Originally Posted By: ewest
I would , over time, expect something near 50% if the 2 subspecies were stocked. Simple statistics would give half the offspring as crosses. That of course assumes a lot of factors are equal which they may not be.

Check your email.


Thanks for the email.

Your statement thaty over time the introgression should be 50% if both species were stocked is only true if they are initially stocked in equal percentages. From the study you sent me:

Quote:
Thus, for a large, randomly mating population, allele frequencies will be at a relatively stable equilibrium (commonly referred to as Hardy�Weinberg equilibrium; Hardy 1908; Weinberg 190826. Weinberg, W. 1908. [On the demonstration of heredity in man]. Jahreshefte des Vereins f�r vaterl�ndische Naturkunde in W�rttemberg , 64: 368�382. (In German with English summary.)


This means that if you stock 85% Florida strain into a new lake, and sample again in 10 years, you should find 85% florida strain alleles. If you stock 50% Tiger bass and 50% Florida strain, you should find 75% florida genes.

That of course assumes that there are not selective pressures favoring either Florida strain or northern strain LMB traits (phenotype). In that case one set of genes should begin to outnumber the other over time.

What is surprising to me, is that I have seen no study that indicates those selective pressures exist in most environments. For instance, in Briery Creek lake, an area thought to be too far north for successful florida strain LMB introduction, the percentage of florida alleles has remained quite high over time. Likewise, in Texas impoundments, the introgression rate seems mostly stable over time, typically changing significantly only when those lakes are stocked, which brings in new genes from the outside.

If northern strain LMB were really significantly better adapted to life in virginia, shouldn't the 25 generations since the stocking of Briery Creek lake be enough for those manifestations to become apparent?

On the flip side, if Florida strain were really better adapted to southern climates, after all of the generations since the fish was introduced into Texas waters with native hybrid LMB, wouldn't the percentage of florida genes have increased?