Hypothesis
Feminization of male fish by estrogenic effluent depresses effective population size and threatens the sustainability of wild populations, as long-term exposures and collapsing breeding colonies implied.
What failed
Effective population size, estimated from microsatellite genotypes by approximate Bayesian computation and sibling assignment at 28 sample sites in English rivers, showed no significant negative correlation with predicted estrogen exposure; population genetic structure further showed that some roach populations had persisted for multiple generations in stretches with a high proportion of estrogenic effluent, apparently without immigration from cleaner sites.
Broken assumption
Reproductive failure seen in laboratory exposures and breeding colonies scales up to decline in wild populations.
Why
The authors note that the wide confidence intervals of the statistical model still leave room for a reduction of up to 65% at the most contaminated sites, so the null is a limit on the effect rather than proof of none.
From the published paper: Hamilton et al. BMC Biology, 2014. ↗CC BY