Adaptations for feeding on rock surfaces and sandy sediment by the fiddler crabs (Brachyura: Ocypodidae) Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758)

Two species of fiddler crab, Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758), which belong to the subgenus Gelasimus, dwell on rocky shores and muddy–sandy tidal flats, respectively, in Phuket Is., Thailand. We investigated their feeding ecology in relation to the morphology of their feeding organs: minor food-handling chelipeds and maxillipeds. U. tetragononfed chiefly on rocks covered by filamentous green algae. U. vocansfed on the emerged sand and in shallow water along the shoreline and in pools. While feeding, both crabs made sand pellets beneath their mouthparts and discarded them, indicating that they divided the matter scooped up with their minor chelipeds into edible and inedible fractions by using the maxillipeds in the water passing through their buccal cavity. The morphology of maxillipeds hardly differed between the two species, which means that both species are flotation-feeders. The morphology of their minor chelipeds, however, differed: the tips of the dactyl and pollex were flat in U. tetragononand pointed in U. vocans.When the minor cheliped was closed, U. tetragononhad a hemispherical space in the distal one-fourth of the gape, which was closed by the framing keratin layers and a few setae of the dactyl and pollex. On the other hand, U. vocanshad an ellipsoidal space in the distal half of the gape. We consider these morphological characters to be adaptations to the different feeding substrates for retaining more food-laden sediment. We discuss the role of the setae on the minor chelipeds on the basis of the morphological differences between populations of U. tetragononin Phuket Is. and East Africa where the crab inhabits muddy–sandy tidal flats.     

Developing methods for quantifying the apparent abundance of fiddler crabs (Ocypodidae: Uca) in mangrove habitats

Counting the number of individuals emerging from burrows is the most practical method for estimating the apparent abundance of Australian Uca species living in mangrove habitats. Experiments were conducted to investigate the effect on counts of quadrat design, distance of observer, quadrat size, recovery time and observational technique. Significant differences in the apparent abundance of one species were found when the subjects were within 2 m of the observer, and when a conspicuous quadrat was used. The largest quadrat tested provided the least variability in counts but an intermediate size (0.56 m²) was more practical. Most Uca active within a 30-min period emerged during the first 10 min regardless of site, species, sex or season. There was a linear correlation between scanning and continuous observation indicating that the former method could be useful when sampling time was limited. Temporal changes in the apparent abundance of Uca suggest that long-term sampling and more detailed studies will be worthwhile.     

Male-like mudballing behavior of some female fiddler crabs (Uca tangeri)

At each low tide, male and female Uca tangeri remove mudballs from inside their burrows and place them on the surface. Previous studies have shown clear intersexual differences in mudball arrangements. However, we noticed that some females placed their mudballs in an arrangement similar to that of males. In this study, we investigated several factors that may have been responsible for this change in female mudballing behavior. We found no significant effect of the lunar cycle, female size and reproductive state, or burrow features. We briefly discuss the avoidance of sexual coercion or parasite modification of host behavior as possible factors. Our study shows that intersexual differences in mudballing behavior are more complex than previously thought. Received: October 18, 2000 / Accepted: May 7, 2001     

The response of a tropical estuarine gastropod,Cerithidea cingulata (Gmelin), to different types of substrata

The behavioural reaction of a tropical estuarine gastropod, Cerithidea cingulata (Gmelin), to different types of substrata was investigated by subjecting the snails to different mixtures of natural sediment. In addition the organic matter in the sediments was estimated, and an attempt has also been made to relate these results to the distribution of snails in the field.     

Substratum preference of the caddisfly Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae)

The position of Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae) larvae on the substratum surface is dependent on the current regime but varies with larval size. All size classes of larvae chose significantly different positions on the substratum under high versus low current velocities. All size classes preferred exposed surfaces under low current velocities. Small larvae preferred the upper surfaces of substrata under low current velocities and were physically displaced under high current velocities. Larger larvae also occurred on upper surfaces, but were more evenly dispersed over all surfaces than smaller larvae, and tended to aggregate on down-stream faces of rocks during high flow.     

Stereotypy and variation in the claw waving display of the fiddler crab <Emphasis Type="Italic">Uca tangeri</Emphasis>

We measured temporal and spatial components of the waving display in a Uca tangeri population to look for inter-individual differences in male waving structure that may convey information about individual identity. We found evidence that the spatial components of wave structure, especially “Maximum amplitude” are responsible for most of the between-male variation of the display. This variation could reflect differences in individuals’ condition and/or could be used by conspecifics to discriminate amongst familiar and unfamiliar individuals.     

Male courtship cycles in three species of tropical Ilyoplax crabs (Decapoda,Brachyura, Ocypodidae)

The courtship behaviour and cycles of male courtship activity and colouration of Ilyoplax orientalis, I. delsmani and I. gangetica were studied in the field in Malaysia and Thailand. Each species had a distinctive chela waving or beckoning display. Depending on species, the chelipeds, carapaces, or both of waving males blanched to white in contrast to the cryptic colour of nonwaving males and females. All three of these tropical Ilyoplax exhibited semilunar cycles in male waving activity at the colony level. It was confirmed for I. orientalis that individual males cycled each semilunar period between waving and non-waving phases and exhibited different behaviour toward females during these two behavioural phases.     

A phylogeny of Pacific fiddler crabs of the subgenus Minuca (Crustacea,Brachyura, Ocypodidae: Uca) with the description of a new species from a tropical gulf in Pacific Costa Rica

The phylogeny of all Pacific fiddler crab representatives of the subgenus Minuca Bott, 1954 (sensu Beinlich and von Hagen, 2006) is reconstructed. For the molecular analysis, Cox1 mitochondrial and 28S ribosomal nuclear DNA sequences were used. According to these data, same transisthmian sister species relationships are confirmed and a new species of the genus Uca Leach, 1814, Uca osa sp. n., is described from Golfo Dulce, a tropical gulf in Pacific Costa Rica. Morphological as well as molecular data confirm distinctness of this species compared with all other members of the subgenus Minuca, to which it belongs. Distinctive morphological traits are presented to distinguish Uca osa sp. n. from its congeners in the Eastern Pacific.     

Taxonomy and biogeography of the fiddler crabs (Ocypodidae: Genus Uca) of the Atlantic and Gulf coasts of eastern North America

Fifteen species of fiddler crabs are reported for eastern North America between Massachusetts and Quintana Roo, Mexico. Thirteen occur in the United States and 11 in Mexico, with eight in common to the two countries. Of 13 species in the Gulf of Mexico, five are endemic and a sixth is restricted largely to the peninsulas of Florida and Yucatan. The status of U. rapax in the northern Gulf remains to be resolved. Range limits of most species approximate one or the other of two sets of intersecting thermal and geological boundaries that subdivide the Gulf of Mexico along north-south and east-west axes. Species belonging to subgenus Minuca tend to replace one another at the thermally-controlled Carolinian-Caribbean marine biotic boundary across the Florida peninsula and northern Gulf. However, only U. minax of all the North American fiddler crabs exhibits the classical disjunct Carolinian distribution, and this appears basically to reflect the discontinuous distribution of temperate salt marshes that are the habitat of the species. Distributions of species belonging to subgenus Celuca adhere for the most part to the subdivision of the Gulf into western terrigenous and eastern carbonate sedimentary provinces. The northern transition occurs in the vicinity of Apalachee Bay and the southern at Laguna de Terminos. A third distributional pattern is shown by U. subcylindrica , a specialized endemic species of the hypersaline Laguna Madre system of the western Gulf. The level of endemism in the fiddler crabs is relatively high in comparison with that of other marine groups within the Gulf of Mexico. This may be a consequence of the adaptations of fiddler crabs as specialized deposit feeders to regional differences in climatic and edaphic characteristics of a marginally marine upper shore habitat. The distributional patterns of the endemics could prove useful in reconstructing palaeoecological events of evolutionary significance within the Gulf of Mexico.     

Population and reproductive biology of the fiddler crab Uca thayeri Rathbun, 1900 (Crustacea: Ocypodidae) in a tropical mangrove from Northeast Brazil

Population and reproductive biology of Uca thayeri Rathbun, 1900 were studied for the first time in a tropical mangrove. Absolute density, sex ratio, population structure, handedness, breeding season and fecundity were investigated. Seven transects were delimited in a mangrove area of the Pacoti River, Northeast of Brazil (3° 43′ 02″ S/38° 32′ 35″ W). On each transect, ten 0.25 m² squares were sampled on a monthly basis during low tide periods from September 2003 to August 2004. A total of 483 crabs were obtained, of which 250 were males, 219 non-ovigerous females, and 14 ovigerous females. The U. thayeri population presented bi-modal size frequency distribution, with males and non-ovigerous females not differing significantly size-wise. Ovigerous females were larger than males and non-ovigerous females. The overall sex ratio (1:1.07) did not differ significantly from the expected 1:1 proportion. The major cheliped was the right one in 50% of the males. The observed density was of 8.5 individuals/m², with the specimens being found mostly in shaded areas. Ovigerous females were found in 5 months of the year, coinciding with the rainy season, suggesting that the population of U. thayeri presents seasonal reproductive events. Juvenile crabs were more abundant during the dry period, while larger crabs were found mainly during the rainy period. The fecundity of the studied population was much smaller than that of subtropical populations of this species. The regression analysis shows that the number of eggs increases linearly with the increase of carapace width.     

Studies on the behaviour and substratum preference in juveniles of the marine prawn,Metapenaeus monoceros (Fabricius)

Circadian rhythmicity in the behaviour of the marine prawn, Metapenaeus monoceros (Fab) and its substratum preference has been observed under laboratory conditions. In the morning at 9. a.m. 80% prawns remain buried and in the afternoon at 3 p.m. 60% burrowing was observed. A contrasting situation was observed in the night i.e. 17% burrowing at 9 p.m. and 30% burrowing at 3 a.m. was registered. In the second set of experiments juveniles were subjected to four types of substrata viz. mud, black fine sand, white coarse sand and stones. It was noted that M. monoceros showed more affinity towards the mud and less preference to other substrata. The obtained results are discussed to provide clues for prawn fishing.This work was supported by I.C.A.R., New Delhi through a project on Reprod. Endocr. Edible prawns.     

Response of fiddler crabs (Uca tangeri) to video playback in the field

The fiddler crab Uca tangeri communicates using a visual waving display and a vibratory drumming signal, both thought to function in mate attraction. Using video playback techniques, images of an empty mudflat, a waving male, a threatening male, and a wandering female were presented to male subjects. All stimuli elicited similar levels of low-intensity waving, but significantly more high-intensity waves were elicited by the female and threatening male stimuli than the mudflat stimulus or the waving male stimulus. This concurs with other research that the waving display is used at a higher intensity to attract females. The threatening male stimulus failed to elicit the same response as an actual threatening male and we discuss the likely reasons for this. The subjects also spent a significantly greater proportion of time drumming during the male waving stimulus than during the female stimulus, suggesting that drumming functions in male-male competition as well as female attraction. Received: 18 October 1999 / Received in revised form: 25 November 1999 / Accepted: 10 December 1999     

Periphyton density and shading in relation to tidal depth and fiddler crab activity in intertidal seagrass beds of the Banc d'Arguin (Mauritania)

Periphyton development was studied on microscopic glass slides and leaves of Zostera noltii Hornem. in an intertidal area in the Banc d'Arguin (Mauritania). The effects of shading, tidal depth and grazing activities by the fiddler crab Uca tangeri Eydoux were evaluated. For all experiments, periphyton ash content was high (52–93%) and ash-free dry weight ranged between 0.10–0.63 mg cm^–2. Slides accumulated more periphyton than leaves.Artificial shading (62–99%) for 13 days had no effect on periphyton densities on leaves. Increased tidal depth resulted in higher ash-free dry weight on slides, but in lower ash-free dry weight on leaves. Significant variation along the coastline also existed. The effect of fiddler crabs was studied using exclosures. Presence of fiddler crabs reduced periphyton density on slides, whereas light transmittance was increased. On leaves, no significant fiddler crab effect was found. This difference between leaves and slides was probably caused by a storm at the day before the end of the experiment, and by the higher periphyton density on slides as compared with leaves. As visual inspection during the experiment showed clear differences in appearance of leaves inside and outside the exclosures, the storm probably sloughed off mainly the older leaves, i.e. those on which the differences in periphyton cover were the highest.It is hypothesized that periphyton accumulation is higher with increased tidal depth, whereas fiddler crab grazing pressure also increases in this direction. The result is a decreased periphyton density with increased tidal depth.The presently found light extinction coefficients (mean 0.8 m^–1) and periphyton light attenuance (up to 25%) in Banc d'Arguin are not likely to affect seagrass leaf growth.     

Localization of substance P-like,leucine-enkephalin-like,methionine-enkephalin-like,and FMRFamide-like immunoreactivity in the eyestalk of the fiddler crab,Uca pugilator

Summary The occurrence and distribution of substance P (SP)-like, methionine-(Met)- and leucine-(Leu)-enkephalinlike, and FMRFamide-like immunoreactivities were determined in the neuroendocrine complex of the eyestalk of the fiddler crab, Uca pugilator, by immunocytochemistry. SP-like immunoreactivity was found in the optic peduncle, sinus gland, medulla externa, medulla interna, lamina ganglionaris, and retinular cells. Met-enkephalin-like and Leuenkephalin-like immunoreactivity was observed in most of the retinular cells, optic peduncle, sinus gland, medulla terminalis, and lamina ganglionaris. However, Met-enkephalin-like, but no Leu-enkephalin-like, immunoreactivity was seen in the medulla terminalis X-organ. FMRFamide-like immunoreactivity could be seen in all parts of the eyestalk except in the sinus gland, lamina ganglionaris, and retinular cells. FMRF-amide-like activity was especially strong in the three chiasmatic regions connecting the optic ganglia. The possibility that these four peptides may function as neuroregulators in the fiddler crab is discussed.This investigation was supported in part by Grant No. PCM-8300064 from the National Science Foundation to MF and Biomedical Research Support Grant No. 2 SO7RRO5373 SUB from the University of Kansas Medical Center to LLV     

A comparison of alternative methods for estimating population density of the fiddler crab Uca annulipes at Saco Mangrove, Inhaca Island (Mozambique)

Visual counts of surface-active crabs both by binocular and burrow counting methods have been used in many studies to estimate population density. However, their reliability has not yet been assessed comparatively. Three methods for estimating the abundance of fiddler crabs Uca annulipes in a mangrove forest (Inhaca Island, Mozambique) were compared from three different sub-areas: two sub-areas inundated only during spring tides and one sub-area inundated in both spring and neap tides. Burrow, binocular and direct (excavation) counting methods were performed by plotting ten 0.25 m² quadrats in each sub-area over the four moon phases. Overall densities (per 0.25 m²) differed according to method, sub-area and lunar phase. Burrow count overestimated crab density by up to 20%, while binocular count underestimated density by up to 41%. Correlation coefficient estimated for both counting methods showed that burrow count gives better density estimates than binocular count (0.91 and 0.56, respectively). Sex ratios were also investigated within the three sub-areas and at the moon phases. Males are dominant throughout the studied period except during new moon and first quarter, indicating that when the number of gravid females is low, sex ratio bias for binocular count is minimal.     

Female's preference for oviposition site and larval performance in the water-lily beetle,Galerucella nymphaeae (Coleoptera: Chrysomelidae)

Water-lily beetles prefer younger rather than older water-lily leaves as oviposition sites. By the time of hatching, however, young leaves have aged consieerably. Larval performance of the water-lily beetle was measured on different types of leaves of the yellow water-lily and compared with oviposition preference of females. The leaf types used in the experiments were categorized as (i) young, (ii) natal (medium-aged) and (iii) old. The natal leaves were the ones on which larvae from a particular egg-batch had hatched. There were two sets of experiments. First, larvae were raised from eggs to pupae on young and on old leaves. Second, the growth of the 1st-instar larvae was measured on young, natal, and old leaves. The development time from egg to pupa did not differ between young and old leaves, but larvae growing on young leaves attained a higher pupal weight. In the second experiment the 1st-instar larvae grew fastest on their natal leaves, but there was also variation in the growth rate of progeny from different egg-batches. Larval growth on young and old leaves did not differ significantly. Larvae tried to emigrate much less from natal than other types of leaves. Females tended to lay eggs on leaves where larval growth was fastest. It seems that medium-aged leaves are best for larval growth, but the leaf characteristics responsible for this remain unresolved.     

Host preference of the facultative hyperparasitoidTetrastichus howardi (Hym.: Eulophidae)

Tetrastichus howardi (Olliff) preferred the lepidopteran hosts,Chilo partellus (Swinhoe) (Pyralidae) andHelicoverpa armigera (Hübner) (Noctuidae) to their parasitoids,Xanthopimpla stemmator (Thunberg) (Hymenoptera: Ichneumonidae) andPalexorista laxa (Curran) (Diptera: Tachinidae). IfT. howardi had previously experienced parasitising a certain host, its preference for that host increased, but not significantly. When reared on a certain host, the preference for that host increased.T. howardi showed no preference to any particular age of its hosts.T. howardi was able to discriminate between parasitised and unparasitised hosts, initially preferring parasitised hosts, but two days later preferring unparasitised hosts.     

Prey-related odor preference of the predatory mites Typhlodromalus manihoti and Typhlodromalus aripo (Acari: Phytoseiidae)

Typhlodromalus manihoti and Typhlodromalus aripo are exotic predators of the cassava green mite Mononychellus tanajoa in Africa. In an earlier paper, we showed that the two predators were attracted to odors from M. tanajoa-infested cassava leaves. In addition to the key prey species, M. tanajoa, two alternative prey mite species, Oligonychus ossypii and Tetranychus urticae also occur in the cassava agroecosystem. Here, we used a Y-tube olfactometer to determine the attraction of the predators to odors from O. gossypii- or T. urticae-infested cassava leaves and their prey-related odor preference. T. aripo but not T. manihoti was slightly attracted to odors from O. gossypii-infested leaves. Both predator species showed a stronger response to odors from cassava leaves infested by M. tanajoa over odors from cassava leaves infested by O. gossypii. Neither predator species was attracted to odors from T. urticae-infested leaves and the predators preferred the odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. When O. gossypii was present together with M. tanajoa on the same leaves or on different sets of leaves offered together as an odor source the two predators were attracted. In contrast, after mixing non-attractive odors from T. urticae-infested leaves with attractive odors from M. tanajoa-infested leaves, neither T. aripo nor T. manihoti was attracted. Ecological advantages and disadvantages of the predators’ behavior and possible implications for biological control of M. tanajoa are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

PO2 and pH changes in the retina of the crab Ocypode ryderi: evidence for aerobic glycolysis

Summary The isolated retina of the terrestrial crab Ocypode ryderi exhibits a pronounced lactate production in spite of being supplied with sufficient O₂ (140 torr). To determine whether this lactate production is caused by hypoxic areas in the tissue or represents aerobic glycolysis, oxygen partial pressure and pH measurements with two-channel glass microelectrodes and additional biochemical analyses were carried out on this organ. Distinct profiles were obtained for O₂ partial pressure and pH inside the tissue. At a depth of 200 m different O₂ partial pressure levels could be observed depending on the O₂ partial pressure in the medium (85 torr at 280 torr and 36 torr at 130 torr, respectively). The extracellular pH displays a similar pattern; it reaches a stable value of 7.15 at 100 m inside the tissue. Lowering bath O₂ partial pressure from 280 torr to about 15 torr (hypoxia) induces a decrease of the O₂ partial pressure in the tissue with different time-courses for different tissue depths. However, hypoxia did not change the extracellular pH. Addition of antimycin A (100 mol · 1^-1) to the medium abolishes the O₂ partial pressure gradient and the delayed recovery of the tissue O₂ partial pressure after hypoxia. These results and the biochemical data suggest that in the crab retina a high glycolytic activity occurs simultaneously with oxydative carbohydrate degradation (aerobic glycolysis).Abbreviations AEC Atkinson energy charge - DC bioelectric potential - dw dry weight - HEPES N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] - PCO₂ carbon dioxide partial pressure - PO₂ oxygen partial pressure - P _tO₂ oxygen partial pressure inside the tissue - P _mO₂ oxygen partial pressure in the medium - pH_t pH inside the tissue - pH_m pH in the superfusion medium