Soru

For decades, evolutionary biologists explained the emergence of eusociality—a cooperative social structure characterized by division of labor and shared brood care—primarily through the lens of kin selection theory, emphasizing high genetic relatedness among nestmates. In hymenopterans like ants and bees, haplodiploidy creates an asymmetric genetic relatedness that ostensibly incentivizes workers to rear sisters rather than produce offspring. Applied broadly, this framework posited that extreme genetic relatedness was a prerequisite for reproductive altruism across animal taxa.

However, the discovery of eusociality in marine sponge-dwelling snapping shrimp (*Synalpheus*) challenged the universality of haplodiploid genetic asymmetry. Unlike hymenopterans, *Synalpheus* shrimp are diploid, meaning full siblings share only 50 percent of their genes, identical to parents and offspring. Initially, researchers attempted to rescue kin selection by pointing to high levels of inbreeding within sponge colonies, arguing that localized mating artificially elevated genetic relatedness to levels mimicking haplodiploidy.

Nevertheless, recent phylogeographic analyses reveal that eusociality in *Synalpheus* evolved independently multiple times in lineages with low inbreeding coefficients and modest colony-wide relatedness. Consequently, ecological constraints—specifically intense competition for defensive host sponges and the severe mortality costs of dispersal—are now recognized as the primary drivers mediating the transition to sociality in these marine invertebrates. Rather than genetic architecture dictating social organization, physical habitat saturation exerts the decisive selection pressure.

Based on the passage, the author introduces the phrase "Nevertheless, recent phylogeographic analyses reveal" in the third paragraph primarily in order to: