Just an addendum with a couple of articles I found that I feel are pertinent to this discussion. I'm pretty sure I can't just post full-text here, since it's copyright of the journal, but I can give the abstracts, and give PDFs to those interested.
A Comparison of Inbreeding Depression in Life-History and Morphological Traits in Animals
Marc A. DeRose, Derek A. Roff
Evolution, Vol. 53, No. 4 (Aug., 1999), pp. 1288-1292
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Originally Posted by abstract
The current study tests the hypothesis that life-history traits (closely related to fitness) show greater inbreeding depression than morphological traits (less closely related to fitness). The mean and median slope of the standardized coefficient of inbreeding depression (the slope of the linear relationship between F and the trait value) for life-history and morphological traits were compared. Slopes for life-history traits were higher than those for morphological traits. At F = 0.25 (full-sibling mating), life-history traits experienced a median reduction of 11.8% in trait value, whereas morphological traits showed a depression in trait value of approximately 2.2%.
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This paper is significant to this discussion because it means we're looking for the wrong things: small size and physical abnormalities are noticably only long after there has been significant reduction in lifespan, fecundity, infant survival rate, etc. The problem is that life history traits are much less obvious and often require controlled observation and testing to detect. Essentially, by the time we're seeing morphological signs, we may have already done a lot of damage.
Inbreeding depression in an isolated population of adders Vipera berus
MADSEN T. ; STILLE B. ; SHINE R. ;
Biological conservation, 1996, vol. 75, no2, pp. 113-118
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Originally Posted by abstract
Although inbreeding depression is well-studied in captive animals, its role in natural populations remains controversial. We provide information on an isolated population of snakes (adders Vipera berus) that has been separated from neighbouring populations by the expansion of agricultural activities in southern Sweden. Total adult population size is < 40 adult individuals, and the mating system is such that a few males have disproportionate reproductive success and hence father most of the progeny each year. The isolation and small effective population size (< 15 adults) promote inbreeding. Compared to other non-isolated Swedish populations of adders, the isolated population shows (i) a smaller litter size relative to maternal body size ; (ii) a higher proportion of deformed and stillborn offspring ; (iii) a lower degree of genetic heterozygosity due to fixation or near-fixation of alleles ; and (iv) a higher genetic similarity among individuals (as measured by DNA fingerprinting). The incidence of inviable offspring was sharply reduced when we introduced males from other areas into the isolated population. These results suggest that the lower reproductive output and viability of adders in the isolated population result from inbreeding depression. We also present data to falsify two alternative hypotheses : the characteristics of the isolated population are not due to environmental contaminants (metal and pesticide residue levels are low) or to poor food supply (adult adders are in good physical condition and their neonates are of the same size as in other populations).
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I present this one because it's directly studying snakes, showing that the same rules apply to snakes as other organisms studies more frequently.
I've got PDFs of both, if anyone wants them (just PM me).
This, of course, leads to a new question: is there a significant different in clutch number or total neonate mass (relative to maternal mass) in albino-line snakes than in normals from diverse backgrounds? I'd predict yes, and I'd be interested to see if the data from breeders supports that.
Henry