Contests between male New Zealand sheet-web spiders, Cambridgea plagiata (Araneae: Desidae)

Abstract

ABSTRACT Male competition for females can often take the form of direct physical contests. The outcome of a given contest or the decision to persist is determined by the resource holding potential (RHP) of rivals, which often corresponds to body size or weapon size. Males of the endemic New Zealand sheet-web spider Cambridgea plagiata Forster & Wilton 1973 have exaggerated chelicerae that are used in contests to gain access to females. We staged male–male contests in the field to determine the factors contributing to contest duration and outcome. The current models which describe how individuals make decisions to persist in a contest fall broadly into (i) energetic war of attrition or pure self-assessment, (ii) mutual assessment, and (iii) cumulative assessment. Our results showed that male body size was the key predictor in determining the winner of a given contest. The durations of contests were more consistent with predictions from either mutual or cumulative assessment models. We highlight that staging contests in the field may result in more realistic results and natural behaviours. Similar to the congener C. foliata, it appears that further development of current contest models may be required to understand male contests in sheet-web spiders.