A large variety of species exists in a group that reproduces by asexual reproduction, in which the females clone themselves without male involvement
Yonat Ashhar and Noam Levithan, Galileo
According to a study published in the journal PLoS Biology, a group of microscopic animals split into many separate biological species over the past 40 million years, although their reproduction is asexual.
The study, conducted by Diego Fontaneto from the University of Milan in Italy and his colleagues from Great Britain, focused on the class of rotifers (Rotifera), which are microscopic invertebrates that live in freshwater reservoirs, such as puddles and streams, as well as in moist soils and on mosses and lichens. Today there are hundreds of species of rotifers adapted to a variety of environments, from hot springs to Antarctica. Rotifers are diploid creatures that reproduce exclusively by virgin reproduction, i.e. asexual reproduction: the mother lays unfertilized eggs, from which daughters develop that are her clones. In such a reproduction there is no need for males, who do not exist.
The accepted assumption is that sexual reproduction is necessary for the formation of genetic variation, and that the genetic variation created as a result of sexual reproduction increases the resistance of a certain biological species to parasites and its chances of survival during changes occurring in the environment. According to this theory, animals and plants that reproduce asexually will have low diversity and therefore, for the most part, will not survive long on an evolutionary scale. The very existence of rotifers seems to challenge this assumption.
There are two main approaches that relate to species-biological differentiation. According to one approach, the group of individuals that make up the biological species are similar to each other and remain cohesive as a single unit, since they continuously exchange and share genetic material. When the transfer of genetic material is not possible - due to a physical or other barrier - the group splits, and separate biological species may be formed, which differ genetically and morphologically from each other. Another approach claims that individuals of the same biological species are similar to each other because they have adapted to live in the same ecological niche. These approaches do not necessarily contradict each other. It is possible to reconcile the different approaches and examine them separately from each other by looking at a group that reproduces by asexual reproduction. If the second approach has more weight, it is expected that the species diversity of creatures that reproduce asexually will be similar to those that reproduce sexually.
In order to test this, Fontanto and his colleagues defined biological species as distinct populations that develop independently of each other, and looked for such species among rotifers of a certain type. Identification of separate populations is done using two genetic markers - the DNA sequence of certain genes - that were isolated from rotifer populations from different habitats around the world, as well as by comparing the jaw dimensions of the rotifers, similar to comparing the shapes of the proboscideans in the Galapagos.
The researchers used each of the three markers to sort and group the rotifers into biological species according to their proximity to each other. The sorting according to these classification methods corresponded to the classical classification of the rotifers. Also, species identified as relatives according to the genetic markers had similar morphology. From the analysis of these findings it appears that each cluster represents a group that developed separately.
Individuals that made up one cluster were much more similar to each other than to individuals from another cluster, as expected in a situation where there is selection against intermediate forms, i.e. splitting selection.
Such divisive selection may occur in different ecological niches, which represent different requirements that are reflected, among other things, in the jaw structure that differs between species. An excellent example of these findings is two different species of rotifers living on the body of a small water crab (Asellus aquaticus). One species lives on the crab's legs and the other on its belly. According to the classical division, as well as according to the current study, these two species are evolutionarily distinct and independent of each other, although they share the same cancer.
Since Fontanto and his colleagues were able to show in their research that creatures that reproduce by asexual reproduction split into distinct groups whose development is independent of each other, they disproved the idea that sex - sexual reproduction - is necessary to create a variety of biological species.
One response
From this article I could not understand the innovation. Maybe I should read the original article.
It is known that even among the parthenogenetic animals there is a variety of species. This is a fact that has been taught at the university for a long time. Now comes an article in which the researchers disproved the idea that sexual reproduction is necessary to create biological species diversity.
The question is where the species diversity is greater. How can you even compare non-sexual animals to sexual ones? You should look for such animals that share overlapping or close ecological niches and compare the internal diversity within the family (how many species and varieties are there in the family).
It should also be remembered that asexual reproduction is not necessarily the creation of a genetic clone of the offspring. There are many causal factors that will cause a change in the hereditary charge. I guess the most important factors are viruses.