MEPS 189:233-240 (1999)  -  doi:10.3354/meps189233

ABSTRACT: Similar to many other species of fiddler crabs, the interactions of Uca tangeri are influenced by 2 characteristic visual signals: the waving display performed by males with their enlarged claw, and the building of structures (mudballs) around the burrow entrance. This study focused on male signalling, male-male competition and female mate choice. Female choice and male mating success were investigated by looking at male quality, male visual signals (waving activity and mudballs) and male interactions and their outcome. Fieldwork was carried out in June and July 1997 at the Ria Formosa Natural Park, Algarve, Portugal, on a sandy beach with an average population density of 2.06 burrows m^-2. Behavioural observations of focal males were made at low tide, 1 h before and after the peak of low tide, that is during the mudballing phase or interaction phase. This was also when measurements of male characteristics, mudballs and burrow characteristics were taken. The results show that the quality of a male's burrow is related to its depth, and depth is correlated with 4 features: claw size, waving rate, mean distance to mudballs and number of mudballs. Therefore, females could use these features as indicators of gallery depth, eliminating the need to enter the burrow for sampling. Males compete for the possession of burrows that are more visited by females, thus taking over burrows is an alternative strategy to burrow digging. Male waving activity, mudball distance and claw size can be considered as multiple visual signals available to females for mate choice. Females' first choice criterion would seem to be burrow quality.

KEY WORDS: Fiddler crabs · Visual signals · Male competition · Mate choice · Burrows