A new analysis indicates that Earth's vertebrate diversity is likely twice as high as previously estimated, with about two genetically distinct 'cryptic' species for every recognized one. Led by University of Arizona researchers, the study highlights how DNA sequencing reveals these hidden lineages that look nearly identical. This finding raises concerns for conservation efforts targeting undocumented species.
Researchers from the University of Arizona have conducted a comprehensive review suggesting that global vertebrate biodiversity is underestimated. By examining more than 300 published studies worldwide, the team found a consistent pattern: for every morphologically identified species of fish, bird, reptile, amphibian, or mammal, there are on average two additional cryptic species that are genetically separate but visually indistinguishable.
Senior author John Wiens, a professor in the Department of Ecology and Evolutionary Biology, explained, "Each species that you and I can see and recognize as distinct may actually be hiding two different species, on average." These cryptic species have often evolved independently for over a million years, as revealed by advances in DNA sequencing, which make genetic comparisons faster and more affordable.
A notable example is the Arizona mountain kingsnake. Once thought to be a single species across the state, genetic analysis in 2011 distinguished northern populations as Lampropeltis pyromelana from southern ones, renamed Lampropeltis knoblochi. First author Yinpeng Zhang, a graduate student, noted, "If you compare those two mountain kingsnakes, they all look pretty much the same with their red, black and yellow-white stripes, but the molecular data show that there are distinct but cryptic northern and southern species."
The study, published in Proceedings of the Royal Society B: Biological Sciences, emphasizes conservation implications. Splitting a single species into multiple cryptic ones reduces each's geographic range, increasing extinction risk. Wiens added, "If we don't know a species exists, then we can't protect it." However, few of these species have been formally described, leaving them without legal safeguards. Zhang stressed, "Hidden diversity is an important consideration to make in our conservation efforts," warning that misidentification could undermine breeding programs.
