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Small Genetic Changes May Hold Key to Formation of New Species

NEW YORK (GenomeWeb) – An international research team has found that it's possible to pinpoint when a subset of a certain population first shows signs that it is evolving into a distinct and different species.

The study, published today in Nature Ecology & Evolution, attempted to unravel some of the complexities of how a larger population might evolve into a separately defined species. The researchers performed a whole-genome analysis of within-species variation of Timema stick insect populations. Timema, commonly referred to as "walking sticks," have evolved to bear cryptic patterns on their bodies, which allows them to hide in plain sight. The better suited a particular walking stick's pattern is to its environment, the better its chance of survival.

"Our work on these insects suggests speciation can be initiated by a few genetic changes associated with natural selection on cryptic color-patterns," Zach Gompert, an evolutionary biologist at Utah State University and corresponding author on the study, said in a statement. "While speciation is much more complicated than these changes, Timema's color-patterns provide a window for studying the early phases of the formation of a species."

The team sequenced 852 new Timema samples and re-sequenced 160 reference genomes to generate over 1,000 low coverage whole genomes. Additionally, the researchers sequenced 473 individuals in a between-generation-transplant-and sequence experiment and 379 individuals from natural populations of eight species. The transplant experiment was done to pinpoint if there was divergent selection between hosts. The researchers aligned all of the sequences to the T. cristinae reference genome and called out SNPs.

Gompert says the scale of the study is rare outside of human population genetic studies, adding, "Having sequenced the genomes of a thousand individuals, we were able to pick up signals and variations that might have been missed in a smaller sample."

After analyzing the combined sequence data, the researchers found that SNPs associated with color pattern reside in regions of accentuated differentiation between ecotypes. The transplant experiment genomes further revealed that the highest concentration of genetic differentiation between populations occurred on LG8.

Gompert and his colleagues concluded in the paper that their results "accord well with models of parapatric speciation, but do not support a strong role for the growth of a few islands of differentiation, at least for early to intermediate phases of speciation."   

They added that while there is still a need for more study on speciation, their study did demonstrate that such integrative studies "allow even complex speciation processes to begin to be understood."