Adaptive droving behavior observed in the fiddler crab Uca vocans vocans

Droving is conspicuous in Uca vocans vocans in summer. The crabs burrowing on the upper habitat have a higher tendency to wander compared to the ones burrowing on the lower habitat. Most of the wandering crabs captured on the low tide levels are relatively large and male. Larger crabs and males prefer to burrow on the upper zones of U. vocans habitat, but the smaller ones and females prefer the lower habitat. The upper level of the U. vocans habitat has relatively low N-content compared to the water's edge. Therefore droving is advantageous in crabs that have burrows on the upper level. Female and smaller resident crabs have faster feeding motions than male and larger ones, and can satisfy their feeding demands more rapidly. Therefore, for males and larger crabs it is advantageous to move away from the burrow area and forage in areas of higher food content near the low tide level where the number of feeding motions increases.     

Parasitic castration in slipper limpets infested by the symbiotic crab Calyptraeotheres garthi

Two ill-explored hypotheses might explain host castration by parasitic pea crabs. The ‘energy drain’ hypothesis states that castration is caused by host-derived nutrient consumption of parasites that ultimately diminishes host-energy intake. The ‘steric interference’ hypothesis states that castration occurs when parasites physically inhibit host reproduction. This study evaluated whether Calyptraeotheres garthi, a pea crab from the southwestern Atlantic, is a parasitic castrator and explored whether the two hypotheses above explain castration in the limpet Crepidula cachimilla. None of three studied limpet species brooded embryos during the reproductive season when infested by mature female pea crabs. Also, limpets of C. cachimilla infested by C. garthi did not reproduce during a 90-day experimental period while crab-free limpets did spawn embryos during this period. Limpets resumed reproduction soon after pea crabs were experimentally removed from their brooding chamber. Thus, C. garthi does castrate limpets, and castration is reversible. Pea crabs ‘steal’ food from limpets, and infested limpets did not modify their feeding behavior to counteract nutrient loss. Thus, infested limpets are expected to ingest less food which provides partial support for the ‘energy drain’ hypothesis. However, the limpet’s body condition increased or was not affected by pea crabs during the breeding season which argues against the same hypothesis. Furthermore, that limpets promptly recovered reproductive activity once pea crabs were experimentally removed, that castration was not induced by the smallest pea crabs in the population (that fill only partially the brooding chamber), and that parasitized limpets did exhibit fully mature ovaries, support the ‘steric interference’ hypothesis explaining parasitic castration.     

Perceived predation risk and mate defense jointly alter the outcome of territorial fights

Virtually all animal conflicts occur over access to mates or resources that affect survival, the two key components of fitness. In this paper, we report that predation risk and mate defense jointly affect the outcomes of contests between male sand crabs (Scopimera globosa) for burrows in which crabs mate and take shelter from predators. We observed the contests under three different conditions: (1) the natural condition of low predation risk and without the presence of a female; (2) the first experiment in which we imposed upon only intruding males the perception of predation risk—by digging them from their burrows, capturing and handling them, and placing them into other males’ burrows—to increase the value of the burrows for the intruders as shelter, and (3) the second experiment in which we repeated this treatment but increased the resource value of the burrow to the resident by placing a female in his burrow. The difference in body size between contestants was the main determinant of victory in all analyses. However, perceived predation risk also partly affected the outcomes of the fights: The motivated intruders were likely to win even when they were a little smaller than the residents. In addition, defense of a female had a significant effect on the outcomes of fights: The motivated residents won more fights than the motivated intruders, indicating that these two treatments caused asymmetric increases of the resource value. This is the first report of two external factors simultaneously raising resource value, affecting motivation of contestants, and altering the outcome of fights.     

Some constraints on reproduction for male bushcrickets,Requena verticalis (Orthoptera : Tettigoniidae) diet,size and parasite load

Summary Reproduction for male bushcrickets is energetically expensive. Male Requena verticalis invest 70% of their daily energy reserves in calling to attract a female and providing her with a nutritious spermatophore. Males are thereby likely to be constrained in their mating frequency. I investigated constraints on reproduction imposed by body size and the levels of a protozoan gut parasite when males were fed diets that differed in their nutritional value. Males suffered a cost of reproduction in terms of an increasing interval between matings that was independent of diet and parasitic infection. After three successive matings, males decreased the magnitude of investment in courtship feeding when fed a diet poor in protein. Furthermore, these males suffered a reduction in the number of times they were capable of mating relative to males fed a diet rich in protein. Male size constrained mating frequency on both rich and poor diets; small males were able to mate less frequently than large males. There was an interaction between the effects of diet and parasitic infection on male mating frequency. Heavily infected males mated less frequently than uninfected individuals when fed the poor diet. However, males fed the rich diet were able to overcome the constraints imposed by parasitic infection. Reproductive constraints are discussed in relation to the costs of reproduction and their effects on courtship roles.     

Reproductive success of parasitized males in a marine reef fish

Parasitism is hypothesized to reduce reproductive success in heavily parasitized males because females may preferentially mate with less parasitized males (parasite-mediated sexual selection) or parasites may compromise male competitiveness. In marine systems, this hypothesis is largely unexplored. This paper provides the first confirmed record of a copepod ectoparasite (Caligus buechlerae Hewitt 1964) on the common triplefin (Forsterygion lapillum) and evaluates the hypothesis that males parasitized with C. buechlerae experience lower reproductive success than unparasitized males (as determined by the presence and area of eggs within male nests). We found that 38 % of males we surveyed were infected with at least one C. buechlerae, with a median of two individuals per infected male. About 32 % of males were defending eggs, with 62.5 % of those males infected with at least one parasite. Males of greater total length (TL) were both more likely to be infected and more likely to be defending eggs. However, when statistically accounting for the effects of TL, parasite infection had no effect on the probability of defending eggs, or the average surface area of eggs when present. Positive covariation in fish length, the presence of eggs and parasite infection observed here potentially suggest that the importance of parasitic infection on reproductive success may depend upon the strength of selection for larger male body size. Our study is one of the few studies to investigate the effects of ectoparasites on reproductive success in reef fish and also provides a quantitative measure of infection for a widespread species within New Zealand.     

Spatial and temporal patterns in the feeding behavior of a fiddler crab

Fiddler crabs consume the surficial microphytobenthos around their burrows during low tide. We studied the spatial and temporal feeding patterns in the species Uca uruguayensis by using sequences of digital pictures of feeding pellets accumulation. Data from 61 crabs, feeding without the interference of neighbors, were fitted to different models using Maximum Likelihood and Bayesian approaches. Initial feeding location was independent from the emergence location, and then, crabs continued holding a main feeding direction (clockwise or counterclockwise), suggesting a systematic mechanism that may avoid feeding over already processed sediment. Crabs used at least half of their potential feeding area, but these areas were heterogeneous. Both sexes developed similar feeding areas; however, females were faster and needed less time to feed than males, suggesting that males are time restricted. Our work also highlights the importance of incorporating other underlying mechanisms of the behavior of species into the study of feeding strategies.     

The assessment of female reproductive state during courtship and scramble competition in the fiddler crab, Uca paradussumieri

Male fiddler crabs, Uca paradussumieri, mate underground during a 4- to 7-day period each full and new moon. As soon as the tide recedes, males enter the burrows of females that will ovulate the following day ('pre-ovigerous' females). Males copulate with and guard these females until they ovulate. When interrupted by an intruding male, the first male to reach the female is usually able to defend her and successfully mate with her. In fiddler crabs, females mate multiply and there is last male sperm precedence. Before each semi-lunar mating period, male U. paradussumieri were more likely to court females with whom they would later mate than other nearby females with whom they did not mate. This suggests that males collect information on female reproductive state prior to the females becoming ovigerous. In this species, aggression was common between males that courted the same female. When previously courted females were approached by other males, the initial courter attempted to forcefully disrupt the courtship. This behavior may allow males the exclusive use of information on female reproductive condition. It also suggests a type of scramble competition between males over females. Furthermore, it indicates that males are able to locate receptive females prior to their becoming ovigerous. The shorter guarding period observed in this species, as compared with other fiddler crabs, is caused by females rejecting longer guarding periods. Male ability to assess female reproductive status may therefore be advantageous because it increases male mating success within a scramble type of competitive polygyny.     

Weapons or mating signals? Claw shape and mate choice in a fiddler crab

Males often possess traits, such as horns, claws, and tusks, which are used during male–male combat. Studies suggest that selection has fine tuned these weapons to improve their effectiveness and that the shape of these weapons provides cues for males to assess the strength of rivals. Similarly, females might also assess a male’s weaponry to determine his value as a mate. The largest weapon relative to body size is the major claw of male fiddler crabs (genus: Uca). Males use their claws both as a weapon and as a courtship signal, waving it to attract females. We used robotic crabs in two-choice experiments to test female mating preferences based on male claw shape in Uca mjoebergi. First, females did not prefer conspecific claws over any of three alternatively shaped stimuli matched for color and for the rate and pattern of waving. The alternative stimuli were two different heterospecific claws and a plain rectangular shape. Second, females significantly preferred the alternative stimuli when they were presented at a faster wave rate. We conclude that claw shape in U. mjoebergi has not evolved under sexual selection imposed by female mating preferences and is more likely to have evolved under selection for effectiveness during male–male competition.     

Female choice for parasite-free male satin bowerbirds and the evolution of bright male plumage

Summary Hamilton and Zuk proposed that bright male plumage may have evolved in males of polygynous species as a result of female preferences for males that are able to demonstrate their resistance to disease. They predicted an inverse correlation between female mating preferences and the level of parasitic infection of males. We found such a correlation between the level of infection by a common ectoparasite (Myrsidea ptilonorhynchi: Menoponidae) and mating success of male satin bowerbirds (Ptilonorhynchus violaceus). In addition, we tested and were able to confirm three other predictions derived from their model: that (1) older males had fewer parasites than their younger counterparts, (2) levels of individual parasitic infection are highly correlated between years, and (3) that individuals resighted in successive years are less parasitized than those that fail to return. These results support the bright male model, but they are also consistent with two other hypotheses that may explain plumage dimorphism based on the level of parasitic infection. The correlated infection model suggests that females choose males with few ectoparasites because of a correlation between the level of ectoparasitic infection and heritable resistance to internal infections. In the parasite avoidance model, females favor parasitefree males because it lowers their own prospects for parasitic infection. Our data did not show the predicted relationship between parasite numbers with plumage quality that is needed to support the bright male hypothesis, nor did it show the inverse correlation between male condition and parasite numbers that is predicted by both the bright male and correlated infection hypotheses. Our results are most consistent with the parasite avoidance hypothesis.     

Female choice over short and long distances: neighbour effects

Fiddler crabs live at high densities and mate-searching females encounter many males at varying distances. Who is the ideal neighbour for a male? There could be a trade-off if having neighbours that invest more in sexual signals increases the rate at which females initially move towards a focal male, but thereafter decrease the likelihood that he is chosen rather than his neighbour. We used robotic crabs to test whether female choice for focal males (identical claw size/courtship wave rate) varied depending on the relative investment in sexual signals of their two neighbours and the distance at which she first saw the males. The neighbours’ phenotype did not affect which of two focal males she initially approached from long-range (50 cm). When a female initially saw a trio of males at a close-range (20 cm), she preferentially chose the focal male over neighbours that invested less in sexual signals (smaller claw/slower wave rate), but did not show a preference for the focal male over neighbours that invested more in sexual signals (larger claw/faster wave rate). However, a female that started to approach a focal male with neighbours that invest more in sexual signals from 50 cm was significantly less likely to choose the focal male than when she first saw the trio at 20 cm. Our results suggest that the initial distance at which males are seen partly determines how neighbours’ sexual signals affect male mating success. In general, if larger males can retain smaller neighbours they might therefore increase their mating success.     

Mate competition in the velvet swimming crab Necora puber: effects of perceived resource value on male agonistic behaviour

Male velvet swimming crabs [Necora puber (L.)] were observed to engage in long and vigorous agonistic interactions to gain possession of a sexually receptive female. The role of agonistic behaviour in male mate competition in this species was examined by investigating the effect of the perceived presence of sexually receptive females on interactions between males. Exposing male crabs to water conditioned by sexually receptive females resulted in prolonged interactions, with a greater incidence of potentially injurious behaviour than interactions between control crabs, exposed only to sea water. Maleconditioned water also resulted in more offensive behaviour, but these interactions were of shorter duration and not significantly different from sea water controls. Agonistic superiority was strongly correlated with contestant relative size when males were exposed to male-conditioned water or sea water, but not when exposed to female-conditioned water. Overall, the results conformed with the general predictions of game theoretic models in relation to the influence of resource value on agonistic behaviour. Crabs were more persistent and probably incurred greater fitness costs in the perceived presence of a sexually receptive female, when interactions may have been resolved on the basis of factors more closely related to actual fighting ability than the relative body sizes of contestants.     

Feeding and reproductive behaviour and their effect on catchability of the spanner crab Ranina ranina

The behaviour of 16 adult (8 male and 8 female) spanner crabs (Ranina ranina), collected off southern Queensland, Australia, was monitored continuously in captivity by closed-circuit television for fifteen months from September 1982. Spanner crabs spent most of the time buried in the substrate, emerging mainly only when food became available. They remained emerged for twice as long on feeding days as on days without food. Females responded significantly faster than males to the presence of food. Response was slowest in October and November. There was no correlation between temperature and response time. The average feeding time was 2.0 min (SE=0.12), with no significant difference between males and females. Crabs without food were aggressive towards crabs with food, which sometimes led to fighting and wounding. These interactions also could result in food being transferred from one individual to another. When males interacted, food was transferred more often than when either females, or males and females interacted. Around moulting, male crabs did not feed for 52 d (SE=9.0) and females for 22 d (SE=2.2). This habit would reduce the frequency with which newly moulted crabs are caught in the baited tangle nets used by commercial fishermen. In mating interactions, copulation was always initiated by the males. Males dug up other crabs but, apparently unable to distinguish the sex of these individuals, attempted copulation with either sex. The majority of copulations occurred between midday and midnight and in the period August to December. The frequency of copulations with a female increased 10 d before she extruded eggs, after which it dropped to zero for the following 41 to 50 d. Eggs were carried for 39 to 44 d in the period September to November. The females remained emerged for long periods before extruding their eggs, but the period shortened immediately afterwards. This behaviour would lead to low catchability of ovigerous females. Because females respond more rapidly than males to a food stimulus, they may be more catchable in baited nets than are males. It is concluded that seasonal changes in the behaviour of spanner crabs could affect the number caught by baited tangle nets and may influence the sex ratio in catches.     

The effect of size and cheliped autotomy on sexual competition between males of the mud crab <Emphasis Type="Italic">Cyrtograpsus angulatus</Emphasis> Dana

Size advantage in male–male competition over mates, combined with male preference over large females, is a common feature that can drive to size assortative mating and, eventually, sexual selection. In crabs, appendage autotomy can affect assortative mating and opportunity for sexual selection by affecting size advantage in mating contests. In this work, we evaluate the effect of size and appendage autotomy in generating assortative mating in the mud crab Cyrtograpsus angulatus. Field observations of guarding pairs in two different populations show a positive correlation between carapace width of males and females in both the populations. In one of the populations, incidence of appendage autotomy was low and the variability in the size of reproductive males was lower than the variability in the size of randomly collected males (i.e. only larger males were successful in getting a female), whereas there was no differences in the other population (i.e. most male sizes were successful) where the incidence of appendage autotomy was very high, indicating that the importance of size is higher when the incidence of autotomy is low. In this context, experiments (in both populations) show that, in contests for a female, larger males outcompete smaller ones only when they had intact appendages. When males had missing chelipeds, winning or loosing against smaller males was random. This may lead to a decrease in the importance of male size in populations with high incidence of cheliped autotomy, affecting assortative mating and opportunity for selection and, thus, affecting selective pressures.     

Satin bowerbird parasites: a test of the bright male hypothesis

Summary The number of a common parasite (Cuclotogaster sp.) on male satin bowerbirds was related to male mating success in a test of Hamilton and Zuk's (1982) bright male hypothesis. The data do not show the expected inverse correlation between female mating preferences and the level of parasitic infection of males predicted by that model. Nearly all matings are accomplished by bower-holding males (Borgia 1985a), but the vast majority of these males were uninfected. There were large differences in mating success among the uninfected bower holders, but this could not be explained by between male differences in the level of parasitic infection. From this I conclude that levels of parasitic infection are not now an important direct cause of intermale variation in mating success. The results are, however, consistent with a hypothesis that a low level of infection is indicative of the overall healthy condition of a male. If this is true, it supports the hypothesis that the ability to hold a bower may be an indicator of male condition to females.     

Sexual signalling and viability in a wolf spider (Hygrolycosa rubrofasciata): measurements under laboratory and field conditions

This study examined the crucial prediction of the conditional-handicap theory, the relationship between male sexual trait size and male viability, in the wolf spider Hygrolycosa rubrofasciata. In this species, males court females by drumming dry leaves with their abdomen, and males with the highest drumming rate enjoy highest mating success. We determined male drumming rate, body mass, and mobility, which reflects mate-searching activity, in relation to male survival. Because it is often difficult to know how results obtained from laboratory studies reflect the natural world, particularly when the measured variable is survival, we repeated our study in both laboratory and field conditions. Males drumming at the highest rate survived better than males drumming at a lower rate in both laboratory and field conditions. These results are in accordance with the predictions of conditional-handicap models of sexual selection. Survival was independent of male body mass and there was no significant correlation between male drumming activity and body mass. However, large males moved further than smaller males, and males moving longer distances lost less mass than those moving shorter distances. These results suggest that, moving, and consequently mate-searching activity, may be a condition-dependent trait and that there may be a advantage for large males in mate searching. Received: 22 October 1998 / Received in revised form: 28 January 1999 / Accepted: 14 February 1999     

Epibiotic community of the horseshoe crab Tachypleus gigas

Horseshoe crabs act as moving substrata for simple to complex communities of small marine organisms. Amplexed adult pairs migrate for breeding once every 2 weeks from deep waters towards nearshore waters during highest high tide. Female horseshoe crabs bury themselves to the level of the lateral eyes to deposit eggs while the male crabs fertilize them. Subsequently eggs are buried by the female. Tachypleus gigas (Müller) is the most abundant horseshoe crab species above available along the Orissa coast (India). Adults reach terminal anecdysis once sexually mature and live with their carapace for 4 to 9 years. In spite of this, epibiosis is limited. In the current investigation, differences in the epibiotic community (diatoms and macro-epibionts) present on horseshoe crabs, according to gender, were evaluated, and the macro-epibiont population from different regions of the carapace was mapped. In general, female horseshoe crabs harbored fewer epibionts than the males. Among the diatoms, Navicula spp., Nitzschia spp. and Skeletonema sp. were dominant in both sexes. However, the abundance and diversity of diatoms was greater on the carapaces of male crabs. Among the macro-epibionts, the acorn barnacle (Balanus amphitrite Darwin) and encrusting bryozoan (Membranipora sp.) were the most dominant forms. Barnacles and bryozoans were greater in abundance in the “rough” zone (cardiopthalmic region and anterior region of the opisthosoma). Mapping of the macro-epibionts from different regions of the carapace revealed differential distribution in males and females. Such differentiated distribution of the macro-epibionts can be related to factors such as changing habitat by the horseshoe crabs during breeding, mechanical abrasion and surface availability during mating and nesting periods, requirements of epizootic larvae and surface properties of the carapace (wettability and roughness). In the case of females, mechanical abrasion and surface availability played an important role in the epibiotic community structure and distribution patterns. The surface wettability measurements indicated male carapace to be slightly more hydrophobic than the female carapace. Scanning electron microscopy revealed that the male carapace was comparatively rough compared to the smooth carapace of females. A comparison of surface properties of the carapace indicated that the male carapace is more conducive for epibiosis. Received: 23 August 1999 / Accepted: 25 January 2000     

No reason to sneak: why males of all sizes can breed in the hole-nesting blenny, Aidablennius sphinx

Most blennioid fishes show a resource-based, promiscuous mating system with alternative 'sneaking' mating tactics. The hole-nesting species, Aidablennius sphinx, however, appears to be an exception; small males did not mimic females, most had their own nest and not once in 20 h of spawning observations did a second male enter a nest. In this field study, we ask if sneaker tactics are constrained and what factors favour independent nesting by small males. Larger males received more eggs sooner and attracted more females than smaller males. Larger males may be preferred because they released more sperm per ejaculation and fanned their eggs more often. In the long-term, however, larger males did not spawn more often than smaller males since: (1) the nests of large males filled up with eggs sooner than the nests of small males; (2) large males refused females more often than small males; and (3) a highly biased ratio of females to preferred large males meant many females had no option but to spawn with small males. Thus, small males nest independently, despite potential for female mimicry tactics (multiple females spawned simultaneously) and simultaneous parasitic spawning (males exited the nest during spawning)     

Effect of acanthocephalan parasites on the behaviour and coloration of the mud crab Macrophthalmus hirtipes (Brachyura: Ocypodidae)

In the field, the numbers of cystacanths of the parasitic acanthocephalan Profilicollis spp. harboured by crabs are relatively high and correlate with carapace width. In a field experiment, the responses of crabs to the simulated approach of a bird predator (the parasite's definitive host) was not influenced by the number of acanthocephalans they harboured. Crabs that were exposed at the surface of the sediments during receding high tide, however, tended to harbour more parasites than nearby crabs hidden in burrows. An analysis of colour patterns on the carapace of crabs showed that infection levels did not influence carapace pigmentation, and thus did not affect the conspicuousness of a crab relative to the background environment. However, the likelihood of a male crab winning a ritualized fight against a conspecific in the field was associated with its infection level, but in a way that suggests that this finding is a consequence of pathology rather than an adaptation of the parasite to increase its transmission rate. Although only weak evidence was found indicating that Profilicollis manipulates the behaviour or colour of its host to its own benefit, the high infection levels observed suggest that the crab population acts as a major reservoir for larval stages of this parasite that are infective to birds.     

The effect of food availability on the semilunar courtship rhythm in the fiddler crab<Emphasis Type="Italic"> Uca lactea</Emphasis> (de Haan) (Brachyura: Ocypodidae)

Semilunar or lunar reproductive rhythms that follow tidal cycles are common in marine animals. For brachyuran crabs, an adaptive explanation for the synchronous release of larvae in phase with the tidal cycle is that females release larvae when their offspring are best able to escape predators. As a corollary to this hypothesis, the synchronous male reproductive cycle is selected to be in phase with female receptivity. As an alternative hypothesis, we propose that variation in food abundance influences the onset and intensity of the semilunar courtship cycle. We tested this hypothesis in male fiddler crabs ( Uca lactea) by experimentally manipulating food availability for 4 weeks. Food-supplemented males built more semidomes and waved for more days than did food-deprived males or untreated control males. Moreover, food-supplemented males began courtship earlier and the median courtship day advanced with an increase in food. Courtship intensity was not related to crab size. These results provide the first evidence in marine animals that changes in food abundance due to the tides, and hence in phase with the semilunar cycle, influence male reproductive rhythm.     

How do weaponless male fiddler crabs avoid aggression?

Mimicry of females enables weaker males in many species to avoid intrasexual aggression. In fiddler crabs (Uca annulipes), males use their major claw in aggressive interactions to acquire and defend a territory. Males that have autotomised their major claw will be disadvantaged in fighting, but might use their temporary resemblance to females to avoid costly aggressive encounters with other males. We investigated whether: (1) courting males mistake clawless male fiddler crabs for females; (2) clawless males are able to acquire, defend and retain territories as successfully as intact males; and (3) clawless males are more cautious than intact males. Clawless and intact males differed in burrow acquisition methods and fighting behaviour, but were equally successful at acquiring and retaining burrows. While courting males treated clawless males as female, we found no evidence that clawless males mimic the behaviour of females, or that they exploit the advantage of their mistaken identity. Clawless males further appear to avoid male aggression by altering their territorial strategies to minimise the potential for conflict.