Display Specificity and Reproductive Isolation in the Fiddler Crabs,Uca panacea and U. pugilator

The factors responsible for reproductive isolation between two sibling species of fiddler crabs (Uca pugilator and U. panacea) were studied under both laboratory and field conditions. ♂♂ showed species differences in their visual and acoustical displays. These differences were exaggerated in the overlap zone, where U. pugilator showed character displacement of its acoustic signals. ♀♀ of U. pugilator confined with ♂♂ of U. panacea produced fewer clutches of young. Occasionally, forced matings took place in the laboratory, resulting in hybrids suffering greater mortality through development. The data indicate that both premating (behavioral) as well as postmating (higher larval mortality) barriers act to prevent interbreeding.     

Behavior of Four Species of Fiddler Crabs,Genus Uca,in Southeast Sulawesi,Indonesia

We studied the behaviors of four species of sympatric fiddler crabs on Kaledupa Island, Indonesia. Species differences in activity level, grooming, burrowing and feeding were related to their habitat and food. Uca chlorophthalmus, living in muddy mangrove areas, were inactive and spent most of the time feeding in place. Females fed 50% faster than males and spent more time feeding. U. vocans was the dominant species at the beach in silty sand and was very active. Its feeding rate was about twice that of the former species, females fed more rapidly than males, and many crabs of both sexes fed in droves at the water’s edge during ebb tides. During ebb tides, they spent most of their time feeding, while at flood tide they engaged in a greater variety of activities, including burrow maintenance. They frequently walked while feeding and interacted aggressively. U. tetragonon lived in a pebbly band along one edge of the beach, by a quay. Their feeding rate was comparable in both sexes and slower than that of U. vocans; they fed largely on filamentous algae growing on the quay, which provides better food, and fed faster during flood tide than ebb tide. They spent more time in waving and other sex-related activities, and were seldom aggressive, except during the week of the full moon. Burrowing activities included placing excavated mud balls some distance away from their burrows and re-arranging them. U. dussumieri inhabited the other end of the beach in muddier substrate. They did not have sex differences in feeding rates and their rate of scooping food into their mouths was slow, but feeding claws made multiple pinches of the substrate, thus accumulating more material in each clawful of food.     

Waving Display in Females of Uca polita and of other Australian Fiddler Crabs

Since 1979 it is known that, in Australian species of Uca, female waving exists in addition to usual male display. The present paper deals mainly with female waving in U. polita studied in Darwin (North Australia). A few remarks on U. dampieri, U. vomeris, U. seismella and U. hirsutimanus are added. The species mentioned are members of two species groups or subgenera, which characterizes female waving as an ancestral (plesiomorph) trait. Frame by frame analysis of film sequences (open air shots) indicate homology of movements in the two sexes of U. polita. As in males, waving of females can be combined with locomotion on radial paths starting from the burrow entrance and the display is performed in series with a corresponding number of gestures. Unlike males, waving females mostly use both their chelipeds and tend to show shorter durations with regard to many of the waving parameters chosen. However, significant differences refer only to a limited number of parameters. The biological context of female waving was gathered from films and field observations. High intensity waving is released by conspecifics approaching from far (wanderers without burrows) and from the neighbourhood. Typically, only females and small males elicit high intensity display in a resident female. Waving normally stops in presence of larger males, especially of the male living in a resident breeding unit with the female in question. In spite of this, a pure agonistic (defensive) character of female waving is unlikely. Advertising of breeding condition seems to play a role similar to that in males. The few displaying females that exist in a given colony (about 2.5% in U. polita) show signs of special sexual excitement: brightening of carapace colours and sometimes spontaneous performance of waving, i.e. display immediately after emergence from the burrow in absence of any conspecific.     

Variation in the Boldness of Courting Sand Fiddler Crabs (Uca pugilator)

Individuals can express boldness in their readiness to resume courtship signaling following a perceived threat. The degree of boldness that is selectively favored depends on the magnitude of costs and benefits that may vary across time and space. We examined within‐ and between‐individual variation in the boldness of courting male sand fiddler crabs, Uca pugilator, across an entire breeding season at a South Carolina (USA) salt marsh where courtship is restricted to supratidal embankments. Boldness was assessed by the time to re‐emergence and the number of re‐emergences of males who were purposely startled into their breeding burrows once every 3 min for a total of five times. The two measures of boldness were significantly positively correlated. Courting males are on average bolder when their density is high and when tidal conditions correspond to peaks in the number of females moving over the embankment surface. Time to re‐emergence increases with successive startles although some males consistently re‐emerge faster than others. Large males are not bolder than small males. When male density is high, nearest neighbors frequently re‐emerge at the same time, suggesting that males cue on the responses of other nearby males, perhaps by assessing substrate vibration. This may reduce the chance of losing a potential mate to a local competitor.     

The Role of Rhythmic Systems in the Adaptation of Fiddler Crabs to the Intertidal Zone

Fiddler crabs inhabiting the intertidal zone must adapt theiractivity to both the day-night cycle and the cycle of the tides.The tidal cycle imposes on the animals a rhythmic alternationbetween terrestrial and marine periods of existence. At thesame time the crabs are influenced by the day-night cycle, sincethey exhibit specific diurnal and nocturnal habits. Moreover,the interaction of daily and tidal rhythms may give rise tosemi-monthly variations in activity. It is now well established that persistent daily and tidal rhythmsin physiological processes underlie rhythmic variations in thebehavior of crabs in the field. The present paper reviews morerecent studies, which have compared the persistent rhythms incrabs from different tidal and non-tidal regions. Rhythmic patternsrecorded in the laboratory are found to be closely correlatedwith tidal conditions in the native habitat of the crabs. Ithas also been shown that the persistent pattern can be modifiedby transplanting crabs to the intertidal zone of another coastwhere they are exposed to tidal cycles which differ in formfrom those in the original habitat.     

Visual and Acoustical Signalling during Courtship by Fiddler Crabs (Genus Uca)

Male fiddler crabs (Genus Uca) employ both visual and acousticalsignals to attract females for mating. In U. pugilator and severalother American species, the males attract females during theday first by waving, then by producing sounds just within theirburrows. At night, the males produce sounds at low rates, butwhen touched by a female, they increase their rate of soundproduction. In the European species, U. tangeri, many elements of courtshipare similar to those in U. pugilator, but two types of soundsare produced. One of these, the short drumwhirl, appears tosubstitute for waving when the male is temporarily obscuredfrom the female during his diurnal courtship activities. Thelong drumwhirl is used under different circumstances. The acoustical responses of a male to a female influence thecourtship behavior of other males in the area. When sounds fromstimulated males are played back to test males during the day,their lates of waving increase. At night, the playbacks elicitincreases in rates of sound production. The influence of tidal oscillations, temperature, and lightcycles on the behavior of males is discussed. Courtship activities of aquatic crabs are compared to thoseof terrestrial Brachyura. In aquatic forms, courtship may beabsent or, if present, does not involve elaborate signallingby the male. Chemical or visual cues at close range are themost important stimuli. In several genera of terrestrial crabs,visual signalling for prolonged periods is common, and soundsare often emitted by males to "call" females from their burrowsto the surface for mating. Some of the factors that may accountfor differences in courtship activities in aquatic and terrestrialspecies are discussed.     

Comparative Burrow Architectures of Resident Fiddler Crabs (Ocypodidae) in Indian Sundarban Mangroves to Assess Their Suitability as Bioturbating Agents

Excavation of burrows by fiddler crabs (genus Uca) is an important component in mangrove ecosystem functioning. This bioturbation activity can be measured by analysing the burrow architecture of these crabs. The aim of the present study is to describe and evaluate inter specific differences in the burrow morphologies of four species of fiddler crabs (Uca rosea, Uca triangularis, Uca dussumieri and Uca vocans) using polyester resin casts of the burrows. For each of the species, sex and carapace width (CW; mm) were determined for all the individuals. Three burrow morphological characters viz. burrow diameter (BD; mm), total burrow depth (TBD; mm) and burrow volume (BV; cm³) were considered during the study. Density of each species throughout the year was also assessed. For all the species BD and BV were higher in case of males compared to the females and they showed significant positive correlation with the CW of the burrow inhabitants. The amount of sediment excavated by each crab was evaluated in terms of BV. Among all the studied species, U. rosea was established as the most potent bioturbative candidate in the studied mangrove due to their greater density and moderate ability to excavate burrow.     

Reproducing on Time When Temperature Varies: Shifts in the Timing of Courtship by Fiddler Crabs

Many species reproduce when conditions are most favorable for the survival of young. Numerous intertidal fish and invertebrates release eggs or larvae during semilunar, large amplitude, nocturnal tides when these early life stages are best able to escape predation by fish that feed near the shore during the day. Remarkably, some species, including the fiddler crabs Uca terpsichores and Uca deichmanni, maintain this timing throughout the year as temperature, and thus the rate of embryonic development, vary. The mechanisms that allow such precision in the timing of the production of young are poorly known. A preliminary study suggested that when temperature decreases, U. terpsichores mate earlier in the tidal amplitude cycle such that larvae are released at the appropriate time. We tested this idea by studying the timing of courtship in U. terpsichores and U. deichmanni as temperature varied annually during two years, at 5 locations that differed in the temperature of the sediment where females incubate their eggs. Uca terpsichores courted earlier at locations where sediment temperature declined seasonally but not where sediment temperature remained elevated throughout the year. In contrast, clear shifts in courtship timing were not observed for U. deichmanni despite variation in sediment temperature. We discuss other mechanisms by which this species may maintain reproductive timing. These two species are likely to be affected differently by changes in the frequency and intensity of cold periods that are expected to accompany climate change.     

Determination of Key Environmental Factors Responsible for Distribution Patterns of Fiddler Crabs in a Tropical Mangrove Ecosystem

In tropical regions, different species of fiddler crabs coexist on the mangrove floor, which sometimes makes it difficult to define species-specific habitat by visual inspection. The aim of this study is to find key environmental parameters which affect the distribution of fiddler crabs and to determine the habitats in which each species was most abundant. Crabs were collected from 19 sites within the mudflats of Sepang-Lukut mangrove forest. Temperature, porewater salinity, organic matter, water content, carbon and nitrogen content, porosity, chlorophyll content, pH, redox potential, sediment texture and heavy metals were determined in each 1 m² quadrate. Pearson correlation indicated that all sediment properties except pH and redox potential were correlated with sediment grain size. Canonical correspondence analysis (CCA) indicated that Uca paradussumieri was negatively correlated with salinity and redox potential. Sand dwelling species, Uca perplexa and Uca annulipes, were highly dependent on the abundance of 250 μm and 150 μm grain size particles in the sediment. Canonical Discriminative Analysis (CDA) indicated that variation in sediment grain size best explained where each crab species was most abundant. Moreover, U. paradussumieri commonly occupies muddy substrates of low shore, while U. forcipata lives under the shade of mangrove trees. U. annulipes and U. perplexa with the high number of spoon tipped setae on their second maxiliped are specialized to feed on the sandy sediments. U. rosea and U. triangularis are more common on muddy sediment with high sediment density. In conclusion, sediment grain size that influences most sediment properties acts as a main factor responsible for sediment heterogeneity. In this paper, the correlation between fiddler crab species and environmental parameters, as well as the interaction between sediment characteristics, was explained in order to define the important environmental factors in fiddler crab distributions.     

The Reproductive Strategy of Hermit Crabs in Temperate Waters

Russian Journal of Marine Biology - This review examines the main characteristics of the reproductive strategy in hermit crabs: the sex ratio, the age (size) of onset of maturity, fecundity, and...     

Contextual Cross-Referencing of Species Names for Fiddler Crabs (Genus Uca): An Experiment in Cyber-Taxonomy

Cyber-taxonomy of name usage has focused primarily on producing authoritative lists of names or cross-linking names and data across disparate databases. A feature missing from much of this work is the recording and analysis of the context in which a name was used—context which can be critical for understanding not only what name an author used, but to which currently recognized species they actually refer. An experiment on recording contextual information associated with name usage was conducted for the fiddler crabs (genus Uca). Data from approximately one quarter of all publications that mention fiddler crabs, including 95% of those published prior to 1924 and 67% of those published prior to 1976, have currently been recorded in a database. Approaches and difficulties in recording and analyzing the context of name use are discussed. These results are not meant to be a full solution, rather to highlight problems which have not been previously investigated and may act as a springboard for broader approaches and discussion. Some data on the accessibility of the literature, including in particular electronic forms of publication, are also presented. The resulting data has been integrated for general browsing into the website http://www.fiddlercrab.info; the raw data and code used to construct the website is available at https://github.com/msrosenberg/fiddlercrab.info.     

Some Thermal Requirements of Fiddler Crabs of the Temperate and Tropical Zones and Their Influence on Geographic Distribution

Thermal stress is one environmental parameter that has greatlyinfluenced the migration of crustaceans from the sea to land.Since a greater number of species of terrestrial crabs are foundin the tropics than in the temperate zone, comparative studiesof the influence of temperature on latitudinally separated populationswere undertaken. Two tropical species, U. rapax and U. thayeri,may occur as far north as St. Augustine, Florida, or, followinga severe winter, may be rare north of Cape Kennedy. The lethaleffect of the low temperatures recorded during one severe winter(1957–58) is supported by laboratory studies in whichLD₅₀, deaths occurred in 4.5 days at 10°C for U. rapax acclimatedto 18°C. The experiment demonstrates that U. rapax cannotacclimate to and survive low temperatures. This contrasts markedlywith the situation in semi-terrestrial crabs of the temperatezone, which are able to acclimate to cold. The distribution of Uca around Cape Cod Bay correlates wellwith the coastal hydrographic thermal gradient and supportsPassano's suggestion that temperatures below 20° may belimiting as they inhibit proecdysis in U. pugnax. Such an inhibitionis found experimentally in U. pugilator and in the tropicalspecies, U. rapax. It is hypothesized that a shift in the thermodynamicsof the processes underlying molting has not occurred in Ucaof the temperate zone. The paucity of semi-terrestrial Brachyurain the temperate zone may be due to the failure of many speciesto evolve capacity-adaptations to carry out all requisite lifeprocesses at temperatures below 20°, or the resistance-adaptationsnecessary to survive the low temperatures of winter.     

Larval Settlement and the Reproductive Phenology of Sympathric Hermit Crabs in Temperate Waters

Russian Journal of Marine Biology - The problem of the coexistence of closely related species of Paguroidea (Decapoda: Anomura) and the main mechanisms of structuring the communities of these...     

粤东海域口虾蛄遗传多样性

采用线粒体COI基因序列对粤东汕尾和深圳2个海域口虾蛄(Oratosquilla oratoria)的遗传多样性进行了分析.研究表明,所分析的口虾蛄mtDNA CO I基因(592 by)共检测到21个变异位点,占总位点的3.55%.转换和颠换位点数分别为18和3个,碱基替换的饱和性分析表明,口虾蛄CO I基因碱基替换...     

Constraint on Reproductive Output in Brachyuran Crabs: Pinnotherids Test the Rule

Brood weight and number of eggs per brood are primarily determinedby female body size in brachyuran crabs. Brood weight exhibitsan isometric relationship spanning more than four orders ofmagnitude in body weight among 33 non-pinnotherid species, withbrood size being constrained to about 10% of female body weightby the space available for yolk accumulation within the cephalothorax.In contrast, two pinnotherids (Pinnotheres ostreum, Fabiasubquadrata)have relative brood sizes which are 66% and 97%, respectively,of body weight. The allometric constraint is circumvented inthese extraordinarily large brood sizes by two pinnotherid featureswhich allow more space for yolk accumulation. Unlike other brachyurans,their ovaries extend out of the cephalothorax into the abdomen,and calcification of their exoskeleton is greatly reduced, potentiallyallowing distension of the body. As in crabs, pinnotherid eggsize is highly variable among species, which tends to increasethe variance among species in fecundity per brood, making pinnotheridfecundities not extraordinary. Thenumber of broods producedper year in these two species is limited by short reproductiveseasons, which tends to bring their annual reproductive outputin line with other brachyurans. The trade-offs among reproductivevariables in pinnotherids is adaptive for the small body sizeand parasitic niche of these species.     

海南3种鹭越冬行为的比较

于2004年1～2月选择了3种鹭类作为研究对象,采用瞬时扫描观察的方法,就其越冬行为差异进行了比较。3种鹭昼间主要行为有所不同,苍鹭(Ardea cinerea)主要以站立和休息为主,白鹭(Egretta garzetta)主要以取食和休息为主,而大白鹭(E.alba)主要以站立和取食为主。本文对3种鹭的取食行为进行了比较分析,3种鹭的取食行为比例从高到低依次为白鹭(40%～60%)、大白鹭(20%～40%)和苍鹭(0.1%以下)。最后,对3种鹭不同的取食对策进行了讨论。     

Visual Displays in Brachyuran Crabs: Field and Laboratory Studies

Study of the visual displays of more than 30 species of crabsallows some generalizations on the Brachyrhyncha. The displaysfall into two groups, the Lateral Merus and the Chela Forward.Each group contains three major subtypes of display, which originatedas discrete signals of intensity. Several special ritualizationsof the Lateral Merus have evolved in certain genera. The LateralMerus seems to be the primitive type of display in the Brachyuraand still exists in most crabs. It is speculated that the ChelaForward arose from a specialized courtship display but has beenadopted for general agonistic use in some genera.     

绞股蓝雌雄种群觅源行为和繁殖对策比较

绞股蓝（Ｇｙｎｏｓｔｅｍｍａ ｐｅｎｔａｐｈｙｌｌｕｍ）雌雄异株,种群性比偏雄。作者利用比较生态学方法,从行为生态学角度探讨相同生境中绞股蓝雌雄种群的觅源行为和繁殖对策,得到如下初步结果和结论：（１）绞股蓝雄性种群的主枝生物量比显著大于雌性种群,这意味着雄性种群的营养繁殖投资显著增加,而两性种群在其它结构中的生物量分配无显著差异;（２）雌性种群的叶面积比和单位叶面积比雄性种群显著增加,这与两性种群     

Orientation Behavior with and Without Visual Cues in Newly Hatched and Adult Praying Mantis

In the praying mantis, vision plays a major role even in newly hatched nymphs, which have compound eyes that are not yet fully developed. This study examines how this factor affects the visual orientation behavior of freely mobile Mantis religiosa. Mantises from three age groups (nymphs newly hatched to 2 h old, three-day-old nymphs, and three- to four-month-old female and male adults) were placed in a completely unprotected open area, either with or without visual cues in the surroundings. As a visual cue, five vertical rods with high-, medium- or low-luminance contrast, having a vertical extension of 45° and overall horizontal extension of 40°, were presented at a distance of 300 mm, simulating a group of plant stems with differing contrasts. The mantis search behavior, probability of reaction to the visual cues, distance at which the first target-related reaction occurred, and target approach behavior were investigated. It was found that the search behavior differed in the different age groups. With high-contrast visual cues, newly hatched nymphs performed similarly to adults, but this was not the case for medium- and low-contrast visual cues. Visual performance was greatly improved 3 days after hatching, presumably due to the complete hardening of the cuticle. Nevertheless, despite differences in visual acuity, it was found that even newly hatched nymphs used visual orientation mechanisms similar to those of adult mantises, including fixation, scanning and peering.     

Short-range Homing in Fiddler Crabs (Ocypodidae, Genus Uca): A Homing Mechanism not Based on Local Visual Landmarks

This field study investigated the spatial strategies and homing ability of two East African fiddler crabs, Uca lactea annulipes and Uca vocans hesperiae, using various experimental procedures. A clear-cut spatial segregation between the two species was observed, with U. l. annulipes occupying areas even a few centimetres above U. v. hesperiae . Females of both species were extremely faithful to their holes while the males exhibited behavioural differences. U. l. annulipes males were quite faithful to their holes; in contrast, U. v. hesperiae males, during a single low tide, visited several holes which they did not defend. Two displacement experiments were conducted in order to identify the stimuli that fiddler crabs use in their homing. In the 'dislocation experiment', the crabs were moved (by hand) 1 or 2 m away from their refuge and released. None of these crabs returned to its burrow and, moreover, the initial directions they followed were not homeward orientated. In the 'translation experiment', the crabs were passively translated while actively feeding. When the crabs attempted to go 'home' after the translation, they darted along a straight path that led them to points that would have corresponded to their homes if the translation had not taken place. After this first response crabs then commenced searching strategies that led half of them home. Short-range homing seems to depend strongly on information actively gathered during the outward journey, other than local visual landmarks.