The Molecular Evidence For Parthenogenesis And Hybrid Origin Of Mauremys Megalocephala

The Mauremys megalocephala is an enigmatic species. FANG(1934) first discovered and named Mauremys megalocephala. Most foreign researchers have been inclined to suggest that M. megalocephal is a variant of M. reevesii, adapted or acclimated to a diet of mollusks. Domestic scholars confirmed it as a valid species based on the significant difference between M. megalocephala and M. reevesii by the osteological characters and chromosome features.We have conducted many investigations in 9 turtle markets in Anhui and Guangxi since 2005, but no male matching the description provided by Fang was found. Some suspected M. megalocephala male confirmed by comparison were M. reevesii male with big head.Summarizing previous studies, we can find an interesting phenomenon—the male of Mauremys megalocephala is noly mentioned by Fang. All other subsequent researchers performed their research solely on females or the sex of the specimens were vague. These case leads an increasing interest in the reproduction of M. megalocephala—sexual reproduction or parthenogenesis.In this study, four female M. megalocephala adults from the same farm were collected in 2008 and fed separately until the beginning of the experiment. One of four produced consecutive eggs in 2012–2013 and a total of 19 out of 21 eggs from two clutches(2012and 2013) successfully hatched and survived. Two alterative hypothesis could explian the litters in 2012 and 2013:(i) long-term sperm stotage before 2009, these offsping were reproduced by sexual.(ii) the litters resulted from parthenogenesis. Here microsatellite DNA molecular markers were used to confirm whether the offspring had been produced by long-term sperm storage or by parthenogenesis. At 7 microsatellite loci, 10 offspring were genetically identical to their mother and highly heterozygous. Probability analysis shows that if these offsprings were produced by long-term sperm storage, P=(0.5)7x10= 8.5×10-22,p<<0.0001.The probability of long-term sperm storage was excluded based on probability analysis. This supports the conclusion that offspring were produced by parthenogenesis.This is the first recorded case of parthenogenesis in order Chelonia.A pattern in parthenogenetic vertebrate is the close association with hybridization.Mauremys megalocephala is distributed in southeastern China, whose distribution region was overlapping with M. reevesii and M. mutica.To explore the origin of M.megalocephala, ITS2 sequence for M. megalocephala, M. reevesii and M.mutica were obtained using PCR 、 cloning by specific primers. To review the hybrid origin of Mauremys megalocephala, the maximum–likelihood(ML) and Bayesian(BI) analyses were conducted based on ITS2 and Manouria emys and Cuora picturata as outgroups. The results of clustering showed that the homology sequences of ITS2 which were cloned, one of M. megalocephala sequence belongs to M. reevesii cluster, another M. megalocephala sequence belongs to M. mutica cluster. Add the evidence of mitochondrial gene, our results suggest that M. megalocephala may be a hybrid origin between M. reevesii and M.mutica-(M. reevesii ♀× M. mutica ♂).In this study, this is the first recorded case of parthenogenesis in order Chelonia.What’s more, we expored the origin of Mauremys megalocephala.The research has important theoretical and pratical implications for the study of sexual reproduction strategies and evolution in general.