The synergistic effects of increasing temperature and CO2 levels on activity capacity and acid–base balance in the spider crab, Hyas araneus

With global climate change ocean warming and acidification occur concomitantly. In this study, we tested the hypothesis that increasing CO2 levels affect the acid-base balance and reduce the activity capacity of the Arctic spider crab Hyas araneus, especially at the limits of thermal tolerance. Crabs were acclimated to projected oceanic CO2 levels for 12 days (today: 380, towards the year 2100: 750 and 1,120, and beyond: 3,000 µatm) and at two temperatures (1° and 4°C). Effects of these treatments on the righting response (RR) were determined 1) at acclimation temperatures followed by 2) righting when exposed to an additional acute (15 min) heat stress at 12°C. Prior to (resting) and after the consecutive stresses of combined righting activity and heat exposure, acid-base status and lactate contents were measured in the haemolymph. Under resting conditions, CO2 caused a decrease in haemolymph pH and an increase in oxygen partial pressure. Despite some buffering via an accumulation of bicarbonate, the extracellular acidosis remained uncompensated at 1°C, a trend exacerbated when animals were acclimated to 4°C. The additional combined exposure to activity and heat had only a slight effect on blood gas and acid-base status. Righting activity in all crabs incubated at 1° and 4°C was unaffected by elevated CO2 levels or acute heat stress but was significantly reduced when both stressors acted synergistically. This impact was much stronger in the group acclimated at 1°C where some individuals acclimated to high CO2 levels stopped responding. Lactate only accumulated in the haemolymph after combined righting and heat stress. In the group acclimated to 1°C lactate content was highest under normocapnia and lowest at the highest CO2 level in line with the finding that RR was largely reduced. In crabs acclimated to 4°C the RR was less affected by CO2 such that activity caused lactate to increase with rising CO2 levels. In line with the concept of oxygen and capacity limited thermal tolerance, all animals exposed to temperature extremes displayed a reduction in scope for performance, a trend exacerbated by increasing CO2 levels. Additionally, the differences seen between cold and warm acclimated Hyas araneus after heat stress indicate that a small shift to higher acclimation temperatures also alleviates the response to temperature extremes, indicating a shift in the thermal tolerance window which reduces susceptibility to additional CO2 exposure

Parasite interactions in the bioturbator Upogebia pusilla (Decapoda: Gebiidae): a case of amensalism?

The mud shrimp Upogebia pusilla is a deep-burrowing bioturbator widespread along the Northeast Atlantic and Mediterranean coasts, where it is recognized as an ecosystem engineer. Parasitism is an important factor impacting such species’ activities, and thus ecosystem functioning. At least two parasite species occur in U. pusilla: the bopyrid isopod Gyge branchialis and an undescribed trematode. This study, carried out in Arcachon Bay, France (44°40′N, 1°10′W), over 2 years (2014–2015), had two goals: (1) to identify the trematode occurring in U. pusilla and (2) to assess the interactions between the two parasites within their host. Using molecular techniques, the trematode was identified as Maritrema sp. (Microphallidae). Monthly samples taken over 2 years at a single site, and a ten-site spatial survey in June 2014 showed that there was a negative association in the occurrence of the two parasites in their host over time and amongst sites: bopyrid-infested mud shrimp harbored lower trematode infections compared to bopyrid-free individuals. In addition, the abundance of trematodes was lower in the bopyrid-infested gill compared to the uninfested gill of bopyrid-infested individuals. It suggests that G. branchialis interferes with Maritrema sp. establishment in the mud shrimp. Conversely, the trematode appeared not to have a negative effect on bopyrid presence. The reduction of Maritrema sp. infection by G. branchialis is mainly due to the alteration of U. pusilla fitness (indirect interaction), and to a lesser extent, to overlap of parasites’ niches (direct interaction). Accordingly, interactions between these two parasites can be classified as amensalism

Olfactory Mechanisms for Discovery of Odorants to Reduce Insect-Host Contact

Insects have developed highly sophisticated and sensitive olfactory systems to find animal or plant hosts for feeding. Some insects vector pathogens that cause diseases in hundreds of millions of people and destroy billions of dollars of food products every year. There is great interest, therefore, in understanding how the insect olfactory system can be manipulated to reduce their contact with hosts. Here, we review recent advances in our understanding of insect olfactory detection mechanisms, which may serve as a foundation for designing insect control programs based on manipulation of their behaviors by using odorants. Because every insect species has a unique set of olfactory receptors and olfactory-mediated behaviors, we focus primarily on general principles of odor detection that potentially apply to most insects. While these mechanisms have emerged from studies on model systems for study of insect olfaction, such as Drosophila melanogaster, they provide a foundation for discovery of odorants to repel insects or reduce host-seeking behavior