When and why do territorial coalitions occur? Experimental evidence from a fiddler crab

Area of Science:

• Animal behavior
• Ecology
• Evolutionary biology

Background:

• The "dear enemy" effect describes reduced aggression between neighbors.
• Territorial defense coalitions, where neighbors assist each other against intruders, are theoretically predicted but lack empirical support.
• African fiddler crabs (Uca annulipes) live in colonies with males defending individual burrows.

Purpose of the Study:

• To investigate the existence of territorial defense coalitions in Uca annulipes.
• To identify the rules governing the formation of these coalitions.
• To test theoretical models suggesting by-product mutualism as an evolutionary driver.

Main Methods:

• Observational studies of territorial interactions in Uca annulipes colonies.
• Experimental manipulations to assess the conditions under which coalitions form.
• Analysis of interactions between resident males, "floaters" (burrowless males), and neighboring residents.

Main Results:

• Documented instances of territorial defense coalitions in Uca annulipes, where a neighbor assists a resident against a floater.
• Identified specific rules that determine when these coalitions are formed.
• Experimental evidence supports the hypothesis that coalitions arise from by-product mutualism.

Conclusions:

• Territorial defense coalitions are a reality in Uca annulipes, expanding our understanding of social defense.
• The findings support theoretical models linking coalition formation to by-product mutualism.
• This study provides the first empirical evidence for the rules governing such cooperative territorial defense.