Study On Reproductive Geographic Variation And Reproductive Isolation In The Locusta Migratoria Linnaeus Of Henan And Okinawa Population

The migratory locust, Locusta migratoria Linnaeus, distributes widely in Asia, Africa, Oceania and parts of Europe. Due to geographical distribution and morphology differences, it can be divided into 9 or 10 subspecies. Study of the reproduction between different geographical populations is of much significance to discuss geographic differentiation of the L. migratoria.In this paper, abilities of parthenogenesis and sexual reproduction in Henan and Okinawa populations of migratory locusts were investigated. The results showed that both populations' females had parthenogenesis, but they had longer pre-oviposition period, few eggs, lower hatching rates and longer life time than sexual reproduction, and there was no significant difference in any of these parameters between the two populations. These results indicated that the female L. migratoria's parthenogenesis ability was very weak, and it had no geographic variation. When the females proceeded sexual reproduction, their pre-oviposition period were shorter, laid-eggs were more, hatching rate were higher than that of those females with parthenogenesis, which meant reproduction ability of the female with sexual reproduction was stronger than that of the female with parthenogenesis. Comparison of reproductive indexes between two populations showed that the females in Okinawa had significantly longer pre-oviposition period and weightier eggs than that of the females in Henan. From above, we may be able to infer that geographic variation exist in female L. migratoria's reproduction.We also observed mating behavior of the male adults in both populations on 15, 25 and 35 days after emergence, and found no significant difference existed in mating rate between populations. It illustrated that the sexual maturation period of the two population male adults were the same, so it was different from the results of female. This may because the sexual glands of males were smaller, requiring few development time, the difference was not as apparent as females. The pre-copulation mounting duration and mating duration of males in Okinawa population were both significantly longer than in Henan population, which indicated that geographic variation existed in males' mating behavior. In addition, with the age increase, males' pre-copulation mounting duration shortened in Okinawa population, while it didn't change significantly in Henan population. The mechanism of age effect on mating behavior appeared differentiation between two populations. This geographic variation in mating behavior might be able to influence the mechanism of male's sperm competition.We found geographic variation existed in reproduction both in female and male's reproduction, so, if this geographic variation could induce reproductive isolation between these two populations? If so, what is the isolating mechanism? To answer these questions, we investigated the mating rate, sperm transfer, hatching rate and survival ability of the offspring under interpopulational copulation.The results showed, under 30℃, LD 12:12 h's condition, the mating behaviors could occur both in light and dark stage, but they were concentrated in light stage. The mating frequentness of Henan population in light stage hold 83% of total mating frequentness, while the mating frequentness of Okinawa population in light stage hold 88.6% of total mating frequentness, and there were no misfit in mating rhythm between each other. We also observed mating between different populations in laboratory.The structure and function of external genitals in different insects are very different. They correspond with a "lock to key" relations between male and female. So, interpopulational copulation does not mean sperm can be transferred successfully. We studied on the sperm transmission between intrapopulational and interpopulational copulation, and the results showed it could complete sperm transmission when interpopulational copulation occurred, sperm transmission rate all reaching 100%. This indicated there was no mechanical isolation mechanism between these two populations.Investigation of hatching rate of the female adults from intrapopulational and interpopulational copulation showed the hatching rate of interpopulational copulation was obvious lower than that of intrapopulational copulation. Hatching rate of interpopulational copulation was only 45% in Henan population, and 47% in Okinawa population, and they were both significantly lower than that of intrapopulational copulation (both of them were higher than 90%). These results indicated that male sperm fertility of interpopulational was lower than intrapopulational copulation, so, it might existed gamete incompatibility in this two population.