Decades-old theory for how insect societies evolve challenged

For over six decades, evolutionary biologists have debated whether a unique genetic system found in ants, bees and wasps contributes to eusociality. A new Arizona State University study challenges this notion, indicating that while haplodiploidy is prevalent in eusocial insects, it alone does not predict the evolution of complex social organization.

The research, published in Current Biology, reveals that haplodiploidy's influence on eusociality is almost entirely driven by a single lineage—the aculeate Hymenoptera, which includes stinging wasps, bees and ants. Across all insects, haplodiploidy does not predict eusociality independently. The findings suggest that eusociality's evolution is more likely influenced by lineage-specific traits rather than chromosome inheritance alone.

Researchers compiled social behavior and genetic data for tens of thousands of insect species, mapping these traits onto large species-level insect family trees. They found no strong association between haplodiploidy and eusociality, except within the aculeate Hymenoptera. Once accounting for this lineage's exceptional evolutionary history, the study showed that haplodiploid insects outside this group exhibit similar rates of eusocial evolution as diploid insects.

The study underscores the importance of comprehensive empirical testing in evolutionary biology, emphasizing that factors such as stingers, specialized nesting behaviors, and other unique life-history traits may play a significant role in the evolution of eusociality among insects.