged from 0.100 to 1.000 and 0.127 to 0.919, respectively. Thirty-two loci were in Hardy-Weinberg equilibrium (HWE)and 25 loci deviated significantly from HWE after Bonferroni correction. Tests for linkage disequilibrium revealed a nonrandom association (P<0.01) between two pair of loci (Rv03-Rv05, Rv35-Rv42).2. Study on the mating mode and sexual choice of R. venosaIn order to explore the mating pattern and the behavior of sexual selection before copulation in R. venosa, six morphological parameters of 99 adult R. venosa were firstly measured and the correlation of the six morphological parameters were investigated. The results showed that aperture width, body whorl height, operculum width and operculum height were significantly and positively correlated with shell height, but no correlation with spire height. Spire height showed a weak correlation with shell height. Moreover, R. venosa showed no sexual dimorphism in the six morphological parameters. R. venosa began to mate in two to four days after putting into the rearing pond, and the copulation behavior was recorded. The duration of each mating was within 96 hours and 83.6% of the mating couples finished copulation within 48 hours. The times of mating of R. venosa ranged from zero to five and mating intervals ranged from 2.67 to 8.80 days.In order to explore the sexual selection after copulation in R. venosa, six polymorphic microsatellite loci were selected. The number of alleles per locus varied from 5 to 14. The observed and expected heterozygosities ranged from 0.607 to 0.919and 0.600 to 0.834, respectively. No linkage disequilibrium between any pair of loci was observed. In the paternity identification with the six microsatellites, the exclusion probability were 99%. Multiple paternity in R. venosa was evidenced in this study. Paternity was found to be skewed, and male mating order affected the survival of his offspring. The fraction of offspring sired by the first male was the highest, suggesting the existence of sperm competition and pre-and postcopulatory female choice, which may be important for avoiding the occurrence of inbreeding and for optimizing genetic variation in offspring.Not found the mating duration of parents and six morphological parametershave a correlation with relative contribution of sires.