Paralytic shellfish poisoning by Spondylus calcifer contaminated with Pyrodinium bahamense, Costa Rica, 1989-1990

This paper describes an outbreak of paralytic shellfish poisoning (PSP), affecting human populations on the Pacific Coast of Costa Rica in October 1989. Numbness in arms, face and legs occurred 30 to 45 minutes after ingestion of the large clam Spondylus calcifer. Paralysis of legs and respiratory symptoms followed, often persisting for one week. Large amounts of the dinoflagellate Pyrodinium bahamense were found in the intestine of the mollusk. A toxin was detected in crude or filtered and heated macerates of intestine, muscle, mantle and hepatopancreas of S. calcifer, and to a lesser extent Tagelus sp., by injection of its crude or diluted extracts in white mice. The effects in mice consisted in paralysis and asphyxia generally leading to death in less than 5 minutes, compatible with saxitoxin. Mice were killed by the toxin in macerates diluted 1:100 to 1:1000. No toxin was detected in Anadara tuberculosa (Bivalvia) or in peneids. Prevention rests on intersectoral actions between state and private sectors in charge of fishing, distribution and marketing of shellfish, as well as on education of the population at large.     

Lysozymes in insects: what role do they play in nitrogen metabolism?

Abstract. Lysozymes are widely distributed in many organisms as one of the components of defence mechanisms. In herbivores, when nitrogen is not contained in sufficient amounts in the diet, bacteria lysed by stomach lysozymes are used as sources of nitrogen. In ruminants, lysozymes function as digestive enzymes in the true stomach. A convergence of amino acid sequence has been shown between the stomach lysozymes of different ruminants, and similar lysozymes have recently been reported in the gut or salivary gland of insects. In this mini review, the enzymatic and ecological functions of lysozymes in insects, particularly in termites, are introduced, together with future studies that are needed in this field.     

Intricate trophic links between threatened vertebrates confined to a small island in the Atlantic Ocean

Trophic networks in small isolated islands are in a fragile balance, and their disturbance can easily contribute toward the extinction vortex of species. Here, we show, in a small Atlantic island (Raso) in the Cabo Verde Archipelago, using DNA metabarcoding, the extent of trophic dependence of the Endangered giant wall gecko Tarentola gigas on endemic populations of vertebrates, including one of the rarest bird species of the world, the Critically Endangered Raso lark Alauda razae. We found that the Raso lark (27%), Iago sparrow Passer iagoensis (12%), Bulwer's petrel Bulweria bulwerii (15%), and the Cabo Verde shearwater Calonectris edwardsii (10%) are the most frequent vertebrate signatures found in the feces of the giant wall gecko. This work provides the first integrative assessment of their trophic links, an important issue to be considered for the long‐term conservation of these small and isolated island ecosystems.     

How invader traits interact with resident communities and resource availability to determine invasion success

Competition for limited resources is considered a key factor controlling invasion success. Resource availability can be viewed in either the long or short‐term. Long‐term availability depends on the baseline nutrient availability in the ecosystem and how those conditions shape the ecological community. Short‐term resource availability fluctuates with disturbances that alter nutrient availability and/or the density and composition of the ecological community. We investigated how species’ traits interact with short and long‐term resource availability to determine the outcome of invasions. We manipulated long‐term baseline resource availability, disturbance intensity, disturbance frequency, and propagule pressure in a fully factorial design using protist microcosms. Our results show that short and long‐term resource availability and the direct mortality from disturbance interact with the traits of resident community members and traits of invaders to determine community invasibility. While competitively dominant invaders with slow growth rates may suffer rather than benefit from short‐term resource fluctuations, quickly growing but competitively inferior invaders can benefit from both the resource fluctuations and the heterogeneity in community composition created by disturbance. Our findings empirically synthesize two explanations for invasion success, namely short‐term resource fluctuations and long‐term resource availability, and highlight the importance of considering traits of invaders and residents, such as growth rate and competitive ability, in the context of productivity and disturbance gradients. This species’ traits approach could resolve idiosyncratic results from natural systems undergoing disturbance and invasion that do not follow patterns predicted by traditional invasion frameworks.     

Dependence of the fluorescence of fluorescein labelled (Ca2+, Mg2+)-ATPase upon the lipid to protein ratio in sarcoplasmic reticulum reconstituted systems

Reconstituted sarcoplasmic reticulum (SR) vesicles have been prepared mixing fluorescein labelled SR, excess endogenous lipids and deoxycholate by a rapid dilution protocol and several freeze-thaw treatments. We have found that both the steady-state level and the polarization of fluorescein fluorescence of these reconstituted systems monotonically increase as a function of the lipid to protein ratio between 80 and 2000 (on a mole per mole basis). The magnitude of this increase is about 15%. Detergents, such as Triton X-100 and deoxycholate, when added to SR labelled vesicles below their critical micelle concentrations also induce similar changes in fluorescein fluorescence. We suggest that lipid dilution of protein in these reconstituted systems induce a decrease of the level of self-quenching by promoting dissociation of (Ca2+, Mg2+)-ATPase.     

Seaweed extracts as a natural control against the monogenean ectoparasite,Neobenedenia sp., infecting farmed barramundi (Lates calcarifer)

Aqueous extracts from common tropical seaweeds were evaluated for their effect on the life cycle of the commercially important ectoparasite, Neobenedenia sp. (Platyhelminthes: Monogenea), through the survival of attached adult parasites, period of embryonic development, hatching success and oncomiracidia (larvae) infection success. There was no significant effect of any extract on the survival of adult parasites attached to fish hosts or infection success by oncomiracidia. However, the extracts of two seaweeds, Ulva sp. and Asparagopsis taxiformis, delayed embryonic development and inhibited egg hatching. The extract of A. taxiformis was most effective, inhibiting embryonic development of Neobenedenia sp. and reducing hatching success to 3% compared with 99% for the seawater control. Furthermore, of the 3% of eggs that hatched, time to first and last hatch was delayed (days 14 and 18) compared with the seawater control (days 5 and 7). Asparagopsis taxiformis shows the most potential for development as a natural treatment to manage monogenean infections in intensive aquaculture with the greatest impact at the embryo stage.