Abstract
Studies in the northern (Río San Juan) watershed in Costa Rica show that the freshwater crab Potamocarcinus nicaraguensis has spread from its original habitat in the Great Lakes region of Nicaragua throughout the Río San Carlos basin into rivers and streams having clear water, a muddypebbly bottom and temperatures above 20 C. Some intraspecific adaptive variation is apparent as to length and width of the carapace and coloration, the San Carlos crabs being darker than those from the Nicaraguan lake region. No other major diferences were found between the two populations, which have not as yet become entirely separated from each other.
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Copyright (c) 1974 Revista de Biología Tropical