F1 LMB and Outbreeding Depression - Pond Boss Forum many good biologists on this one Wes Neal , D Willis , Overton , Grimes and others – lots of good stuff in this one
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=184554&page=1Wes notes --
wneal
Lunker
W
Joined: Sep 2009
Posts: 10
United States
Hey Eric, and thanks for the "warm" welcome all. I agree completely with Eric that inbreeding is much more of a concern. However, I want to argue one point...
You cannot compare intergrade bass (have both strain's alleles) that are naturally produced and adapted over 1000s of years with Fx generation hybrids produced through man-made causes in a small pond. The natural intergrades have had much time to select for the genes from both sides that best fit their environment. . .
This speaks to what I was saying above. An intergrade population which has undergone natural selection over many generations is very different from the F1 combination of two isolated populations. Each population has genetics concentrated in traits important to their waters and the fish that survive to reproduce are reflections of these dominate genes. Each population is in essence an inbred line that has been naturally selected for its particular environment.
When inbred lines are crossed, many dominate traits are expressed in the offspring from both lines. The next generation allows more variation to one side or the other. I don't consider this depression in terms of the quality of the genetic pool, only that the individuals have a broader spectrum of traits expressed in the Fx generations. In truth, the F1s are more genetically diverse than offspring of the pure strains. Intergrading between connected bodies of water is probably important to genetic diversity in general allowing the larger populations to share genes over time scales important to evolution.
No such selective pressures occur in ponds in the time frames we are discussing, so the bad combinations will persist and their inferior traits may become evident in only a few generation. That is the risk of outbreeding depression. . .
Here I think that Wes may be underestimating the speed of selection. In addition to fishing harvest, the natural selection acting on fish populations is rather intense. Only a minute fraction of swim up fry will successfully reproduce. The genetics favorable to reproductive success in this environment will dominate the adults that are recruited. LMB live for 9+ years. The individuals initially stocked (but not culled) will dominate the catch of large fish during this time frame, when they have passed, natural selection and fishing mortality will be what has selected the generations that take over.
