Researchers have found out something surprising about one of the most successful invasive amphibians in the world: Despite the low genetic diversity, the Johnstone's whistle frog, notorious for its shrill calls, was able to conquer many new habitats. This proves that a broadly diversified genome does not necessarily have to be part of the recipe for the success of invasive species, say the scientists. In the case of the small pests, anthropogenic and ecological factors in particular apparently made it possible to spread. This has implications for conservation management, the researchers said.
"Aliens" are spreading in many regions of the world: Through trade, traffic or targeted naturalization, humans have brought numerous animal and plant species to Earth, which are causing problems in their new home. Due to certain characteristics, they can multiply there and spread further and further. The conquerors can affect the original ecosystems in a variety of ways. Invasive species thus play an important role in global change. Various representatives of the amphibians belong to the abducted conquerors.
In the Caribbean region as well as in Central and South America, Johnstone's pipe frog (Eleutherodactylus johnstonei), which can grow to a size of up to 35 millimeters, has developed into a particularly successful invader. In addition, the noisy little creatures have even been able to establish themselves in the greenhouses of some botanical gardens in Europe. "The frog, originally only native to the Lesser Antilles, can look back on a long history of distribution that goes back at least to 1880," says Raffael Ernst from the Senckenberg Natural History Collections in Dresden. "Today, the Johnstone's pipefrog is considered one of the most widespread and successful invasive amphibian species - it is only surpassed by the cane toad and the American bullfrog," says the scientist.
Even the real estate market is affected
A special aspect is that the whistle frogs not only displace native species, transmit diseases and thus confuse the ecosystems: With their very loud and shrill calls, they also become a nuisance for humans. “These tiny frogs are even having an impact on the real estate market—their nightly, deafening concerts are already causing real estate prices to plummet in parts of South America,” says Ernst. A loud video clip can be found on the Senckenberg Gesellschaft für Naturforschung website under the heading "Caribbean invaders"..
Ernst and his working group have been researching Johnstone's whistling frog and aspects of its distribution history for some time now. The importance of human influences, such as the plant trade and anthropogenic changes in the ecosystems, became clear. In the current study, the researchers, together with international colleagues, have now pursued a fundamental question: does the whistling frog's recipe for success also include high adaptability due to genetic wealth within the species? "It is generally assumed that genetic diversity favors a successful invasion - we wanted to get to the bottom of this assumption with solid data," says lead author Franziska Leonhardt from the Technical University of Dresden.
Surprisingly little diversity
To this end, the scientists examined the genetic characteristics of the Johnstone's pipe frog and another invasive frog species in their distribution regions and in their original populations. They then compared the results with sequencing results from a non-invasive frog species. It turned out: "Contrary to the usual thesis, our results show that the two immigrated frogs are genetically impoverished in contrast to the reference species. Even in their original populations, these animals show a low level of genetic diversity and differentiation between the populations,” reports Leonhardt. The result thus shows that genetic diversity per se does not lead to higher invasion success. "Successful invasive species are apparently not necessarily genetically more diverse than their non-invasive relatives," says Leonhardt.
At least in the case of the Johnstone's pipe frog, ecological and anthropogenic factors seem to be more decisive for the dispersal processes, say the researchers. According to them, these include recurring import events and other human influences as well as the establishment of invasive populations in specific habitats similar to native habitats. "Taken together, these aspects seem to have a greater impact on the dispersal potential of the frogs than their genetic diversity," sums up Ernst. "This information could now be helpful in order to be able to take successful management measures for the invasive frogs and to effectively protect the native wildlife," concludes the scientist.
Source: Senckenberg Research Institute and Natural History Museums, specialist article: NeoBiota, doi: 10.3897/neobiota.79.86778