Researchers Remain Divided on Whether Tuatara or Cichlid Fish is the Fastest Evolving Vertebrate.
Evolution occurs over millennia, but it can also happen in just a few generations. For instance, Darwin’s finches in the Galapagos rapidly evolved specialized beak shapes as food sources changed, Carolina anoles (Anolis carolinensis) developed larger toe pads allowing them to climb higher to escape predators, and peppered moths (Biston betularia) turned darker as the Industrial Revolution darkened urban environments with soot. However, the scientific community has yet to reach a consensus on which vertebrate evolves the fastest, according to Live Science.
Over 500 species of cichlid fish evolved in Lake Victoria. (Photo: JethuynhCan)
Michael Benton, a vertebrate paleontologist at the University of Bristol, UK, suggests that there are two main factors to consider. “One is that there are intrinsic factors in living organisms that cause them to evolve quickly, while others evolve slowly. The other factor is that all organisms can evolve rapidly, but this depends on environmental changes,” Benton stated.
The title of the fastest evolving species is therefore contentious. Some scientists argue that this title belongs to the tuatara (Sphenodon punctatus), a lizard-like creature found only in New Zealand today. This reptile is the last surviving member of the once-diverse order Rhynchocephalia, which existed during the Mesozoic Era (66 – 251.9 million years ago), compared to the modern order Squamata, which includes lizards and snakes.
A 2008 study published in the journal Trends in Genetics analyzed the DNA of ancient and modern tuataras and found that this living fossil exhibits the fastest recorded molecular evolution rate in vertebrates. This means that although their external appearance has barely changed over millions of years, tuataras have rapidly evolving DNA. Similarly, scientists found that Adélie penguins (Pygoscelis adeliae) have evolved at a rate 2 to 7 times faster than previously estimated genetically, even though their appearance has changed very little.
However, not all scientists agree that genetic evolution makes tuatara the fastest evolving species. In fact, they appear not to have evolved much anatomically, as they are perfectly suited to their environment in New Zealand, according to Michael Lee, an evolutionary biologist at Flinders University and the South Australian Museum.
Instead, Lee contends that Lake Victoria cichlid fish are the fastest evolving vertebrates. Lake Victoria is the largest and most recent lake in Africa, spanning Uganda, Tanzania, and Kenya. Over 500 species of cichlid fish have evolved there in the past 15,000 years, a relatively short period for adaptive radiation to occur. This is when a single species rapidly diversifies into many different species. “They not only split into new species but also change in appearance to suit different areas within their habitat,” Lee explained.
For example, some species feed on plankton higher in the water column, while others scavenge for larvae at the muddy lake bottom. Their ability to inhabit specialized niches within the ecosystem partly explains how they evolved into many different species. Their second set of jaw bones positioned deeper in their throat allows cichlids to feed more flexibly on various prey types. Another reason is that cichlids undergo selective mating and can reproduce quickly. By selectively breeding only with individuals that share similar traits, they can create distinct species in just a few generations. Subsequent cross-breeding between these different species can produce hybrids.
In addition to cichlids, guppies (Poecilia reticulata) are another candidate, according to James Stroud, an evolutionary biologist at the Georgia Institute of Technology. Research shows that guppies in a predator-free tributary in Trinidad evolve at rates of 3,700 – 45,000 darwin, a unit used to standardize evolutionary rates, much faster than the 200,000 observed in house mice under artificial selection.
