Marine population structure in an anadromous fish: life‐history influences patterns of mitochondrial DNA variation in the eulachon, Thaleichthys pacificus

Abstract

Due to the apparent decline in size of a number of populations, eulachon, Thaleichthys pacificus, have recently become the focus of a conservation movement in the northeast Pacific. Little is known of the marine life-history phase of this anadromous fish, and although it has been suggested that eulachon spawning in different rivers may form distinct populations, nothing is known of their population structure. Molecular genetic data were used to investigate population structure and possible management schemes. Mitochondrial DNA genotypes, determined through restriction fragment length polymorphisms (RFLP) analysis, were resolved in fish from several rivers throughout the geographical range of eulachon. Our data support the idea that extant eulachon populations result from postglacial dispersal from a single Wisconsinan glacial refuge. Further, while three of the 37 haplotypes recovered account for approximately 79% of the samples, many private haplotypes were observed, suggesting possible regional population structure. While a great deal of genetic variation was observed (37 haplotypes in 315 samples), an AMOVA showed that > 97% of the total variation was detected within populations. As yet, it is unclear whether genetically distinct populations of eulachon exist, or if these fish may be treated as one or a few large populations. Results were tested against predictions made from hypotheses concerning the origin and persistence of subdivided populations in marine species, and seem to be more consistent with the Member-Vagrant hypothesis than isolation by distance. Eulachon present an interesting situation that illustrates the difficulties involved in defining management units in organisms with high levels of gene flow.

Mitochondrial DNA Diversity of Orchid Bee Euglossa fimbriata (Hymenoptera: Apidae) Populations Assessed by PCR-RFLP

“…In our study, fragment A differed the most in terms of the frequency of haplotypes, with AAAAAA showing the lowest frequency and / st value in this forest fragment. The low values of haplotype diversity within samples detected in the current study could be attributed to the predominance of mitotype A (AAAAAA), which was found to occur in frequencies above 76.92% in all the sites (except for the sample from fragment A; Table 4), and the low values of nucleotide diversity could be interpreted as probable close relationships among the haplotypes present within samples, as proposed elsewhere (McLean et al 1999). As for nucleotide diversity, although samples from fragments A and D differed in the number of haplotypes (5 and 3, respectively), both the samples showed similar values of p (around 0.2).…”

Glacial biogeography of North American coho salmon (Oncorhynchus kisutch)

“…Comparable shifts in intraspecific mtDNA diversity associated with the glacial maxima have been documented for several other species (summary by Bernatchez & Wilson 1998). McLean et al . (1999) proposed that eulachon ( Thaleichthys pacificus ) radiated from a single refuge based on low sequence divergence between haplotype groups (0.4%) relative to that of a species which dispersed from multiple refugia [0.7% in rainbow smelt ( Osmerus mordax )] (Bernatchez 1997).…”

Differential population structuring of two closely related fish species, the mackerel (Scomber scombrus) and the chub mackerel (Scomber japonicus), in the Mediterranean Sea

“…Hence, to better understand speciation mechanisms in the marine environment, it is mandatory to characterize not only population dynamics and structure, but also life‐history strategies. At least three competing, but not exclusive, hypotheses may explain population structuring in marine pelagic and demersal fish species (Palumbi 1994; McLean et al . 1999; Avise 2000; Bahri‐Sfar et al .…”