Molecular ecology of introduced species in South Africa : the bud gall-forming wasp Trichilogaster acaciaelongifoliae and the Argentine ant Linepithema humile

[摘要] ENGLISH ABSTRACT: Introduced species displace native species and alter ecological communities, affectagriculture as well as human health and are economically costly to eradicate. Long termmonitoring of introduced species including the documentation of levels of genetic variation istherefore of the utmost importance. This study investigated the distribution of genetic variationin two introduced species distributed across South Africa the bud gall-forming waspTrichilogaster acaciaelongifoliae and the Argentine ant Linepithema humile.The bud gall-forming wasp was introduced into South Africa as a biological controlagent to curb the spread of the invasive long-leaved wattle Acacia longifolia. In addition to theintended (target) host, the bud gall-forming wasp has also colonised A. floribunda, a noninvasiveornamental plant. Limited genetic variation was found across South Africa based onthe mitochondrial DNA cytochrome oxidase subunit I (COI) gene. Only 3 haplotypescharacterized 53 individuals collected from 23 localities (nucleotide diversity £k = 0.002 ¡Ó0.001, haplotype diversity h = 0.482 ¡Ó 0.045). No significant partitioning of genetic variationwas found across South Africa including between host plants (target host = A. longifolia, nontarget host = A. floribunda) or between the core (sites of introduction) and edge (naturallydispersed) sites (ƒ¶ST = 0.094, P = 0.288). The limited genetic variation and the absence ofsignificant genetic structure are congruent with patterns described for many other introducedspecies and may suggest that propagule pressure plays only a minor role in speciesestablishment and spread of the gall-forming wasp across South Africa.Mitochondrial and nuclear markers were used to describe the distribution of geneticvariation within Argentine ants across their introduced range in South Africa. For themitochondrial DNA, low genetic diversity was found for the COI gene with only five haplotypes, separated by single mutational changes, characterizing 101 specimens from 35localities (nucleotide diversity π = 0.001 ± 0.001, haplotype diversity h = 0.151 ± 0.048).Notwithstanding the low levels of genetic diversity, mitochondrial variation was significantlystructured (ST = 0.54, P < 0.001) across the landscape. In contrast, microsatellite analyses of230 ants from 23 localities, employing six polymorphic microsatellite markers, revealed arelatively high amount of genetic diversity (HE = 0.51 ± 0.22). Significant population structurewas similarly evident (RST = 0.14, P < 0.001) with the localities of Elim2, Porterville2 andBloemfontein2 clustering as a distinct population from the remainder of the localities.Importantly, individuals from these localities also had a unique mitochondrial haplotype and,when taken with the nuclear results, may indicate the occurrence of more than one introductionevent (and possibly more than one colony) in South Africa. This is further underscored by thepresence of unique microsatellite alleles in these three populations.In an attempt to establish the source populations for the introduction of Argentine antsinto South Africa, mitochondrial cytochrome b sequences were generated for a subset of antsrepresenting the two major genetic clades across South Africa. A comparison with thepublished data from across the world including the native range of the Argentine ant in SouthAmerica grouped Argentine ants from South Africa with three potential source populationsnamely Ocampo and Rosario in Argentina and Passo do Lontra in Brazil.The results of this study underscore the role of human-mediated dispersal in shaping thelevels of genetic variation in both species. Human-mediated dispersal can lead to genetic homogenization across populations.

[发布机构] Stellenbosch University