Founder effect biocontrol agents
The psyllids feed on the sap of leaves of melaleuca seedlings and mature trees, and excrete a distinctive white flocculence. quinquenervia and three other closely related species in the M. We investigated population genetics of the insect B. We analyzed spatial genetic variation and population genetic structure within and across populations and continents to examine the genetic consequences of the introduction of this biological control agent. We extracted nuclear and mitochondrial DNA (mtDNA) from individual adult psyllids and sequenced the nuclear DNA for highly variable microsatellite (SSR) markers and mtDNA for sequence variation in a known variable region. We sampled adult psyllids from natural populations throughout the native range of Australia and the introduced range in Florida, as well as from individuals stored in quarantine that were originally used as the founding populations (Table 1). Not only are the precise collection locations in Australia and introduction locations in Florida known, there were preserved insects from the population that had been transferred through a quarantine facility, the sole point of entry, prior to release. 1997 Serbesoff-King 2003 Wineriter et al. The melaleuca psyllid Boreioglycaspis melaleucae (Moore) (Hemiptera: Psyllidae) is a sap-feeding insect that was introduced into Florida in 2002 to aid in the control of the tree Melaleuca quinquenervia (Cav.) Blake (melaleuca), which is originally from Australia and is one of the most invasive species in the Florida Everglades (Purcell et al. We took advantage of a unique opportunity to investigate the population genetics of an introduced species with a very well characterized introduction history and with genetic material available from the original founding population. Work on intentionally introduced species such as biological control agents can often take advantage of a large amount of information on the timing, duration and intensity of a demographic bottleneck because of records of the introduction (Debach and Rosen 1991 Hufbauer et al. However, it is difficult to test assumptions and relative merits of these approaches unless the actual demographic information is known. Other approaches assume that the largest effect of a bottleneck is a loss of rare alleles (Slatkin 1985). Some approaches assume that following a demographic bottleneck, allelic diversity is reduced faster than heterozygosity, so that a bottleneck can be inferred if observed heterozygosity is larger than expected at mutation-drift equilibrium given a particular mutation model (Cornuet and Luikart 1996). Most studies of genetic bottlenecks attempt to infer demographic factors such as the minimum population size and duration of the reduction based on genetic data (Chen et al. Loss of genetic diversity could be one factor limiting successful establishment of biological control agents. While many biological control agents have established, others have not been as successful (Debach and Rosen 1991 Pemberton 2000 Louda et al. Genetic diversity may be further reduced due to mortality in transit and inbreeding in quarantine. Genetic bottlenecks can occur in species intentionally released as biological control agents against invaders, since they are often collected in limited quantities from a small number of sites (Debach and Rosen 1991). This evolutionary potential can be particularly critical to success in a novel environment (Cox 2004). 1975 Templeton 1980 Barton and Charlesworth 1984 Hartl and Clark 2007), which can limit the evolutionary potential of the populations (Avise and Hamrick 1996 Frankham and Ballou 2003). This bottleneck may result in a loss of genetic diversity (Nei et al. When species colonize a new location, a relatively small number of individuals may found the new populations (Elton 1958 Debach and Rosen 1991). Overall, the data showed that the demographic bottleneck had a limited effect on the genetics of populations in the new range. However, there was little genetic differentiation between the home and introduced ranges, and no evidence for a genetic bottleneck based on an analysis of heterozygosity with the microsatellite markers. There was a clear loss of mtDNA haplotype diversity, as well as a loss of rare microsatellite alleles, in the introduced range. We sampled psyllids in the native and introduced ranges as well as individuals stored from the original founding population. We examined mtDNA sequence data and four variable microsatellite loci (SSRs) in the melaleuca psyllid Boreioglycaspis melaleucae, which was introduced from Australia to Florida as a biological control agent of the invasive plant Melaleuca quinquenervia. Population bottlenecks may result in the loss of genetic diversity, with potentially negative consequences for species of interest in conservation biology, including rare species, invasive species and biological control agents.