Freethought & Rationalism Archive

DetectedDestiny · 10-11-2004, 02:08 PM

Hello,

In a discussion i'm having with a creationist on a Dutch forum, he linked me to an article discussing founder populations and how the evidence supposedly supports creationism.

The argument basically boils down to 'evolution claims founder populations are an important factor in the speciation process. Creationism claims speciation is caused by selection of existing genetic material and if the gene pool loses to much information (because of isolation or 'overselecting') a species dies out.'

Then they discussed an article about the Florida Panther (here) that tells this (among other things):

Quote:

Lost Gene Flow
Natural gene exchange which occurred historically between F.c. coryi and other contiguous populations of Felis concolor ceased to occur when the panther became geographically isolated from other populations of the species. Gene flow occurs as individuals disperse among populations and breed. Just as dispersal is the natural mechanism for gene exchange and maintenance of genetic health within populations, those same dispersing breeders minimize the occurrence of inbreeding within populations. Inbreeding accelerates when dispersing breeders can no longer emigrate into the fragmented population, resulting in inbreeding depression, loss of genetic variation, declining health, reduced survivability, lower numbers and eventual extinction. It is this biological circumstance that most seriously affects the health and survivability of the Florida population.

Literature indicates that gene exchange between the Florida panther (Felis concolor coryi) and other F. concolor subspecies occurred from the north through F. c. cougar, and from the west and northwest through F. c. stanleyana and F. c. hippolestes (Young and Goldman 1946).

The natural gene flow ceased at the time the Florida panther became geographically isolated, likely a century or longer ago. Isolation and accompanying population declines and inbreeding have resulted in the loss of genetic diversity and health. Recent population viability analyses project that genetic heterozygosity is being lost at a rate of approximately 6% per generation (Seal et al. 1992). Low heterozygosity levels (0.019) indicate that the Florida panther is inbred and has lost approximately half of its genetic diversity (Roelke 1990).

Genetic Reduction
Based on results of genetic testing, as summarized below from Roelke et al. (1993), surviving Florida panthers have experienced substantial inbreeding and concomitant loss of genetic diversity in their recent history. The level of mtDNA variation in the Florida panther is the lowest reported in any similarly studied feline population, including leopards, cheetahs, and other pumas subspecies. Electrophoretic results indicated that the Florida panther had less variation than any other puma subspecies and is nearly as low as the level of allozyme variation reported in the two cheetah subspecies. DNA fingerprint variation seen in the Florida panther is nearly as low as the extremely compromised genetic variation in Asiatic lions from the Gir Forest Sanctuary in India.

Does anyone with more biology knowledge then me (basically anyone here

) have any comments on this?

Was the Florida Panther population just too small to begin with and are 'founder populations' traditionally larger then this? I couldn't find anything on the population size at the time it became isolated.

Are there other reasons why some populations might degenerate and go extinct because of inbreeding and other populations keep thriving and evolving and become a new species (as in the Punctated Equilibrium theory)?

wildlifer · 10-11-2004, 03:56 PM

The Florida population was in a genetic bottleneck, but habitat is a greater problem than was the genetic diversity. They could have possibly recovered from the bottleneck had all things been equal, but we'll never know as (3) western cougars were introduced to add some genetic diversity.

Look here

As you can tell from the article the forecast was grim:

Quote:

By the late 1980's, genetic tests and physical evidence showed that because of extensive inbreeding, the big cats — males can grow to 7 feet, tail to nose, and weigh as much as 140 pounds, females to 6 feet and 90 pounds — had entered a genetic bottleneck they could not escape.

Outward signs of "inbreeding depression" were kinked tails and cowlicks, recessive traits found in no other puma population. Heart defects were common, and the animals were increasingly susceptible to parasites and disease.

Most of the males were cryptorchid — with one or both testicles failing to descend — and had an extraordinarily high percentage of malformed sperm. The World Conservation Union warned that without human help, the Florida panther would probably be extinct by 2055.

But even so, I don't believe the theory would predict all founding populations would survive to speciate. We are also looking at something a little different from "founders," in that we had a population being constantly killed and squeezed into smaller and smaller habitat - not a species new to a habitat.

KC · 10-12-2004, 05:30 AM

Quote:

Originally Posted by DetectedDestiny

Does anyone with more biology knowledge then me (basically anyone here

) have any comments on this?

Was the Florida Panther population just too small to begin with and are 'founder populations' traditionally larger then this? I couldn't find anything on the population size at the time it became isolated.

Are there other reasons why some populations might degenerate and go extinct because of inbreeding and other populations keep thriving and evolving and become a new species (as in the Punctated Equilibrium theory)?

Wildlifer is correct. There are lots of factors that can affect the eventual survival or extinction of fragmented populations. Size at the time of fragmentation, as you pointed out, is definitely one of these. The smaller the subpopulation, the more stochastic, or chance, factors come into play. In some cases the inbreeding can bring about fixation of deterious alleles before natural selection can get rid of them, which can result in local extinction. On the other hand, there are examples of populations which undergo chronic, long-term inbreeding, but manage to thrive. Of course, any population's long-term prospects are better the higher the genetic diversity, which provides a bank of variation with which to respond to changing environmental conditions. So, even if these low-diversity populations can thrive in a particular environment, they are vulnerable to extinction should the conditions deteriorate.

KC

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