They live in the few bodies of water in the desert state of Oman: these freshwater fish from the Arabian Peninsula have a previously undiscovered biodiversity, researchers report. They identified four so-called cryptic species that were created through genetic isolation. Since they differ only in their genetic makeup, but hardly externally, they are called cryptic species. However, the threat to their small and isolated habitats could soon make them disappear, the researchers say.
When talking about freshwater fish, very few people think of the desert-shaped Arabian Peninsula. But even in this rather hostile region there are small habitats: In the north of Oman, springs gush in the Hajar Mountains and there are surface waters and underground water connections in which various freshwater organisms exist. This is also the home of the up to eight centimeters long “Oman barbel”, which has long been assigned to a species: Garra barreimiae.
For some time now, the biologists around Sandra Kirchner from the University of Vienna have been researching these interesting inhabitants of the desert region. Initially, the focus was on the blind and pale pink cave shape of the barbel, which occurs in the underground lakes of a cave system in the Hajar Mountains. Through genetic analyzes, the researchers were able to show genetic differences between the cave barbel and their sighted relatives from the surface waters, which made it clear that there was a long isolation between the populations.
Biodiversity is emerging
Kirchner and her colleagues then devoted themselves to the genetic characterization of the fish from the various surface waters. It turned out that the barbel of the various populations differ genetically as much as one would expect between species. The researchers come to the conclusion that the barbel of the surface waters represent four different species. However, this genetic differentiation was not reflected in physical differences: There are no clear characteristics that could be used to differentiate the populations, the scientists report.
Such genetically different populations, which, however, do not appear to differ from one another in terms of their external characteristics, are referred to as “cryptic species” or “twin species”. As the researchers explain, species do not necessarily develop externally visible differences in the course of evolution. This is the case when it was not a different environment or adaptations to certain diets that were the most important drivers of species splitting, but rather the long isolation of subgroups. This was apparently the case with the fish of Oman: Similar environmental conditions prevail in their limited range. This leaves little room for deviations in well-adapted external features. However, the long geographical isolation allowed genetic peculiarities to arise, as a result of which the populations split into species, the researchers explain.
Endangered cryptic species
As they emphasize, such “secret” species are particularly threatened: “Based on the current state of knowledge, we can assume that many cryptic species exist in animals that become extinct before they are even discovered,” says Kirchner. The discovery of the cryptic fish species of the Garra genus in northern Oman suggests that biodiversity in many regions of the world is underestimated and thus “underestimated”, according to the biologist.
The desert fish are also particularly endangered in this context. Because their freshwater habitat in the desert region is in the focus of people: The fish are threatened by construction projects, the growing exploitation of water resources and salinization. “The distribution areas of the Garra species are small and mostly isolated, so they are particularly vulnerable to changes in the environment,” Kirchner concludes.
Source: University of Vienna, specialist article: Journal of Zoological Systematics and Evolutionary Research, doi: 10.1111 / jzs.12438