Hidden Biodiversity: Earth May Harbor Twice as Many Vertebrate Species as Previously Thought
Earth’s vertebrate diversity may be far richer than scientists previously estimated. A sweeping analysis of over 300 studies suggests that for every known fish, bird, reptile, amphibian, or mammal species, there are approximately two additional “cryptic” species – genetically distinct but nearly identical in appearance – hiding in plain sight.
What are Cryptic Species?
Cryptic species are organisms that appear almost indistinguishable to the human eye but are genetically distinct. These species have evolved separately, sometimes for over a million years, resulting in different genetic lineages despite their similar physical characteristics. Advances in DNA sequencing are now allowing scientists to uncover these long-separated lineages.
The University of Arizona Study
A recent study led by researchers at the University of Arizona synthesized results from more than 300 studies worldwide to determine the prevalence of cryptic species among vertebrates. The findings, published in the Royal Society Publishing: Proceedings B, indicate that global vertebrate biodiversity may be significantly underestimated.
“Each species that you and I can see and recognize as distinct may actually be hiding two different species, on average,” said John Wiens, senior author of the paper and a professor in the University of Arizona Department of Ecology and Evolutionary Biology. “This means that across vertebrates, there may be twice as many species as we previously thought, and many of these hidden species could already be at risk of extinction.”
An Example: Arizona Mountain Kingsnakes
A well-documented example of cryptic species comes from Arizona. For years, kingsnakes in different regions of the state were considered a single species due to their similar appearance. However, molecular data revealed in 2011 that populations in Northern Arizona are genetically distinct from those in Southern Arizona. The southern population was subsequently classified as a separate species, Lampropeltis knoblochi, while the northern population remains Lampropeltis pyromelana.
“If you compare those two mountain kingsnakes, they all look pretty much the same with their red, black and yellow-white stripes,” says Yinpeng Zhang, a graduate student and the paper’s first author. “But the molecular data show that there are distinct but cryptic northern and southern species.”
Implications for Conservation
The discovery of widespread cryptic species has significant implications for conservation efforts. When a species is divided into multiple cryptic species, each newly recognized species has a smaller geographic range, increasing its vulnerability to extinction.
Researchers emphasize the importance of formally naming and recognizing these cryptic species to ensure they receive appropriate legal protection. Accurate identification is crucial to avoid unintentional breeding between different species during conservation programs.
“If we don’t know a species exists, then we can’t protect it,” Wiens stated.