Mutations of esterase 3 confer two forms of organophosphate resistance on contemporary Australasian Lucilia cuprina. One form, called diazinon resistance, is slightly more effective against commonly used insecticides and is now more prevalent than the other form, called malathion resistance. We report here that the single amino acid replacement associated with diazinon resistance and two replacements associated with malathion resistance also occur in esterase 3 in the sibling species Lucilia sericata, suggesting convergent evolution around a finite set of resistance options. We also find parallels between the species in the geographic distributions of the polymorphisms: In both cases, the diazinon-resistance change is absent or rare outside Australasia where insecticide pressure is lower, whereas the changes associated with malathion resistance are widespread. Furthermore, PCR analysis of pinned specimens of Australasian L. cuprina collected before the release of organophosphate insecticides reveals no cases of the diazinonresistance change but several cases of those associated with malathion resistance. Thus, the early outbreak of resistance in this species can be explained by the preexistence of mutant alleles encoding malathion resistance. The pinned specimen analysis also shows much higher genetic diversity at the locus before organophosphate use, suggesting that the subsequent sweep of diazinon resistance in Australasia has compromised the scope for the locus to respond further to the ongoing challenge of the insecticides.Lucilia cuprina ͉ Lucilia sericata ͉ mutation ͉ convergent evolution ͉ organophosphates O ne of the major unresolved issues in our understanding of adaptive evolutionary change is the extent to which the acquisition of newly beneficial traits proceeds by the selection of existing (preadaptive) rare variants, rather than waiting on new mutations to arise once the selection pressure is imposed. These two scenarios could have very different consequences for the nature of the acquired adaptation, its rate of uptake, and the fate of genetic variation in the chromosomal region surrounding the selected locus. Direct evidence discriminating the two possibilities in natural populations of eukaryotes has been lacking because the critical data needed must include samples that have not been exposed to the selection pressure.The phenomenon of insecticide resistance is proving an informative model for studying microevolutionary processes in eukaryotes because it represents a rapid contemporary acquisition of a major new biochemical phenotype and it generally has a relatively simple genetic basis. The rapidity with which resistance often follows the first use of new pesticides has prompted much speculation about preadaptation at the relevant loci (1, 2). However, many cases have also been recorded where resistant genotypes have fitness costs in the absence of insecticide (3, 4), which would seem at odds with the preadaptation hypothesis. In this paper, we present evidence that tests the hypothesis direct...

Metrosideros subg. Metrosideros (Myrtaceae) comprises Ϸ26 species distributed widely across the Pacific basin. They occur on the ancient Gondwanan landmasses of New Zealand and New Caledonia, as well as on the volcanic islands of the remote Pacific, from Melanesia to tropical Polynesia and the Bonin Island. Phylogenetic analysis based on nuclear ribosomal DNA spacer sequences from all named species showed Metrosideros umbellata of New Zealand as basal in the subgenus, with the remaining species falling into three monophyletic clades. One includes the seven New Caledonian species together with three daughters in western Oceania that probably dispersed during the mid͞late Tertiary. A second contains six taxa located in east Melanesia and Samoa that may also have arisen from a mid͞late Tertiary dispersal, in this instance from New Zealand. The third includes three New Zealand endemics along with all of the taxa in remote Polynesia and accounts for much of the total range of the subgenus. These dispersed taxa in Polynesia either are identical to the New Zealand species Metrosideros excelsa or differ by a single nucleotide change. We suggest that they are all derived from a Pleistocene dispersal out of New Zealand. A relatively recent dispersal is surprising, given that this winddispersed genus has occupied New Zealand for much of the Tertiary and that some of the islands in remote Polynesia date to at least the Miocene. We attribute this dramatic range expansion to climate change-specifically changes in wind flow patterns-in the southern hemisphere during worldwide glaciation.climate change ͉ dispersal

Aim The majority of Hawaii's plants are derived from the south and west of the Paci®c rim, suggesting that at least some of the founders have crossed the climatic discontinuity at the equator. However, the pathways of these dispersal events are not well understood. We sought to elucidate such a pathway for the plant genus Metrosideros Banks ex Gaertn., which appears to have colonized Hawaii from New Zealand.Location We have previously analysed the internal transcribed spacer (ITS) sequence of nrDNA for thirty-six taxa of Metrosideros subgenus Metrosideros distributed across Melanesia and Polynesia. Further we collected two taxa from the Austral and Marquesas Islands.Methods Phylogenetic analysis was undertaken using both the ITS and external transcribed spacer (ETS) regions of nrDNA for twenty-three taxa from Polynesia and East Melanesia. ResultsThe increased resolution achieved by combining ETS data with that of ITS allowed discrimination of two subclades in eastern Oceania. One subclade groups all the Hawaiian taxa together with M. collina (J. R. & G. Forst.) A. Gray from the Marquesas Islands.Main conclusions From an origin in New Zealand, the woody angiosperm Metrosideros is likely to have crossed the equator to Hawaii using a staging point in the remote Marquesas Islands. Colonization of Hawaii by the wind-borne seed of these plants has been achieved against the¯ow of the prevailing Trade winds north of the equator. A possible climatic mechanism for this dispersal is described.

Sequences of the esterase gene alpha E7 were compared across 41 isogenic (IV) strains of the sheep blowfly, Lucilia cuprina, and one strain of the sibling species, L. sericata. The 1.2-kb region sequenced includes sites of two insecticide resistance mutations. Gly137Asp confers resistance to organophosphorus insecticides (OPs), particularly preferring diethyl OPs such as diazinon, while Trp251Leu prefers dimethyl OPs, and particularly malathion, with the additional presence of carboxylester moieties. We found that there are just eight haplotypes among the 41 chromosomes studied: two Gly137Asp containing haplotypes, two Trp251Leu containing haplotypes, and four susceptible haplotypes, including the L. sericata sequence. While phylogenetic analysis of these haplotypes suggests that the Asp137 and Leu251 mutations each arose at least twice, evidence for recombination was detected across the region, therefore single origins for these resistance mutations cannot be ruled out. Levels of linkage disequilibrium in the data are high and significant hitchhiking is indicated by Fay and Wu' s H test but not the Tajima test. A test of haplotype diversity indicates a paucity of diversity compared with neutral expectations. Both these results are consistent with a very recent selective sweep at the Lc alphaE7 locus. Interestingly, gene duplications of three different combinations of OP resistant haplotypes were identified in seven of the isogenic (IV) strains. All three types of duplication involve an Asp137 and a Trp251 haplotype. To examine whether more haplotypes existed before the hypothesised selective sweep, fragments of alpha E7 surrounding the resistance mutations were amplified from pinned material dating back to before OPs were used. Four new sequence haplotypes, not sampled in the survey of extant haplotypes, were obtained that are all associated with susceptibility. This is suggestive of a higher historical level of susceptible allelic diversity at this locus.