Male Claw Research Articles

Diet impact on the reproductive characters of male red claw Cherax quadricarintus during the juvenile-adult transition

Male decapod reproduction involves gametogenesis, spermatozoa packaging in spermatophores, changes in cheliped´s growth, and specific behaviors such as courtship, male-male agoniztic interactions, and territory defense. These reproductive-related morpho-functional processes are supported by feed, one of the higher operative costs in aquaculture. This study aimed to evaluate the reproductive variables during the juvenile-mature transition of the male red claw Cherax quadricarinatus fed with two low-cost diets (T1 and T2). Pre-adult males (∼7 g) were individually distributed in plastic containers and fed a diet with fish silage (T1) (n = 9), a diet without fish silage (T2) (n = 8), and a commercial diet for ornamental fish used as a reference diet (T3) (n = 7). The proximal composition of T1, T2, and T3 was 34 %, 28 %, and 47 % for crude protein; 13 %, 9 %, and 6.5 for lipids; and 34 %, 47 %, and 28 % for carbohydrates, respectively. All males acquired sexual maturity with a body weight between 16 and 21 g. All groups showed similar chelae growth (based on the evaluation of the chelae height, and chelae thickness indexes) and red patch development. The gonadosomatic index was significantly lower in the T2 group with respect to T1. The lowest proportion of mature testicular lobes (filled with spermatids/spermatozoa) was detected in the T2 group (49 %), followed by T1 (59 %) group. There was also a lower protein content (∼ 27 %) in the vasa deferentia of the T2 group. However, all males showed a well-developed reproductive system and the histology of the testes and vasa deferentia showed no evidence of structural differences among groups. Under transmission electron microscopy analysis, both the primary and secondary layers of the spermatophore did not show qualitative differences among groups, including the spermatozoon morphology and acrosome size. This study highlights that males fed low-cost diets (0.56 and 0.65 U$S kg− 1, for T1 and T2 respectively), in particular T1, showed reproductive performances as good as the group fed on the reference diet. This is the first analysis of a pool of morpho-functional and biochemical reproductive variables in red claw males, to evaluate the effects of formulated diets on male sexual maturation.

Thin-fingered fiddler crabs display a natural preference for UV light cues but show no sensory bias to other hypertrophied claw coloration

Although color cues play an important role in sociosexual signaling, when communication is exploited as a foraging cue by predators, prey must pay the due cost for sustaining information interchange. In this regard, fiddler crabs draw attention by having flashy enlarged claws that could potentially attract the interest of many predators. Surprisingly, the adaptive function of claw coloration in fiddler crabs is not entirely understood and have barely been studied in American species. Here, we examine the spectral reflectance of thin-fingered (Leptuca leptodactyla) fiddler crabs’ hypertrophied claws and evaluate whether female conspecifics prefer UV-light or other color cues. We test whether male claws reflect UV light and whether females use UV light and/or other color cues when making mating decisions. Our results reveal that only the most flamboyant enlarged claws should be detected by female conspecifics, which show a clear preference for male UV signals. Moreover, while the anterior portion of the enlarged claws (pointing towards conspecifics) reflect UV light, claws’ dorsal portion and carapaces (which possibly point upwards and might attract airborne predators) do not show an UV peak. We also discuss the possibility of hypertrophied claws working as honest aposematic signals or playing an important role as decoys.

Claws and claw waving attract both sexes in the dotillid crab Ilyoplax pusilla

During the breeding season, courting males of many ocypodoids (famously, fiddler crabs) perform claw-waving displays, in which they rhythmically raise, often extend, and lower their chelipeds when they are near their burrows. This conspicuous display sometimes attracts wandering (burrow-less) sexually receptive females to males’ burrows where the crabs mate. However, since most of the claw waving is not directed to a particular receiver, the display may also attract males and unreceptive females that are searching for new burrows, not mates. We conducted two types of choice experiment using claw models to examine the preferences of wandering males and females in the dotillid crab Ilyoplax pusilla: (1) between burrows with and without static claw models, (2) between waving and static claw models set up 10 cm apart (for only males). More crabs of both sexes ran to the burrows with claw models, and more males preferred the waving claw model. Like the structures some courting male fiddler crabs build, male claws and the claw waving of I. pusilla may reveal to unintended receivers the locations of burrows that these crabs can use temporarily as refuges.

Identification of differentially expressed genes and signalling pathways to elucidate molecular mechanisms underlying growth differences among the male morphotypes of Macrobrachium rosenbergii

The giant freshwater prawn (GFP) Macrobrachium rosenbergii is an economically important aquaculture species in China. In culture, it is common for males to show unique morphotypes, which exhibit distinct heterogenous individual growth. Little information is currently available on the molecular mechanisms underlying growth differences among male morphotypes of GFPs. Thus, we herein aimed to identify key genes and signalling pathways to elucidate molecular mechanisms underlying growth differences among the male morphotypes of GFPs. We performed transcriptome analyses using RNA-Seq to compare the following male morphotypes of GFPs: orange claw males, old blue claw males and small males. In total, 97.44 Gb clean data were obtained, and 1,857,760 unigenes were annotated by alignment with public protein databases. Moreover, we found 2,072 and 22,431 differentially expressed genes (DEGs) from the eyestalk and gonads respectively. Gene ontology analyses revealed that ‘system process’ and ‘multicellular organismal process’ were the most enriched in the eyestalk and gonad tissue samples respectively. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that pathways associated with gene regulation may play a key role in GFP growth. To summarize, this study provides a valuable repository of novel transcripts for various male morphotypes of GFPs and gives further insights into the molecular mechanisms underlying growth differences in GFPs, which should promote the breeding of commercially cultivated GFPs.

The role of claw color in species recognition and mate choice in a fiddler crab

Many animal signals are brightly colored and convey information about species identity as well as information about individual conspecifics. Colorful bird and lizard signals have received much attention, and many studies have related specific spectral properties of these signals to variation in mating success and territory defense. Far less attention has been given to invertebrates even though there are spectacularly colorful species. The enlarged claw of the male banana fiddler crab Austruca mjoebergi, for example, is bright yellow and contrasts vividly against the mudflat substrate. It is used in waving displays to attract females and in male territory defense and combat. Claw color varies among males in the degree of “yellowness,” ranging very pale yellow to orange. In this study, we examined female responses to claw color variation in two-choice tests using robotic crabs. We found that although females strongly discriminate against colors that fall outside the natural range of intensity, hue, and chroma, they show no consistent preferences for different claw colors within the natural range, and no single component of claw color (hue, chroma, or intensity) independently affected female choices. Using three-choice tests, we also showed that female preferences induce stabilizing selection on male claw color. We conclude that, although claw color is sufficient to facilitate species recognition, it is unlikely to be used in intraspecific mate choice to provide information about male quality.Significance statementFiddler crabs are often brightly colored, are visually orientated animals, and have a highly complex social system. Despite this, there are few studies that have looked at the role of color in species recognition and mate choice in these animals. In this study, we use robotic crabs with painted claws to determine the role of claw color in species recognition and mate choice in the banana fiddler crab, Austruca mjoebergi. We found that color is important in conspecific mate recognition but the variation among males in claw “yellowness” is unlikely to be used by females in intraspecific mate choice decisions.

Harder, better, faster, stronger: Weapon size is more sexually dimorphic than weapon biomechanical components in two freshwater anomuran species.

Sexual selection influences the evolution of morphological traits that increase the likelihood of monopolizing scarce resources. When such traits are used during contests, they are termed weapons. Given that resources are typically linked to monopolizing mating partners, theory expects only males to bear weapons. In some species, however, females also bear weapons, although typically smaller than male weapons. Understanding why females bear smaller weapons can thus help us understand the selective pressures behind weapon evolution. However, most of our knowledge comes from studies on weapon size, while the biomechanics of weapons, such as the size of the muscles, efficiency, and shape are seldom studied. Our goal was to test if the theoretical expectations for weapon size sexual dimorphism also occur for weapon biomechanics using two aeglid crab species. Males of both species had larger claws which were also stronger than female claws. Male claws were also more efficient than females' claws (although we used only one species in this analysis). For weapon shape, though, only one species differed in the mean claw shape. Regarding scaling differences, in both species, male claws had higher size scaling than females, while only one species had a higher shape scaling. However, male weapons did not have higher scaling regarding strength and efficiency than females. Thus, males apparently allocate more resources in weapons than females, but once allocated, muscle and efficiency follow a similar developmental pathway in both sexes. Taken together, our results show that sexual dimorphism in weapons involves more than differences in size. Shape differences are especially intriguing because we cannot fully understand its causes. Yet, we highlight that such subtle differences can only be detected by measuring and analysing weapon shape and biomechanical components. Only then we might better understand how weapons are forged.

Graptodytes exsanguis (Bedel, 1925) n. stat., a newly recognised species of diving beetle from North Africa, Corsica and Sardinia, with notes on other taxa of the varius/ignotus complex (Coleoptera: Dytiscidae)

SummaryA species of the genus Graptodytes Seidlitz, 1887 (varius/ignotus complex) is newly recognised and described based on recently sampled specimens from Corsica and Sardinia, and material in various collections from Algeria, Tunisia, Corsica and Sardinia. The name exsanguis, created by Bedel in 1925 for a variety of what he then called Hydroporus varius Aubé, 1838, is shown to be available for the newly recognised species, therefore named Graptodytes exsanguis (Bedel, 1925) n. stat. (type locality: Algeria, La Calle – nowadays El Kala). This species is similar in size and colour pattern to G. fractus (Sharp, 1882), from which it can be distinguished by strong differentiation of the male protarsal claws, features of the habitus and elytral punctation, and shape of the median lobe of aedeagus. Morphological features of G. exsanguis and G. fractus are illustrated, and pictures showing for each species the variability of habitus and median lobe are provided. For comparison, the habitus and median lobes of other species of the varius/ignotus complex are also illustrated. Habitat preferences of G. exsanguis are described based on field observations in Corsica and Sardinia, and a distribution map of validated records is presented. Analysis of a partial CO1 alignment yielded a basal and divergent position within the varius/ignotus complex for the sequenced G. exsanguis haplotypes from Corsica and Sardinia. Lectotypes are designated for Hydroporus varius var. exsanguis Bedel, 1925, Hydroporus fractus Sharp, 1882 and Graptodytes ignotus var. fallaciosus Guignot, 1932, and the latter is established as a junior synonym of G. fractus.

Male morphotypes and alternative mating tactics in freshwater prawns of the genus Macrobrachium: a review

AbstractThe discontinuous variation in male mating behaviour is termed alternative mating tactics. A distinction is commonly made between alternative mating tactics that are fixed for life or flexible with simultaneous or sequential switches between tactics over the sexually mature life. Freshwater species of the genus Macrobrachium demonstrate flexible tactics with sequential (i.e. developmental) switch between tactics. Sexually mature populations of the commercially important giant freshwater prawn M. rosenbergii consist of three morphologically and behaviourally distinct male morphotypes: small males, orange claw and blue claw males, representing (respectively) successive stages in the developmental pathway of sexually mature males. The dominant blue claw males secure mating by guarding receptive soft‐shelled females with their long chelipeds while the subordinate SM use an alternative tactic of sneak mating to fertilize females. Current knowledge of the mating behaviour and reproductive success of these male morphotypes, including male competition over females, female mate choice and the involvement of pheromones, is reviewed. So far, the occurrence of distinct sexually mature male morphotypes has been described in 24 species within the genus Macrobrachium. The prevalence of distinct male morphotypes and alternative mating tactics among Macrobrachium species is discussed in view of the phylogeny of the genus, based on molecular markers. The environmental and genetic determination of the male morphotypes is discussed, as well as the evolution of the developmental alternative mating tactics in the genus Macrobrachium. Possible implications for prawns’ aquaculture and future research are suggested.

Water beetles (Coleoptera) of coastal areas of the Bolshezemelskaya Tundra, extreme northeastern Europe

ABSTRACTThe fauna of water beetles in coastal areas of the Bolshezemelskaya Tundra and on the Vaygach and Dolgiy islands, Pechora Sea, comprises a total of 42 recorded species; in local faunas, the number of species decreases northward from 19–26 in southern mainland tundra to nine in typical tundra of the Vaygach Island. The faunal similarity between pairs of areas is 21%–52% (39%–52% between mainland areas). The family Haliplidae is represented by three species, Dytiscidae – 32 species, Helophoridae – four species, Hydrophilidae – two species and Hydraenidae – one species. Most of the species have large ranges both longitudinally and latitudinally. Cryophile species are rather few (five species, 12%). There are clear differences between the beetle assemblages of weakly brackish lakes marshes and waterbodies of the bedrock coast. The strongest preferences for particular habitats have been revealed in species associated with sand substrates in waterbodies or with the floodplain of a large river. The male genitalia and male protarsal claws of Agabus luteaster (Zaitzev, 1906), recently recorded as new to Europe, are illustrated for the first time as well as Ochthebius kaninensis Poppius, 1909.

Leptin-like immunoreactivity in the central nervous system, digestive organs, and gonads of the giant freshwater prawn, Macrobrachium rosenbergii

Leptin, a highly conserved adipocyte-derived hormone, plays important roles in a variety of physiological processes, including the control of fat storage and metabolic status which are linked to food intake, energy homeostasis, and reproduction in all vertebrates. In the present study, we hypothesize that leptin is also present in various organs of the fresh water prawns, Macrobrachium rosenbergii. The existence and distribution of a leptin-like peptide in prawn tissues were verified by using Western blotting (WB) and immunohistochemical detection (ID) using primary antibody against human leptin. With WB, a leptin-like peptide, having a molecular weight of 15kDa, was detected in the brain, thoracic ganglia, abdominal ganglia, parts of the gastro-intestinal tract, hepatopancreas, adipocytes and gonads. By ID, leptin immunoreactivity (leptin-ir) was detected in the brain, thoracic ganglia and intersegmental commissural nerve fibers of abdominal ganglia. In the gastrointestinal tract, there was intense leptin-ir in the apical part of the epithelial cells of the cardiac and pyloric parts of the stomach. In the midgut and hindgut, the leptin-ir was detected in epithelial cells and basal cells located near the basal lamina of the epithelium. In addition, there was leptin-ir in the Restzellen cells in the hepatopancreas which produce digestive enzymes. In the ovary, the strong intensity of a leptin-ir was detected in the cytoplasm of middle to late stage oocytes, whereas no positive staining was detected in follicular cells. An intense leptin-ir was detected in spermatocytes and sustentacular cells in the seminiferous tubules in the testes of small and orange claw males. Taken together, the detection of the leptin-ir in several organs implicates the existence of a leptin-like peptide in various organs of the freshwater prawn; and like in vertebrates this peptide may be an important hormonal factor in controlling feeding and reproductive process.

Thermal constraints on microhabitat selection and mating opportunities

Hot tropical environments constrain ectotherm mating opportunities when mate selection occurs on the surface. Thus, microhabitats and refugia can become a qualitative trait in mate selection. In fiddler crabs, the enlarged claw of males can act as a heat sink, which becomes advantageous when surface temperatures reach 50 °C during the day and crabs are actively seeking to mate. Uca mjoebergi females prefer male burrows found in the shade; therefore, we investigated the thermal constraints imposed on males and females in shaded and unshaded habitats. Crab surface activity decreased and body temperature increased as the day progressed, with more crabs active in shaded than sunny microhabitats. Body temperature was lower in male crabs found in burrows relative to crabs on the surface. Male claw size explained 10% of body temperature. Our results add further support to the hypothesis that thermal constraints imposed on males can be overcome by the large claw acting as a heat sink and the burrow acting as a refuge from heat. Classic sexually selected traits, including ornaments and behaviours, can have a secondary purpose in thermoregulation.

Variation in proximate composition and fatty acid profiles of mud crab meat with regard to sex and body parts

Mud crabs are the most widely distributed and cultured group among portunid crabs. The meat yield, proximate composition and fatty acid profile of two species of mud crabs Scylla serrata and Scylla tranquebarica were compared with respect to gender and different body parts and the results showed significant differences (p<0.05) in biochemical composition. Meat yield was higher in males, whereas females had higher protein content. The lowest moisture content (78.5%) was in the female body meat of both the species and the highest (83.85%) in male claw meat of S. serrata. Health beneficial polyunsaturated fatty acids (PUFA) content was found in the range of 28.81-42.66% with a higher n3 to n6 PUFA ratio of 1.34-5.28. Principal component analysis (PCA) revealed higher n3 PUFA content in the claw meat of S. tranquebarica and body meat of S. serrata. The results throw light on the possibilities for both farmers as well as processors to judiciously select the species, gender and the meat source based on their compositional features in order to cater specifically to the market requirements.

Variation in proximate composition and fatty acid profiles of mud crab meat with regard to sex and body parts

Mud crabs are the most widely distributed and cultured group among portunid crabs. The meat yield, proximate composition and fatty acid profile of two species of mud crabs Scylla serrata and Scylla tranquebarica were compared with respect to gender and different body parts and the results showed significant differences (p<0.05) in biochemical composition. Meat yield was higher in males, whereas females had higher protein content. The lowest moisture content (78.5%) was in the female body meat of both the species and the highest (83.85%) in male claw meat of S. serrata . Health beneficial polyunsaturated fatty acids (PUFA) content was found in the range of 28.81-42.66% with a higher n3 to n6 PUFA ratio of 1.34-5.28. Principal component analysis (PCA) revealed higher n3 PUFA content in the claw meat of S. tranquebarica and body meat of S. serrata . The results throw light on the possibilities for both farmers as well as processors to judiciously select the species, gender and the meat source based on their compositional features in order to cater specifically to the market requirements.

A North American Biodiversity Hotspot Gets Richer: A New Species of Whirligig Beetle (Coleoptera: Gyrinidae) From the Southeastern Coastal Plain of the United States

A new species of Dineutus Macleay, 1825 is described from the Southeastern Coastal Plain of the United States. Habitus and aedeagus images as well as illustrations of elytral apices, protarsus, palps, and male mesotarsal claws are provided for Dineutus shorti n. sp. and compared to those of D. discolor Aube, 1838. The importance of the southeastern Coastal Plain as a biodiversity hotspot and the potential conservation concern of D. shorti n. sp. also are discussed.

Are female reproductive status and male morphotypes of the giant freshwater prawn Macrobrachium rosenbergii altered by selection for high growth?

Understanding genetic changes in the hierarchical population structure of the giant freshwater prawn (GFP) Macrobrachium rosenbergii is important to improve productivity and profitability of prawn farming. We examined correlated responses in male morphotype and female reproduction status resulting from a selection programme for high growth in a GFP population undergoing four generations of selection. Two contemporary lines (selection and control) were maintained and produced simultaneously; the selection line was selected for high breeding values for harvest body weight and the control for average breeding values of the population. A total of 21,459 individual prawns were measured for body traits and morphotypes. Individual morphotype was recorded as a binary trait (0 and 1) and were analysed using a generalised threshold mixed model with a logit link function. Correlated genetic changes in three important male morphotypes (small, orange and blue claw males) were significant (p < 0.05–0.001) only in generation 2010 but not in the last generation (2012). Selection for high growth did not have an adverse effect on reproduction status of females, except that the selection line had a greater proportion of spawned females than the control (p = 0.01). Our results pointed out that selection for high growth may have had both positive and negative impacts on the social population structure of male morphotypes in GFP. Undesired changes in important morphotypes should be taken account of in genetic improvement programmes for GFP in order to minimise social competition effects and increase total biomass and consequently economic returns of the sector.

Effect of cold shock and hormone on growth and male morphotypes of freshwater prawn,Macrobrachium rosenbergii(de Man)

A study was carried out to determine the effects of cold shock and 17α-methyl testosterone hormone on growth in male morphotypes of giant freshwater prawn Macrobrachium rosenbergii. Juvenile males were exposed at 18 ± 0.25°C for 24 h with normal feed and cultured at 27 ± 0.7°C for 70 days as well as administrated feed with hormone separately at 400 mg kg−1 feed for the first 30 days of culture period (70 days). The growth (Mean ± SD) of male juveniles at harvest was closely homogenous in the cold shock (CLS) treated group; while it was heterogeneous in hormone-treated (MH) and control (CO) groups. Although total body weight of blue claw (BC) males was not significantly different in the controls and the treatments, the 2nd pereiopods (claw) weight and length of the BC was significantly lower in CLS (0.52 ± 0.05 g, 10.02 ± 0.65 cm) than that in the CO (0.71 ± 0.16 g, 12.53 ± 0.57 cm) and MH (0.75 ± 0.08 g, 12.85 ± 1.18 cm) treatments. Survival of prawns was similar in treatments. The morphotypes of male prawn were significantly different with 59% of BC males with small-sized claws in CLS and, 45% and 30% of BC males with large-sized claws in MH and CO respectively. Cold shock adversely affected male morphotypes of the prawn so that numbers of BC males with small-sized claw was the highest in CLS tank. However, the CLS treatment resulted in more uniform marketable prawns and suggested a high production of BC males in an all-male culture system.

Production Characteristics of All‐male and Mixed‐sex Giant River Prawns, Macrobrachium rosenbergii, Grown in Earthen Ponds in Kentucky and Mississippi USA

AbstractProduction and population characteristics of monosex male (all‐male) giant river prawns, Macrobrachium rosenbergii, were compared with a normal (mixed‐sex) population in separate studies in Mississippi and Kentucky (USA) under low and high density stocking conditions, respectively. In Study 1 (Mississippi), juvenile prawns were stocked into eight 0.05–0.06 ha ponds at 24,700/ha. The mean stocking weight of all‐male was 0.34 g and mixed‐sex was 0.39 g. Prawns were fed 23% crude protein “range cubes” and harvested after 120 d for the all‐male prawns and 112 d for mixed‐sex prawns. In Study 2 (Kentucky), juvenile prawns from each group were stocked into six 0.04 ha ponds at 60,000 juveniles per hectare. The mean stocking weight for all‐male was 0.38 g and for mixed‐sex juveniles was 0.34 g. Prawns were fed a commercial sinking pellet (33% protein) once daily at a standardized rate and harvested after 105 d. In both locations survival of mixed‐sex prawns and all‐male prawns was not significantly different and the final average weight of all‐male prawns was significantly greater than the average weight of mixed‐sex prawns. For the study in Kentucky, total production was not significantly different between treatments, whereas in Mississippi total production in the all‐male ponds was significantly higher than in the mixed‐sex ponds. For both studies, the production size index of all‐male prawns was significantly greater than that of mixed‐sex prawns. In terms of population structure, in all‐male ponds there was a significant increase in orange claw (OC) males compared with the mixed‐sex ponds both as a percent of sex and a percent of total population. The increase in OC numbers in all‐male populations may be due to a lack of females to stimulate the transition of males to the final, sexually mature, blue claw stage. As target weights increase from 20, 30, and 40 g, the all‐male populations were increasingly superior in terms of production (kg/ha) of those target sizes. The economic benefit of all‐male over mixed‐sex populations will be principally based on an examination of tradeoffs that primarily consider the cost difference of juveniles relative to the price differences for different final harvest weights.

Stag Beetle Battle Behavior and its Associated Anatomical Adaptations

Male stag beetles battle for females with their impressive, oversized mandibles. We describe their fighting behavior, which is essential to understand the evolution and morphology of their weaponry. Our behavioral analysis reveals several anatomical structures that are important for fighting, and our morphological investigations show how these may be adapted for their functions. Stag beetle fights are much more variable than other armed beetles’ battles. They spend considerable time and effort in dislodging their opponent, that clings to the substrate with its tarsal claws. These tarsal claws are also indispensable to maintain balance in the most spectacular battles, when they lift a rival high in the air. The male claws are highly curved and have an increased height for this purpose. The prothoracic muscles are hypertrophied to support the lifting movement. The largest beetle wins in 85 % of the fights and the smaller the difference in mandible length is between the rivals, the longer the battles can last. The long mandibles enable males to reach the opponent’s legs in order to dislodge it. For this purpose, they bite with all parts of their mandibles, even though the distal part is more vulnerable for failure and transfers less bite force. Blindfolded experiments prove that visual information is not a requisite for a successful battle.

Building a dishonest signal: the functional basis of unreliable signals of strength in males of the two-toned fiddler crab, Uca vomeris.

Males of many species use signals during aggressive contests to communicate their fighting capacity. These signals are usually reliable indicators of an individual's underlying quality; however, in several crustacean species, displays of weapons do not always accurately reflect the attribute being advertised. Male fiddler crabs possess one enlarged claw that is used to attract females and to intimidate opponents during territorial contests. After the loss of their major claw, males can regenerate a replacement claw that is similar in size but considerably weaker. As this inferior weapon can still be used to successfully intimidate rivals, it represents one of the clearest cases of unreliable signalling of strength during territorial contests. We investigated the functional mechanisms that govern signal reliability in the two-toned fiddler crab, Uca vomeris. Male U. vomeris exhibit both reliable and unreliable signals of strength via the expression of original and regenerated claw morphs. We examined the morphological, biomechanical and biochemical characteristics of original and regenerated claws to establish the best predictors of variation in claw strength. For a given claw size, regenerated claws have less muscle mass than original claws, and for a given muscle mass, regenerated claws were significantly weaker than original claws. The mechanical advantage was also lower in regenerated claws compared with original claws. However, the activity of three catabolic enzymes did not differ between claw types. We conclude that the structural and physiological predictors of force production influence the frequencies of reliable and unreliable signals of strength in U. vomeris. This study furthers our understanding of the proliferation of unreliable signals in natural populations.

Female preferences for timing in a fiddler crab with synchronous courtship waving displays

Studies of sexual communication typically focus on the design and information content of a signal of interest, but the timing of signal production relative to nearby competitors can be crucial. Male fiddler crabs, Uca mjoebergi , court females with a stereotyped claw-waving display, and males are often observed waving in synchrony with nearby claw-waving males. Using female mate preference experiments with robots that imitate male claw waves, we found evidence that females are more attracted to males whose waves immediately precede a synchronous group of waves (leaders); females also favoured males that waved in opposite phase to a synchronous group (alternators). By contrast, males whose waves lagged behind a group of synchronous wavers (laggards) were no more attractive. We discuss a simple sensory process that could explain how this female preference arises. Our results agree with past findings suggesting that synchrony in fiddler crabs occurs as an epiphenomenon of adaptive male responses to female preferences. • We used robotic males to investigate female preferences in a fiddler crab. • We examine the effect of male signal timing on attractiveness. • Males who signal just before a synchronous group are favoured. • Males who signal in alternation with the group are also favoured. • These preferences could drive synchronous signalling in wild males.