|The rise of the Panama Isthmus, from about
12Mya until 3Mya ago (Coastes & Obando, 1996), caused the closure
of the Tropical American Seaway, which connected the tropical Pacific
and Atlantic Oceans. From this geological event resulted an isolation
and genetic divergence of the populations on both sides of the isthmus,
a process commonly reffered to as trans-isthmian divergence
Knowlton & Weigt (1998) showed that sister-species of
pistol shrimp from the genus Alpheus living in mangroves on both sides
of the isthmus had a lower genetic differentiation than pairs of
sister-species in this highly diversified genus. Mangroves are supposed
to be the last environment allowing genetic exchange between the
Pacific and Atlantic Ocean during the final closure of the Panama
Isthmus, about 3Mya ago.
To investigate how the ecological characteristics (as
habitat, length of larval stage or behaviour) may have influenced the
process of speciation, I use littoral grapsoid crabs as model organisms
comparing species from mangroves and rocky shore environments.
Grapsoid crabs represent an important part of the
worldwide mangrove diversity with approximately 60 genera and 400
species. They are found from subtidal to freshwater environments and
the American species are characterized by a wide distribution (Florida
to Brazil and Baja California to Peru), with some species considered to
have trans-isthmian and amphi-atlantic distributions.
My project focuses on two aspects :
1) Studying the connectivity of populations of grapsoid
crabs along the western Atlantic Ocean, and the influence of the Amazon
and Orinoco freshwater plume (see Lessios, 2003).
2) Investigating the trans-isthmian differentiation for
the same species of grapsoid crabs with emphasis on the ecological
characteristics of these species and the search of unnamed species
(Schubart & Cuesta, 2005).
Additionally, data concerning amphi-atlantic
differentiation will be acquired for the studied species that also have
an amphi-atlantic distribution (3).
parsimony haplotype networks of Pachygrapsus transversus (top) and
Cyclograpsus integer (bottom) based on the Cox1 gene. Green: Caribbean
population; orange: Brazilian population.
Coates, A.G., and Obando, J.A. (1996) The geological evolution
of the Central American Isthmus. In Evolution and environment in
tropical America. Jeremy B. C. Jackson, J.B.C., Budd, A.F. and Coates,
A.G. (eds). Chicago: University of Chicago Press, pp. 21-56.
Knowlton, N., and Weigt, L.A. (1998) New dates and new rates for
divergence across the Isthmus of Panama. Proceeding of the Royal
Society of London, B 265: 2257-2263.
Lessios HA, Kane J, Robertson DR (2003) Phylogeography of the
pantropical sea urchin Tripneustes: contrasting patterns of population
structure between oceans. Evolution 57: 2026-2036.
Lessios, H.A. (2008) The Great American Schism: Divergence of
marine organisms after the rise of the Central American Isthmus. Annual
Review of Ecology, Evolution, and Systematic 39: 63-91.
Schubart, C.D., Cuesta, J.A., and Felder, D.L. (2005)
Phylogeography of Pachygrapsus transversus (Gibbes, 1850): The effect
of the American continent and the Atlantic Ocean as gene flow barriers
and recognition of Pachygrapsus socius Stimpson 1871 as a valid
species. Nauplius 13: 99-113.