Related Experiment Video
Updated: Jul 20, 2026
07:57
Fish Sperm Assessment Using Software and Cooling Devices
Published on: July 28, 2018
Rates of mitochondrial DNA evolution in sharks are slow compared with mammals
A P Martin1, G J Naylor, S R Palumbi
1Department of Zoology, University of Hawaii, Honolulu 96822.
Nature
|May 14, 1992
Summary
Molecular clock rates vary significantly across vertebrate species. Shark mitochondrial DNA evolution is seven- to eightfold slower than in primates, necessitating taxon-specific calibrations for accurate molecular dating.
Area of Science:
- Evolutionary Biology
- Molecular Evolution
- Genomics
Background:
- Mitochondrial DNA (mtDNA) evolution rates are primarily calibrated in primates.
- A constant molecular clock across vertebrates is widely assumed but untested.
- Previous assumptions may lead to inaccurate divergence time estimations.
Purpose of the Study:
- To test the molecular clock constancy hypothesis in vertebrates.
- To examine mitochondrial DNA sequence variation in sharks.
- To compare evolutionary rates between sharks and other vertebrate groups.
Main Methods:
- Analyzed mtDNA sequence variation in 13 shark species.
- Sequenced cytochrome b and cytochrome oxidase I genes.
- Compared substitution rates with primate and ungulate data, including species separated by the Isthmus of Panama.
Main Results:
- Shark mtDNA substitution rates are seven- to eightfold slower than in primates or ungulates.
- This rate difference is not attributable to nucleotide bias, selection, or gene choice.
- Confirmed slower rates in recently diverged shark species.
Conclusions:
- The molecular clock is not constant across all vertebrate taxa.
- Using primate-based calibrations for other groups is inappropriate.
- Taxon-specific calibrations are essential for high-resolution molecular evolutionary studies.
Related Concept Videos
01:07Speciation Rates
Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and punctuated equilibrium. Both patterns explain how new species arise, but they differ in the tempo and continuity of evolutionary change. In both cases, evolutionary change arises from heritable variation within populations, with natural selection often shaping traits that improve survival and reproduction under specific environmental conditions.
02:55The Evidence for Evolution
Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution.
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...
02:59Animal Mitochondrial Genetics
Among all the organelles in an animal cell, only mitochondria have their own independent genomes. Animal mitochondrial DNA is a double-stranded, closed-circular molecule with around 20,000 base pairs. Mitochondrial DNA is unique in that one of its two strands, the heavy, or H, -strand is guanine rich, whereas the complementary strand is cytosine rich and called the light, or L, -strand. Compared to nuclear DNA, mitochondrial DNA has a very low percentage of non-coding regions and is marked by...
02:54Evolutionary Relationships through Genome Comparisons
Genome comparison is one of the excellent ways to interpret the evolutionary relationships between organisms. The basic principle of genome comparison is that if two species share a common feature, it is likely encoded by the DNA sequence conserved between both species. The advent of genome sequencing technologies in the late 20th century enabled scientists to understand the concept of conservation of domains between species and helped them to deduce evolutionary relationships across diverse...
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...