FIGHTING IN MALES OF THE AUTUMN SPIDER, METELLINA-SEGMENTATA - EFFECTS OF RELATIVE BODY-SIZE, PRIOR RESIDENCY AND FEMALE VALUE ON CONTEST OUTCOME AND DURATION

Males of the autumn spider, Metellina segmentata (Araneae: Metidae), c ompete for access to mates by guarding the orb webs oi mature females. We investigated the influences of relative male fighting ability and resource value on fighting behaviour br staging interactions in the fi eld on webs occupied by females. In these contests, the larger male ne arly always defeated its opponent when it was at least 10% greater in size. For smaller size asymmetries between opponents, che male previou sly resident on the female's web usually won the contest. Contest dura tion decreased exponentially with increasing size asymmetry between op ponents, as predicted if each male assessed its relative size and adju sted its fighting strategy according to its likelihood of winning. Con test duration was also greater when the prior resident was the lighter opponent, or when size and residency asymmetries favoured different o pponents as winners. Prior residents fought longer over larger, more f ecund females, indicating an adjustment of fighting effort according t o assessments of resource value. In contrast, intruders did not increa se their fighting effort over larger females, suggesting an inability to assess female size quickly and accurately. Assessment appears to re duce the costs of settling conflicts, but imperfect information can re sult in inaccurate assessments and unexpected outcomes. Assessment str ategies are used by other types of spiders to resolve contests, but th is appears to be the first evidence for such strategies among orb-web- building spiders.