Decades-Old Theory of Insect Society Evolution Comes Under Fire

A landmark study published in Current Biology challenges a textbook theory of how insect societies evolve, SciTechDaily reported this week. For more than 60 years, W.D. Hamilton's haplodiploid hypothesis has argued that eusociality — advanced social organization with division of reproductive labor, cooperative brood care and overlapping generations — evolves more readily in insects with haplodiploidy, a genetic system in which females carry two chromosome sets and males carry only one.

The Classic Argument

Under haplodiploidy, sisters can be more closely related to each other than to their own offspring, making it theoretically advantageous to help raise siblings rather than reproduce independently. That logic made the hypothesis one of the most famous in evolutionary biology.

Putting It to the Test

Arizona State University researchers Sachin Suresh and Timothy A. Linksvayer assembled social behavior and genetic data for nearly 69,000 insect species and mapped those traits onto two of the largest available species-level insect family trees using phylogenetic comparative methods. Initial results seemed to support the established hypothesis — haplodiploid insects appeared to transition to eusociality more frequently. But detailed analysis revealed that nearly all of this pattern came from a single evolutionary branch: the aculeate Hymenoptera, the ants, bees and stinging wasps.

No Real Association

Once that lineage's exceptional history was accounted for, haplodiploid insects outside it developed eusociality at rates similar to diploid insects. When we formally tested it, we found there is no real association between the genetic determination system and eusociality, Suresh said. It has more to do with environmental factors and the life-history traits of insects. The findings shift attention toward other characteristics — such as stingers, specialized nesting behaviors and environmental conditions — that may have favored the repeated evolution of cooperative colonies in ants, bees and wasps.