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. (c) 2005 The Association for the Study or Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Contest duration in animals is often interpreted as being a consequence of mutual assessment of the difference in the competitors' resource-holding potential (RHP), allowing the inferior individual to avoid costly interactions it is likely to lose. Duration is thus predicted by the relative size of the competitors, and increases as the difference between them decreases. Alternatively, each individual may persist in accordance with thresholds determined by its own RHP, and weaker rivals retreat because they have lower thresholds. Contest duration depends on the RHP of the contestant that gives up first. Recent work suggests that even though duration is determined by the loser's size, this hypothesis also predicts a negative correlation between duration and the relative RHP of the contestants. However, it predicts (unlike the mutual assessment hypothesis) that contest duration should increase with the mean size of the contestants. We studied the determinants of fighting duration in the fiddler crab Uca mjoebergi. Fight duration increased with increasing size of the loser, and decreased, but to a lesser extent, with increasing size of the winner. Fights between size-matched individuals increased in duration with increasing mean size of the competitors. Neither the mutual assessment nor own-RHP-dependent persistence hypotheses can accurately explain the data. Instead, we present a modification of recent modelling work, and suggest that in U. mjoebergi individual cost thresholds may determine duration, but that larger opponents may inflict those costs more rapidly, consistent with the cumulative assessment game of animal conflict. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Do predator–prey 'waiting games' where prey hide from potential predators have inherently unstable evolutionary outcomes, making it impossible to generate quantitative predictions about hiding times? Fiddler crabs, Uca lactea perplexa, respond to potential predators by retreating into their burrows. Time inside the burrow during unprovoked retreats during normal activity provides a 'null model' to test whether sex, tidal cycle and body size affect hiding time from potential predators. Using experimentally created predator-like stimuli we found that males hid for significantly longer than females, and larger crabs of both sexes also hid for longer. This differs from burrow use during unprovoked retreats, suggesting hiding time varies depending on the potential risk of predation on re-emergence. If risk prior to hiding predicts risk on emergence, the closer the proximity of a predator-like stimulus when first encountered the longer crabs should hide. We confirmed this experimentally (stimuli at 0.5 versus 2.5 m). Finally, we tested whether males hide for longer when a predator-like stimulus approaches them directly rather than tangentially. None of three pairwise comparisons was statistically significant, but crabs hid less as the angle of approach became more tangential. These results suggest prey can use stimuli prior to hiding to predict predation risk on re-emergence, but studies on predators are required to test this claim. Finally, theoretical models must explain why hiding time has a lognormal distribution and low variance such that a predator can predict when most prey will re-emerge. For example, 95% of crabs re-emerged within 2.3 min of hiding. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Courting male fiddler crabs, Uca musica, sometimes build sand hoods at the entrances of their burrows to which they attract females for mating. On average, females visit 17 males in as many minutes before they choose a mate, and they preferentially visit males with hoods. When moving between burrows, fiddler crabs of both sexes sometimes approach and temporarily hide against objects on the surface. Hence, mate-searching females may approach hoods because they resemble (mimic) other objects that crabs approach to reduce their predation risk. We conducted two experiments to test this sensory trap hypothesis. First, we determined whether sexually receptive and nonreceptive female U.musica and nonreceptive female U.stenodactylus, a species that does not build structures, spontaneously approach hoods (replicas), stones, pieces of wood and shells. As predicted by the sensory trap hypothesis, both species, irrespective of sexual receptivity, approached these objects and neither preferred hoods. Second, to determine whether female U.musica show a preference for hoods when they search for a mate, we recorded the frequency with which females approached males with natural hoods, hood replicas, wood, stones and shells. Again as expected, females approached males with these different structures at the same rates. We conclude that hoods are effective mimics of objects that females approach for safety whether they are searching for a mate or not. Males benefit by using this sensory trap because hoods make them more attractive, and receptive females may benefit when they approach hoods because they reduce their mate-search risk. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

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.

Courting male fiddler crabs Uca musica sometimes build hoods at the entrances of their burrows to which females come for mating. Females differentially orient to burrows with hoods and thereby show a mate preference for hood builders. Here we describe how this mode of sexual selection may affect hood design and building. Larger males built generally larger but not higher hoods. Small males may build relatively high hoods so that they will be conspicuous to females of all sizes and construction or other costs may limit hood height. Most males built only one hood each biweekly reproductive cycle, typically on a day that many females chose mates, and they finished construction before females began mate searching. Both patterns fit predictions based on applying ideal free theory to the timing of sexual signaling. Sexual selection may favor more frequent hood building but the timing of hood building appears to be optimal.

Great-tailed grackles, Quiscalus mexicanus, prey on fiddler crabs, Uca beebei, either by running straight at them or by running past them then angling sharply back to strike. Grackles that used angled runs caught only males and were twice as successful as birds that used straight runs and caught equal numbers of males and females. Why do grackles that use angled runs catch only males? Males were not differentially available, nor did grackles prefer them to females in choice tests. Fewer crabs entered their burrows when we moved a model predator past them than when we moved it directly towards them and crabs allowed the model to get closer when it passed then returned to strike. Although crabs may take more risks when birds use angled runs, the sexes did not differ in their escape responses. Hence, differential risk taking cannot explain male-biased predation by birds using angled runs. We suggest that males, with their large claws and lighter colours, are more conspicuous than cryptic females. When a bird runs past then turns to dash back at a crab it may be able to keep track of a male much better than a female. Indeed, grackles missed all females they struck at using angled runs. Hence, males may be conspicuous and preferred prey to birds using angled runs. Males' enlarged claws, bright colours and other sexually selected traits may increase male predation rate in this context.

Animal communication theory predicts that low-frequency cheating should be common in generally honest signalling systems. However, perhaps because cheats are designed to go undetected, there are few examples of dishonest signals in natural populations. Here we present what we believe is the first example of a dishonest signal which is used commonly by males to attract mates and fight sexual rivals. After losing their large claw male fiddler crabs (Uca annulipes) grow a new one which has less mass, is a less effective weapon and costs less to use in signalling than an equivalent-length claw of the original form. Males with original claws do not differentially fight males with regenerated claws even though they are likely to win. Regenerated claws effectively bluff fighting ability and deter potential opponents before they fight. During mate searching, females do not discriminate against males with low-mass, regenerated claws, indicating that they are deceived as to the true costs males pay to produce sexual signals. Up to 44% of males in natural populations have regenerated claws, a level unanticipated by current signalling theory. The apparent rarity of cheating may be an artefact of the usual difficulty of detecting cheats and dishonesty may be quite common.

In the fiddler crab,Uca annulipes, males attract receptive females into their burrows by waving their greatly enlarged major claw. We have previously shown that males clustered around a female wave in close synchrony. Females may have a preference for leading signals and synchronised waving may arise as an epiphenomenon of competition between males to signal first. Indeed, the males in clusters that females approach and visit in their burrows are more likely to produce leading waves than are their neighbours. Here we document two other differences in the waving behaviour of visited males and their neighbours. First, visited males complete the downward component of the wave more rapidly than their neighbours. Second, the interval between the end of one wave and the start of the next is shorter for visited males. How can waving be synchronous if visited males wave faster than their neighbours? While only 9% (40/431) of waves by neighbours did not overlap those of the visited male, 22% (110/501) of visited male waves did not overlap the wave of a focal neighbour (111 visited male‐neighbour dyads). Hence, while overlapping waves are nearly synchronous, visited males produce additional, ‘nonoverlapping’ waves that result in a higher wave rate than that of their neighbours.

We investigated among-male variation in courtship waving in the fiddler crab Uca annulipes. Wave rate is positively correlated with both male carapace size and relative claw size (controlled for body size), and relative claw size is positively correlated with an index of body condition. An experimental reduction in the availability of food decreased male wave rate. These data suggest that some of the variation in wave rate among males is due to variation in male condition combined with energetic costs to waving (differential costs). However, we also found that the correlation between male size and wave rate decreased over the semilunar cycle. Later in the cycle, smaller males increase their wave rate relative to that of larger males. Previous work has shown that females are more likely to accept a smaller male as a mate later in the cycle. We suggest that smaller males invest disproportionately more in courtship later in the cycle because the potential benefits are greater due to their increased attractiveness to females (differential benefits). Alternative explanations for the observed temporal trend are also discussed.

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance ('surface mating') or leave their own burrow and sequentially enter and leave ('sample') courting males' burrows, before staying in one to mate underground ('burrow mating'). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.

We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the fighting success of male fiddler crabs (Uca annulipes). We removed males from their burrows and released them back into the colony (n=82). Released males tended to initiate encounters with burrow owners slightly smaller than themselves. Several general predictions of Sequential Assessment Game models of contest behaviour were supported: (1) residents won more encounters; (2) intruders were more likely to win when larger than residents. When body size (carapace width) was controlled for, intruders with relatively large claws for their body size were more likely to win contests; (3) the duration of encounters was related to the size difference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters won by the resident tended to be of shorter duration than those won by intruders (P=0·07); (6) on average, encounter duration was longer when the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing and the inter-locking of claws and did not unambiguously escalate from initial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by ‘all-out fights’ during physical encounters may also provide a plausible explanation for our results.

1. Two-choice phonotaxis experiments were used to investigate female responses to short-term variation in call timing in the African painted reed frog, Hyperolius marmoratus. The number of calls produced per stimulus in each choice test were equalised over either 10 or 20 seconds. 2. All alternative stimuli were tested against a regular stimulus with an invariant inter-call interval (ICI = duration between the onset of successive calls). There were three categories of alternative call timing; bouts of rapid calling (short ICI) where the period of silence between bouts was shorter than the bouts of calling; bouts of rapid calling where the period of silence between bouts was longer than the bout of calling; and irregular calling (variable ICI) without prolonged periods of silence. 3. The only stimuli females discriminated against were rapid bouts of calling with prolonged periods of silence. Females showed significant differences in the number of responses when presented with two stimuli that differed in call timing over as short a period as 10 seconds. 4. We also calculated variability in the ICI of 25 males in the field. There was a significant negative relationship between mean call rate (calls/min) and variability in the ICI. Faster callers showed lower variability in ICI. 5. The phonotaxis experiments did not show a female preference for regular versus irregular call timing. So female mate choice of males with higher call rates in the field is not due to a preferencc for males with less variability in ICI.

Female painted reed frogs were offered a choice between artificial advertisement calls differing in frequency. Repeatability of mate choice was assessed by multiple testing of females. When the difference between the stimuli was 400 Hz, almost all females, regardless of size, consistently chose the low frequency call. When the frequency difference between the calls was smaller (200 Hz), females as a group appeared to choose at random. However, individual females seemed to show repeatability of mate choice. There was also a relationship between female size and the number of times they chose the lower frequency stimuli. This suggests that the manner in which females respond to stimuli that differ in frequency may be size-dependent. Larger females may be more sensitive to variation in call frequency, and therefore more likely to express a mating preference for low frequency calls.

Numerous studies in sexual selection have been interpreted as showing that components of the signalling system involved in mating are under strong directional selection due to female preferences for elaborate traits. Conversely the recognition concept of species predicts strong stabilizing selection on the specific-mate recognition system. We document directional preferences in a population of the African painted reed frog, Hyperolius marmoratus, in two-choice phonotaxis experiments, utilizing synthesized calls. Females failed to respond consistently to population mean values of specific-mate recognition system signal components in choice experiments presenting mean and extreme value stimuli. Even the least-preferred extremes of coupled signal components were still effective in eliciting phonotactic responses. Our results provide no evidence for stabilizing selection within the tested range. However there is also no evidence an open-ended directional preference spanning the natural range of male stimuli. The claims of the recognition concept are examined, We believe that it is incorrect to argue whether or nor the recognition concept is 'correct'. Rather, it provides an explicit null hypothesis. Studies in sexual selection are concerned with instances in which the assumptions of the recognition model are violated (e.g. where males signal variation in the benefits that they provide males). Understanding this issue should reduce the amount of confusion in the literature, and clarify our objectives when it comes to investigating the selective forces manifest in signalling systems.

Acoustic signals are widely used as sexual displays to attract mates. The choice of display site can strongly influence the male call characteristics and their attractiveness to females. Males can improve the conspicuousness of their signals by increasing sound amplitude and expanding their broadcast area thereby reaching more potential mating partners and influencing female choice. Insects possess a rather limited degree of signal plasticity. To increase the intensity of their calls, insects have been known to manipulate and engineer their display locations. Mole crickets, for example, build burrows that are shaped like horns, designing the burrow such that its resonance closely matches that of their call frequency, thereby boosting sound amplitude. Tree crickets manipulate plant leaves, using them as baffles for optimal sound radiation. In this study, we show for the first time that an insect species can enhance its advertisement calls by using novel, anthropogenic environments as singing sites. During this study, the tropical cricket Anurogryllus muticus was frequently found singing beside the walls of houses, on concrete stairs or in storm drains. These locations significantly increased the sound amplitude of its calls, by an average of 13 and 7 dB SPL, respectively, as measured above and in front of the singing animals compared to the sound amplitude measured in their natural grassland habitat. To evaluate the effect of calling site choice on the male's life span, we conducted a 35-day population survey using the mark and recapture method. Our results revealed that those males that called in grassland habitat without occupying burrows had the shortest minimum life spans.

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