A pheromone bouquet controls the reproductive behaviour of the male shore crab, Carcinus maenas

The reproduction of many brachyuran crustaceans involves the formation of mating pairs often around the time of the female moult with attraction of a sexual partner and mating behaviour controlled by sex pheromones. In shore crabs, Carcinus maenas, females produce sex pheromones that are released in the urine. High Performance Liquid Chromatography analysis (HPLC) of female urine shows that the pheromone, identified as the nucleotide uridine diphosphate (UDP), elutes as an unresolved peak with structurally related nucleotides. We examined female urine samples over the moult cycle and detected UDP as well as uridine triphosphate (UTP). Bioassays were conducted to establish the possibility of a blend of nucleotides forming a sex pheromone bouquet in C. maenas. Whilst UDP induced the male mate guarding behaviour (cradling), a mixture of the two nucleotides at a ratio of 4:1 UDP:UTP elicited an even stronger mating response than either UDP or UTP individually. The urine concentration and composition of these nucleotides changes over the moult period pre and post ecdysis, providing evidence that a pheromone bouquet composition is not always constant. The change of the bouquet is related to the physiological state of the sender, here the moult cycle. Our study unravels the functionality of reaction-specific molecules in a pheromone bouquet. Whilst UDP is the mating signal, UTP acts as an attractant and combined they maximise the reproductive response. The use of bouquets provides species-specificity, potentially enabling reproductive isolation of sympatric species, and contains valuable information on the physiological state of the sender.

Behavioural Competition in the Intertidal Shore Crab, Petrolisthes elongatus

<p>Competition is a well-documented ecological interaction that underpins community structures and much of population ecology. Physical characteristics such as size, age, sex and weaponry all have an important part to play in how an organism competes, and for many animals, competition is mediated by behavioural patterns. Outcomes of these competitive interactions are not only driven by these characteristics, but by the environmental conditions and external pressures that influence them. The focal species of my study is Petrolisthes elongatus (H. Milne Edwards, 1837), a porcellanid crab that aggregates in high densities among cobblestone beaches along the intertidal shores of New Zealand and Tasmania. They utilize rocks and crevices as shelter spaces to protect themselves from environmental and predation pressures, displaying variation in physical characteristics, such as sexual dimorphism and autotomy, as well as high levels of behavioural complexity. I used laboratory experiments with crabs collected from the field and placed them in shelter-limited tanks under the following comparisons; 1) adult and juvenile males, 2) males and females, 3) ovigerous and non-ovigerous females, and 4) autotomized and non-autotomized males. For each of these experiments I used three different environmental conditions; 1) a control high tide, 2) a low tide treatment (where water was drained from the experimental tank), and 3) with the presence of a predator, a juvenile spiny rock lobster (Jasus edwarsii). Each experiment was recorded for 8 hours, where time spent under shelter and shoving interactions among individuals were counted. In the adult vs. juvenile and male vs. female experiments, smaller individuals spent a significantly more time under shelter than larger conspecifics, but increasing size resulted in more time spent under shelter in the autotomized vs. non-autotomized experiment. In all experiments, smaller individuals initiated the least amount of competitive interactions, and each size class was more likely to displace a smaller individual from a shelter, than a larger one. There was no significant difference in the time spent under shelter between males and females, but ovigerous females and autotomized males spent significantly more time under shelter than their respective competitors. Males also engaged in more shoving interactions than females, with smaller classes of males displacing larger classes of females from shelter spaces. Ovigerous females also outcompeted non-ovigerous conspecifics in the large majority of competitive interactions, and autotomized individuals engaged in significantly more contests than non-autotomized conspecifics. In all experiments, the presence of a predator had no effect on the number of shoving interactions and only resulted in an increase in time spent under shelter for individuals in the male vs. female and ovigerous vs. non-ovigerous experiments. A field survey on body to cheliped size ratios, autotomy and claw punctures counts was also conducted in support of the shelter-competition experiments. Crabs were collected over a one-month period in November 2018, brought back to the lab to be sexed, measured (Carapace Width, BW; and Cheliped Length, CL) and then surveyed for autotomy and claw puncture wounds. Juveniles of both sex (BW =</p>

Behavioural Competition in the Intertidal Shore Crab, Petrolisthes elongatus

<p>Competition is a well-documented ecological interaction that underpins community structures and much of population ecology. Physical characteristics such as size, age, sex and weaponry all have an important part to play in how an organism competes, and for many animals, competition is mediated by behavioural patterns. Outcomes of these competitive interactions are not only driven by these characteristics, but by the environmental conditions and external pressures that influence them. The focal species of my study is Petrolisthes elongatus (H. Milne Edwards, 1837), a porcellanid crab that aggregates in high densities among cobblestone beaches along the intertidal shores of New Zealand and Tasmania. They utilize rocks and crevices as shelter spaces to protect themselves from environmental and predation pressures, displaying variation in physical characteristics, such as sexual dimorphism and autotomy, as well as high levels of behavioural complexity. I used laboratory experiments with crabs collected from the field and placed them in shelter-limited tanks under the following comparisons; 1) adult and juvenile males, 2) males and females, 3) ovigerous and non-ovigerous females, and 4) autotomized and non-autotomized males. For each of these experiments I used three different environmental conditions; 1) a control high tide, 2) a low tide treatment (where water was drained from the experimental tank), and 3) with the presence of a predator, a juvenile spiny rock lobster (Jasus edwarsii). Each experiment was recorded for 8 hours, where time spent under shelter and shoving interactions among individuals were counted. In the adult vs. juvenile and male vs. female experiments, smaller individuals spent a significantly more time under shelter than larger conspecifics, but increasing size resulted in more time spent under shelter in the autotomized vs. non-autotomized experiment. In all experiments, smaller individuals initiated the least amount of competitive interactions, and each size class was more likely to displace a smaller individual from a shelter, than a larger one. There was no significant difference in the time spent under shelter between males and females, but ovigerous females and autotomized males spent significantly more time under shelter than their respective competitors. Males also engaged in more shoving interactions than females, with smaller classes of males displacing larger classes of females from shelter spaces. Ovigerous females also outcompeted non-ovigerous conspecifics in the large majority of competitive interactions, and autotomized individuals engaged in significantly more contests than non-autotomized conspecifics. In all experiments, the presence of a predator had no effect on the number of shoving interactions and only resulted in an increase in time spent under shelter for individuals in the male vs. female and ovigerous vs. non-ovigerous experiments. A field survey on body to cheliped size ratios, autotomy and claw punctures counts was also conducted in support of the shelter-competition experiments. Crabs were collected over a one-month period in November 2018, brought back to the lab to be sexed, measured (Carapace Width, BW; and Cheliped Length, CL) and then surveyed for autotomy and claw puncture wounds. Juveniles of both sex (BW =</p>

The role of changing pH on olfactory success of predator–prey interactions in green shore crabs, Carcinus maenas

Arguably climate change is one of the biggest challenges faced by many organisms. One of the more significant of these is the decreasing pH level of the ocean, a consequence of the increasing amount of atmospheric CO2 being absorbed. With the current open ocean pH level of 8.15 projected to fall to just over 7.6 in 2100, the impacts could be devastating for marine species reliant upon olfaction to survive. Here, we show that Carcinus maenas (shore crab) can detect and respond to the presence of odour cues from predatory species with no significant change between both current and projected pH conditions. In contrast, C. maenas ability to detect and respond to prey cues is altered in the projected climate change conditions, with a delayed response being observed at pH 7.6. A difference can be seen between males and females, with males detecting prey cues faster than females in reduced pH, suggesting the potential for males to be better acclimated to future climate change conditions. The change in ocean chemistry is postulated to have a fundamental impact on chemical communication systems in aquatic species. Here, we show such negative impacts of altered pH on feeding responses in Carcinus maenas, a typically robust keystone intertidal species and confirm that not all behaviours are affected equally with potentially significant implications for such functional traits and species interactions.

Identification and Full Characterisation of Two Novel Crustacean Infecting Members of the Family Nudiviridae Provides Support for Two Subfamilies

Multiple enveloped viruses with rod-shaped nucleocapsids have been described, infecting the epithelial cell nuclei within the hepatopancreas tubules of crustaceans. These bacilliform viruses share the ultrastructural characteristics of nudiviruses, a specific clade of viruses infecting arthropods. Using histology, electron microscopy and high throughput sequencing, we characterise two further bacilliform viruses from aquatic hosts, the brown shrimp (Crangon crangon) and the European shore crab (Carcinus maenas). We assembled the full double stranded, circular DNA genome sequences of these viruses (~113 and 132 kbp, respectively). Comparative genomics and phylogenetic analyses confirm that both belong within the family Nudiviridae but in separate clades representing nudiviruses found in freshwater and marine environments. We show that the three thymidine kinase (tk) genes present in all sequenced nudivirus genomes, thus far, were absent in the Crangon crangon nudivirus, suggesting there are twenty-eight core genes shared by all nudiviruses. Furthermore, the phylogenetic data no longer support the subdivision of the family Nudiviridae into four genera (Alphanudivirus to Deltanudivirus), as recently adopted by the International Committee on Taxonomy of Viruses (ICTV), but rather shows two main branches of the family that are further subdivided. Our data support a recent proposal to create two subfamilies within the family Nudiviridae, each subdivided into several genera.

Prey preferences, consumption rates and predation effects of Asian shore crabs (Hemigrapsus takanoi) in comparison to native shore crabs (Carcinus maenas) in northwestern Europe

The Asian brush-clawed shore crab Hemigrapsus takanoi was introduced to the northern Wadden Sea (southeastern North Sea) in 2009 and now represents one of the most abundant brachyuran crab species. Abundance studies revealed an increase of mean crab densities on mixed reefs of native blue mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) from 18 individuals m−2 in 2011 to 216 individuals m−2 in 2020. Despite its current high densities only little is known about the feeding habits of H. takanoi, its effects on prey populations and on the associated community in the newly invaded habitat. We summarize results of individual field and laboratory experiments that were conducted to assess feeding habits and consumption effects caused by Asian brush-clawed shore crabs and, additionally, compare the feeding ecology of H. takanoi with the one of the native shore crab Carcinus maenas. Field experiments manipulating crab densities revealed that both crab species affected the recruitment success of blue mussels, Pacific oysters and Australian barnacles (Austrominius modestus) with highest number of recruits at crab exclusion. However, endobenthic polychaetes within the reefs were differently affected. Only the native C. maenas caused a significant reduction in polychaete densities, whereas the introduced H. takanoi had no effect. Additional comparative laboratory studies revealed that single C. maenas consume more juvenile blue mussels than Asian brush-clawed shore crabs of the same size class. When offering amphipods as a mobile prey species, we found the same pattern with higher consumption rates by C. maenas than by H. takanoi. For Asian but not for native shore crabs, we detected a sex-dependent feeding behavior with male H. takanoi preferring blue mussels, while females consumed more amphipods. Considering mean crab densities and feeding behavior, our results suggest that despite lower consumption rates of single crabs, Asian brush-clawed shore crabs can cause stronger impacts on prey organisms than the native C. maenas, because H. takanoi exceeds their densities manifold. A strong impact of the invader on prey populations is supported by low amphipod occurrence at sites where H. takanoi density is high in the study area. Thus, the introduced Asian brush-clawed shore crab is an additional consumer with significant effects on the associated community of mixed reefs of mussels and oysters in the Wadden Sea.

Predation risk increases in estuarine bivalves stressed by low salinity

Salinity drops in estuaries after heavy rains are expected to increase in frequency and intensity over the next decades, with physiological and ecological consequences for the inhabitant organisms. It was investigated whether low salinity stress increases predation risk on three relevant commercial bivalves in Europe. In laboratory, juveniles of Venerupis corrugata, Cerastoderma edule, and the introduced Ruditapes philippinarum were subjected to low salinities (5, 10 and control 35) during two consecutive days and, afterwards, exposed to one of two common predators in the shellfish beds: the shore crab Carcinus maenas and the gastropod Bolinus brandaris, a non-indigenous species present in some Galician shellfish beds. Two types of choice experiment were done: one offering each predator one prey species previously exposed to one of the three salinities, and the other offering each predator the three prey species at the same time, previously exposed to one of the three salinities. Consumption of both predators and predatory behaviour of C. maenas (handling time, rejections, consumption rate) were measured. Predation rates and foraging behaviour differed, with B. brandaris being more generalist than C. maenas. Still, both predators consumed significantly more stressed (salinity 5 and 10) than non-stressed prey. The overall consumption of the native species C. edule and V. corrugata was greater than that of R. philippinarum, likely due to their vulnerability to low salinity and physical traits (e.g., thinner shell, valve gape). Increasing precipitations can alter salinity gradients in shellfish beds, and thus affect the population dynamics of harvested bivalves via predator–prey interactions.