Hidden Species: Earth’s Vertebrate Biodiversity May Be Twice as High as Estimated

The remarkable diversity of life on Earth may be even greater than previously imagined. A latest study suggests that for every known vertebrate species – that’s mammals, birds, reptiles, amphibians, and fish – there are, on average, two additional, currently unrecognized species. This finding, published in the Royal Society Publishing: Proceedings B, highlights the significant underestimation of global vertebrate biodiversity and carries important implications for conservation efforts.

Hidden in Plain Sight: The Challenge of Cryptic Species

For centuries, scientists have relied on observable physical characteristics – what’s known as morphology – to classify and distinguish between species. Different species of snakes, for example, might be identified by variations in color patterns or scale arrangements. However, a growing body of research reveals the existence of “cryptic species,” which are nearly indistinguishable in appearance but genetically distinct. These species have evolved separately over long periods, accumulating differences in their DNA despite maintaining similar physical traits.

“Each species that you and I can notice and recognize as distinct may actually be hiding two different species, on average,” explains John Wiens, a professor in the University of Arizona’s ecology and evolutionary biology department and senior author of the study. “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.”

The ability to uncover these cryptic species is largely due to advances in molecular sequencing technologies. These tools allow researchers to compare the genetic makeup of different populations, revealing hidden evolutionary lineages. As Yinpeng Zhang, a graduate student and the paper’s first author, notes, many taxonomy papers are now uncovering these cryptic species as a byproduct of broader biodiversity or taxonomic studies.

Consistent Patterns Across Vertebrate Groups

What’s particularly striking about this new research is the consistency of the pattern across diverse vertebrate groups. The study, which synthesized data from over 300 published studies, found that fishes, birds, mammals, reptiles, and amphibians all appear to harbor roughly two cryptic species for every morphologically defined species. This suggests that the phenomenon isn’t limited to specific environments or evolutionary histories.

A local example from Arizona illustrates this point. The Arizona mountain kingsnake, long considered a single species based on its appearance, was revealed to be two distinct species through molecular analysis in 2011. Populations in Northern and Southern Arizona, despite looking nearly identical with their characteristic red, black, and yellow-white stripes, were found to have significant genetic differences. The southern population was subsequently classified as Lampropeltis knoblochi, separate from the northern Lampropeltis pyromelana.

Implications for Conservation

The discovery of widespread cryptic species has profound implications for conservation. When a species is divided into multiple cryptic species, each newly recognized species typically has a smaller geographic range. This is a critical factor, as smaller ranges are often associated with a higher risk of extinction. As Wiens points out, “People have generally found that the smaller a species’ range size is, the more likely that species is to go extinct.”

Currently, many of these cryptic species lack formal recognition and legal protection. Despite being identified through molecular data, they haven’t been officially named or classified, leaving them vulnerable to habitat loss and other threats. The researchers emphasize the urgent need to formally describe and name these species to ensure their conservation.

The Risk of Unintentional Hybridization

Beyond formal recognition, accurately identifying cryptic species is crucial for effective conservation management. Zhang highlights a potential risk: if cryptic species aren’t correctly identified, conservation efforts aimed at boosting population numbers could inadvertently lead to breeding between members of different species. This could compromise the genetic integrity of each species and potentially reduce their long-term viability.

The researchers also point to the importance of considering this hidden diversity when assessing the conservation status of species. A species that appears relatively abundant based on its overall range might actually consist of several rare and vulnerable cryptic species. As noted in a related study, morphology-based species of limited conservation concern can contain cryptic species that are in imminent danger of extinction.

The Role of Genetic Data and Future Research

The study also touched upon the use of different types of genetic data – mitochondrial and nuclear – in identifying cryptic species. While mitochondrial data is often more readily available, the researchers found that it sometimes overestimated the number of cryptic species compared to nuclear data. However, the differences were generally not statistically significant, suggesting that both types of data can be valuable tools for species delimitation.

The team acknowledges that uncovering cryptic species is an ongoing process. Research suggests that accounting for cryptic species might significantly impact overall estimates of global biodiversity, potentially tripling the number of insect species alone.

What’s Next: Prioritizing Cryptic Species Research

The researchers emphasize that testing for cryptic species across morphology-based vertebrate species should be an urgent priority for conservation. The first step, according to Wiens, is formally naming these distinct species. This will provide them with official recognition and the potential for legal protection. Further research is needed to understand the ecological roles and conservation needs of these newly identified species, and to develop effective strategies for their protection. Continued advances in genomic technologies will undoubtedly play a crucial role in uncovering even more hidden diversity in the years to come.