The light brown apple moth (LBAM), Epiphyas postvittana (Walker), is native to Australia but invaded England, New Zealand, and Hawaii more than 100 years ago. In temperate climates, LBAM can be a major agricultural pest. In 2006 LBAM was discovered in California, instigating eradication efforts and quarantine against Hawaiian agriculture, the assumption being that Hawaii was the source of the California infestation. Genetic relationships among populations in Hawaii, California, and New Zealand are crucial to understanding LBAM invasion dynamics across the Pacific.
We sequenced mitochondrial DNA (mtDNA) from 1293 LBAM individuals from California (695), Hawaii (448), New Zealand (147), and Australia (3) to examine haplotype diversity and structure among introduced populations, and evaluate the null hypothesis that invasive populations are from a single panmictic source. However, invasive populations in California and New Zealand harbor deep genetic diversity, whereas Hawaii shows low level, shallow diversity.
LBAM recently has established itself in California, but was in Hawaii and New Zealand for hundreds of generations, yet California and New Zealand show similar levels of genetic diversity relative to Hawaii. Thus, there is no clear relationship between duration of invasion and genetic structure. Demographic statistics suggest rapid expansion occurring in California and past expansions in New Zealand; multiple introductions of diverse, genetically fragmented lineages could contribute to these patterns. Hawaii and California share no haplotypes, therefore, Hawaii is not the source of the California introduction. Paradoxically, Hawaii and California share multiple haplotypes with New Zealand. New Zealand may be the source for the California and Hawaii infestations, but the introductions were independent, and Hawaii was invaded only once. This has significant implications for quarantine, and suggests that probability of invasion is not directly related to geographic distance. Surprisingly, Hawaiian LBAM populations have much lower genetic diversity than California, despite being older.
5 Figures and Tables
Table 1. AMOVA results reveal that molecular variance was approximately equivalent within populations and among populations, and the vast majority of diversity was found among groups plus within populations.
Table 2. Genetic variability of COX1 sequences (n = 1293, 1318 bp) in Epiphyas postvittana.
Table 3. Pairwise FST values (below diagonal) and genetic distances DXY (above diagonal) based on COX1 sequences (n = 1293, 1318 bp).
Figure 3. Mismatch distribution plot for California LBAM. Demonstrates strong evidence for demographic expansion (Harpending’s raggedness index = 0.4824, t= 0.000, hi = 0.000, hf = 99,999, p = 0.000). doi:10.1371/journal.pone.0016361.g003
Figure 4. Mismatch distribution plot for Hawaii LBAM. Observed and expected curves were nearly identical (Harpending’s raggedness index = 0.7599, t= 3.000, hi = 0.00, hf = 0.072, p = 0.850). doi:10.1371/journal.pone.0016361.g004
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