Particularly interesting for the researchers were the endemic species – species that are only found in a very narrow geographic area. Luiz Jardim de Queiroz, researcher at the aquatic research institute Eawag and the University of Bern as well as lead author of the study recently published in the scientific journal Proceedings of the Royal Society B: Biological Sciences, says: "While the endemic species of amphipods, amphibians, butterflies and flowering plants are largely very old and originated during or even before the Pleistocene, most of the endemic fish species are surprisingly young. The vast majority of them only appeared after the end of the last glacial period about 15,000 years ago."
Since many, if not all, alpine and perialpine waters were covered by a thick layer of ice during the Pleistocene Ice Ages, freshwater habitats were unsuitable for fish species, and local fish populations most probably died out in the Alps. Only after the end of the last Ice Age were they able to migrate again likely from lower-lying river sections of the large rivers such as the Danube, the Rhine or the Rhone. "In the perialpine lakes, a few of these colonisers then specialised within a short time, adapting to several ecological niches in the same lakes and thus formed several new species in most lakes, all of which endemic," says Luiz Jardim de Queiroz.
The amphipods examined in this study did not suffer the same fate as the fish. Since unlike fish they do not depend on large, open water habitats, they were able to survive the Ice Ages in small outlets or under the glaciers in caves and in groundwater. Therefore, most of the endemic amphipod species of the Alps are ancient and some even predate the Pleistocene. The amphibians, in turn, need free water for breeding only in spring and summer and spend the rest of their lives on land. They therefore also found refugia in the Alps during the Ice Ages. And as for the terrestrial species, many of the butterflies and plant species found refugial habitats to persist through the Ice Ages too.
The fish are slow, but creative colonisers
The researchers suggest that the difference in the pace of speciation between fish and the other groups is due to how fast they could colonise the new habitats that opened up after the last Ice Age. Terrestrial species should have colonised those areas relatively fast, as they can disperse in any direction. Butterflies, for example, fly from place to place without facing great obstacles. The seeds of many plants, in turn, can be transported by the wind or by birds over great distances.