Aim To determine and analyse the distribution of the freshwater cyclopine

copepod fauna of the Yucatan Peninsula (YP) and its relationship with the

geological and climatic history of this Neotropical karstic zone.

Methods Plotting of georeferenced sites, analysis of local and regional geological

and climatic history, analysis and comparison of regional and local faunistic

records.

Results Distinct dispersal and/or vicariant processes seem to be linked to the

current distributions of the seven genera known in the YP. In general, the

endemic hypogean or benthic crevicular forms (i.e. Diacyclops chakan, D. puuc

and Mesocyclops chaci), derived from epigean, tropical, widely distributed forms

(some of them South American) may have been among the earliest colonizers of

the subterranean habitats in the YP. The distribution of these and other endemic

forms seem to be related to the Holocene dry periods that desiccated the largest

bodies of water and isolated local populations of different species. These vicariant

processes resulted in forms with restricted distributional areas; some of these

formed sister species that speciated in geographically close localities but related to

a common identifiable ancestor. Overall, the processes of cyclopine colonization

of the YP show the influence of the South American fauna, as the closest relatives

of some species endemic to the YP are South American forms; the Nearctic

influence is low. The cyclopine fauna of the YP is formed by a mixture of

Nearctic-derived (species of Acanthocyclops), Neotropical (i.e. M. edax,

M. longisetus, A. panamensis, Thermocyclops inversus and T. tenuis), and

epigean and hypogean endemic forms. The highly dynamic geomorphology of

the YP and the recent climatic changes in the Holocene define the YP as a peculiar

subregion that harbours a diverse fauna of cyclopine copepods with a high

endemism.

Main conclusion The current distribution of cyclopine copepods reflects

relatively recent, post-Pliocene biogeographical patterns; probably older patterns

are involved as well. The eastern coast of the Yucatan is the most recently

colonized by cyclopine copepods. Most of the genera are linked with South

American forms, and the Nearctic influence is weakly represented. This group has

no marine relatives, but there is evidence of vicariant events involving cavedwelling

forms.