A new article with a catchy title (I’m a sucker for those) in BMC Evolutionary Biology using the endangered shorebird the southern dunlin (dunlins Calidris alpina schinzii) as an example looks for evidence of why inbreeding and it’s associated loss of genetic variation are causes of extinction.
I’m not gonna say this article is telling us much that we don’t already know. But, its refining the reasons why inbreeding has such negative effects by using longer term studies and genetic markers.
Here’s the abstract: (Bold is mine)
Inbreeding and loss of genetic diversity are expected to increase the extinction risk of small populations, but detailed tests in natural populations are scarce. We combine long-term population and fitness data with those from two types of molecular markers to examine the role of genetic effects in a declining metapopulation of southern dunlins Calidris alpina schinzii, an endangered shorebird.
The decline is associated with increased pairings between related individuals, including close inbreeding (as revealed by both field observations of parentage and molecular markers). Furthermore, reduced genetic diversity seems to affect individual fitness at several life stages. Higher genetic similarity between mates correlates negatively with the pair’s hatching success. Moreover, offspring produced by related parents are more homozygous and suffer from increased mortality during embryonic development and possibly also after hatching.
Our results demonstrate strong genetic effects in a rapidly declining population, emphasizing the importance of genetic factors for the persistence of small populations.
One of the consequences of such a study has to do with conservation. If we ignore the negative genetic effects of small population size, we are not paying attention to one of the driving factors present in extinction. That is, as soon as a population gets below a certain threshold in numbers, then the risk of serious inbreeding is imminent. This only furthers the downward spiral toward extinction.
The species find themselves in a catch 22. They need to have a larger population to lower their incidence of inbreeding. But, they need to breed more to get that larger population.