The scale of diversity of life on this planet is a significant challenge for any scientific programme hoping to produce a complete catalogue, whatever means is used. For DNA barcoding studies, this difficulty is compounded by the realization that any chosen barcode sequence is not the gene 'for' speciation and that taxa have evolutionary histories. How are we to disentangle the confounding effects of reticulate population genetic processes? Using the DNA barcode data from meiofaunal surveys, here we discuss the benefits of treating the taxa defined by barcodes without reference to their correspondence to 'species', and suggest that using this non-idealist approach facilitates access to taxon groups that are not accessible to other methods of enumeration and classification. Major issues remain, in particular the methodologies for taxon discrimination in DNA barcode data.

A ustralian gall-inducing thrips gain food and shelter, in the form of a gall, from species of Acacia trees (1-6). The gall is formed as a female feeds on a developing phyllode (a petiole modified to serve as a stem and leaf) that encapsulates her and in some cases a male (4, 6). The foundress oviposits within the gall, and the developing thrips feed by sucking out the contents of plant cells on the gall's inner wall (1). In eusocial species, the first cohort to eclose are gall-bound soldiers, which are distinguished by robust forelimbs, reduced or absent wings, and self-sacrificing behavior exhibited in defense of the gall to the benefit of dispersing sisters and brothers (2, 4, 7). However, in at least one species, Kladothrips hamiltoni, it is suspected that soldiers could also be defending a few of their own offspring, as well as nieces and nephews, because soldiers are suspected of at least some egg laying within their natal gall (8). The foundress usually lives long enough to overlap with the adult soldiers, and she usually dies some time before the next group of individuals, the dispersive macropterae, reach the adult stage. Two lifehistory observations indicate that relatedness of individuals within a gall may be high: (i) multiple founding by females, which would reduce relatedness among brood, is not observed for any of the gall-inducing species on Acacia (3, 4), and (ii) sex ratios of dispersing brood are markedly female-biased (3, 9), which suggests the presence of strong local mate competition and inbreeding.We developed microsatellite markers (10) for species of gall-inducing thrips with soldiers and used them to estimate genetic relatedness [refs. 11 and 12; RELATE 4.2c (http:// gsoft.smu.edu/GSoft.html) by K. R. Goodnight and D. C. Queller] and inbreeding in five of the species with soldiers ( Fig. 1; Table 1). In the four species for which multiple populations were sampled, the intraspecific similarity of relatedness and inbreeding estimates for populations that were up to 500 km apart indicates that these genetic parameters can be treated as speciesspecific values. These estimates of relatedness and inbreeding are among the highest ever recorded for social animals, and their magnitude is consistent with a high incidence of single-mating by foundresses, and brother-sister mating by both soldiers and dispersers (10). In addition, the strong relatedness asymmetries expected in outbred haplodiploid species (13) (e.g., a brood produced by a singly mated foundress is expected to exhibit relatedness among sisters of 0.75 whereas relatedness of sisters to brothers is expected to be 0.5) are not at a detectable level in the four species in which they can be estimated, as expected given their high levels of inbreeding (14). For example, from Table 1, K. hamiltoni population 3 exhibits among-sister relatedness of 0.85 and sister to brother relatedness of 0.82 (t ϭ 1.95, P Ͼ 0.05, n ϭ 12).Mapping of the relatedness and inbreeding estimates onto a phylogeny of Australian gall-inducing thrips on Acacia (15) i...

We used microsatellite data to estimate levels of inbreeding in four species of solitary gall thrips that are in the same clade as the six species with soldier castes. Three of the four species were highly inbred (Fis 0.54-0.68), and the other apparently mated randomly (Fis near zero). These estimates, combined with previous data from species with soldiers, suggest that inbreeding is a pervasive life-history feature of the gall-inducing thrips on Australian Acacia. Mapping of inbreeding estimates onto the phylogeny of the gall inducers showed that the ancestral lineage that gave rise to soldiers was apparently highly inbred, and therefore, inbreeding could have played a role in the origin of sociality within this group. Moreover, there was a trend from high levels of inbreeding at the origin of soldiers to low levels in the most derived species with soldiers, which exhibits the highest levels of reproductive division of labor and soldier altruism. These patterns are consistent with considerations from population genetics, which show that the likelihood of the origin of soldier altruism is higher in inbreeding populations but that, once soldiers have evolved, a reduction in inbreeding levels may facilitate the evolution of enhanced division of labor and reproductive skew.

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