Visual signalling and sexual selection in male fiddler crabs

Similar to many other species of fiddler crabs, the interactions of Uca tangeri are influenced by 2 characteristic visual signals: the waving d~sp lay 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 carrled out In June and July 1997 at the Rla Formosa Natural Park, Algarve, Portugal, on a sandy beach with an average populat~on dens~ ty of 2.06 burrows m-'. Behdvioural observations of focal males were made at low tide, 1 h before and after the peak of low tlde, that IS during the mudbahng phase or interaction phase. This was also when measurements of male characteristics, mudballs and burrow charactelistics were taken. The results show that the quality of a male's burrow IS related to ~ t s depth, and depth is correlated with 4 features: claw size, waving rate, mean dlstance 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. h4ales compete for the possession of burrows that are more vlslted 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 cn tenon would seem to be burrow quallty