Genetic and phenotypic diversity of guppy population pre- and post-flood disturbance

Rare extreme “black swan” disturbances can impact ecosystems in many ways,
such as destroying habitats, depleting resources, and causing high
mortality. In rivers, for instance, exceptional floods that occur
infrequently (e.g., so-called “50-year floods”) can strongly impact the
abundance of fishes and other aquatic organisms. Beyond such ecological
effects, these floods could also impact intraspecific diversity by
elevating genetic drift or dispersal and by imposing strong selection,
which could then influence the population’s ability to recover from
disturbance. And yet, natural systems might be resistant (show little
change) or resilient (show rapid recovery) even to rare extreme events –
perhaps as a result of selection due to past events. We considered these
possibilities in two rivers where native guppies experienced two extreme
floods - one in 2005 and another in 2016. For each river, we selected four
sites and used archived “historical” samples to compare levels of genetic
diversity and phenotypic mean traits before versus after floods. Genetic
diversity was represented by 33 neutral microsatellite markers, and
phenotypic diversity was represented by body length and male melanic
(black) color. We found that genetic diversity and population structure
was mostly resistant to even these extreme floods; whereas the larger
impacts on phenotypic diversity were short-lived, suggesting additional
resilience. We discuss the determinants of these two outcomes for guppies
facing floods, and then consider the general implications for the
resistance and resilience of intraspecific variation to black swan
disturbances.