Size,but not sex,predicts pinch force and exoskeleton mechanical properties in crayfish of the genus Faxonius

Studies of animal weaponry and defensive structures rarely take into consideration their underlying mechanical properties. We measured the compressive strength and thickness of the exoskeleton of the claw (chela) in two North American crayfish species, Faxonius virilis and F. limosus. We performed similar measures on the carapace, a body region not directly involved in agonistic contests. Males of both species generated significantly stronger maximum pinch forces than females. However, these differences can be attributed to differences in claw size between the sexes. The thickness (ultrastructure) of the claw exoskeleton was a significant predictor of its compressive strength and likely explained the difference in compressive strength we observed between the two species. Neither claw thickness nor claw compressive strength was correlated with maximum pinch force. Additionally, we found that crayfish body size was a strong predictor of carapace compressive strength and thickness, whereas sex was not. The claw had greater compressive strength and thickness than the corresponding values for the carapace. Our study shows that the mechanical properties of the crayfish exoskeleton are largely a function of size and highlights the need to integrate mechanical properties into studies of animal morphology and performance.     

The intensity and spectrum of artificial light at night alters crayfish interactions

ABSTRACT

Ecological light pollution (ELP) is quickly becoming a worldwide concern and can negatively affect aquatic ecosystems. The given intensity and spectrum of a light source can influence how organisms function within their environment. These properties of artificial lighting at night (ALAN) and their impacts on the physiology and behaviour of crayfish were examined in this work. Hemolymph was obtained from crayfish to quantify a physiological response. Behavioural data were measured as the number, duration, and maximum intensity of agonistic fights. Exposure to higher intensities of light and the presence of ultraviolet light induced a behavioural trend, resulting in significantly altered social interactions within both species of crayfish. The number and maximum intensity of lights significantly decreased, whereas the duration of time spent fighting significantly increased. Due to the importance of freshwater environments and the role crayfish play as a keystone species, examining how crayfish are impacted from ALAN is imperative to maintaining the health of aquatic ecosystems.     

Differences in refuge function for prey and tolerance to crayfish among macrophyte species

The invasive crayfish Procambarus clarkii is an omnivore and an ecosystem engineer whose feeding mechanism has reduced the abundance of many native invertebrates and macrophytes. Since macrophytes provide refuges for aquatic insects, macrophyte depletion by crayfish might have indirect negative effects on animal prey in aquatic habitats. We postulated that the prey refuges provided by macrophytes and macrophyte tolerance to crayfish cutting and feeding vary among macrophyte species. We conducted two experiments to (1) investigate differences in macrophyte refuge function for dragonfly larvae against crayfish, and (2) test the tolerance to crayfish cutting and feeding among macrophyte species. Elodea nuttallii (submerged plant), Potamogeton crispus (submerged plant), and Carex idzuroei (emergent plant) had greater refuge effects than Trapa japonica (floating-leaved plant), an effect that might result from the larger total cover of E. nuttallii, P. crispus, and C. idzuroei, and the hardness of C. idzuroei leaves. Tolerance to crayfish cutting and feeding was greater in C. idzuroei than in the other species. As the macro-invertebrate assemblages in submerged vegetation are more abundant and species-rich than those in emergent and floating-leaf vegetation, conservation of E. nuttallii and P. crispus should be prioritized for restoring native aquatic animals in ecosystems invaded by the introduced crayfish.     

红螯螯虾体表附生切头涡虫类研究概述

随着红螯螯虾(Cherax quadricarinatus)养殖业的发展,附着于红螯螯虾体表的切头涡虫及其危害已引起养殖业者的广泛关注。本文介绍了切头涡虫的分类地位和分布,详细描述了切头涡虫外部形态和内部构造,并对切头涡虫的共生特性、食性、生活史、运动方式等生物学特点进行了概述,对切头涡虫的危害和防治进行了总结和讨论。本综述可为红螯螯虾的养殖、切头涡虫病的了解与防治以及相关研究提供参考。     

Pinching forces in crayfish and fiddler crabs,and comparisons with the closing forces of other animals

The pinching forces of crustaceans are in many respects analogous to the biting forces of vertebrates. We examined the effects of body size and chelae size and shape, on the closing forces of the fiddler crab, Uca pugilator, and the crayfish, Procambarus clarkii. We hypothesized that the allometric relationships would be similar among species, and comparable to those reported for other decapod crustaceans. We further hypothesized that the scaling of the closing forces of crustaceans, with respect to body size and with the geometry of the pinching or biting structures, would be similar to that of vertebrates. We found that pinching forces increased with body mass, claw dimensions, and claw mass in U. pugilator, but only with claw height and claw mass in P. clarkii. Contraction time increased with body mass for both species combined, whereas contraction speed decreased. Pooled data for these and 17 other species of decapod crustacean revealed a positive correlation between the pinching force and body mass with a scaling exponent of 0.71. These data are remarkably comparable to the values on closing forces of vertebrate jaws, with the pooled data having a scaling exponent of 0.58, slightly below the value of 0.67 predicted for geometric similarity. Maximum closing forces vary tremendously among both crustaceans and animals in general, with body size and food habits being among the most important determining factors.     

Enhanced ecological indication based on combined planktic and benthic functional approaches in large river phytoplankton ecology

Environmental DNA (eDNA) is a powerful method for assessing the presence and distribution of invasive aquatic species. We used this tool to detect and monitor several invasive crayfishes Procambarus clarkii, Orconectes limosus and Pacifastacus leniusculus present in, or likely to invade, the ponds of the Brenne Regional Natural Park. A previous study showed that the eDNA method was not very efficient in detecting P. clarkii. In the present study, we explored new improvements in the detection of invasive crayfish. We designed specific primers for each crayfish species, and set up an experimental mesocosm approach to confirm the specificity of the primers and the sampling protocol. We analysed samples taken from ponds in 2014 and 2015. We compared two qPCR protocols involving either SybrGreen or TaqMan assays. Using these same primers, we were able to detect crayfish eDNA with both assays during the mesocosm experiment. However, crayfish from field samples could only be detected by performing qPCR with a SybrGreen assay. We successfully monitored the presence of three invasive species of crayfish using eDNA. This method is a powerful tool for establishing the presence or absence of invasive species in various freshwater environments.     

Relationship between gape size and feeding selectivity of fish larvae from a Neotropical reservoir

Larvae feeding selectivity of Iheringichthys labrosus , Hypophthalmus edentatus and Plagioscion squamosissimus was assessed, examining the role of mouth gape in prey selection. Fish larvae were sampled in the Itaipu Reservoir (Brazil–Paraguay). Iheringichthys labrosus and H. edentatus larvae, with small and similar gape sizes, exhibited slightly different diets; I. labrosus preferred cladocerans ( Bosmina hagmanni , Bosmina huauriensis and Bosminopsis deitersi ) and the rotifer Brachionus calyciflorus . Hypophthalmus edentatus , however, primarily ingested the cladocerans B. hagmanni , Ceriodaphnia cornuta , Daphnia gessneri and Diaphanosoma spinulosum . Plagioscion squamosissimus , with a greater gape size, preferred Calanoida. The mechanistic processes that determine food selectivity of fish larvae in temperate aquatic systems were similar in the Neotropical system. The trophic spectrum of these species is characterized by small- to intermediate-sized prey. Plagioscion squamosissimus larvae, which have larger mouths, exploit primarily larger prey differing from the most abundant species or size classes; consequently, their diet is quite different from I. labrosus larvae and modestly similar to H. edentatus larvae, opportunistic feeders that they eat more abundant prey.     

Niche breadth and trophic diversity: feeding behaviour of the red swamp crayfish (Procambarus clarkii) towards environmental availability of aquatic macroinvertebrates in a rice field (Portugal)

The red swamp crayfish, Procambarus clarkii (Girard 1852), an alien species in Portugal, may have dramatic effects on aquatic communities by depleting all food resources available, just after its introduction. The purpose of this study was to evaluate, through the concept of niche breadth, whether the diet of this species reflected the temporal changes of aquatic macroinvertebrate availability once it is acclimated. Petraitis’ index of niche breadth and Herrera’s trophic diversity index were used to evaluate the trophic behaviour of P. clarkii towards available resources over time and intraspecifically (size classes and sex) in a rice field in Portugal. Results from this study showed that the consumption of aquatic macroinvertebrates by P. clarkii reflected their seasonal availability. The high values of niche breadth and trophic diversity indicated resource use according to trophic availability, diversified diets and different individual exploitation of resources regardless of size or sex. These findings suggest that in habitats where P. clarkii is already acclimated, it adjusted its trophic behaviour to the seasonal availability of aquatic macroinvertebrates. The large niche breadth and high trophic diversity presented by P. clarkii enables it to successfully expand its range to new areas, when other environmental conditions are favourable, as has been observed in Portugal and worldwide.     

Invasive Crayfish Threaten the Development of Submerged Macrophytes in Lake Restoration

Submerged macrophytes enhance water transparency and aquatic biodiversity in shallow water ecosystems. Therefore, the return of submerged macrophytes is the target of many lake restoration projects. However, at present, north-western European aquatic ecosystems are increasingly invaded by omnivorous exotic crayfish. We hypothesize that invasive crayfish pose a novel constraint on the regeneration of submerged macrophytes in restored lakes and may jeopardize restoration efforts. We experimentally investigated whether the invasive crayfish (Procambarus clarkii Girard) affects submerged macrophyte development in a Dutch peat lake where these crayfish are expanding rapidly. Seemingly favourable abiotic conditions for macrophyte growth existed in two 0.5 ha lake enclosures, which provided shelter and reduced turbidity, and in one lake enclosure iron was added to reduce internal nutrient loading, but macrophytes did not emerge. We transplanted three submerged macrophyte species in a full factorial exclosure experiment, where we separated the effect of crayfish from large vertebrates using different mesh sizes combined with a caging treatment stocked with crayfish only. The three transplanted macrophytes grew rapidly when protected from grazing in both lake enclosures, demonstrating that abiotic conditions for growth were suitable. Crayfish strongly reduced biomass and survival of all three macrophyte species while waterfowl and fish had no additive effects. Gut contents showed that crayfish were mostly carnivorous, but also consumed macrophytes. We show that P. clarkii strongly inhibit macrophyte development once favourable abiotic conditions for macrophyte growth are restored. Therefore, expansion of invasive crayfish poses a novel threat to the restoration of shallow water bodies in north-western Europe. Prevention of introduction and spread of crayfish is urgent, as management of invasive crayfish populations is very difficult.     

Functional groups in piscivorous fishes

Piscivory is a key ecological function in aquatic ecosystems, mediating energy flow within trophic networks. However, our understanding of the nature of piscivory is limited; we currently lack an empirical assessment of the dynamics of prey capture and how this differs between piscivores. We therefore conducted aquarium‐based performance experiments, to test the feeding abilities of 19 piscivorous fish species. We quantified their feeding morphology, striking, capturing, and processing behavior. We identify two major functional groups: grabbers and engulfers. Grabbers are characterized by horizontal, long‐distance strikes, capturing their prey tailfirst and subsequently processing their prey using their oral jaw teeth. Engulfers strike from short distances, from high angles above or below their prey, engulfing their prey and swallowing their prey whole. Based on a meta‐analysis of 2,209 published in situ predator–prey relationships in marine and freshwater aquatic environments, we show resource partitioning between grabbers and engulfers. Our results provide a functional classification for piscivorous fishes delineating patterns, which transcend habitats, that may help explain size structures in fish communities.     

Disturbance and species displacement: different tolerances to stream drying and desiccation in a native and an invasive crayfish

1. Crayfish are among the most threatened taxa in the world and invasive crayfish are the primary cause of the decline of native crayfish. Most research has emphasised biotic interactions as the mechanism by which native crayfish are displaced by invasives, although crayfish occupy variable environments and the role of disturbance in facilitating crayfish invasion and displacement is understudied. 2. We compared tolerance to a disturbance, stream drying, in a native and invasive crayfish as a potential mechanism to explain their distribution. Our experiments and observations were conducted across scales, from laboratory environmental chambers to stream mesocosms to field sampling. We hypothesised that the invasive crayfish would be more tolerant of desiccation than the native, and that this physiological distinction between the two would be reflected in their distribution in relation to stream drying. 3. In the laboratory, the native crayfish Orconectes eupunctus was less tolerant of desiccation than the invasive Orconectes neglectus chaenodactylus, with all native crayfish dying within 2 days without water, while some of the invasive crayfish survived for nearly 2 weeks. Under simulated stream drying in mesocosms, only the native O. eupunctus survived less well than in a control. Field sampling demonstrated a significant negative relationship between O. eupunctus density and low summer flows, while O. neglectus density was positively associated with low summer flows. The greater resistance of O. neglectus to drying could, through priority effects, inhibit recolonisation by O. eupunctus once flow resumes. 4. Abiotic disturbances are potentially important to the displacement of native by invasive crayfish. Disturbance mediated displacement of aquatic species provides both an opportunity to conserve native species by maintaining or restoring habitat and disturbance regimes and is also a challenge due to increasing human water demand, flow regime alteration and global climate change.     

Bilateral linkage of monomorphic and dimorphic limb sizes in fiddler crabs

In this study, the subject of whether investment in one bilateral structure was linked to investment in the homologous bilateral opposite structure was investigated. Male fiddler crabs (genus Uca, family Ocypodidae) displayed strong bilateral claw differentiation of function and size, which are used for feeding (minor claw) or display/combat (major claw). Females had similar‐sized feeding claws. Linkage between claw size was investigated by estimating the deviations from an overall fitted regression of claw length to body size. The positive correlations of the deviations of claw size for major and minor claws of males and between right and left claws of females, relative to body size, suggested a linkage in investment between one claw and the corresponding claw on the other side of the body, for both monomorphic females and dimorphic males. A signal to send resources may be effectively gated to the claw complex, suggesting that positively correlated resources are allocated to both claws. Positive correlations were also found at the interspecific level. The fiddler crab model, described here, gives access to study the linkage in symmetric and asymmetric bilateral structures in the same species with a connection to the macroevolutionary level.     

Mud crabs (Xanthidae) in Chesapeake Bay: claw characteristics and predation on epifaunal bivalves

Abstract. We examined claw characteristics of mud crabs (Eurypanopeus depressus, Rhithropanopeus harrisii) to determine if one crab species was potentially more powerful than the other. We related our findings to the abilities of individuals of each species to open epifaunal mytiliform bivalves (Ischadium recurvum; Mytilopsis leucophaeata) that occur on beds of eastern oysters (Crassostrea virginica) in mesohaline Chesapeake Bay. There were high correlations between claw width or height and claw length, and between claw length and carapace width for both mud crab species. The mechanical advantage or “grip strength’ of the crusher and cutter claws of both species did not change with crab size (carapace width) and did not differ between sexes in each species, nor did the cutter data differ between species. However, individuals of E. depressus had a significantly stronger crusher claw grip than did those of R. harrisii. Data on mechanical advantage for both species were similar to values reported in the literature for members of other xanthid crab species. These values in turn overlapped those reported for calappid, cancrid, majid, and grapsid crabs, and were greater than those of various species of portunid crabs and individual species of fiddler crab, lobster, crayfish, and ghost shrimp. When simultaneously presented with the two species of bivalves, the mud crabs E. depressus chose mussels of M. leucophaeata first and crabs of R. harrisii chose mussels of I. recurvum first about two‐thirds of the time; ultimately, the crabs ate both bivalve species in >50% of the choice experiments. The size range in E. depressus was greater than that in R. harrisii, and crabs of E. depressus opened larger bivalves than did crabs of R. harrisii, although similar‐sized individuals of the two crab species overlapped in their ability to open bivalves of both species. In Mytilopsis leucophaeata, there is probably no size refuge from predation by the mud crabs whereas the larger mussels of I. recurvum do have a refuge in size.     

Preventing overexploitation in a mutualism: partner regulation in the crayfish–branchiobdellid symbiosis

For a symbiosis to be a mutualism, benefits received must exceed costs incurred for both partners. Partners can prevent costly overexploitation through behaviors that moderate interactions with the other symbiont. In a symbiosis between crayfish and branchiobdellidan annelids, the worms can increase crayfish survival and growth by removing fouling material from the gills. However, overexploitation by the worms is possible and results in damage to host gills. We used behavioral observations to assess the degree to which two species of crayfish (Cambarus chasmodactylus and Orconectes cristavarius) use grooming to moderate their interaction with branchiobdellids. We found that grooming could effectively reduce worm numbers, and the proportion of total grooming directed at worms differed between crayfish species and as a function of worm number. O. cristavarius increased grooming in response to the addition of a single worm, while C. chasmodactylus only increased grooming in response to ten worms. These differences in the number of worms that trigger grooming behavior reflect differences between crayfish species in field settings. We also assessed whether antibacterial compounds in circulating crayfish hemolymph could limit bacterial gill fouling. O. cristavarius hemolymph inhibited some test bacteria more effectively than C. chasmodactylus did. Differences in the antibacterial properties of crayfish hemolymph may therefore help explain differences in both worm-directed grooming and worm loads in the field. We conclude that crayfish can use grooming to reduce worm numbers, which could lower the potential for gill damage, and that the level of grooming varies between crayfish species.     

Differences Found in the Macroinvertebrate Community Composition in the Presence or Absence of the Invasive Alien Crayfish,Orconectes hylas

Introductions of alien species into aquatic ecosystems have been well documented, including invasions of crayfish species; however, little is known about the effects of these introductions on macroinvertebrate communities. The woodland crayfish (Orconectes hylas (Faxon)) has been introduced into the St. Francis River watershed in southeast Missouri and has displaced populations of native crayfish. The effects of O. hylas on macroinvertebrate community composition were investigated in a fourth-order Ozark stream at two locations, one with the presence of O. hylas and one without. Significant differences between sites and across four sampling periods and two habitats were found in five categories of benthic macroinvertebrate metrics: species richness, percent/composition, dominance/diversity, functional feeding groups, and biotic indices. In most seasons and habitat combinations, the invaded site had significantly higher relative abundance of riffle beetles (Coleoptera: Elmidae), and significantly lower Missouri biotic index values, total taxa richness, and both richness and relative abundance of midges (Diptera: Chironomidae). Overall study results indicate that some macroinvertebrate community differences due to the O. hylas invasion were not consistent between seasons and habitats, suggesting that further research on spatial and temporal habitat use and feeding ecology of Ozark crayfish species is needed to improve our understanding of the effects of these invasions on aquatic communities.     

Shelter-seeking behavior of crayfish, <Emphasis Type="Italic">Procambarus clarkii,</Emphasis> in elevated carbon dioxide

Carbon dioxide has been found to produce various negative consequences for a number of aquatic species and is projected to rise in the future for many aquatic ecosystems. Crayfish act as indicators of water quality and function as keystone species in aquatic food webs; however, there is a paucity of research on how crayfish may respond to elevated CO₂. This study quantified how shelter-seeking behavior in freshwater crayfish (e.g., family Cambaridae), a behavior critical for survival and fitness, may change following exposure to elevated pCO₂. Red Swamp crayfish (Procambarus clarkii, Girard, 1852) were exposed to one of three potential levels of dissolved CO₂ that could be found in freshwater basins currently or under future climate change conditions: Control (2 levels as the respective initial exposure. The treatment aquarium contained a shelter and was divided into three equal sections based on proximity to that shelter. Crayfish proximity to the shelter (defined by the tank sections) in the treatment aquarium was monitored every 5 s for a 2-min trial. Crayfish spent differing amounts of time in differing zones of the experiment and had different levels of activity, depending on their pCO₂ exposure; crayfish acclimated to High pCO₂ increased their time spent hiding and decreased their overall activity when compared to the Low pCO₂ and Control treatments. Augmented shelter-seeking behavior may affect crayfish social hierarchies, feeding, mating, and mortality, which could generate cascading effects on the ecology of many freshwater ecosystems.     

Ecological redundancy between coral reef sharks and predatory teleosts

Reef sharks may be ecologically redundant, such that other mesopredatory fishes compensate for their functions when they decline in number, preventing trophic cascades. Oral jaw gape, hereafter referred to as gape, determines maximum prey size in many piscivores and therefore affects the size structure of prey assemblages. Here, we examine whether gape and maximum prey size differ between five species of reef shark and 21 species of teleost (n?=?754) using data collected from 38 reefs in the Indo-Pacific. Sharks displayed relatively small gape dimensions compared to most teleost species and, at smaller sizes, the giant trevally Caranx ignobilis and other teleosts may be able to consume larger prey than similar-sized sharks. However, ecological redundancy between reef sharks and teleosts appears to decline at larger sizes, such that the grey reef shark Carcharhinus amblyrhynchos, for example, may be capable of consuming larger prey than any other reef predator at its largest sizes, regardless of prey body shape. Moreover, sharks may be able to consume proportionally larger prey as they grow, in contrast to reef teleosts, which may largely be limited by their gapes to ever-smaller prey as a proportion of their body size. Our results also suggest that reef sharks may be unable to swallow whole prey that are >?36% of their length, consistent with gut-content studies. Conservation of reef ecological function may therefore depend not only on the protection of sharks but also particular size classes and key components of the mesopredatory guild.

     

The diet of the spiny-cheek crayfish Orconectes limosus in the Czech Republic

The composition of the diet of the invasive spiny-cheek crayfish Orconectes limosus was studied using qualitative and quantitative analyses of stomach contents. A total of 368 specimens collected in 2003–2005 and 2008 in Czech localities were examined, predominantly from the Labe (Elbe) and Vltava River basins. Food components were compared for three size classes of crayfish and both sexes. The following conclusions were reached: (1) the spiny-cheek crayfish is an omnivorous species consuming plants, animals and detritus; (2) quantitatively, the main food component of O. limosus is detritus, while the plant component was second; (3) O. limosus may swallow whole food particles up to 4 mm in size, and the bodies of small animals may sometimes be found undamaged in their stomachs.     

AFLP-PCR and RAPD-PCR evidences of the transmission of the pathogen Aphanomyces astaci (Oomycetes) to wild populations of European crayfish from the invasive crayfish species, Procambarus clarkii

Aphanomyces astaci (Oomycetes) is responsible for the crayfish plague disease. This species is endemic of North America and five genotypes have been described using RAPD-PCR. The red swamp crayfish, Procambarus clarkii, is one of the most widely spread North American species and invasive in the world. However, no outbreaks on its specific genotype, i.e., genotype D, have ever been described in nature. We investigated three major series of crayfish plague outbreaks in indigenous crayfish populations of Austropotamobius pallipes, located in the areas of influence of P. clarkii. All samples collected tested positive for A. astaci using a rnDNA ITS-PCR test. We also performed an AFLP-PCR analysis on 19 isolates, and found that all isolates belong to genotype D. These isolates exhibited similar properties, i.e., adaptation to warm temperatures. We demonstrate, for the first time, the transmission of A. astaci genotype D to indigenous European populations of crayfish, and confirm that the properties of adaptation to warm water temperatures seem to be a specific character of genotype D. The results of this work emphasize once more the need of controlling invasive species and its trade, since they can carry harmful pathogens with specific adaptations or increased virulence in new environments.     

Complex impact of an invasive crayfish on freshwater food webs

Invasive alien species can have complex effects on native ecosystems, and interact with multiple components of food webs, making it difficult a comprehensive quantification of their direct and indirect effects. We evaluated the relationships between the invasive crayfish, Procambarus clarkii, amphibian larvae and predatory insects, to quantify crayfish impacts on multiple levels of food webs, and to evaluate whether crayfish predation of aquatic insects has indirect consequences for their preys. We used pipe sampling to assess the abundance of crayfish, amphibian larvae and their major predators (Ditiscidae, Notonectidae and larvae of Anisoptera) in invaded and uninvaded ponds within a human dominated landscape. We disentangled the multivariate effects of P. clarkii on different components of food web through a series of constrained redundancy analyses. The crayfish had a negative, direct impact on both amphibian communities and their predators. Amphibian abundance was negatively related to both predators. However, the negative, direct effects of crayfish on amphibians were much stronger than predation by native insects. Our results suggest that this crayfish impacts multiple levels of food webs, disrupting natural prey-predator relationships.