Patterns of Distribution in Helminth Parasites of Freshwater Fish of Mexico: Can We Detect Hotspots of Richness and Endemism?

Abstract

We analysed the patterns of the distribution of richness and endemism of helminth parasites of freshwater fishes of Mexico based on occurrence data of 184 recorded helminth species in 17 freshwater fish families from 26 hydrological basins. Species richness was calculated as direct diversity counts from each drainage and each of the fish families. The corrected weighted endemism index (CWEI) was calculated as the sum of the inverse of the ranges of the component species of each drainage and the proportion of the species in each basin that have restricted ranges. Our results suggest a wide diversification of helminth parasites of freshwater fishes in most Mexican basins and most fish families. This diversification has been most dynamic in most of the neotropical characids, cichlids, heptapterids and eleotrids but also in the Nearctic ictalurids. The poeciliids and Goodeinae range among the least favourable families for diversification of helminths. A clear separation between basins north and south of the Transmexican Volcanic Belt is observed. Also, analyses show a clear difference in richness and endemism values between eastern basins draining towards the Gulf of Mexico and western basins on the Pacific Ocean slope. The ichthyological composition of the basins explains the observed patterns of the geographical distribution of richness and endemism. The positive relationship between high endemism and high richness allows us to suggest ten basins as possible hotspots. These results suggest that there are indeed basins that favour the diversification of helminths in concordance with some fish families.