The Effect of Size Asymmetry on the Expression of Territoriality in Northern Crayfish

(Orconectes virilis) Mae Kindler and Jenna McCullough University of Minnesota – Itasca Biological Station Animal Behavior – June 29, 2010 Abstract Territoriality in female northern crayfish, Orconectes virilis, was studied through the observation of resident-intruder crayfish pair interactions based on size asymmetry. Resident-intruder pairings were chosen among 18 crayfish, with a total of 51 asymmetric interactions observed. Resident crayfish were allowed to establish themselves immediately within shelters, followed by the placement of intruder crayfish within the territory of the resident. One of three possible interactions was noted for each resident-intruder pair and shelter, including resident eviction, resident-intruder union, or resistance of intruder. It was found that resident-intruder pairs having high percent size asymmetry resulted in high eviction rates of small residents by large intruders.