Burrows represent a prominent example of animal architecture that fundamentally alters the surrounding physical environment, often with important consequences for social life. Crustaceans, in particular, offer a model system for understanding the adaptive functions of burrows, their ecological costs and benefits, and their long-term evolutionary impacts on sociality. In general, burrows are central to the life history of many species, functioning as protective dwellings against predators and environmental extremes. Within the refuge of a burrow, one or multiple inhabitants can feed, molt, grow, mate, and raise offspring in relative safety. Depending on the substratum, substantial construction costs can be incurred to excavate a burrow de novo or enlarge a preexisting natural crevice. This investment has been evolutionarily favored because the benefits afforded by the burrow outweigh these costs, making the burrow an “extended phenotype” of the architect itself. Yet even after a burrow is fully constructed, the architect must incur continued costs over its life history, both in maintenance and defense, if it is to reap further benefits of its burrow. Indeed, because burrows accumulate value based on the work involved in their construction, they can attract conspecific intruders who seek to shortcut the cost of construction by evicting an existing occupant and usurping its burrow. Consequently, a burrowing lifestyle can lead to escalating social competition, with many crustaceans evolving elaborate weapons and territorial signals to resolve conflicts over burrow ownership. Some burrows even outlast the original architect as an “ecological inheritance,” serving as a legacy that impacts social evolution among subsequent generations of kin and nonkin. Comparative studies, using cutting-edge technology to dig deeper into the natural history of crustacean burrows, can provide powerful tests of general theoretical models of animal architecture and social evolution, especially the extended phenotype and niche construction.
