Uca Annulipes Research Articles

A Comparative Study of Some Mouthpart Adaptations of Uca Annulipes (H. Milne Edwards, 1837) and U. Vocans (Linnaeus, 1758) (Brachyura, Ocypodidae) in Relation to their Habitats

The density of spoon-tipped setae (ST setae) along the inner edge of the merus of the left second maxilliped of two Singapore species of fiddler crabs, Uca annulipes and U. vocans, was studied. A larger proportion of the inner merus edge was covered with ST setae in U. annulipes as compared to U. vocans (two-thirds vs. half of the edge, respectively). The number of ST setae did not differ significantly between males and females in both species (ANCOVA, slopes and intercepts, p > 0.05) suggesting there is no sexual dimorphism in mouthpart adaptations for these species. The combined regression equation (male + female data; CW = carapace width) for U. annulipes (n = 91) was #ST setae = 15.6 + 14.7CW with r2 = 0.63, that for U. vocans (n = 100) being #ST setae = 32.4 + 9.91CW with r2 = 0.66. For any given size of crab, significantly more ST setae were present in Uca annulipes (a sandy habitat crab) than in U. vocans (a muddy habitat species). These results provide quantitative evidence that fiddler crabs that inhabit sandy habitats possess more ST setae (an adaptation for processing sandy sediments), than those occurring in muddy habitats.

Fecundity of the pantropical fiddler crab Uca annulipes (H. Milne Edwards, 1837) (Brachyura: Ocypodidae) at Costa do Sol mangrove, Maputo bay, Southern Mozambique

Key words: mangroves, Uca annulipes, fecundity, Mozambique Uca annulipes (H. Milne Edwards, 1837) is probably the most abundant brachyuran crab inhabiting mangrove forests in East Africa. However, its fecundity is poorly understood. Crabs were randomly sampled during spring low tides from January to April 2002 at Costa do Sol mangrove, Maputo Bay, southern Mozambique. Carapace width (CW), abdomen width (AW), weight (W) and egg numbers (EN) were recorded. The average fecundity was 1599 842 eggs, ranging from 529 (CW = 5.0 mm) to 4250 (CW = 24.1 mm) eggs respectively. Egg number increased significantly with increase in crab size. This information contributes to our knowledge of the reproductive potential and the reproductive processes occurring in this species of crab. Western Indian Ocean Journal of Marine Science Vol.3(1) 2004: 87-91

Burrow-morphological Characters of the Fiddler Crab, Uca Annulipes (h. Milne Edwards, 1837) and Ecological Correlates in a Lagoonal Beach on Pulau Hantu, Singapore

[Nine burrow-morphological characters (burrow diameter, BD; burrow volume, BV; total burrow depth, TBD; burrow neck height, BNH; curved burrow length, CBL; horizontal length, HL; chamber diameter, CD; angle between descending neck of burrow and the substrate surface, β; angle between the bend in the burrow and the perpendicular, Θ) were defined from a study of 127 complete burrow casts of the fiddler crab, Uca annulipes. Crabs in 14 one-m2 quadrats randomly sited in low, mid, and high shore levels on a lagoonal beach were sexed and categorized into small, medium, and large size-classes. Sediment type in each quadrat was assessed as anoxic or non-anoxic. Density was estimated at 12.8 crabs m-2; mean sex ratio was 2.75 ♂ : 1♀. Five burrow-morphological characters (BV, TBD, BNH, CBL, and CD) differed significantly between sexes, being larger in male than in female crab burrows (p < 0.05). Differences in these burrow characters were indicative that males excavated larger burrows than females. Burrow mid-angle was significantly more obtuse in female crab burrows (p < 0.05), indicative of a more gradual turn in the descent of the burrows made by males. We attributed this to the poorer manoeuvrability of the males in the burrows due to their large chelipeds. Burrows of larger-sized crabs had greater BD, larger BV, and bigger CD than burrows of small- and medium-sized crabs. Significantly deeper burrows were dug at the high shore level than at both mid- and lower shore regions. We hypothesize that digging deeper burrows in the high intertidal is one way in which the fiddler crab can maintain lower burrow temperatures when the tide recedes. Burrows in anoxic sediments had significantly shorter TBD, BNH, and CBL than burrows in nonanoxic sediments. We postulate that shorter burrows in anoxic sediments may help improve the aeration of the burrows as opposed to longer burrows that accumulate a greater amount of stagnant air., Nine burrow-morphological characters (burrow diameter, BD; burrow volume, BV; total burrow depth, TBD; burrow neck height, BNH; curved burrow length, CBL; horizontal length, HL; chamber diameter, CD; angle between descending neck of burrow and the substrate surface, β; angle between the bend in the burrow and the perpendicular, Θ) were defined from a study of 127 complete burrow casts of the fiddler crab, Uca annulipes. Crabs in 14 one-m2 quadrats randomly sited in low, mid, and high shore levels on a lagoonal beach were sexed and categorized into small, medium, and large size-classes. Sediment type in each quadrat was assessed as anoxic or non-anoxic. Density was estimated at 12.8 crabs m-2; mean sex ratio was 2.75 ♂ : 1♀. Five burrow-morphological characters (BV, TBD, BNH, CBL, and CD) differed significantly between sexes, being larger in male than in female crab burrows (p < 0.05). Differences in these burrow characters were indicative that males excavated larger burrows than females. Burrow mid-angle was significantly more obtuse in female crab burrows (p < 0.05), indicative of a more gradual turn in the descent of the burrows made by males. We attributed this to the poorer manoeuvrability of the males in the burrows due to their large chelipeds. Burrows of larger-sized crabs had greater BD, larger BV, and bigger CD than burrows of small- and medium-sized crabs. Significantly deeper burrows were dug at the high shore level than at both mid- and lower shore regions. We hypothesize that digging deeper burrows in the high intertidal is one way in which the fiddler crab can maintain lower burrow temperatures when the tide recedes. Burrows in anoxic sediments had significantly shorter TBD, BNH, and CBL than burrows in nonanoxic sediments. We postulate that shorter burrows in anoxic sediments may help improve the aeration of the burrows as opposed to longer burrows that accumulate a greater amount of stagnant air.]

Quantifying the density of mangrove crabs: Ocypodidae and Grapsidae

Numerous studies have highlighted the importance of crabs within mangrove ecosystems, but tested methods of enumeration are virtually non-existent. The aim of the present study was to assess the accuracy of quick, non-invasive methods for estimating the population density of three species of mangrove crabs in East Africa: Uca annulipes, Sesarma guttatum and Neosarmatium meinerti. Methods employed depended on the behaviour and habitat of each species. Counts of U. annulipes and N. meinerti individuals that were active on the surface (visual counts) and burrow counts (of U. annulipes) were compared to actual densities. Actual densities were determined by excavation of U. annulipes, and by multiplying counts of N. meinerti burrows by the mean number of crabs per burrow. Visual counts of marked individuals of S. guttatum were compared to known densities of marked crabs. For N. meinerti two visual counting methods were tested: (1) instant counts – crabs were counted every 5 min during 0.5 h and the highest count taken; and (2) continuous counts – all burrows were tagged, and those from which a crab emerged during 0.5 h were totalled. For U. annulipes on Inhaca Island (Mozambique) visual counts underestimated excavated numbers by 27%, whereas burrow counts overestimated numbers by 46%. These values were similar for both sexes, and on both spring and neap tides. Burrow counts and visual counts estimated absolute numbers of U. annulipes with equal consistency. At Mida Creek (Kenya) visual counts underestimated U. annulipes numbers by 37%, again with no differences between spring and neap tides. In Zanzibar 81% of N. meinerti burrows contained a crab. The instant visual count underestimated N. meinerti numbers by 41%, the continuous count, by 12%. Visual counts of S. guttatum in Zanzibar (Tanzania) underestimated crab numbers by 49%.

Intersexual differences in the mudballs of Uca annulipes (Decapoda: Ocypodidae)

This study investigated the features of mudballs produced by male and female Uca annulipes. Both sexes formed mudballs from mud excavated from within the burrow during the final hour of the low tide period. Males placed the centre of the mudball aggregation and the furthest mudball significantly further from the burrow than females. These observations suggest that the placement of male mudballs was not simply a by-product of burrow excavation.

Dishonest signalling in a fiddler crab

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.

Female Choice in the Synchronously Waving Fiddler CrabUca annulipes

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.

Variation in courtship rate in the fiddler crab Uca annulipes: is it related to male attractiveness?

We investigated among-male variation in courtship waving in the fiddler crab Uca annulipa. 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 die 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 die cycle because die potential benefits are greater due to their increased attractiveness to females (differential benefits). Alternative explanations for die observed temporal trend are also discussed. Kty words: courtship, female choice, fiddler crabs, male choice, ornaments, sexual selection, Uca annulipes. [Behav Ecol 9:605—611 (1998)]

Time constraints and multiple choice criteria in the sampling behaviour and mate choice of the fiddler crab, Uca annulipes

Active female sampling occurs in the fiddler crab Uca annulipes. Females sample the burrows of several males before remaining to mate in the burrow of the chosen partner. Females time larval release to coincide with the following nocturnal spring tide and must therefore leave sufficient time for embryonic development after mating. Here we show how this temporal constraint on search time affects female choosiness. We found that, at the start of the sampling period (when time constraints are minimal), females selectively sample the larger males in the population. Towards the end of the sampling period (when the temporal constraints increase the costs of sampling), females are less selective. Furthermore, we suggest that the number of males sampled (and other indices of ‘‘sampling effort’’) may not be reliable indicators of female choosiness and may not reflect the strength of female mating preferences under certain conditions. Burrow quality also emerged as an important criterion in final mate choice. Burrow structure potentially influences reproductive success, and mate acceptance based on burrow structure appears to involve a relatively invariant threshold criterion. Since there is no relationship between male size and burrow quality, females are using at least two independent criteria when choosing potential mates. We envisage mate choice as a two-stage process. First, females select which males to sample based on male size. They then decide whether or not to mate with a male based on burrow features. This sampling process explains how two unrelated variables can both predict male mating success.

Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes

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.

Residency and size affect fight duration and outcome in the fiddler crabUca annulipes

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.

Heavy metal contamination in fiddler crabs (Uca annulipes) and hermit crabs (Clibanarius sp.) in a coastal area of northern peninsular Malaysia

Abstract A preliminary study on heavy metals contamination in fiddler crabs and hermit crabs was carried out. As they are easily found in river mouth areas, they can probably serve as good indicators for heavy metals pollution. The results show Pb and Cd concentrations were high whereas Zn and Cu concentrations were within the permissible limits.

Zinc accumulation in fiddler crabs Uca annulipes latreille and Uca triangularis (milne edwards)

The effect of exposure time and concentration on the tissue-specific accumulation of Zn in two fiddler crabs, Uca annulipes and Uca triangularis, obtained from polluted (Visakhapatnam Harbor) and unpolluted (Bhimilipatnam) areas was studied. Hepatopancreas registered major accumulation of Zn when the crabs were exposed to sublethal concentrations (6.38 to 15.39 ppm) for 30 days. However, when the crabs were exposed to different concentrations of Zn (LC 0, LC 25, LC 50, LC 75) ranging from 12.93 to 99.38 ppm, higher accumulation was recorded in gills than in hepatopancreas. There was a progressive increase in the percentage body burden of Zn in hepatopancreas, but that in gills showed a decreasing trend. The standardized body burdens for both species of crabs were calculated to evaluate their sensitivity to exposure time as well as to concentration. The fractional retention coefficients for exposure time estimated for exposed crabs indicate that U. triangularis from Bhimilipatnam, having the highest value, is sensitive and U. annulipes from Visakhapatnam Harbor, showing the lowest value, is resistant.

Heavy metal toxicity to fiddler crabs, Uca annulipes latreille and Uca triangularis (Milne Edwards): respiration on exposure to copper, mercury, cadmium, and zinc.

Respiration of animals is considered to be an indicator of their metabolic index and is used to evaluate the effect of stress or toxic substances in the environment. In an earlier investigation, an attempt was made to study the toxic effects of four heavy metals viz., Cu, Cd, Hg and Zn on fiddler crabs Uca annulipes and Uca triangularis obtained from polluted (Viskhapatnam Harbor) and unpolluted (Bhimilipatnam) environs. The present paper deals with respiratory metabolism of fiddler crabs Uca annulipes and Uca triangularis of Visakhapatnam Harbor by exposing them to different test concentrations of heavy metals i.e. Cu, Cd, Hg and Zn as these are the chief pollutants in their environment. A comparison has also been made with the respiratory metabolism of their counterparts collected from an unpolluted environment i.e. Bhimilipatnam.

Cadmium accumulation in fiddler crabs Uca annulipes latrelle and Uca triangularis (Milne Edwards)

Cadmium accumulation in fiddler crabs Uca annulipes latrelle and Uca triangularis (Milne Edwards)

Heavy metal toxicity to fiddler crabs, Uca annulipes Latreille and Uca triangularis (Milne Edwards): tolerance to copper, mercury, cadmium, and zinc : Uma Devi, V., 1987. Bull. environ. Contamin. Toxicol., 39(6):1020–1027. Dept. of Zool., Andhra Univ., Waltair 530 003, India

Heavy metal toxicity to fiddler crabs, Uca annulipes Latreille and Uca triangularis (Milne Edwards): tolerance to copper, mercury, cadmium, and zinc : Uma Devi, V., 1987. Bull. environ. Contamin. Toxicol., 39(6):1020–1027. Dept. of Zool., Andhra Univ., Waltair 530 003, India

Heavy metal toxicity to fiddler crabs, Uca annulipes Latreille and Uca triangularis (Milne Edwards): tolerance to copper, mercury, cadmium, and zinc.

Heavy metal toxicity to fiddler crabs, Uca annulipes Latreille and Uca triangularis (Milne Edwards): tolerance to copper, mercury, cadmium, and zinc.

Burrowing behavior and ecology of the crab-eating Indian snake eel Pisoodonophis boro

The snake eel Pisoodonophis boro burrows, causing leaks in the embankments and damaging the paddy fields and salt pans near estuaries. Field observations and laboratory experiments were made to study this behavior. P. boro was burrowing to eat the fiddler crab Uca annulipes in the mud flats. The eel showed a patchy distribution within the Uca zone. Salinity and the physical nature of the deposits controlled the distribution of the eel. Eel population density was low when the estuary was completely filled with neritic waters during the summer and fresh water during the monsoon period. The region of greatest abundance contained a good mixture of sand, silt and clay. Eels were not found where medium and fine sand formed the bulk of the substratum. The laboratory experiments showed that P. boro preferred loam soil although it could invariably burrow into hard substratum like sand for protection. The eel adapted itself to the experimental substrates ranging from sand to fine clay. However, their natural distribution was determined by Uca distribution. As U. annulipes is not found either in salt pans or in paddy fields P. boro rarely occurs in these habitats.

Observations on the biochemical changes in gonads and other organs of Uca annulipes, Portunus pelagicus and Metapenaeus affinis (Decapoda: Crustacea) during the reproductive cycle

The fluctuations in biochemical constituents such as water, nitrogen, non-protein nitrogen, protein, lipid and glycogen in gonad, muscle and hepatopancreas have been followed in 3 decapod crustaceans, Uca annulipes (Latreille), Portunus pelagicus (Linnaeus) and Metapenaeus affinis (Milne-Edwards). The water and ash content of the entire body show no systematic fluctuation in relation to the annual reproductive cycle. The water content of the ovary diminishes as it matures. In the ovary of these crustaceans, the lipid fluctuated greatly in relation to the reproductive cycle. The maturing ovary contains more lipid than an immature or spent ovary per unit tissue weight. The changes in the biochemical constituents in the testis are not so pronounced as in the ovary, since the testicular cycle is often drawn-out and almost continuous in these crustaceans. There is an inverse relationship between water content and lipid content of the hepatopancreas; the greater the fat content, the lesser the water content. The hepatopancreas in these crustaceans is apparently a storage organ and contains much lipid and glycogen. At the height of the breeding season, when gonad production is intense, there is an indication of the mobilisation of at least a part of the lipid from hepatopancreas to gonad.

Habituation to disturbance in the fiddler crab ( Uca annulipes) in its natural environment

Crabs of both sexes and of various sizes were subjected to a standardized test of ten consecutive disturbances in their natural habitat. Males and females reacted alike: 53 per cent became fully habituated within less than ten disturbances, and a further 12 per cent showed slower habituation. The remainder of the test individuals showed various other patterns of reactions. Reaction pattern and efficiency of habituation are size- (or age-) dependent, and they are modifiable by social interaction and by tide-determined activity phases. The structure and species composition (with regard to ocipodid crabs only) of the Uca habitat is considered briefly, and some observations on display and ‘rapping’ or drumming behaviour are reported.