Pleistocene expansion, anthropogenic pressure and ocean currents:
Disentangling the past and ongoing evolutionary history of Patella
aspera Röding, 1798 in the archipelago of Madeira
Rising sea-level following the Last Glacial Maximum lead to
fragmentation of coastal limpet populations between islands of the
Archipelago of Madeira. This fragmentation is reinforced by recent heavy
exploitation reducing effective population size on Madeira Island. We
use the limpet P. aspera to understand how the role of processes at
different time scales (i.e. changes in the sea level and
overexploitation) can influence the genetic composition of an extant
species, relating these processes to reproductive phenology and seasonal
shifts in ocean currents. Twelve microsatellite genetic markers were
used. A power analysis was used to evaluate the power of the
microsatellite markers to detect a signal of population differentiation.
Long-term past migrations were assessed using a Bayesian Markov
Montecarlo approach in the software MIGRATE-n to estimate
mutation-scaled migration rates (M = m/μ; m, probability of a lineage
immigrating per generation; μ, mutation rate). Two scenarios were
evaluated using an Approximate Bayesian Computation (ABC) in the
software DIYABC 2.1 (i) Scenario 1: considered a population scenario
from a reduced Ne at time t3 to a higher Ne at time t2; and (ii)
Scenario 2 considering a reduction of Ne from a time t3 to a time t2.
Colonization of the archipelago by Portuguese settlers six centuries ago
probably led to an important decrease in the genetic diversity of the
species (Ne). Contemporary gene flow strongly support a pattern of high
asymmetric connectivity explained by the reproductive phenology of the
species and spatio-temporal seasonal changes in the ocean currents.
Spatio-temporal reconstructions using Bayesian methods, including
coalescent and Approximate Bayesian Computation (ABC) approaches,
suggest changes in the migration patterns from highly symmetric to
highly asymmetric connectivity with subtle population differentiation as
consequence of post-glacial maximum sea level rise during the Holocene.