Three-spined Stickleback

Three-spined sticklebacks demonstrate predator inspection behavior similar to guppies—pairs approach predators together, gaining information while sharing risk. Sticklebacks adjust their approach based on partner behavior: if the partner hangs back, the focal fish hangs back too. If the partner approaches, the focal fish approaches. This contingent cooperation matches tit-for-tat reciprocity.

The reciprocity is sophisticated. Sticklebacks don't simply match partner position—they track whether partners are being cooperative relative to the danger level. A partner who hangs back when danger is low is defecting; one who hangs back when danger is high might be appropriately cautious. Context matters for identifying defection.

Body size affects inspection roles. Smaller sticklebacks gain more from inspection (predators preferentially target small fish) and thus should be more willing to approach. Larger sticklebacks gain less but face lower risk. Optimal inspection behavior differs by size, creating potential for mismatched expectations between size-disparate partners.

Repeated interactions strengthen cooperation. Sticklebacks inspecting together repeatedly cooperate more reliably than new partnerships. The relationship history creates expectations that stabilize cooperation. First inspections are tentative; repeated inspections are confident.

For organizations, sticklebacks demonstrate that partner reliability develops through repeated interaction. New partnerships require testing; established partnerships can proceed confidently. The early investment in testing cooperation pays off in long-term coordination efficiency.