Reproduction of most animal species requires mating between a female and a male. But some nematodes have evolved the ability to self-fertilize. In these species, individuals are able to self-fertilize and reproduce offspring. In a new study, researchers from the University of Maryland, Cornell University, the University of California and the University of Toronto in Canada found that the ability to acquire autosemination can cause a nematode to lose a quarter of its genome, including genes that give male sperm a competitive advantage when mating. The findings were published in the January 5, 2018 issue of the journal Science, titled "Rapid genome shrinkage in a self-fertile nematode reveals sperm competition proteins."
Image credit: UC San Diego.
A million years ago, a small nematode called Caenorhabditis briggsae evolved the ability to reproduce through autosenching. Therefore, most C. Briggsae is hermaphrodite and has both male and female organs. Eric Haag, a professor of biology at the University of Maryland, and his research team specialize in sex evolution and have long studied C. Lee. Briggsae because they have unusual reproductive behavior.
To investigate how autosequentation affects C. Briggsae Evolution, Erich Schwarz, Assistant Professor of Molecular Biology and Genetics at Cornell University, and C. Scott Caenorhabditis Nigoni, who is closest to Briggsae, performs genome sequencing. By comparing the genomes of the two nematode species, the researchers found that autosenched C. Briggsae is better than C. Nigoni has 7,000 fewer genes. Over time, C. Briggsae lost about a quarter of its genome.
Given that the two nematodes differ primarily in their reproduction patterns, the researchers suspect that the transition from outcrossing to autoforgulation led to gene loss. To confirm this, they compared male C. Nigoni and female C. Gene activity in nigoni and the discovery of C. Briggsae loses nearly three-quarters of its genes in male C. The activity in nigoni is higher than that in female C. Strong in nigoni.
To look for possible sex-related functions in these missing genes, the researchers focused on a family of genes called mss (male secreted short), which exists in C. nigoni, but not in C. Briggsae. In fact, no known autoforested Caenorhabditis species have the MSS gene. According to research conducted by Haag, Schwarz, former University of Maryland graduate student Cristel Thomas, and former University of Maryland undergraduate Rebecca Felde, the mss gene is only active in heterotypic hybridized male nematode species.
The researchers used a gene-editing tool called CRISPR to remove 4 mss genes from the heterotypical hybrid nematode species Caenorhabditis remanei. As a result, male C. from males lacking these MSS genes. Remanei's sperm competition however comes from wild-type male C. with these MSS genes. Remanei's sperm. Conversely, when they insert the MSS gene into male C. When briggsae, their sperm is in conflict with male C. from the wild type. Briggsae and Wild-type C. Briggsae hermaphrodite sperm compete to win.
The researchers also found that these MSS genes encode short proteins on the surface of sperm cells. Taken together, these results suggest that these MSS genes give male nematodes sperm a competitive advantage during mating.
Haag said, "The fact that all inbred species have lost the MSS gene suggests that these genes that are very useful for heterotypic hybrid nematodes are harmful to nematodes that no longer perform heterotypic hybridization." What we're seeing is how a species fine-tuned its reproductive behavior over the course of evolution. ”
According to Haag, this autofortified nematode species may have lost these MSS genes because competitive male sperm is harmful. During the study, the researchers found that male sperm with a stronger competitiveness biased the sex ratio of this nematode species toward producing more male nematodes. This change may put the survival of these nematodes at risk because too many male nematodes slow the growth of nematodes populations, and in the wild, these nematodes must reproduce as quickly as possible in order to survive.
According to Da Yin, the paper's first author and a biological science student on Haag's team, male sperm that confirmed a competitive advantage may be more likely to be able to compete with C. Briggsae's harmful experiments are underway.
Yin said, "We have begun to compare C. Kelly with and without the MSS gene. The growth of the briggsae population allows us to test by screening whether the MSS gene may have been removed from C. Briggsae is cleared in the genome. Our guess is that C. with the mss gene The briggsae population grows more slowly because it has more males. ”
Going forward, Haag and his collaborators also plan to study how the MSS gene gives sperm a competitive advantage. They also wanted to screen the remaining 7,000 lost genes in order to find them in C. The role of briggsae.
Resources:
Da Yin, Erich M. Schwarz, Cristel G. Thomas et al. Rapid genome shrinkage in a self-fertile nematode reveals sperm competition proteins. Science, 05 Jan 2018, 359(6371): 55-61, doi:10.1126/science.aao0827
Source: Bio Valley