In an article to appear in PNAS, a team of researchers led by Dustin R. Rubenstein of Columbia University, professor of ecology, evolution and environmental biology, found that within a same genus of marine serpentine shrimp, Synalpheus, the size genome and social behavior not only vary widely, but they also co-evolve over time.
Researchers have studied this group of serpentine shrimp for years because they contain the only known marine animals that evolved to live in eusocial societies similar to ants and bees, where some individuals in a colony forgo their own reproduction. to help raise the offspring of others. But it wasn’t until a few years ago that the research team discovered that the crunchy shrimp exhibited extreme variation in genome size, with some species having very large genomes that are more than four to five times the size. size of the human genome.
“We also noticed,” said Rubenstein, “that the eusocial species seemed to have the largest genomes.” This is exactly the opposite of what is found in certain lines of insects. This scheme led the research team to dig deeper into the genomes of these sponge shrimp, many of which are the size of a grain of rice, to understand why eusocial species might have such large genomes.
The authors – who, in addition to Rubenstein, include former Columbia postdocs Solomon TC Chak and Stephen E. Harris, both now assistant professors at SUNY; Kristin M. Hultgren of the University of Seattle; and Nicholas W. Jeffery of the Bedford Institute of Oceanography in Toronto – not only did they confirm that eusocial serpentine shrimp species have larger genomes than their less social parents, they also found that this increase in genome size is due to an accumulation of transposable elements which have proliferated over the course of evolutionary time. Other less social serpentine shrimp species have retained small genomes with fewer transposable elements.
The research team also explored why eusocial shrimp species had more transposable elements in their genome than non-eusocial species. They speculated that “the accumulation of transposable elements in the eusocial shrimp is likely the result of a strong reproductive division of labor where the queen is often the only breeding individual within a colony,” said Chak. Evolutionary modeling has confirmed that transposable elements proliferate in the genomes of eusocial species due to their unique form of social organization. However, since transposable elements are DNA sequences that can “jump” from one place in the genome to another, they are also a source of mutation and can lead to genomic rearrangement. Since scientists have long recognized that transposable elements can fuel adaptive genomic changes, the moderate abundances of transposable elements in ancestral Synalpheus species may have contributed to the initial transition to eusociality, although the researchers note that testing this idea will require additional work.
According to the authors, there is a powerful relationship between genome evolution and social evolution in shrimp capture in which social traits can influence genome architecture. “Understanding how to live in complex societies can provide information about the architecture of the genome represents an intriguing new area of study that has implications for all types of social animals, possibly even humans,” said Rubenstein. After all, transposable elements make up almost half of the human genome, and like breaker shrimp, we too live in complex societies that share many of the same characteristics.
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