Effects of competition, female size, and their distance on the claw-waving rate of male fiddler crabs (Brachyura, Ocypodidae)

Abstract

The alteration of signals of animals in response to changes in environmental factors is a common phenomenon. In male fiddler crabs, waving major claws towards females is energetically costly; thus, males need to adjust their waving in a way that increases the chance of potential mate attraction while reducing the waving cost. In this study, I examined how Austruca perplexa males adjusted their waving rate based on male-male competition (male numbers in a cluster [Austruca perplexa males make groups and wave synchronously towards females]), female body size, and the distances of the receiver females from the signaller males. Forty clusters were selected randomly; from each cluster, I randomly selected one male, video recorded his waving behaviour and calculated waving rate (waves/min). Body size (carapace width) and distances of receiver females were measured. To analyze the effects of competition, female size, and their distances on male waving rate through binary logistic regression analysis, all variables were divided into two categories (male waving rate: low and high, competition: low and high, female size: small and large, and female distances: short and long) based on a median split method. Afterwards a series of binary logistic regression models were built and the relative supports of various models were assessed based on the corrected Akaike information criterion. Results showed that competition, female body size and their distances affected the male waving rate in an additive manner, but their interactions did not show any effect. Further research can be conducted to investigate how breeding season and predation risk along with competition, female size and female distances affect the claw-waving display of male fiddler crabs.

Size‐dependent mating preference of the male fiddler crab Austruca perplexa

“…The results of this study reveal that large A. perplexa males showed a preference for large females by increasing their waving rates towards them. This finding supports the previous findings of Tina et al (2018a) and Tina (2019), who observed that large Austruca bengali and A. perplexa males waved more rapidly towards large females than towards small females. Not only male fiddler crabs but also males from several other animal species like isopods, zebra finch, spotted hyenas, garter snakes and poeciliid fish demonstrate a preference for large or highly fecund females over small or less fecund females (Arriaga & Schlupp, 2013;Jones, Monaghan, & Nager, 2001;Shine et al, 2003;Shuster, 1981;Szykman et al, 2001).…”

“…Male fiddler crabs adjust their waving rates based on several factors, including male–male competition, receiver female body size and distance to the females. Male fiddler crabs wave slowly when the intensity of competition is low, females are small, and when females come very near and show their mating choice (Reading & Backwell, ; Tina, ; Tina et al, ). However, though small males spend less time and energy on courting females, they spend more time on feeding (Callander et al, ; Tina et al, ), perhaps because greater investment in feeding increases their growth rate and future reproductive success (Hasaba et al, ; Muramatsu, ; Tejedo, ).…”

“…The results of producing higher waving rates towards large females and lower waving rates towards small females indicate the fiddler crab male's ability to distinguish between large and small females. A few previous studies (Reading & Backwell, 2007;Tina, 2019;Tina et al, 2018a) have also reported that male fiddler crabs are able to differentiate between females of different sizes and wave accordingly. Fiddler crabs are not only able to determine the body sizes of receiver females but also the distances between themselves and receiver females or neighbours (Backwell & Jennions, 2004;How, Hemmi, Zeil, & Peters, 2008;Reading & Backwell, 2007).…”

“…obs, by FW Tina). Usually, male A. perplexa build breeding burrows and wave their major claws repetitively towards wandering females to attract them to the burrows for mating (Backwell, Jennions, Wada, Murai, & Christy, 2006;Murai & Backwell, 2005;Tina, 2019). If a female selects a mate, she approaches and enters the male burrow.…”

“…A few studies have shown that male fiddler crabs are choosy and exhibit their mating preference for large females by increasing their waving rates (Reading & Backwell, ; Tina, ; Tina, Jaroensutasinee, & Jaroensutasinee, ). Since body size affects mating success and reproductive fitness, it may influence the crabs' costly claw‐waving displays.…”