The islands of the province of Bocas Del Toro lie off the Caribbean
coast of northwestern Panamá. These land bridge islands were formed by rising
sea levels within the last 10,000 years. The islands vary in size, age, and
distance from the adjacent mainland. Recent bathymetric studies have provided
time estimates for the disappearance of the land bridges connecting the islands
with the mainland. This estimate of time since isolation provides evolutionary
biologists a time reference from which to draw theoretical conclusions concerning
the role island biogeography plays in the systematics of faunal assemblages
of the various Bocas islands. Biological expeditions to these islands have
provided a series of the echimyid rodent Hoplomys gymnurus. There has
been little recent study of these most interesting rats. In the context of
the unique island biogeographical history of the rats, a comparative analysis
of discrete cranial and pelage characters was done to delimit taxa within
the monotypic genus Hoplomys. Quantitative data were statistically
analyzed to determine the extent of differentiation within and between islands
versus amount of variation within the entire distributional range of the rat.
Qualitative characters were also noted and likewise compared. Overall cranial
size accounted for the most intra- and inter-population character differences.
However, in three island populations there were significant cranial differences
not related to size. Rats from Isla Escudo de Veraguas, Isla Colon, and Isla
Cayo Agua were found to have sufficiently differentiated from the mainland
populations to warrant recognition as being subspecies of Hoplomys gymnurus.
This research was supported by biology grant from the National
Science Foundation Research Experiences for Undergraduates, award # DBI-9531331.
