Natural populations are increasingly fragmented as human use of the landscape changes.  As populations decline in size and connectivity, they become  vulnerable to inbreeding, stochastic effects such as genetic drift, and novel challenges like introduced pathogens and changing environmental conditions.  Their response to these changes determines their ability to persist over evolutionary time.


 

Recolonization after plague


Prairie dog populations are threatened by the compounded effects of habitat fragmentation and sylvatic plague, caused by the non-native bacterium Yersinia pestis.  Plague is highly virulent to prairie dogs, and epizootics eliminate entire colonies.  As a result, populations may undergo severe bottlenecks when extirpated colonies are repopulated by few individuals in nearby colonies.  Conversely, if recolonization occurs from multiple source populations, genetic diversity may be maintained.


We recently found that some black-tailed prairie dog colonies are able to regain genetic diversity during the recolonization process, provided there is a sufficient number of source populations for immigrants.  In contrast, other colonies--those with few source populations--suffer from a loss of genetic diversity (figure, left side).  In many cases, the founders of extirpated colonies are genetically different from the individuals present before plague (figure, right side).






Plague extinctions and recolonization also influence genetic diversity at the scale of individual prairie dogs:  After recolonization, heterozygosity was significantly higher than before plague (left figure, below).  Moreover, heterozygosity of six survivors was strikingly higher than expected due to chance (right figure, below).  You can read the full paper here.