Comparative genomics of widespread and narrow-range white-bellied rats in the Niviventer niviventer species complex sheds light on invasive rodent success

Widespread species that inhabit diverse environments possess large population sizes and exhibit a high capacity for environmental adaptation,thus enabling range expansion.In contrast,narrow-range species are confined to restricted geographical areas and are ecologically adapted to narrow environmental conditions,thus limiting their ability to expand into novel environments.However,the genomic mechanisms underlying the differentiation between closely related species with varying distribution ranges remain poorly understood.The Niviventer niviventer species complex(NNSC),consisting of highly abundant wild rats in Southeast Asia and China,offers an excellent opportunity to investigate these questions due to the presence of both widespread and narrow-range species that are phylogenetically closely related.In the present study,we combined ecological niche modeling with phylogenetic analysis,which suggested that sister species cannot be both widespread and dominant within the same geographical region.Moreover,by assessing heterozygosity,linkage disequilibrium decay,and Tajima's D analysis,we found that widespread species exhibited higher genetic diversity than narrow-range species.In addition,by exploring the“genomic islands of speciation”,we identified 13 genes in highly divergent regions that were shared by the two widespread species,distinguishing them from their narrow-range counterparts.Functional annotation analysis indicated that these genes are involved in nervous system development and regulation.The adaptive evolution of these genes likely played an important role in the speciation of these widespread species.

The fecal shield is a double-edged sword for larvae of a leaf beetle

Larvae of some leaf beetles carry masses of feces covering parts or all of the body,which is called a"fecal shield'In general,the shield is thought to be a defense structure against natural enemies.However,some studies have suggested that defense effectiveness varies depending on the natural enemy.In this study,we used a fecal retention leaf beetle Ophrida xanthospilota(Coleoptera:Chrysomelidae),and 2 local generalist predators(an ant,Camponotus japonicus(Hymenoptera:Formicidae)and a stinkbug,Arma custos(Hemiptera:Pentatomidael)as a system to test the hypothesis that the fecal shield of O.xanthospilota plays different roles in predation behavior of different predators and can provide multiple chemical communication signals in predator-prey interactions.Prey bioassays showed that the fecal shield of O.xanthospilota larvae repelled the ant C.japonicus while attracting the stinkbug A.custos.The results also strongly demonstrated that hexane extracts of the fecal shield significantly repelled C.japonicus,while dichloromethane(DCM)extracts did not inhibit ant predation.Interestingly,DCM extracts attracted A.custos,but hexane extracts did not.Therefore,we suggest that the fecal shield is a double-edged sword for the larvae of O.xanthospilota.Our results also indicated that the risk-benefit tradeoff of an insect should be estimated at a community level involving multiple enemies(predators and parasites)and herbivores,rather than in a single prey-predator pair.