Claw Waving Research Articles

Claws and claw waving attract both sexes in the dotillid crab Ilyoplax pusilla

During the breeding season, courting males of many ocypodoids (famously, fiddler crabs) perform claw-waving displays, in which they rhythmically raise, often extend, and lower their chelipeds when they are near their burrows. This conspicuous display sometimes attracts wandering (burrow-less) sexually receptive females to males’ burrows where the crabs mate. However, since most of the claw waving is not directed to a particular receiver, the display may also attract males and unreceptive females that are searching for new burrows, not mates. We conducted two types of choice experiment using claw models to examine the preferences of wandering males and females in the dotillid crab Ilyoplax pusilla: (1) between burrows with and without static claw models, (2) between waving and static claw models set up 10 cm apart (for only males). More crabs of both sexes ran to the burrows with claw models, and more males preferred the waving claw model. Like the structures some courting male fiddler crabs build, male claws and the claw waving of I. pusilla may reveal to unintended receivers the locations of burrows that these crabs can use temporarily as refuges.

Claw Waving for Sex: An Inquiry-Based Lab to Teach Sexual Dimorphism and Behavior in Fiddler Crabs.

We designed a three-week guided inquiry-based lab for non-biology majors revolving around the ideas of sexual dimorphism, selection, and behavior, using fiddler crabs (Uca pugilator) as a model. Specifically, students worked in small teams to design experiments, collect data, and present findings in a short oral presentation. Students gained exposure to scientific skills, including designing an ethogram, understanding the purpose of inter-observer reliability, graphing, statistics, and oral communication.

Choosing a mate in a high predation environment: Female preference in the fiddler crab Uca terpsichores.

The interplay between a receiver's sensory system and a sender's courtship signals is fundamental to the operation of sexual selection. Male courtship signals that match a female receiver's preexisting perceptual biases can be favored yet the message they communicate is not always clear. Do they simply beacon the male's location or also indicate his quality? We explored this question in a species of fiddler crab Uca terpsichores that courts under elevated predation risk and that mates and breeds underground in the safety of males' burrows. Sexually receptive females leave their own burrows and are thereby exposed to avian predators as they sequentially approach several courting males before they choose one. Males court by waving their single greatly enlarge claw and sometimes by building a sand hood next to their burrow entrance. Hoods are attractive because they elicit a risk‐reducing orientation behavior in females, and it has been suggested that claw waving may also serve primarily to orient the female to the male. If the wave communicates male quality, then females should discriminate mates on the basis of variation in elements of the wave, as has been shown for other fiddler crabs. Alternatively, variation in elements of the claw waving display may have little effect on the display's utility as a beacon of the location of the male and his burrow. We filmed courting males and females under natural conditions as females responded to claw waving and chose mates. Analysis of the fine‐scale courtship elements between the males that females rejected and those they chose revealed no differences. When predation risk during courtship is high, males' courtship displays may serve primarily to guide females to safe mating and breeding sites and not as indicators of male quality apart from their roles as beacons.

Courtship tactics by male Ilyoplax pusilla (Brachyura, Dotillidae)

Mating in the dotillid crab Ilyoplax pusilla occurs after the female enters the male’s burrow in the tidal flat. Males use two tactics to cause females to enter their burrows for mating: the male either directs claw waving to the female (courting-wave display), to which the females responds by following the male to his burrow, or the male runs rapidly away from, then back toward, his burrow (dash-out-back display), which startles the female into his burrow. Males more often used the courting-wave than the dash-out-back display, but mating success did not differ between the two tactics. Male use of either tactic was influenced by date, female density and male size; the courting-wave display was used by larger males, later in the breeding period, and under higher female density.

Performance capacity of fiddler crab males with regenerated versus original claws and success by claw type in territorial contests

Laboratory measures of whole-animal performance are expected to correlate with morphological indices and success in activities that contribute to fitness. Males of the sand fiddler crab, Uca pugilator Bosc (Brachyura Ocipodidae), possess a single enlarged claw that is used in ritualized contests for possession of breeding burrows. Contests may escalate to pinching actions, suggesting claw closing force as a relevant performance indicator. When a claw is lost, it is regenerated. Within a western Atlantic salt marsh, regenerated claws are less massive and operate at reduced mechanical efficiency relative to original claws, suggesting a less powerful weapon. In the laboratory, the closing force of regenerated claws is less than that of original claws of the same length or mass. Perhaps as a consequence, males with regenerated claws are unlikely to use pinching behaviors and usually lose contests against males with original claws. Males with regenerated claws are less likely to possess breeding burrows that females find acceptable and tend to possess burrows during non-peek breeding times, when the frequency of contests is low. As crabs grow, claw power is sacrificed for greater length. This may facilitate advertising burrow ownership to passing females through claw waving displays. The reduced mass of regenerated claws may permit males to resume effective waving sooner than if they regenerated a stout claw, but at the cost of competency in contests.

Does the environmental context of a signalling male influence his attractiveness?

How sexually selected male signals and female sensory systems have evolved so that females can continue to detect and discriminate between potential mates in the face of environmental noise and changes in signaller density has been well studied for acoustic signals. Far less is known about visual signals. We examined the influence of the local signalling environment on male signal attractiveness in the fiddler crab Uca mjoebergi. We used custom-built robotic crabs in two-stimulus mate choice experiments. Females were presented with two identical signals produced in two different signalling environments (simple and complex). The conspicuousness/attractiveness of male claw waving was unaffected by the local environment (physical or social). Male U. mjoebergi appear to produce a signal that is highly conspicuous across a wide range of naturally occurring signalling environments and females seem to have a sensory system that is capable of coping with high levels of environmental noise.

More signalling for earlier mating: conspicuous male claw waving in the fiddler crab, Uca perplexa

The male courtship display of the fiddler crab Uca perplexa is a conspicuous claw waving that is directed at females to attract them to their burrows for mating. Like most other fiddler crabs, this species has an approximately biweekly reproductive cycle with mating spread over about 10 days. However, most mating takes place in the 3 days immediately preceding new and full moons. We examined the relation between the time males spend waving to females and the time they subsequently spend underground in their burrow, guarding their mates until they ovulate and then fertilizing their eggs. Early in the mating period, males courted females for about 3–5 s before the female entered their burrows, and males guarded these females for 3–5 days. During the 3 days of peak mating activity, courting time decreased significantly to about 2 s and guarding time decreased to about 1 day. This pattern cannot be explained by females preferring extended waving periods, decreased female choosiness towards the end of the mating period or variation in male waving over the mating period. We conclude that males of this species modulate their investment in courtship according to changing levels of female responsiveness to courtship.

Changes in blood glucose and lactate levels of male fiddler crabs: effects of aggression and claw waving

Determining the costs of a given behaviour is critical in the framework of game theory. We estimated the energy costs of male aggression and claw waving in a fiddler crab Uca lactea perplexa, by examining blood glucose and lactate levels under natural conditions. Male fiddler crabs have a single enlarged claw used in courtship waving and fighting. The greatest variation in glucose level was found at the beginning of the activity period, implying variation in ‘male quality’. Blood lactate level increased significantly from the early to the middle part of the crabs' activity period. The associated temporal change in behaviour indicated that the increase in lactate was due to vigorous waving. This was confirmed by an enclosure experiment using opaque and transparent fences: the waving frequency was not affected by enclosures with transparent fences but was strikingly lower in cages with opaque fences in which the males could not see and wave at females. The lactate level was significantly higher in transparent fence treatments than in opaque fence treatments. Since the transparent fence prevented aggressive contact between males, the higher lactate concentration in control males than in males enclosed with the transparent fence indicated that aggressive interactions were also costly. In contrast to some vocal displays in songbirds, our results showed that the waving display of the fiddler crab, as well as agonistic behaviour, is energetically costly.

Adapt or Die

variety of forms, including symmetric conflicts, pitting closely matched competitors that fight for dominance but seek to avoid deadly clashes; and far more lethal asymmetric conflicts involving unequal opponents, in which the weaker combatant resorts to unanticipated, often insidious tactics. The Cold War was a symmetric conflict in which the two rivals had enough weaponry to guarantee that a hot war would result in mutual destruction. Superpower tensions played out in what biologists call dominance displays. In evolutionary terms, the annual May Day parade of missiles in Moscow's Red Square and former U.S. President Richard Nixon's madman strategywhen he put the United States on secret nuclear alert in 1969 to rattle the Soviets-were no different than the ritualistic claw waving between competing male fiddler crabs. Terroris n two ks such as al Qaeda represent a d cidedly asymmetric threat. Like a virus, al Qaeda is a infect ous organism, capable of lying dormant for long periods of time. It then hijacks the critical machinry of its victims to weaken their evolutionary fitness. And just as the treatment for viruses is more complex than the remedy for blunt trauma, combating al Qaeda r ires a more subtle approach than the chest puffing generally used to meet a symmetric challenge. In 1987, biologist Geerat Vermeij published a provo ative treatise titled Evolution and Escalation: An Ec logical History of Life. The book focuses on the fossil history of snails and crabs, but it makes fiv observations about evolutionary strategies that can also serve as a blueprint for improving U.S. homeland security. Form good relationships. An organism can survive, an thrive, in th presence of an enemy by forming symbiotic relationships that can take a multitude of forms. These relationships can link aggressive, highly toxic sp cies (clown fish living in anemone tentacles, for example), or they can link small and large organisms (such as bioluminescent bacteria living within the organs of deep-sea fish). Sometimes the relationships are transient, sometimes permanent. Raphael Sagarin is a postdoctoral rese rch ellow at the University of California, Los Angeles.

Sexual selection for structure building by courting male fiddler crabs: an experimental study of behavioral mechanisms

Males of the fiddler crab Uca musica sometimes build sand hoods at the entrances of their burrows, to which they attract females for mating with claw waving and other displays. Females significantly more often approached males with hoods than males without hoods, but once at a burrow, they were just as likely to stay and mate whether the male had a hood or not. To determine how hoods affect male attractiveness, we conducted experiments that controlled for other differences in courtship behavior between builders and nonbuilders; we removed hood builders’ hoods and we added hood models to nonbuilders’ burrows. We then measured the attractiveness of hood builders and nonbuilders with and without hoods. Neither manipulation measurably affected male courtship behavior. The presence of a hood did not increase male–female encounter rates, suggesting that hoods do not attract distant females into a male’s courtship range. However, once a male courted a female, she was significantly more likely to approach if he had a real or model hood. We obtained direct evidence that females orient to hoods by replacing them with hood models positioned about 3 cm away from the openings to males’ burrows. Females approached the models, not the courting males, about 27% of the time. We conclude that hood building is sexually selected because courted females differentially approach hoods, not because hoods attract distant females and not because females prefer to mate with hood builders.

Testing function of fiddler crab claw waving by manipulating social context

Many territorial advertisement signals are thought to be dual-function signals, directed to both rival male and receptive female conspecifics. However, few studies have tested this assumption by examining whether in fact both sexes are likely to elicit signaling behavior from territorial males. In this study, I experimentally manipulated the social context of male sand fiddler crabs (Uca pugilator) to investigate the effect of different audiences on the performance of the claw-waving display, a territorial signal that is often presumed to be directed to both males and females. To test whether males perform this signal to both audiences, I measured the frequency of waving behavior by focal males when housed in field enclosures alone, with only males, with only females, or with both males and females. Focal males waved at a low frequency when alone, and the presence of males had no effect on their level of waving. However, in the presence of females, focal males showed a significantly higher level of waving, whether or not males were also present. In addition, there was no association between fighting and waving behavior. This experiment provides evidence that from the perspective of the signaling male, the claw-waving display of U. pugilator is not a dual-function signal but rather is primarily directed to receptive females.

VIDEO PLAYBACK EXPERIMENTS TESTING THE FUNCTION OF CLAW WAVING IN THE SAND FIDDLER CRAB

Like many territory advertisement signals, the claw waving display of fiddler crabs (genus Uca) is commonly thought to have the dual function of simultaneously repelling males and attracting females. I have found, however, that male sand fiddler crabs (U. pugilator) wave significantly more in the presence of females than males, suggesting that their waves are primarily directed to females. Here I use laboratory video playback experiments to ask whether male and female U. pugilator are both responsive to the display. Males and females were presented with video of an example of either a waving or a feeding male conspecific, or no video, and their behavior was measured in seven behavioral categories that were then collapsed into three principal components. Analysis of variance of females' principal component scores revealed significant differences in their behavior in the presence of waving male video compared with feeding male video or no video, demonstrating that females attend to the display. Male behavior, however, was not significantly different between the three treatments, which is inconsistent with the hypothesis that claw waving serves to repel or threaten other males. These results, together with my recent work on male signaling behavior, suggests that the claw waving display of U. pugilator is a signal primarily directed to females and attended to by females, and thus is not an example of a dual function signal.

Claw size, waving display and female choice in the European fiddler crab, Uca tangeri

Fiddler crabs present an accentuated sexual dimorphism wherein males have one of the chelipeds greatly enlarged, compared to the other chela or to the two small feeding chelipeds of females. Available observational data in the literature suggest a dual function for this trait both as an armament to fight other males and as an ornament to court females by claw waving. We experimentally tested female Uca tangeri for possible preferences based on the size and elevation (waving posture) of the male large cheliped and on male handedness. Dead, resin-coated males were used as test objects. Females significantly more often approached males with larger claws and males with raised claws. Male handedness had no effect on female responses. These results are consistent with a female mating preference based on claw size and position and hence with the evolution of claw size and the waving display as a result of sexual selection by female choice.

Fiddler Crabs Use the Visual Horizon to Distinguish Predators from Conspecifics: A Review of the Evidence

Male fiddler crabs,Uca pugilator(Crustacea: Decapoda), respond to conspecifics by claw waving, and to predators by freezing or escape. In field experiments it was found that this distinction was not made on the basis of angular size and speed, nor was shape important. The remaining possibilities were either the absolute size of the stimulus, determined from angular size and distance, or the position of the stimulus relative to the horizon. To distinguish between these, a crab was placed in a glass dish, and moved black stimuli on a white background, at a distance of 22 cm. Stimuli below the crab's horizon hardly ever evoked escape. However, identical stimuli partially or wholly above the crab's horizon produced escape responses whose frequency varied with the angular size of the stimulus. Halving the distance of the stimulus showed that it was angular and not absolute size that determines escape frequency; and experiments with a tilted horizon showed that it is the position of the stimulus relative to the eye equator that is important, rather than the geographical horizon itself. It has been concluded that crabs categorize stimuli as dangerous or otherwise by their position relative to the crabs’ visual horizon.

Mate acceptance and guarding by male fiddler crabs Uca tetragonon (Herbst)

The fiddler crab, Uca tetragonon (Herbst) mates both on the surface near female-defended burrows and underground in male-defended burrows. In underground mating, which requires relatively high male investment, males attract both non-ovigerous and ovigerous females into their burrows by claw waving. Males aggressively expel some females soon after they enter their burrows and others after pair formation, but before females spawn. Finally males guard some females in their burrows until they spawn, which presumably ensures paternity. Males do not select mates of a particular body size, but they do differentially accept females with late-stage eggs, those about to release larvae and spawn another clutch. Except at the beginning of the reproductive season, few ripe non-ovigerous females are available because females spawn successively and only in moderate synchrony. By differentially accepting late stage ovigerous females, males may increase their fertilization rates because they minimize the time they spend guarding each of their mates to ensure their paternity. A male-biased operational sex ratio and a high last male advantage in sperm competition are two conditions that may have favored male choice based on female guarding time in this species.