An in-depth analysis reveals that for each identified vertebrate species, there may be two others, nearly identical in appearance but genetically distinct.
Scientists have long classified animals based on their morphology, such as color or shape. However, with advances in DNA sequencing, it has become possible to detect differences barely visible to the naked eye. These "cryptic species" share similar external traits, but their genetic material shows they have evolved separately over long periods, sometimes more than a million years.
Lampropeltis knoblochi, a species of kingsnake from southern Arizona, was distinguished from its northern counterpart thanks to genetic data.
Credit: Yinpeng Zhang
To assess the scale of this phenomenon, a research team compiled the results of more than three hundred studies conducted worldwide. This work, often carried out as part of taxonomy or biodiversity projects, revealed that this pattern is consistently repeated in fish, birds, mammals, reptiles, and amphibians, with an average of two cryptic species per recognized species.
A concrete example comes from the mountain kingsnakes in Arizona. For years, they were thought to be a single species due to their identical appearance. But in 2011, molecular analyses showed that the northern and southern populations were genetically different, leading to the recognition of two distinct species, Lampropeltis pyromelana and Lampropeltis knoblochi.
The discovery of these hidden species has important implications for conservation. When a species is divided into several cryptic entities, each typically occupies a smaller geographic range, which increases the risks of extinction. Without official recognition, these species do not benefit from legal protections, and conservation programs might even inadvertently mix them.
Lampropeltis pyromelana, the northern Arizona kingsnake, is genetically distinct from the southern species, illustrating the concept of cryptic species.
Credit: Yinpeng Zhang
For researchers, as indicated by John Wiens and Yinpeng Zhang in their study published in
Proceedings of the Royal Society B: Biological Sciences, it is important to formally name and describe these species to better protect them. This requires an approach combining morphological observations and genetic analyses, in order to accurately map the true diversity of vertebrates on our planet.
The role of DNA in species identification
DNA, or deoxyribonucleic acid, contains the unique genetic information of each organism. By comparing the DNA sequences of different individuals, scientists can detect variations that indicate an evolutionary separation. This method has become accessible thanks to technological advances, allowing for rapid and inexpensive analyses.
For vertebrates, DNA is often extracted from samples such as blood, saliva, or tissue fragments. Specific genetic markers, such as mitochondrial or nuclear genes, are examined to identify significant differences between populations. These differences can reveal that seemingly identical groups have evolved independently over long periods.
The use of DNA complements traditional approaches based on morphology. While external appearance can be misleading due to evolutionary convergences or environmental variations, the genetic code offers a more objective measure of diversity. This helps avoid classification errors and better understand the relationships between species.
In practice, this approach requires collaboration between geneticists and taxonomists. It allows for the revision of existing species catalogues and the addition of new entities.