New research by evolutionary biologists from Syracuse University, University of Siena, and University of Szeged reveals that cooperative behavior among sperm can improve fertilization success in arthropods, according to a July 31 announcement. The study challenges the traditional view of fertilization as a competition among individual sperm, suggesting instead that cooperation plays a significant role.
The scientists focused on arthropods—a group that includes spiders, crabs, insects, and centipedes—and examined cases where sperm form coordinated groups to enhance their chances of reaching and fertilizing an egg. This process is known as sperm conjugation. Their findings indicate that this phenomenon is widespread across arthropods and has evolved repeatedly over time.
Sperm conjugation often involves a membrane-bound substance called sperm-associated material (SAM), which binds or organizes sperm into groups. Researchers believe SAM originally evolved to package or protect sperm but now facilitates coordinated movement through the female reproductive tract. Lead author R. Antonio Gomez said, "Evolution has effectively run the same experiment over and over again across different groups of arthropods... That allows us to see not only when sperm cooperation emerges, but also when it disappears and reappears under different evolutionary conditions."
The team conducted a large-scale comparative analysis using decades of published studies to map the evolution of these traits across hundreds of species onto an evolutionary family tree. Their results show repeated gains and losses of both SAM and conjugated sperm forms throughout more than 600 million years.
Senior author Scott Pitnick said, "Sperm are the most rapidly evolving cell type... They are shaped by the unique challenge of operating outside the body in the complex environment of the female reproductive tract." The study suggests that understanding how sperm cooperate could have implications for fertility research and pest control strategies targeting invasive species such as the spotted lanternfly.
Co-author Dorus concluded, "What makes this pattern so fascinating is that evolution keeps arriving at similar cooperative solutions in very different groups and across vast expanses of time... These examples remind us that cooperation can be just as important as competition in shaping biological success."
