Interspecific Hybridization And Maintainance Of Species Independence Between The Two Reticulitermes Termites

The two closely related species Reticulitermes flaviceps Oshima and Reticuliterme chinensis Snyder have the overlapping habitat and dispersal seasons,similar sex pheromone and reproductive behavior.These similar ecological and biological characters imply that the two termite species have the possibility of interspecific hybridization.However,it is almost unclear whether there is interspecific hybridization between R.flaviceps and R.chinensis or not.If interspecies hybridization exists between the two termite species,it is unknown what mechanism maintains the independence of there biological and morphological characteristics(species independence)under the background of introgression and hybridization until now.Thus,this study explored the possibility of interspecific hybridization between R.flaviceps and R.chinensis in the lab and field,analyzed the fitness and fertility of the hybrid offspring of the two species in the lab.Moreover,we constructed,deduced and verified the role of neotenic backcross model in maintaining the independence of Reticulitermes termites.These findings can provide new insights into the deep understanding of speciation and species maintenance of termites.The main results are as follows:1.Verification of interspecific hybridization between the two Reticuliermes termites under laboratory conditionsThe frequency of acceptance was significantly higher than that of aggression after their dealates encountered between R.flaviceps and R.chinensis(t=-8.35,p<0.0001).There were no significant differences in frequencies of tandem(F=1.106,p=0.34)and duration of tandem(t=2.31,p=0.22)between interspecific and conspecific partners.The allogrooming frequencies of interspecific partners were significantly higher than intraspecific partners(F=23.84,p<0.05),but the duration of allogrooming each time was not significantly different between interspecific and conspecific partners(t=-0.96,p=0.34).There were no significant differences in frequencies of mating(F=2.53,p=0.134)and duration of mating(t=1.27,p=0.21)between interspecific and conspecific partners.Importantly,the two termite species can mate and produce the offspring.These results indicate that the interspecific hybridization between the two termites R.flaviceps and R.chinensis can happen in the lab.2.The fitness analysis of the offspring produced by interspecific hybridization between R.flaviceps and R.chinensisIn the lab,the hybrid colonies established by R.flaviceps and R.chinensis laid more eggs(F=8.98,p<0.001),had shorter egg-hatching period(F=68.15,p<0.0001)and higher egg-hatching rate(F=7.53,p<0.001),produced more larvae(F=14.32,p<0.001)than the conspecific colonies established by R.flaviceps or R.chinensis.Also,the workers of F1generation in the hybrid colonies had the higher speed(F=4.46,P=0.008)and longger movig distance(F=6.12,P=0.001)than those of F1 generationin the conspecific colonies established by R.flaviceps or R.chinensis.The above results showed that the hybrid offspring of the two termites had the heterosis.In the other hand,there was no significant difference in the weight(F=3.24,p=0.037),activities of superoxide dismutase(F=2.14,p=0.14)and catalase(F=0.33,p=0.72)between the F1 generation worker produced by hybrid and conspecific colony.Both male and female offspring of F1 generation produced by hybrid colony were alive and there were no significant differences in sex ratio of F1generation offspring between hybrid colonies and conspecific colonies(p>0.05).In addition,the hybrid workers of F1 generation could develop into secondary reproductives,secondary reproductives could mate with heterosexual primary reproductives,secondary queens could mate with secondary kings,and the offspring of F2 generation could be produced through the above backcross and inbreeding.These results indicated that the offspring of F1 generation produced by interspeicific hybridization between the two termite species was fertile and had no hybrid depression.3.Molecular identification of the interspecific hybridization between R.flaviceps and R.chinensis in the fieldThis study combined microsatellite DNA with mitochondrial COII gene to investigatethe genetic structure of the R.flaviceps and R.chinensis populations in the field,and found that the asymmetric interspecific genetic differentiation between mitochondrial gene and nuclear gene between R.flaviceps and R.chinensis.Our results showed that there was the low genetic divergence and frequent gene flow in microsatellite DNA(N_m>1)but the high genetic divergence and few gene flow in mitochondrial COII gene(N_m<1)between the two Reticulitermes termites.The analysis of gene exchange based on microsatellite DNA showed that there were R.chinensis-specific nuclear genetic infromaterial in R.flaviceps colonies,and similarly there were R.flaviceps-specific nuclear genetic material in R.chinensis colonies.These results indicated that interspecific gene change and hybridization happened between R.flaviceps and R.chinensis in the field.4.Neotenic backcross model maintained species independence of ReticulitermesNeotenic backcross model was constructed based on the mating and reproduction characteristics of Reticulitermes species.Our deductioin on neotenic backcross model found that the genetic contributions of the first replaced primary reproductives to the hybrid colony was decreased along with the increasing times of replacements,whereas those of the later replaced or surviving primary reproductive was increased along with the increasing times of replacements.We used one-time replaced hybrid colonies in the lab to verify the model and found that the percentage of gene contributions of replaced primary reproductives in hybrid colonies declined from 50%in F1 generation to 22%in F2generation.However,the percentage of gene contributions of surviving primary reproductives in hybrid colonies improved from 50%in F1 generation to 78%in F2generation.There was significant difference in the gene contributions of primary reproductives to subsequent generations of hybrid colonies between pre-replacement and post-replacement(Z=3.11,p=0.002).We used the two Reticulitermes colonies in the field to verify the model and found that after the reproducives of R.flaviceps firstly were replaced,the proportion of genetic material of R.flaviceps was decreased and gradually was diluted by genetic material of R.chinensis along with the increasing times of replacements,and vice versa for the replaced reproducives of R.chinensis.Thus,we suggest that genetic dilution caused by neotenic backcross model may be an important mechanism that maintains the speices independence in Reticulitermes termites.