No genetic bottleneck proves no global flood

RAZD writes:A little overstated imho. Small phenotypic change - fur color, length, curliness, some increase or decrease in size, for example - can occur and would not be unexpected.

Faith writes:I think what are called by those names are nothing but such small changes brought about by the usual microevolutionary processes that have proceeded to the point where there is enough of a genetic mismatch to prevent continued breeding with the former population. I don't think that takes much, just a series of phenotypic changes of what you call the "irrelevant" sort, from the new gene frequencies, that accumulate in the population over a number of generations until there is that genetic mismatch with former populations.

I'm suggesting this can happen when the new population's genetic diversity is appreciably reduced from that of the former populations.

RAZD writes:Seems the models are missing something: I would expect that cheetahs would have a much larger bottleneck impact than rabbits due to the difference in numbers of offspring

AbstractMammal species characterized by highly fluctuating populations often maintain genetic diversity in response to frequent demographic bottlenecks, suggesting the ameliorating influence of life history and behavioral factors. Immigration in particular is expected to promote genetic recovery and is hypothesized to be the most likely process maintaining genetic diversity in fluctuating mammal populations.Most demographic bottlenecks have been inferred retrospectively, and direct analysis of a natural population before, during, and after a bottleneck is rare. Using a continuous 10-year dataset detailing the complete demographic and genetic history of a fluctuating population of golden-mantled ground squirrels (Spermophilus lateralis), we analyzed the genetic consequences of a 4-year demographic bottleneck that reduced the population to seven adult squirrels, and we evaluated the potential ‘‘rescue effect’’ of immigration.Analysis of six microsatellite loci revealed that, while a decline in allelic richness was observed during the bottleneck, there was no observed excess of heterozygosity, a characteristic bottleneck signature, and no evidence for heterozygote deficiency during the recovery phase. In addition, we found no evidence for inbreeding depression during or after the bottleneck. By identifying immigrants and analyzing their demographic and genetic contributions, we found that immigration promoted demographic recovery and countered the genetic effects of the bottleneck, especially the loss of allelic richness. Within 3 years both population size and genetic variation had recovered to pre-bottleneck levels, supporting the role of immigration in maintaining genetic variation during bottleneck events in fluctuating populations.Our analyses revealed considerable variation among analytical techniques in their ability to detect genetic bottlenecks, suggesting that caution is warranted when evaluating bot- tleneck events based on one technique

Analysis of six microsatellite loci revealed that, while a decline in allelic richness was observed during the bottleneck, there was no observed excess of heterozygosity, a characteristic bottleneck signature, and no evidence for heterozygote deficiency during the recovery phase.

Faith writes:With a bottleneck you can get such depleted genetic diversity that breeding with other members of the pseices has become impossible, unless the others are reintroduced very soon after the bottleneck. But in the examples I focus on I've specifically ruled out immigration because that is only putting back formerly lost genetic material, it is not new genetic material. I've specifically said this many times. Gene flow keeps genetic diversity up.

That's when you get reduction of genetic diversity, through the processes of evolution.

The current infestation appears to have originated with the release of 24 wild rabbits[4] by Thomas Austin for hunting purposes in October 1859, on his property, Barwon Park, near Winchelsea, Victoria. While living in England, Austin had been an avid hunter, regularly dedicating his weekends to rabbit shooting. Upon arriving in Australia, which had no native rabbit population, Austin asked his nephew William Austin in England to send him twelve grey rabbits, five hares, seventy-two partridges and some sparrows so he could continue his hobby in Australia by creating a local population of the species. William could not source enough grey rabbits to meet his uncle's order, so he topped it up by buying domestic rabbits. One theory as to why the Barwon park rabbits adapted so well to Australia is that the hybrid rabbits that resulted from the interbreeding of the two distinct types were particularly hardy and vigorous.

Many other farms released their rabbits into the wild after Austin.