Environmental effects on local adaptation, genetic connectivity and morphology of generalist (Phaulacridium) versus specialist (Kosciuscola) Australian grasshoppers
thesisposted on 28.03.2022, 19:11 by Sonu Yadav
Environmental variables can exert strong effects on a species' morphology, neutral, and adaptive genetic variation. Understanding how environmental variables affect species' genetic connectivity and adaptive genetic responses has implications for conserving species subject to climate change and habitat fragmentation. With field data, statistical modelling and a landscape genomics approach applied to endemic Australian grasshoppers, I compare how patterns of morphology, abundance, gene flow and selection interact in a generalist grasshopper, Phaulacridium vittatum, versus three specialist grasshoppers of the genus Kosciuscola (K.usitatus, K. tristis, and K. cognatus), restricted to alpine regions. Single nucleotide polymorphism (SNP) data from double digest restriction-site associated (ddRAD) DNA sequencing was obtained for P. vittatum, K. usitatus and K. tristis. For P. vittatum, I identified a positive effect of solar radiation on body size and stripe polymorphism, with increasing Foliage Projective Cover (FPC) associated with the presence of winged individuals. Furthermore,latitude, soil moisture, wind speed and FPC were significantly correlated with relative abundance. Mean annual temperature had a stronger positive non-linear effect on genetic connectivity compared to land cover, and despite high gene flow across the 900 km sampling gradient, Environment Association Analysis (EAA) detected signatures of selection in relation to mean annual temperature, latitude and body size. Candidate adaptive SNPs were annotated to gene functions for olfaction, metabolic detoxification and ultra-violet shielding that may be important for environmental adaptation. For the three specialist Kosciuscola grasshopper species, the relative abundance of K. usitatus and K. tristis changed differentially and significantly with elevation, and the relative abundance of K. cognatus changed significantly with FPC. Body sizechanges were observed with increasing elevation that differed within sexes and across species.EAA analysis of SNP data for K. usitatus and K. tristis indicated that climatic variables including elevation (used as a proxy for temperature due to its high correlation), precipitation seasonality and number of frost days were more strongly associated with selection signatures in both species compared to soil or terrain variables. However, K. tristis, with a narrow elevational niche and lower cold tolerance, showed stronger genetic structure and more pronounced signatures of local adaptation compared to the more widely found K. usitatus. Some candidate loci putatively underselection were shared by both species with a greater number associated with elevation, indicating the likelihood of parallel adaptation driven by climatic variables. The highest number of candidate outlier loci were annotated to genes involved in lipid metabolism and development.The study suggests that species with wider environmental niches are likely to maintain higher gene flow and exhibit weaker signatures of selection than species with narrower niche breadths.Furthermore, co-occurring species encountering similar environmental challenges may show parallel adaptation. Taken together, this thesis demonstrates that generalist species are more likely to successfully move and adapt under shifting environments due to land use or climate change than specialist species occupying narrow thermal environments -- summary.