First this is still a work in progress. Second the below can be read to contradict the conclusions in BM's post above as it relates to his pond which is in the intergrade zone. The premise is stocking F-1s (they are intergrades) into waters in the intergrade zone (an area naturally populated by LMB with both Fla and Northern genes) will not lead to a greater chance of outbreeding depression nor inbreeding (regression) than would stocking pure northerns or Flas. There are 2 genetic concepts involved. Outbreeding depression (crossing separate species which can lead to hybrid vigor followed by reduction in fitness in Fx generations) and inbreeding (genetic regression from continued reproduction from too small a related population leading to reduced fitness). One is from too diverse a gene set from 2 species when crossed over time and the other from too small of a gene set from related individuals. Any population of LMB , whether Fla ,Nort or intergrades in limited numbers ( fish from a small set of brood fish) in a closed environment will be subject to less fitness over time from inbreeding. That is not the reason nor question here involved as type of LMB has no bearing on that. A bunch of Northern LMB in that circumstance is just as likely as F-1s to exhibit the inbreeding problem. The fix on this problem is easy - remove some LMB and replace them with fish from another set of brood fish (add new genes) from a similar location. The second problem , outbreeding depression, is what was suggested in BM's post. In the article below , which is by some of the same cited writers, genetic testing over the entire US LMB population (90 locations) showed higher gene diversity in intergrades than in Fla or Norts. This same mix of intergrade genes is the naturally occurring gene mix in the intergrade locations. See map below. As such it is the set of genes best adapted for that location (intergrade zone). I suggest that stocking intergrade genetics into the intergrade zone is less likely to result in outbreeding depression than would stocking pure Flas or pure Norths because they are the best adapted genes for that location. This is consistent with these writers premise that you should not stock genes from one population into a separate different population because the mixing with
non-native genes will be more apt to result in outbreeding depression. As per the article cited in BM's post " This kind of population mixing (termed stock transfer) potentially affects the fitness of the recipient population deleteriously as a result of outbreeding depression. Outbreeding depression is the reduction in fitness in the progeny of two parents that were too distantly related to each other. " In LMB terms this would mean parents from for example from different geographic regions not parents (whether Fla or northern) from the same location (the intergrad zone). More later.
A Biochemical Genetic Evaluation of the Northern and
Florida Subspecies of Largemouth Bass 1
DAVID P. PHILIPP
WILLIAM F. CHILDERS
GREGORY S. WnXTT
We also have calculated for each population
the mean number of alldes present per locus,
the percentage of loci which were polymorphic,
and the mean observed and expected heterozygosity
(Table 1). The lowest levels of allelic
polymorphism were observed in the populations
of the pure northern subspecies (1.09 allele
per locus; 8.3% polymorphic loci; observed
mean heterozygosity of 0.024). Pure Florida
largemouth bass populations were considerably
more polymorphic (1.14 allde per locus; 11.0%
polymorphic loci; mean heterozygosity of 0.041),
but the intergrade populations were, as expected,
the most polymorphic (1.22 allde per
locus, 15.5% polymorphic loci; heterozygosity
of 0.051). These represent statistically significant
differences between groups. The observed
heterozygosity levels for the two pure subspecies
were somewhat lower than that reported
for teleosts in general: 0.051 by Nevo (1978)
and 0.048 by Winans (1980). The intergrade
populations, however, demonstrated a mean
heterozygosity consistent with these values
(0.051). It remains to be determined if the
higher heterozygosity in the intergrade zone,
relative to the pure subspecies, is a consequence
of heterosis. However, that maximal heterogeneity
is located in intergrade populations may
help to explain, in part, the existence of a "bigbass
belt" in northern Florida and southern Alabama
and Georgia, as well as the largemouth
bass of "trophy" size being taken from certain
lakes in Texas and California.
In any case, the intergrade zone today must
be considered to consist of northern Florida, as
well as at least substantial portions of the states
of Mississippi, Alabama, Georgia, South Carolina,
North Carolina, Virginia, and Maryland.
The extent of influence of some of the genes
characteristic of the Florida subspecies in certain
more peripheral states within the intergrade
zone, particularly those of Mississippi,
Maryland, Virginia, and North Carolina is uncertain.
Some bodies of water in these states still
may contain populations of pure northern
largemouth bass. The presence of Florida alldes
in populations in Texas, California, Arkansas,
Illinois, and perhaps Louisiana, probably
are the result of deliberate introductions.
Further investigation to determine the status of
numerous populations throughout several states
is required to delineate the true extent of the
intergrade zone. Once genetic differences between
populations are better understood, and
once we understand the roles that short-term
and long-term fitness play in determining the
range and distribution of phenotypes, we will
be in a better position to design effective management
programs.
In addition, populations within each group
(northern subspecies, Florida subspecies, and
intergrades) were compared and the groups as
a whole were all compared based on Nei's (1978)
identity coefficient, I (Table 9). Intragroup
variation was least among populations of pure
Florida subspecies (I = 0.997), intermediate
among populations of the nortfiern subspecies
(I = 0.992) and greatest among the intergrade
populations (I = 0.972). The intergrade populations
were approximately as closely related
to populations of the pure Florida subspecies
(I = 0.960) as to populations of the pure northern
subspecies (I = 0.962). Finally, as expected,
the two most distantly related groups were the
two pure subspecies (I = 0.911).
In an environment with high thermal variability,
the long-term success of stocked largemouth
bass might be greatest for cohorts with
the highest levels of genetic variability. However,
the two subspecies have evolved quite different
tfiermal requirements (Hart 1952; Latta
1977; Cichra et al. 1981), and it would be unrealistic
to expect those fish in the intergrade
zone, those fish with the higfiest genetic variability,
to be well suited for either an extreme
northerly or southerly environment. Introduction
of Florida alleles into northern populations
of largemouth bass could lower tfie overall fitness
of these populations under the normally
lower temperatures encountered by the northern
subspecies. A similar but reverse situation
may result from the introduction of northern
alleles into populations of Florida largemouth
bass
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