Tl. King et al., Intraspecific phylogeography of Lasmigona subviridis (Bivalvia : Unionidae): conservation implications of range discontinuity, MOL ECOL, 8(12), 1999, pp. S65-S78
A nucleotide sequence analysis of the first internal transcribed spacer reg
ion (ITS-1) between the 5.8S and 18S ribosomal DNA genes (640 bp) and cytoc
hrome c oxidase subunit I (COI) of mitochondrial DNA (mtDNA) (576 bp) was c
onducted for the freshwater bivalve Lasmigona subviridis and three congener
s to determine the utility of these regions in identifying phylogeographic
and phylogenetic structure. Sequence analysis of the ITS-1 region indicated
a zone of discontinuity in the genetic population structure between a grou
p of L. subviridis populations inhabiting the Susquehanna and Potomac River
s and more southern populations. Moreover, haplotype patterns resulting fro
m variation in the COI region suggested an absence of gene exchange between
tributaries within two different river drainages, as well as between adjac
ent rivers systems. The authors recommend that the northern and southern po
pulations, which are reproductively isolated and constitute evolutionarily
significant lineages, be managed as separate conservation units. Results fr
om the COI region suggest that, in some cases, unionid relocations should b
e avoided between tributaries of the same drainage because these population
s may have been reproductively isolated for thousands of generations. There
fore, unionid bivalves distributed among discontinuous habitats (e.g. Atlan
tic slope drainages) potentially should be considered evolutionarily distin
ct. The DNA sequence divergences observed in the nuclear and mtDNA regions
among the Lasmigona species were congruent, although the level of divergenc
e in the COI region was up to three times greater. The genus Lasmigona, as
represented by the four species surveyed in this study, may not be monophyl
etic.