Mites do the right thing: Spider mites bring light into the dark

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Image: Researchers at Tsukuba University and Ryutsu Keizai University have found that patterns of reproductive isolation in a spider mite support the prevailing view of the evolution of reproductive barriers in other animal species. Reproductive isolation is key to understanding how populations become different species. The results of this study are important to understand how reproductive isolation evolves and to enable comparisons between different animal groups.
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Credit: Tsukuba University

Ibaraki, Japan – They may be tiny, but mites have shown we can learn from them. Researchers from Japan have found that mites can help understand the evolution of reproductive barriers.

In a study published this month in BMC ecology and evolution, researchers from the University of Tsukuba and Ryutsu Keizai University have shown that their research on a particular species of spider mite supports the prevailing view of species divergence.

Speciation – the process by which populations become distinct species – is driven by reproductive isolation, which allows closely related groups to separate by restricting the flow of genes. The evolution of reproductive isolation is therefore key to understanding speciation. Existing studies have focused on diploid animals (that is, those with paired chromosomes, one from each parent) and support the prevailing view that reproductive isolation develops gradually through accumulated genetic changes. This view is supported by comparative studies of different taxonomic groups, which have shown a positive association between genetic distance and the degree of reproductive isolation.

“In order to understand speciation, different types of organisms have to be examined,” says the lead author of the study, Professor Yukie Sato. “Haplodiploid animals are intended to provide further insights into this evolutionary story. But only a few studies have examined whether this is the case – we have examined that. “

Haplodiploidy is a sex determination system in which males are haploid (that is, have only one set of chromosomes) and develop from unfertilized eggs, and females are diploid and develop from fertilized eggs. The research team examined populations of the spider mite Amphitetranychus vinnensis by measuring the genetic distance via the differences in their mitochondrial DNA and by performing cross-breeding experiments between the population samples. They investigated how the lack of fertilization rate, in addition to non-viability and sterility in hybrids, changes with genetic distance.

“With the crossbreeding combinations, we found that the degree of reproductive isolation was different,” explains Professor Tetsuo Gotoh, lead author. “There was also a positive correlation between genetic distance and all three measures of reproductive isolation.”

The researchers also found asymmetries in reproductive isolation. In combination with the different degrees of reproductive isolation, these asymmetries underline the importance of increased reproductive isolation at an early stage of development through reproductive incompatibility and the importance of interactions within cells, e.g. mites.

“Our results support the prevailing view of the development of reproductive isolation,” says Professor Sato.

The results of this study are important in understanding how reproductive isolation develops in haplodiploid animals. The team’s results will also enable comparisons between large model organisms and other taxonomic groups to reveal factors underlying evolutionary differences.

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The article “Patterns of reproductive isolation in a haplodiploid mite, Amphitetranychus vinnensis: Prezygotic Isolation, Hybrid Inviability, and Hybrid Sterility ”, was published in. released BMC ecology and evolution at DOI: 10.1186 / s12862-021-01896-5

Funding: This work was supported in part by JSPS KAKENHI Grant number 17H03775
(Grant for scientific research B to TG).


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