| After Parker proposed the concept of the sperm competition in 1970, the studies of the sperm competition become the hot point of the evolutionary biology. Sperm competition is the competition among the sperms from two or more males for the fertilization of the ova, and it is the last step of the reproductive competition. The purpose of the research is to reveal the pattern of the sperm using and the mechanism of the sperm competition. In recent years, the scientists have proposed several hypotheses about the mechanism of the sperm competition, such as sperm stratification, sperm displacement, sperm incapacitation and cryptic female choice.Harmonia axyridis is a species of the Coccinellidae and it feeds on aphid. For its high reproductive and survival ability, Harmonia axyridis is used for the pest biological control. However, when it is introduced in a new place, the number of the population grows very fast and threatens the species diversity of the local place. For this reason, scientists begin to focus on how to make the population of Harmonia axyridis under control when it is introduced.Like many other species, Harmonia axyridis have multiple mating behaviors and it can storage sperm in the spermatheca, which are sufficient for the occurrence of the sperm competition. The study on the sperm competition of Harmonia axyridis will help us to unravel its reproductive mechanism and sperm utilization pattern, and may provide theoretical basis for the utilization of Harmonia axyridis.The development of the DNA molecule marker provides the technical supports for the study of sperm competition. In the recent 20 years, because DNA molecule marker technique is simpler, more precise and more convenient than many traditional techniques, it is widely used for animal and plant breeding, gene mapping, gene localization, assessment of blood relationship, gene bank construction, and gene cloning and so on. Until now, more than 10 kinds of DNA molecular marker technique have been developed and used for research and practice, such as RAPD, SSR and ISSR. In this research we use RAPD, SSR and ISSR to explore the sperm competition of Harmonia axyridis, and ISSR is proved to be more efficient to study the sperm competition of Harmonia axyridis. The results are as follows: (1) Though RAPD technique is more convenient and provides more polymorphism bands than the other two techniques, it is uneasy to find the different bands between two fathers. Also the experiment results aren't steady, for some bands can not be repeated. SSR technique is widely used in paternity testing, but we can not get high-resolution polymorphism bands, because the silver-staining condition is difficult to control. ISSR technique is developed on the base the two above technique. Adopting this technique we obtain high-resolution polymorphism bands, and find the different bands between two fathers, so ISSR is used to study the sperm competition of Harmonia axyridis in this research.(2) The P2 value had been tracked for 40 days after the onset of sperm competition, and we found the sperm competition pattern of Harmonia axyridis is the last male sperm precedence, and the last male sperm precedence is high (P2>80%).(3) The sperm precedence of Harmonia axyridis is influenced by the interval time between two males. The change for 14d group is smaller than Od and Id groups with time. P2 decreases significantly in the Od and 1d groups, and Od group decreases more significantly than 1d group. The longer the interval time between two male is, the more significant the last male's sperm precedence is.(4) The research suggested that longer intervals between mating bouts might result in more complete and persistent last-male sperm precedence. After inseminations, male ejaculates may 'stratify' in the narrow and elongate storage tubules of the spermatheca, and the spermatheca is a cul-de-sac and has a single entrance duct through which sperm also exit, so sperm precedence in this species may occurs via a mechanism of stratification. |
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