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  • Author or Editor: Fahmida Wazed Tina x
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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.

In: Animal Biology

Abstract

Females often choose mates based on their courtship signals. Males may signal their heritable genetic quality, defended resources, or parental care efforts; however, the reasons why females choose males based on their signals are often not clear. Here, we show that, in the fiddler crab Austruca perplexa, male signals (major-claw waving rates) were correlated with important characteristics of their defended resources (width and depth of breeding burrows). By using the male signals, females may be able to roughly predict the burrow quality and decide whether to enter and check the burrow characteristics. The signals are predicted to be honest because the female’s final decision is based on burrow quality. Since females can reject males if their burrow quality is insufficient for breeding, the courtship efforts of deceptive males will be dismissed. The honesty of the signals is beneficial for both sexes and thus easily evolved in their signalling system.

In: Behaviour

Abstract

This study determines the winning status of regenerated-clawed males (regenerated males) in contests with original-clawed males (original males) in Austruca perplexa (H. Milne Edwards, 1852), and how they deal with original opponents. We observed that the numbers of regenerated and original winners were not different. The regenerated contestants, who were either burrow owners, or larger than their opponents, or avoided escalated contests (claw-interlock/fling), had the same chance of winning in comparison to their original opponents, and had a higher winning chance than regenerated contestants, who were either intruders, or smaller than their opponents, or did engage in escalated contests. Regenerated intruders tended to challenge opposite-handed opponents for avoiding claw-interlock (the risk of injury is high during claw-interlock), because claw-interlock is mechanically difficult between opposite-handed contestants. This study shows that regenerated contestants, who are either residents, or larger than opponents, or avoid fighting escalation, are able to compensate for the detrimental effect of regenerated claws during contests.

In: Crustaceana

We investigated whether male Uca vocans (Linnaeus, 1758) have behaviourally or morphologically compensated for having only one feeding claw while females have two. We predicted that (1) females will have a higher feeding rate/crab per min, (2) males will have a higher feeding rate/claw per min, (3) males will have larger feeding claws (dactyl length and width) than comparable-sized females, and (4) smaller crabs will feed faster than larger ones and thereby satisfy their feeding demand more rapidly than larger crabs. Our results supported all four predictions. Males compensated for having one feeding claw by feeding faster/claw per min with larger claws.

In: Crustaceana

We observed the outcomes of fights of smaller contestants against larger opponents during male-male contests in Uca annulipes (H. Milne Edwards, 1837), Uca bengali Crane, 1975, and Uca rosea (Tweedie, 1937). Smaller contestants won 30, 31 and 37% of the contests in U. annulipes, U. bengali and U. rosea, respectively, regardless of body size disadvantages. Smaller contestants won when body size asymmetries were lesser, but took a longer time to win the contests, while with greater size-asymmetries, smaller ones lost the contests in a short time. In U. bengali and U. rosea, most of the smaller winners were residents (burrow owners), but not in U. annulipes. This study shows that longer fighting duration or high motivation enables the smaller contestants, especially the residents, to overcome their inferior fighting ability and win contests against larger opponents.

In: Crustaceana

We video-recorded and examined the burrow building behaviour of small and large males and females of Uca annulipes (H. Milne Edwards, 1837). Males took a longer time than females, and larger crabs took a longer time than smaller ones, to build burrows. Higher numbers of mudballs were excavated from inside the burrows during the build of the burrows by males than by females, and by larger crabs than by smaller ones. Crab carapace width was positively correlated with the time required to build burrows, and with the number of mudballs excavated from inside the burrows during the build of these burrows. We observed that 82% of the females placed the mudballs near their burrow entrance, whereas 85% of the males placed the mudballs far from their burrow entrance. After building the burrows, 71% of the females went inside the burrow and plugged the burrow entrance, and 90% of the males foraged for food.

In: Crustaceana

We tested the effects of body size, resident status, handedness, and claw originality on Uca rosea (Tweedie, 1937) male fights. We observed 67 pairs of combats between residents and intruders, recorded fighting duration and winner identity (resident/intruder, larger/smaller), identified handedness (right/left claw) and claw types (original/regenerated claw), and measured carapace width and major claw length. Larger/smaller males were determined based on major claw length instead of carapace width. Results showed that (1) body size and resident status jointly and (2) body size, resident status, handedness and claw types together, affected fighting success. Residents won more combats than intruders regardless of handedness. Original clawed residents won more combats than regenerated clawed intruders. Fighting duration was longer in same claw type (original-original and regenerated-regenerated) combats than in different claw type combats. Carapace width was more strongly correlated with original claw length than with regenerated claw length.

In: Crustaceana

We investigated how male Uca rosea (Tweedie, 1937) have behaviourally or morphologically compensated for having only one functional feeding claw while females have two. We found that male U. rosea used four compensatory mechanisms: (1) larger feeding claws (dactyl length and width), (2) higher feeding rate/claw per min, (3) higher numbers of pinches/feeding claw per min than similar sized females, and (4) higher numbers of pinches/feeding claw lift than females of similar feeding rate/feeding claw per min. This study is the first one to demonstrate that taking higher numbers of pinches/feeding claw per min than comparable sized females, and taking higher numbers of pinches/feeding claw lift than females of similar feeding rate/claw per min are used as additional compensatory mechanisms for male fiddler crabs to compensate for having only one feeding claw.

In: Crustaceana

We investigated the effects of body size, resident status, and handedness on fighting success of male Uca bengali Crane, 1975. We predicted that residents as well as larger males would win more combats, heteroclawed combats would be more common than homoclawed combats, only larger males in the population would engage in combats, and fighting duration would be negatively correlated with body size asymmetry of fighting pairs. We observed 70 pairs of naturally engaged combats between residents and intruders, sampled 80 non-fighting males, and measured their body size, claw size, and handedness. We found that only larger males in the population were involved in combats. Resident status and body size together showed effects on fighting success, but handedness had no effect on fighting behaviour. Fighting duration was negatively correlated with body size asymmetry of fighting pairs.

In: Crustaceana

Abstract

We studied the effects of claw regeneration on male waving rate and burrow characteristics (i.e., important mate choice criteria) by examining the waving rates and burrow characteristics (diameter, total and horizontal lengths, depth, volume, maximum width, entry and burrow angles, and presence and location of chambers) of large-sized original-clawed males (OCMs) and regenerated-clawed males (RCMs) of Austruca perplexa (H. Milne Edwards, 1852). Female burrows were also examined. The results showed that female burrows were smaller than male burrows, with no chamber and, thus, female burrows are not used for breeding; however, 80% of RCM burrows, and 65% of OCM burrows, had chambers. Other characteristics were not different between RCM and OCM burrows, except for maximum width, which was larger in RCM burrows. The waving rates of OCMs and RCMs were not different. Our results indicate that claw regeneration do not have detrimental effects on male waving rate and burrow characteristics.

In: Crustaceana