Animal contests and microplastics: evidence of disrupted behaviour in hermit crabs Pagurus bernhardus

Microplastics are ubiquitous in global marine systems and may have negative impacts on a vast range of species. Recently, microplastics were shown to impair shell selection assessments in hermit crabs, an essential behaviour for their survival. Hermit crabs also engage in ‘rapping’ contests over shells, based on cognitive assessments of shell quality and opponent fighting ability and, hence, are a useful model species for examining the effects of microplastics on fitness-relevant behaviour in marine systems. Here, we investigated how a 5-day microplastic exposure (25 microplastics/litre) affected the dynamics and outcome of 120 staged hermit crab contests. Using a 2 × 2 factorial design, we examined how microplastics (i.e. presence or absence) and contestant role (i.e. attacker or defender) affected various behavioural variables. Significantly higher raps per bout were needed to evict microplastic-treated defenders when attackers were pre-exposed to control conditions (i.e. no plastic). Also, significantly longer durations of rapping bouts were needed to evict control-treated defenders when attackers were pre-exposed to microplastics. We suggest that microplastics impaired defenders' ability to identify resource holding potential and also affected attackers’ rapping strength and intensity during contests. These impacts on animal contests indicate that microplastics have broader deleterious effects on marine biota than currently recognized.

Ocean Acidification Amplifies the Olfactory Response to 2-Phenylethylamine: Altered Cue Reception as a Mechanistic Pathway?

With carbon dioxide (CO2) levels rising dramatically, climate change threatens marine environments. Due to increasing CO2 concentrations in the ocean, pH levels are expected to drop by 0.4 units by the end of the century. There is an urgent need to understand the impact of ocean acidification on chemical-ecological processes. To date, the extent and mechanisms by which the decreasing ocean pH influences chemical communication are unclear. Combining behaviour assays with computational chemistry, we explore the function of the predator related cue 2-phenylethylamine (PEA) for hermit crabs (Pagurus bernhardus) in current and end-of-the-century oceanic pH. Living in intertidal environments, hermit crabs face large pH fluctuations in their current habitat in addition to climate-change related ocean acidification. We demonstrate that the dietary predator cue PEA for mammals and sea lampreys is an attractant for hermit crabs, with the potency of the cue increasing with decreasing pH levels. In order to explain this increased potency, we assess changes to PEA’s conformational and charge-related properties as one potential mechanistic pathway. Using quantum chemical calculations validated by NMR spectroscopy, we characterise the different protonation states of PEA in water. We show how protonation of PEA could affect receptor-ligand binding, using a possible model receptor for PEA (human TAAR1). Investigating potential mechanisms of pH-dependent effects on olfactory perception of PEA and the respective behavioural response, our study advances the understanding of how ocean acidification interferes with the sense of smell and thereby might impact essential ecological interactions in marine ecosystems.

The effect of plastic leachates on respiration and foraging behaviour in hermit crabs

<p>Plastic production has soared since the 1950s, with the last decade seeing an  increase of 43% from 250Mt (million tonnes) in 2009 to 368Mt in 2019. Plastics and their associated chemical congeners (variants of chemical structures) which enter the environment further exacerbate pollution within already contaminated ecosystems. In this study, we investigated the effect of plastic leachate on the common littoral marine hermit crab Pagurus bernhardus,  a species  at great risk from potential adverse effects of microplastics. The effects of  plastic additives released into the environment via microplastic leaching, and of contaminants adsorbed and accumulated onto the surface of microplastics on marine organisms is understudied. This study sought to (I) investigate whether plastic leachate has an effect on the respiration rate of hermit crabs and, (II) investigate whether plastic leachate has an effect on the foraging behaviour of hermit crabs. We found that within repeated measures design hermit crabs exposed to plastic leachate had different levels of oxygen consumption when compared to their control; with there being an increase or decrease dependent on the leachate type. This is potentially problematic due to high concentrations of microplastics along coastlines which may lead to impaired filtration within crustaceans resulting in lethality and reduced food intake.</p>

Ocean Acidification Amplifies the Olfactory Response to 2-Phenylethylamine: Altered Cue Reception as a Mechanistic Pathway?

With carbon dioxide (CO2) levels rising dramatically, climate change threatens marine environments. Due to increasing CO2 concentrations in the ocean, pH levels are expected to drop by 0.4 units by the end of the century. There is an urgent need to understand the impact of ocean acidification on chemical-ecological processes. To date, the extent and mechanisms by which the decreasing ocean pH influences chemical communication are unclear. Combining behaviour assays with computational chemistry, we explore the function of the predator related cue 2-phenylethylamine (PEA) for hermit crabs (Pagurus bernhardus) in current and end-of-the-century oceanic pH. We demonstrate that this dietary predator cue for mammals and sea lampreys is an attractant for hermit crabs. Furthermore, we show that the potency of the cue increases at pH levels expected for the year 2100. In order to explain this increased potency, we assess changes to PEA’s conformational and charge-related properties as one potential mechanistic pathway. Using quantum chemical calculations validated by NMR spectroscopy, we characterise the different protonation states of PEA in water. We show how protonation of PEA could affect receptor-ligand binding, using a possible model receptor for PEA (human TAAR1). Investigating potential mechanisms of pH dependent effects on olfactory perception of PEA and the respective behavioural response, our study advances the understanding of how ocean acidification interferes with the sense of smell and thereby might impact essential ecological interactions in marine ecosystems.

Evolutionary loss of threat display in more social species: phylogenetic comparisons, natural interactions in the wild, and experiments with models

Fitness can be increased dramatically by communication. So why, given the benefits of communication, would displays ever be completely lost evolutionarily? Threat displays, in particular, are relatively cheap to produce and are precursors of attack, so should be especially hard for both senders and receivers to lose completely. Here we explore an evolutionary transition in sociality, testing whether complete evolutionary loss of threat display has occurred in ‘more social’ hermit crab species, which interact more frequently with conspecifics. First, we synthesised literature and observations on the presence versus absence of threat display across hermit crab species, mapping this information onto a phylogenetic tree. We found that all ‘less social’ species — marine and terrestrial — produce threat displays, consistent with threat display being the ancestral state. But ‘more social’ terrestrial species, which are highly derived, do not produce a threat display, suggesting an evolutionary loss. Next, we contrasted natural interactions in the wild within a less social species (Pagurus bernhardus) versus within a more social species (Coenobita compressus), finding that the less social species, despite a lower rate of social encounter, had a higher rate of display per encounter (24%). In contrast, the more social species’ rate of display per encounter was negligible (<1%), effectively indicating a loss in production. Finally, we experimentally reanimated threat display in the more social species, using postured models to test whether receivers retained any responsiveness to threat display. Starkly, receivers were not deterred by threat display, showing equal responsiveness across both threat and non-threat models, regardless of whether the models were stationary or dynamically moving. Our results thus reveal a case of complete collapse of communication involving threat display, implicating the social environment in this loss. In more social species, an extreme dependence on conspecific-derived shells likely drove a ‘desperado effect’, with threat displays being lost because they could not stop others from pursuing these valuable resources.

Animal Personality and Investment in Reproduction: Hermit Crabs and Other Crustaceans as Model Organisms

Animal personality has been demonstrated in a wide range of taxa, including crustaceans. This chapter defines personality as consistent variation in behavior among individuals. It describes related ideas about how individuals can differ in the way they adjust their behavior to match the current situation (“behavioral plasticity”) and how they might differ in how consistent their behavior is within a particular situation (“within individual variation”). Such behavioral variation may represent a component of wider syndromes encompassing among-individual differences in life history traits such as growth, metabolism, and fecundity. First, the chapter reviews studies that have tested these ideas in a range of crustacean species. It then focuses on a series of studies on the common European hermit crab Pagurus bernhardus. In both cases, it describes details of the experimental approaches and analyses used to study personality in crustaceans. While boldness appears to be a key personality trait in hermit crabs and other crustaceans, bold individuals are not necessarily those with the greatest success in acquiring resources or with the greatest life history productivity (i.e., investment in growth and reproduction). Rather, individuals that win fights and invest heavily in respiratory pigments and in reproduction appear to behave consistently more cautious when compared to other individuals from the same population. Despite these initial findings, there is a paucity of studies that investigate links between personality and mating behavior in crustaceans, or that investigate the behavior of females; these areas should be priorities for future work.

First insights into the phylogeography and demographic history of the common hermit crab Pagurus bernhardus (Linnaeus, 1758) (Decapoda: Anomura: Paguridae) across the Eastern Atlantic and North Sea

The common hermit crab Pagurus bernhardus (Linnaeus, 1758) is an abundant and ecologically important benthic crustacean in the northeastern Atlantic Ocean. While this species has been intensively studied in terms of its ecology, physiology, behavior, and larval development, knowledge about its population structure and demographic history is still lacking. We examined, for the first time, the genetic variability of P. bernhardus by analyzing two mitochondrial gene fragments (CO1 and 16S) from more than 150 specimens collected from various locations from the Iberian Peninsula to Norway. Our results provide evidence for a significant genetic structure according to the sampled regions for both genetic markers. Furthermore, a comprehensive demographic history reconstruction, mainly based on neutrality tests and a Bayesian Skyline Plot (CO1), revealed a recent demographic expansion of P. bernhardus that preceded the Last Glacial Maximum. Such pattern of retrieved demographic trend could have been likely a successive process to historical contraction of the species into potential climate refugia within the surveyed geographic spectrum.

Microplastics disrupt hermit crab shell selection

Microplastics (plastics < 5 mm) are a potential threat to marine biodiversity. However, the effects of microplastic pollution on animal behaviour and cognition are poorly understood. We used shell selection in common European hermit crabs ( Pagurus bernhardus ) as a model to test whether microplastic exposure impacts the essential survival behaviours of contacting, investigating and entering an optimal shell. We kept 64 female hermit crabs in tanks containing either polyethylene spheres ( n = 35) or no plastic ( n = 29) for 5 days. We then transferred subjects into suboptimal shells and placed them in an observation tank with an optimal alternative shell. Plastic-exposed hermit crabs showed impaired shell selection: they were less likely than controls to contact optimal shells or enter them. They also took longer to contact and enter the optimal shell. Plastic exposure did not affect time spent investigating the optimal shell. These results indicate that microplastics impair cognition (information-gathering and processing), disrupting an essential survival behaviour in hermit crabs.

Development of Learning Media Based on Arthropoda (Crustacea) Filum Diversity in Kampai Island of SD Negeri 050778 Langkat District, Sumatera Utara

This study aims to develop learning media that can be used by natural science teachers in SD Negeri 050778 by referring to RND-based media development methods (Research and Development) which will later use descriptive analysis methods and development methods. In making Blended Learning media where this media is in the form of learning videos using the Camtasia and Wondershare Quiz Creator application contains recorded video clips and questions about how to sample species, species diversity, and species collection techniques from Phylum Arthropods at SD Negeri 050778 Kampai Langkat Island, North Sumatra. The purpose of this research is descriptive analysis which is to obtain data on the diversity of the Artrhopoda Phylum from the Crustacean class which is very numerous and easily found around the coast of the island of Kampai. Crustacean diversity data obtained were analyzed using species abundance analysis method. Then the learning video development data will then be tested on students and science teachers as a test sample. From the field results found 8 dominant species of the Decapoda Order, including the Mangrove Crab (Scylla serrate), tiger shrimp (Panaeus monodon), Lobster Shrimp (Panulirus sp.), Ghost Crab (Ocypode kuhlii), Crab Uca Viola (Uca vocans) , Uca Petarung Crab (Uca annulipes), Centipede Shrimp (Squilla mantis), Klomang (Bernhardus Pagurus). From the three stations where Crustacea species sampling locations were obtained a diversity index of 0.85% at Station 1 with Species dominance, namely Centipede Shrimp, then 1.76% at Station II with Species dominance, namely Klomang (Pagurus bernhardus), and 0 , 43% with species dominance, namely Shrimp Prawn (Panaeus monodoni). From the analysis calculations of 30 students the results of a large group trial for development data are: (a) a group of 30 students an average of 97.85% (very decent), (2) Science Teacher Test Data of 87% (feasible category).