SREL Reprint #0368
Biochemical Genetics of Dunfish. I. Geographic Bariation
and Subspecific Intergradation in the Bluegill, Lepomis macrochirus
J.
C. Avise and M. H. Smith
Summary
Electrophoretic variation
in proteins encoded by 15 genetic loci was analyzed in 2415 bluegill (Lepomis
macrochirus) representing 47 populations from 7 Southern states.
Populations from the Florida peninsula and southeastern Georgia (L.
m. Purpurescens) differ in allelic composition at several loci
from populations in central and western Georgia west to Texas (L. m.
macrochirus), yielding coefficients of genetic similarity below the range
generally found for continuously distributed conspecific populations in other
vertebrates, but quite comparable to previous reports for various semispecies
pairs.
Populations of L. m.
purpurescens are essentially monomorphic for Es-3100 and Got-258,
while populations of L. m. macrochirus are segregating for
Es-396 and Es-398, and are fixed for Got-2100.
Within several river drainages in South Carolina and eastern Georgia,
bluegill populations are segregating for all of these alleles.
In particular, a highly significant correlation between frequencies of
Got-258 and Es-3100 indicates that the two subspecies are
intergrading in a wide zone of overlap. A
closer examination of genotypic class proportions of a large population of
bluegill from the intergrade zone confirms that the two subspecies are
backcrossing and area apparently fully interfertile.
Degrees of introgression
appear equal for alleles at these loci. The
high correlation ion population allele frequencies across loci is compatible
with the hypothesis that the alleles are behaving as neutral markers of
intergradation. However, mildly
significant deviations from expected genotypic proportions may indicate
influences of selection.
The pattern of
intergradation evidences a secondary meeting of allopatrically evolved races.
Since populations of pure L. m. purpurescens are
largely confined to the Florida peninsula, it is likely that Pleistocene rises
in sea level were important in their original isolation from L. m.
macrochirus.
Populations of bluegill
within reservoirs are generally homogeneous from frequencies of common alleles
at polymorphic loci. However, there
is significant heterogeneity in allele frequencies between reservoirs within any
drainage system. The magnitude of
this variance is greatest in the intergrade populations within the Savannah
River basin, and is far less in “pure” samples of L. m. macrochirus.
The bluegills examined may be characterized by three areas of relative
regional uniformity, in which genetic differences within a drainage system are
probably as great as those between drainage systems:
(1) the Florida populations of L. m. purpurescens 2)
the intergrade populations and 3) populations of L. m. macrochirus.
Keywords: Par Pond Reservoir System
SREL Reprint #0368
Avise, J.C. and M.H. Smith. 1974. Biochemical genetics of sunfish. I. Geographic variation and subspecific
intergradation in the bluegill, Lepomis macrochirus. Evolution 28(1):42-56.
