Sympatric Speciation Demonstrated Among the Midas Cichlid Species Complex

The Midas cichlid, Amphilophus citrinellus, was once thought to extend throughout the entirety of the San Juan River basin, including throughout both the Nicaraguan Great Lakes and many volcanic crater lakes along their western shores, habitat that only includes the southern half of Nicaragua and the northern half of Costa Rica. Thanks to work published by our research group in the past several years, two crater lakes are known to have multiple species, each endemic to its respective lake. More recently we have studied chromosomal and mitochondrial DNA profiles among the Midas cichlid forms found throughout much of its range, in which we found that each volcanic crater lake has its own group of species, suggesting dozens of species among this group yet to be discovered. Matthias Geiger, Jeffrey McCrary and Uli Schliewen demonstrated and interpreted the DNA profiles in "Not a simple case – A first comprehensive phylogenetic hypothesis for the Midas cichlid complex in Nicaragua (Teleostei: Cichlidae: Amphilophus)" in Molecular Phylogenetics and Evolution. This article confirms our suspicion, that the Midas cichlid species complex consists of dozens of species not yet discovered, in addition to the eleven currently recognized species.

Each isolated stock of Midas cichlids, particularly those in volcanic crater lakes, formed its own species flock by sympatric speciation. The inhabitants of each lake are evolutionarily closer to each other, than to any of the Midas cichlids in any of the other bodies of water.

Amphilophus astorquii pair with fry in Lake Apoyo, Nicaragua. Photo by Ad Konings.

The implications of the publication mentioned above include that each lake harbors its own set of species in the Midas cichlid complex, and that those species are likely not shared among lakes. The ranges of each fish species are very limited, meaning threats to their populations can be very high. One species from this group, the arrow cichlid (Amphilophus zaliosus), has been classified as Critically Endangered on the IUCN Red List. By extrapolation, we can expect many species to be ranked as Endangered or Critically Endangered when their conservation status is finally evaluated.

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