Molecular evidence for sequential colonization and taxon cycling in freshwater decapod shrimps on a Caribbean island.
Abstract:
Taxon cycling, i.e. sequential phases of
expansions and contractions in
species' distributions associated with ecological or morphological
shifts, are postulated to characterize dynamic biogeographic histories
in various island faunas. The Caribbean freshwater shrimp assemblage is
mostly widespread and sympatric throughout the region, although one
species (Atyidae: Atya lanipes) is geographically restricted and
ecologically and morphologically differentiated from other Atya
species. Using patterns of nucleotide variation at the COI mtDNA gene
in five species of freshwater shrimp (A. lanipes, A. scabra, A.
innocuous; Xiphocarididae: Xiphocaris elongata; Palaemonidae:
Macrobrachium faustinum) from Puerto Rico, we expected to detect a
signature of sequential colonization in these shrimp, consistent with
the concept of taxon cycling, and expected that A. lanipes would be at
a different taxon stage (i.e. an early stage species) to all other
species. We also examined patterns of genetic population structure in
each species expected with poor, intermediate and well-developed
abilities for among-river dispersal. Population expansions were
detected in all species, although the relative timing of the expansions
varied among them. Assuming that population expansions followed
colonization of Puerto Rico by freshwater shrimp, results bear the
hallmarks of sequential colonization and taxon cycling in this fauna.
A. lanipes had a star phylogeny, low mean pairwise nucleotide
differences and recent (Holocene) estimates for an in situ population
expansion in Puerto Rico, and it was inferred as an early stage species
in the taxon cycle undergoing a secondary phase of expansion. All other
species were inferred as late stage species undergoing regional
population expansions, as their mean pairwise nucleotide differences
were relatively high and phylogenetic patterns were more complex than
A. lanipes. High rates of gene flow without isolation by distance among
rivers were detected in all species, although results should be treated
cautiously as some populations are unlikely to be in mutation-drift
equilibrium. Nested clade analysis produced inconsistent results among
species that all have high rates of gene flow and expanding populations.
Cook, B. D., C. M. Pringle and J. M. Hughes. 2008. Molecular evidence for sequential colonization and taxon cycling in freshwater decapod shrimps on a Caribbean island. Molecular Ecology 17: 1066-75.
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