'Hidden' species may be surprisingly common

NewScientist.com news service
Phil McKenna

Cryptic species – animals that appear identical but are genetically quite distinct – may be much more widespread than previously thought. The findings could have major implications in areas ranging from biodiversity estimates and wildlife management, to our understanding of infectious diseases and evolution.

Reports of cryptic species have increased dramatically over the past two decades with the advent of relatively inexpensive DNA sequencing technology.

Markus Pfenninger and Klaus Schwenk, of the Goethe-Universitat in Frankfurt, Germany, analysed all known data on cryptic animal species and discovered that they are found in equal proportions throughout all major branches of the animal kingdom and occur in equal numbers in all biogeographical regions.

Scientists had previously speculated that cryptic species were predominantly found in insects and reptiles, and were more likely to occur in tropical rather than temperate regions (see Trends in Ecology and Evolution, vol 22, p 148).

"Species that are seemingly widespread and abundant could in reality be many different cryptic species that have low populations and are highly endangered," says Pfenninger. Until the genetic information of all species in at least one taxon is thoroughly studied, no one will know just how many cryptic species exist. "It could be as high as 30%," Pfenninger says.

Call to arms
"I'm flabbergasted by their results," says Alex Smith of the University of Guelph in Ontario, Canada. "It's a call to arms to keep doing the broad kind of genetic studies that we are doing." Smith is a part of the Consortium for the Barcode of Life, an international effort to map a unique genetic "barcode" for all species on earth.

Sampling as many individuals as possible, they hope to complete work on all fish and birds in another 5 to 10 years. Once either of these taxonomic groups is completed, Pfenninger says researchers will able to extrapolate how many cryptic species exist throughout the animal kingdom.

Examples of cryptic species include the African elephant. A 2001 study found the elephants were actually two genetically distinct, non-interbreeding species, the African bush elephant and the African elephant. The species are currently listed as vulnerable and threatened, respectively, by the World Conservation Union. In the case of the neotropical skipper butterfly, genetic testing revealed the "species" was actually 10 distinct cryptic species.

Mistaken mosquitoes
The reclassifications are more than an academic exercise. They define populations that have evolved independently of each other and whose genetic differences can have significant consequences.

In the early 1900s misidentification of mosquito species based on morphology confounded attempts to control malaria in Europe. Ultimately, what was thought to be a single species was actually made up of six sibling species, only three of which transmitted the disease.

"The basic unit in biology is always the species, and you have to know what you are dealing with," Pfenninger says. Much previous research is now obsolete, he says, because it is not clear what species was being studied.

Pfenninger is now trying to determine whether cryptic differentiation is simply an early stage of morphological differentiation – but preliminary results suggest not.