Visual signalling and sexual selection in male fiddler crabs Uca tangeri

摘要

Similar to many other species of fiddler crabs, the interactions of Uca tangeri are influencedby 2 characteristic visual signals: the waving display performed by males with their enlargedclaw, and the building of structures (mudballs) around the burrow entrance. This study focused on malesignalling, male-male competition and female mate choice Female choice and male mating successwere investigated by looking at male quality, male visual signals (waving activity and mudballs) andmale interactions and their outcome. Fieldwork was carrled out In June and July 1997 at the Ria FormosaNatural Park, Algarve, Portugal, on a sandy beach with an average population density of2.06 burrows m-2. Behavioural observations of focal males were made at low tide, 1 h before and afterthe peak of low tide, that is during the mudballing phase or interaction phase. This was also when measurementsof male characteristics, mudballs and burrow charactelistics were taken. The results showthat the quality of a male's burrow IS related to its depth, and depth is correlated with 4 features: clawsize, waving rate, mean dlstance to mudballs and number of mudballs. Therefore, females could usethese 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 vlslted by females, thus taking over burrowsis an alternative strategy to burrow digging Male waving activity, mudball distance and claw size canbe considered as multiple visual signals available to females for mate choice. Females' first choice cntenonwould seem to be burrow quality.