Tanya Detto, Michael Jennions and Patricial Blackell's paper "When and why do territorial coalitions occur? Experimental evidence from a fiddler crab" was featured in Nature highlights.
Neighboring territory owners are often less aggressive toward each other than to strangers ("dear enemy" effect). There is, however, little evidence for territorial defense coalitions whereby a neighbor will temporarily leave his/her own territory, enter that of a neighbor, and cooperate in repelling a conspecific intruder. The paper documents territorial defense coalitions in the African fiddler crab Uca annulipes, which lives in large colonies wherein each male defends a burrow and its surrounding area against neighbors and "floaters" (burrowless males).