Effects of covering behavior and exposure to a predatory crab Charybdis japonica on survival and HSP70 expression of juvenile sea urchins Strongylocentrotus intermedius

Metabolomics and microbiome co-analysis reveals altered innate immune responses in Charybdis japonica following Aeromonas hydrophila infection

A comprehensive bioinformatics analysis was conducted to elucidate the innate immune response of Charybdis japonica following exposure to Aeromonas hydrophila. This study integrated metabolomics, 16S rRNA sequencing, and enzymatic activity data to dissect the immune mechanisms activated in response to infection. Infection with A. hydrophila resulted in an increased abundance of beneficial intestinal genera such as Photobacterium spp., Rhodobacter spp., Polaribacter spp., Psychrilyobacter spp., and Mesoflavibacter spp. These probiotics appear to suppress A. hydrophila colonization by competitively dominating the intestinal microbiota. Key metabolic pathways affected included fatty acid biosynthesis, galactose metabolism, and nitrogen metabolism, highlighting their role in the crab's intestinal response. Enzymatic analysis revealed a decrease in activities of hexokinase, phosphofructokinase, and pyruvate kinase, which are essential for energy homeostasis and ATP production necessary for stress responses. Additionally, reductions were observed in the activities of acetyl-CoA carboxylase and fatty acid synthase. Gene expression analysis showed downregulation in Peroxiredoxin 1 (PRDX1), Peroxiredoxin 2 (PRDX2), glutathione-S-transferase (GST), catalase (CAT), and glutathione (GSH), with concurrent increases in malondialdehyde (MDA) levels, indicating severe oxidative stress. This study provides insights into the molecular strategies employed by marine crabs to counteract bacterial invasions in their natural habitat.

Top-down effects of intraspeciflic predator behavioral variation

Among-individual variation in predator traits is ubiquitous in nature. However, variation among populations in this trait variation has been seldom considered in trophic dynamics. This has left unexplored (a) to what degree does among-individual variation in predator traits regulate prey populations and (b) to what degree do these effects vary spatially. We address these questions by examining how predator among-individual variation in functional traits shapes communities across habitats of varying structural complexity, in field conditions. We manipulated Chinese mantis (Tenodera sinensis) density (six or twelve individuals) and behavioral trait variability (activity level by movement on an open field) in experimental patches of old fields with varying habitat complexity (density of plant material). Then, we quantified their impacts on lower trophic levels, specifically prey (arthropods > 4 mm) and plant biomass. Predator behavioral variability only altered prey biomass in structurally complex plots, and this effect depended on mantis density. In the plots with the highest habitat complexity and mantis density, behaviorally variable groups decreased prey biomass by 40.3%. In complex plots with low mantis densities, low levels of behavioral variability decreased prey biomass by 32.2%. Behavioral variability and low habitat complexity also changed prey community composition, namely by increasing ant biomass by 881%. Our results demonstrate that among-individual trait variation can shape species-rich prey communities. Moreover, these effects depend on both predator density and habitat complexity. Incorporating this important facet of ecological diversity revealed normally unnoticed effects of functional traits on the structure and function of food webs.

The dopamine receptor antagonist haloperidol disrupts behavioral responses of sea urchins and sea stars

Despite lacking a brain and having an apparent symmetrically pentaradial nervous system, echinoderms are capable of complex, coordinated directional behavioral responses to different sensory stimuli. However, very little is known about the molecular and cellular mechanisms underlying these behaviors. In many animals, dopaminergic systems play key roles in motivating and coordinating behavior, and although the dopamine receptor antagonist haloperidol has been shown to inhibit the righting response of the sea urchin Strongylocentrotus purpuratus, it is not known whether this is specific to this behavior, in this species, or whether dopaminergic systems are needed in general for echinoderm behaviors. We found that haloperidol inhibited multiple different behavioral responses in three different echinoderm species. Haloperidol inhibited the righting response of the sea urchin Lytechinus variegatus and of the sea star Luidia clathrata. It additionally inhibited the lantern reflex of S. purpuratus, the shell covering response of L. variegatus and the immersion response of L. variegatus, but not S. purpuratus or L. clathrata. Our results suggest that dopamine is needed for the neural processing and coordination of multiple different behavioral responses in a variety of different echinoderm species.

Exposure of adult sea urchin Strongylocentrotus intermedius to stranded heavy fuel oil causes developmental toxicity on larval offspring

Heavy fuel oil (HFO) spills pose serious threat to coastlines and sensitive resources. Stranded HFO that occurs along the coastline could cause long-term and massive damage to the marine environment and indirectly affect the survival of parental marine invertebrates. However, our understanding of the complex associations within invertebrates is primarily limited, particularly in terms of the toxicity effects on the offspring when parents are exposed to stranded HFO. Here, we investigated the persistent effects on the early development stage of the offspring following stranded HFO exposure on the sea urchin Strongylocentrotus intermedius. After 21 d exposure, sea urchins exhibited a significant decrease in the reproductive capacity; while the reactive oxygen species level, 3-nitrotyrosine protein level, protein carbonyl level, and heat shock proteins 70 expression in the gonadal tissues and gametes significantly increased as compared to the controls, indicating that HFO exposure could cause development toxicity on offspring in most traits of larval size. These results suggested that the stranded HFO exposure could increase oxidative stress of gonadal tissues, impair reproductive functions in parental sea urchins, and subsequently impact on development of their offspring. This study provides valuable information regarding the persistent toxicity effects on the offspring following stranded HFO exposure on sea urchins.

Macroalgae and interspecific alarm cues regulate behavioral interactions between sea urchins and sea cucumbers

Sea urchins and sea cucumbers are mutually beneficial organisms in kelp ecosystem. As herbivores, sea urchins process kelp through feeding and egestion, providing inaccessible food for benthic consumers such as sea cucumbers. Sea urchins in turn profit from the sediment cleaned by sea cucumbers. However, behavioral interactions between them remain poorly understood, which greatly hampers our understanding on the relationship between ecologically important benthic species in marine ecosystems and the regulating mechanism. The present study investigated behavioral interactions between sea urchins Strongylocentrotus intermedius and sea cucumbers Apostichopus japonicus in laboratory conditions. We revealed that the presence of sea urchins caused significant higher speed movement of A. japonicus. Interestingly, the negative effects of S. intermedius on A. japonicus were significantly reduced in the shared macroalgal area. For the first time, we found the interspecific responses to alarm cues between sea cucumbers and sea urchins. Conspecific responses were significantly larger than the interspecific responses in both sea urchins and sea cucumbers. This indicates that interspecific response to alarm cues is an efficient approach to anti-predation and coexistence in mutually beneficial organisms. The present study shed light on the interspecific relationships and coexistence between sea urchins and sea cucumbers in kelp ecosystem.

Best Dressed Test: A Study of the Covering Behavior of the Collector Urchin Tripneustes gratilla

Many sea urchin genera exhibit cryptic covering behaviors. One such behavior has been documented in the sea urchin Tripneustes gratilla, and previous studies have theorized that this behavior serves as protection from UV radiation. However, other hypotheses have been presented such as protection from predators or added weight to help T. gratilla resist strong currents. A field study was conducted in October-November 2015 in Moorea, French Polynesia to assess urchin covering behavior in natural habitats. The study found that urchins partially underneath rocks covered more, and with more algae, than urchins totally underneath rocks. To test if this behavior was driven by light intensity, a series of 30-minute experimental trials were run on 10 individuals in bright and dim conditions. Individuals were given red and clear plastic, and percent cover of each was recorded. These tests were repeated once fifty percent of spines had been removed from the urchin, in order to determine whether spine loss affects T. gratilla covering behavior. The study found that urchins had a distinct preference for cover that best protects them from UV radiation. Spine loss did not significantly affect urchin ability to cover, and urchins with removed spines still preferred opaque cover. Additionally, covering behavior was mapped onto a phylogeny of echinoderms to determine how it might have evolved. Understanding urchin covering behavior more fully is a step towards an understanding of the evolution of cryptic behavior across species.