Ea. Orbacz et Pm. Gaffney, Genetic structure of tautog (Tautoga onitis) populations assayed by RFLP and DGGE analysis of mitochondrial and nuclear genes, FISH B, 98(2), 2000, pp. 336-344
The tautog (Tautoga onitis) is one of two temperate labrid species commonly
inhabiting the coastal marine and estuarine waters of the mid-Atlantic coa
st of the United States. To delineate population structure throughout its p
rimary range, we examined samples collected from three sites (Rhode Island,
Delaware, Virginia). Five regions of the mitochondrial genome (COI, ATPase
6, cyt b, ND2 and control region) and one nuclear intron were amplified by
PCR and screened for sequence variation with a battery of restriction enzy
mes (RFLP analysis), or by denaturing gradient gel electrophoresis (DGGE).
With RFLP analysis an average of 129 restriction sites per individual were
revealed and 532 bases per individual were surveyed. Polymorphisms were obs
erved in the ND2 and control region fragments, but not in the COI, ATPase 6
, or cyt b fragments. Mean within-sample haplotype diversity was 0.6905 (+/
-0.00184), within the range of values reported for other marine species. Ho
wever, mean nucleotide diversity was 0.000782, one of the lowest values rep
orted for a marine teleost. Corrected nucleotide divergence between samples
was essentially zero, suggesting the absence of population structuring alo
ng the mid-Atlantic Coast. DGGE analyses of GOT, cyt b, and a lactate dehyd
rogenase (LDH) intron revealed little additional variation; each product po
ssessed a single common haplotype and occasional rare variants.
The low level of genetic diversity observed in the tautog may reflect a sma
ll effective population size resulting from historical population bottlenec
ks or large variance in reproductive success. The apparent absence of geogr
aphic differentiation suggests that tautog from Rhode Island to Virginia fo
rm a single genetic stock: data from additional genetic polymorphisms are n
eeded to confirm or disprove this conclusion.