Susceptibility to a sexually transmitted disease in a wild koala population shows heritable genetic variance but no inbreeding depression

The koala, one of the most iconic Australian wildlife species, is facing
several concomitant threats that are driving population declines. Some
threats are well known and have clear methods of prevention (e.g., habitat
loss can be reduced with stronger land-clearing control), whereas others
are less easily addressed. One of the major current threats to koalas is
chlamydial disease, which can have major impacts on individual survival
and reproduction rates and can translate into population declines.
Effective management strategies for the disease in the wild are currently
lacking, and to date we know little about the determinants of individual
susceptibility to disease. Here we investigated the genetic basis of
variation in susceptibility to chlamydia using one of the most intensively
studied wild koala populations. We combined data from veterinary
examinations, chlamydia testing, genetic sampling and movement monitoring.
Out of our sample of 342 wild koalas, 60 were found to have
chlamydia. Using genotype information on 5007 SNPs to investigate
the role of genetic variation in determining disease status, we found no
evidence of inbreeding depression, but a heritability of 0.11 (95%CI =
0.05 – 0.23) for the probability that koalas had chlamydia. Heritability
of susceptibility to chlamydia could be relevant for future disease
management, as it suggests adaptive potential for the population.