Receiver female body size and distances affect the claw-waving rate of signaller males in fiddler crabs (Brachyura, Ocypodidae)

Abstract

We tested for the first time how Austruca bengali Crane, 1975 signaller males adjusted their waving rates based on receiver female body sizes and their distances. We video recorded the waving display of 46 males (9–12 mm carapace width) for 30 s, and counted their waving rate. Receiver females were categorised as small (8–10 mm carapace width) and large (>10 mm). Distances between males and females were categorised as short (⩽12 cm) and long (>12 cm) distances. Our results indicate that males are able to measure distances and female sizes, and adjust their waving display by actively reducing waving rate (1) towards small females, as usually small females have lower fecundity compared to large ones and (2) towards females at very close distance because at this point, the females would make their mating decision, and thus males start to lead/hit the females towards their burrow rather than waving vigorously.

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).…”

“…The mean carapace width (±SE) of males and females was 13.74 ± 0.42 mm and 12.68 ± 0.33 mm, respectively. In this study, males and females were categorized as large-or small-sized based on mean sizes in accordance with the previous studies (see Tina, Jaroensutasinee, & Jaroensutasinee, 2016b;Tina et al, 2018a); males more than 14 mm and females more than 13 mm in carapace width were considered large. By categorizing the size classes, we can detect the behavioural difference between large and small males towards large-and smallsized females more clearly.…”

“…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.…”