Author: Emma Wear
Institution: Indiana Wesleyan University
Date: February 2008
Two studies suggest that what appear to be unified animal species can in fact include genetically separate subpopulations that may more accurately be classified as multiple "cryptic" species, potentially greatly increasing the number of species yet to be identified. A study published in December in the online journal BMC Evolutionary Biology found three distinct species in Ecuador that had previously been grouped as the terrestrial leaflitter frog. Another study that was published simultaneously in BMC Biology determined that African giraffes have at least six genetic strains showing such few traces of interbreeding that they may also be individual species.
"Even within well known and highly mobile species, subdivisions can exist and their lack of recognition could lead to further endangerment or even extinction," write the authors of the giraffe study.
Researchers from Canada's Queen's University and Spain's Instituto de Investigacion en Recursos Cinegeticos examined markers in the mitochondrial and nuclear DNA of the leaflitter frogs across their range. They found three groups whose markers had diverged sufficiently to indicate that they no longer interbred and therefore should be considered distinct species, despite their close resemblance. Phylogenetic analyses, used by evolutionary biologists to investigate the relationships between species of similar ancestry, suggest the frog species separated over 5 million years ago.
"Our research coupled with other studies suggests that species richness in the upper Amazon is drastically underestimated by current inventories based on [similarity of appearance]," explain the authors.
A similar approach was used to investigate genetic similarity among giraffe sub-populations, which display regional differences in coloration and number of ossicones, the antler-like structures on their foreheads, in a collaboration of researchers from University of California, Los Angeles, Omaha's Henry Doorly Zoo, and Kenya's Mpala Research Center. They found genetic evidence that these subpopulations based on appearance actually compose six groups that only interbreed on very rare occasions. In fact, the two subpopulations located closest to each other, in northern and southern Kenya, essentially stopped mating with each other 0.5 to 1.5 million years ago.
Perhaps the most important finding of these studies is the geographic distribution of the newly differentiated groups and those distributions' implications for conservation biology. The frog species occupy roughly distinct geographic regions of their range, but since they diverged before the Andes that today divide their range were formed, this pattern does not follow the natural boundaries that conservationists often follow when measuring an area's biodiversity or establishing reserves.
Likewise, while biologists would expect a wide-ranging animal such as the giraffe to have some interbreeding between subpopulations that are not separated by a physical barrier, this study suggests that instead they may remain genetically distinct due to coloration preferences or slightly different mating times. Since some of these populations number only a few hundred individuals, they would be recognized as highly endangered if considered as separate from the currently unified giraffe species, which today is thought to be at little risk of extinction. Recognition of genetic differences would require subpopulation-specific management plans, both of wild populations and of breeding programs for captive animals.
Written by Emma Wear
Reviewed by Brittany Raffa
Published by Pooja Ghatalia.