Data from: Hurricanes overcome migration lag and shape intraspecific genetic variation beyond a poleward mangrove range limit

Expansion of many tree species lags behind climate-change projections.
Extreme storms can rapidly overcome this lag, especially for coastal
species, but how will storm-driven expansion shape intraspecific genetic
variation? Do storms provide recruits only from the nearest sources, or
from more distant sources? Answers to these questions have ecological and
evolutionary implications, but empirical evidence is absent from the
literature. Hurricane Irma provided an opportunity to address this
knowledge gap at the northern range limit of the neotropical black
mangrove (Avicennia germinans) on the Atlantic coast of Florida, USA. We
observed massive post-hurricane increases in beach-stranded A. germinans
propagules at, and past, this species’ present-day range margin when
compared to a previously-surveyed, non-hurricane year. Yet, propagule
dispersal does not guarantee subsequent establishment and reproductive
success (i.e., effective dispersal). We also evaluated prior effective
dispersal along this coastline with isolated A. germinans trees identified
beyond the most northern established population. We used 12 nuclear
microsatellite loci to genotype hurricane-driven drift propagules from
nine sites (n = 896 propagules) and isolated trees from four sites (n = 10
trees), determined their sources of origin, and estimated dispersal
distances. Almost all drift propagules and all isolated trees came from
the nearest sources. This research suggests that hurricanes are a
prerequisite for poleward range expansion of a coastal tree species and
that storms can shape the expanding gene pool by providing almost
exclusively range-margin genotypes. These insights and empirical estimates
of hurricane-driven dispersal distances should improve our ability to
forecast distributional shifts of coastal species.