Speciation with Gene Flow: Speciation Mechanisms and Hybridization between Psolodesmus Mandarinus Subspecies

As the foundation of evolution, ecology and biodiversity, speciation has long been the focus of biological studies. After decades of investigation, we have accumulated some knowledge of speciation mechanisms. However, our understanding on the interactions between different speciation mechanisms in wild animals, especially under the condition of gene flow, is largely depended on comprehensive studies of a few model species. In this study, I proposed to disentangle the interaction between natural selection, sexual selection and gene flow between two potentially interbreeding damselfly subspecies. The Psolodesmus mandarinus mandarinus and P. m. dorothea are two geographical subspecies that have diverged recently. The pigmented-winged P. m. mandarinus distribute in northern Taiwan with cooler temperature while the light-winged P. m. dorothea distribute in central and southern Taiwan with warmer temperature. The combination of their wing pigmentation and distribution nicely meets the predictions of the thermal melanism hypothesis. In order to test if their wing pigmentations are under natural selection, I proposed to investigate the effects of wing pigmentations on their body temperature by an indoor experiment and a field observation on their daily activity in contact zones. Moreover, their wing pigmentations might also be under sexual selection because it is common in other damselflies. To test this possibility, I proposed to evaluate if their wing pigmentations have any effect on pre-mating isolation through both observation on natural mating and behavioural experiment. Larva rearing will also be conducted to identify potential post-mating isolation. Last but not least, there are morphologically intermediate individuals in their contact zones, indicating the possible occurrence of gene flow. I therefore proposed to apply a population genomics analysis using restriction-site associated DNA sequence (RADseq) to identify the amount and direction of genetic introgression. The combination of our results, along with the quantified strength of each selection force and direction of genetic introgression, will provide us a clear view of how these selections interact under the condition of gene flow. The results are expected to be used to predict the consequence of this ongoing speciation process.