One working definition of codivergence is “a process of parallel cladogenesis [when a species splits to become two or more species]; the speciation of one biological entity resulting in the speciation of those entities that are associated with it” (Charleston and Perkins). A simpler definition might be: when two closely associated species change (or evolve) together.
Codivergence vs. Cospeciation
Codivergence and cospeciation are often used interchangeably. Some scientists consider codivergence to be the process where the associated populations separate into distinct groups, while cospeciation defines the point at which they have evolved independently to become separate species (Light and Hafner).
Figure 1 illustrates codivergence of viruses and plants. The heavy lines in this illustration represent host plant species, while the lighter lines running parallel to heavy lines represent viruses codiverging with the plants (click on the image for a larger view). It’s important to note that not all instances of species apparently evolving in a parallel fashion are the result of codivergence.
What Species Codiverge?
Codivergence occurs when two (or more) species live in such close association that they are dependent on each other for survival, or one is dependent on another. If one of these associated species changes (evolves), the other must either be able to continue to depend on the changed species, adapt and evolve along with the changed species, or die out.
Because of their inherent position of dependence on a host, parasites are often obliged to codiverge with the host, and much of the research on codivergence has been done on host species and their parasites. A process of many codivergences over time can produce groups of closely related parasites infesting closely related hosts.
An Example of Codivergence
The last common ancestor of modern humans and chimpanzees is thought to have lived about seven million years ago. When populations of that species separated – one to evolve over millennia to modern chimps, one to modern humans, any parasites they had were necessarily separated as well. The parasites that survived the split continued to evolve in each primate group; they and the primates codiverged.
One type of parasite that was likely present is the ancestor of today’s malaria parasites. As the two populations of primates and malaria parasites moved farther apart over time, they evolved in different ways, becoming separate species. Today, most malaria parasites of other primates do not infect humans (though some do) and vice versa.
Why Study Codivergence?
The idea of codivergence has been a subject for scientific investigation since Charles Darwin proposed the theory of evolution. Darwin himself recognized “the potential of using the parasites of two seemingly identical hosts living in geographically distinct areas to provide additional information on the relationships of these hosts” (Charleston and Perkins). Today, cophylogeny, the study of codivergence and other parallel evolution, typically uses molecular methods – analysis of genes – not available in Darwin’s time.
Among other things, researchers use codivergence to investigate:
- relationships of hosts and parasites
- origins of parasites, especially those that cause disease
- past evolution of hosts and parasites
The science of codivergence and cophylogeny is still developing, with rapid changes in technology and theory. In the future this research promises to provide a much clearer understanding of relationships between codivergent species both now and in the past.
Sources
Charleston, Michael A. and Susan L. Perkins. 2006 “Traversing the Tangle: Algorithms and Applications for Cophylogenetic Studies.” Journal of Biomedical Informatics 39: 62-71.
Light, Jessica E. and Mark S. Hafner. 2008 “Codivergence in Heteromyid Rodents (Rodentia: Heteromyidae) and Their Sucking Lice of the Genus Fahrenholzia (Phthiraptera: Anoplura).” Systematic Biology 57(3):449-465
Image: Wu, Beilei, Ulrich Melcher, Xingyi Guo, Xifeng Wang, Longjiang Fan, and Guanghe Zhou. 2008 “Assessment of Codivergence of Mastreviruses With Their Plant Hosts.” BMC Evolutionary Biology, 8:335 Biomed Central Open Access
Rosemary Drisdelle - Rosemary Drisdelle has been published many times as a nonfiction writer and several times as a poet. Her first book, Parasites: Tales of ...
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