Where are they now? The fates of two genetic lineages in an introduced Hawaiian reef fish.

Department of Biology, Box 42451, University of Louisiana atLafayette, Lafayette, LA 70504, USAHumans, both wittingly and unwittingly, have beentransporting marine organisms beyond their nativeranges for centuries (Ruiz et al. 1997). A central challengeof invasion biology is to identify the factors thatdetermine whether introduced species fail to becomeestablished, become benign members of a community, orspread so far and reach such densities as to be consid-ered invasive. Organismal features such as physiologicaltolerance, niche breadth and fecundity are critical, but bythemselves are inaccurate predictors of the fates of intro-duced species (Sakai et al. 2001). The size, age distribu-tion, and genetic makeup of founder populations are alsoimportant, but because they are usually unknown theyare most often viewed as sources of uncertainty. Formarine species with planktonic larvae, the challenge iseven greater because the consequences of a planktonicphase for dispersal and population viability are not wellunderstood. In this issue, Gaither et al. (2010a) present aremarkable account of the introduction of a reef ﬁsh forwhich the number and genetic makeup of the foundersare known. Between 1956 and 1961, the Division of Fishand Game for the Territory of Hawaii introduced 12 non-indigenous ﬁsh species into Hawaiian waters to establishcommercial and sport ﬁsheries. The introduction of Lutj-anus kasmira, the bluestriped snapper, was the most suc-cessful (Fig. 1). There were two releases of ﬁsh fromFrench Polynesia. In 1958, 2431 ﬁsh from the MarquesasIslands were released on Oahu, followed in 1961 with anadditional 728 ﬁsh from the Society Islands. The bluestriped snapper rapidly spread to the other HawaiianIslands, reaching the northwestern end of the archipelagoby 1992. The choice of the Marquesas as one of twosources for the introduction was fortuitous. Gaither et al.(2010b) found that the Marquesas population is geneti-cally distinct from all other Indo-Paciﬁc populations ofL. kasmira. Mitochondrial cytochrome b sequences of ﬁshfrom the Marquesas belong to a separate lineage thatdiverged from others in the species roughly half a Ma.Allele frequencies for several nuclear loci are also dis-tinct. This provided Gaither et al. (2010a) with anextraordinary opportunity to examine what became of themixed genetic heritage of Hawaiian blue striped snappersafter 50 years.Received 14 November 2009; revision received 14 December2009; accepted 19 December 2009The bluestriped snapper is now one of the most abun-dant reef ﬁsh in Hawaii, but at ﬁrst there were just a fewthousand juveniles. It is conceivable that Allee effects couldhave eliminated such a small population; individuals couldhave become too dispersed to ﬁnd mates, or their larvaecould have been carried off to unsuitable habitats.Although there are few documented examples of Alleeeffects in marine ﬁsh (Gascoigne & Lipcius 2004), the riskof extinction for populations that are severely reduced insize has been a growing concern among ﬁsheries and con-servation biologists (Reynolds et al. 2005). One ﬁnding thatsuggests small populations of marine ﬁsh are vulnerable toextinction is that estimates of genetically effective popula-tion size are often several orders of magnitude less thanestimates of census size (Hauser & Carvalho 2008). Thissuggests that either marine ﬁsh populations undergo largeﬂuctuations in size, or they are subject to ‘sweepstakesreproduction’, in which a few individuals have very highreproductive success while the rest of the population hasvery little (Hedgecock 1994). Sweepstakes reproduction isbelieved to result from the combination of high fecundityand planktonic larval dispersal that is common in marinespecies. In theory, the vagaries of ocean currents carrymost larvae to unsuitable habitats while the larvae that aresuccessful are the progeny of a small number of highlyfecund individuals that chanced to spawn under favourable