Paradigm lost: reconsidering functional form and group hypotheses in marine ecology

Although functional form and functional group models for marine algae have been used extensively, there is little general literature support for these models, and many studies have shown that associated hypotheses are often incorrect. In functional form/group models, a wide range of ecological and physiological functions are assumed to be correlated with general algal form or morphology. In contrast, functional group approaches have been used most successfully in terrestrial and aquatic systems when groupings are based on a particular function rather than overall plant morphology, and when addressing ecosystem-level questions. In this type of functional group approach, a given set of species would likely be grouped differently depending on the function under consideration. Functional groupings are appropriate for many situations and questions, but not all. Certainly, grouping taxa by a particular function can be very useful and often necessary for many ecosystem-level questions and modeling, especially where qualitative results are more important than quantitative predictions, and when there are too many species in a system to consider them all individually. However, when one considers species–species interactions or questions about population biology, the specific responses of individual species must be considered. To make functional group models more useful, we recommend that groupings be based on specific functions (e.g. nutrient uptake rates, photosynthesis rates, herbivore resistance, disturbance resistance, etc.) rather than gross morphology. Explicit testing of performance of a particular function should be made before generalizations can be assumed, and groupings should be used for questions/approaches where they are most appropriate. If models fail when tested, they should be modified using the additional information to generate new hypotheses and models, and then retested.     

Use of benzimidazole chemotherapy in human helminthiases: indications and efficacy

The past two decades have seen some remarkable developments in anthelmintic chemotherapy in clinical medicine. Whereas praziquantel has revolutionized the management of many cestode and trematode infections, Gordon Cook explains how the introduction of the benzimidazoles - most importantly thiabendazole, mebendazole and recently albendazole (flubendazole, cambendazole, ciclobendazole, and triclabendazole have also been used on a very limited scale) - has had a major impact upon the safe and effective management of several important intestinal and systemic nematode and, to a leser extent, cestode infections.     

Paradigm shifts in malaria parasite biochemistry and anti-malarial chemotherapy

A fatty acid synthesis (FAS) pathway was recently discovered and established in the obligate human parasite Plasmodium falciparum. Its inhibition by triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) leads to its classification as a type II FAS. Humans, the vertebrate host for the malarial parasite utilize type I FAS, which is not inhibited by triclosan. This discovery thus paves the way for novel approaches to the treatment of malaria. In direct contrast to the delayed-death phenotype associated with poisoning of the apicoplast using certain other drugs, the rapid and striking action of triclosan suggests the possibility of developing new drug(s) for the treatment of malaria.     

Linking proteome and genome: how to identify parasite proteins

Parasite genome projects are generating an avalanche of sequence data. If this resource is to be exploited effectively for drug and vaccine design, there is an urgent need to make the link between these DNA sequences and the functional proteins of the parasite, which they encode. Here, we seek to demystify the revolutionary advances in protein identification based on mass spectrometry.     

Reduction in DALYs lost due to soil-transmitted helminthiases and schistosomiasis from 2000 to 2019 is parallel to the increase in coverage of the global control programmes

Preventive chemotherapy interventions for the control of soil-transmitted helminthiases (STH) and schistosomiasis scaled up from a global coverage level of around 5% in the year 2000 to a coverage that surpassed 60% in the year 2019. The present paper analyses the concomitant reduction in the number of disability-adjusted life years (DALYs) lost due to STH and schistosomiasis during the same period, from 6.3 to 3.5 million DALYs. The cumulative gain during the 19-year period was estimated at over 26 million DALYs. Given the low cost of the intervention, our study suggests that deworming for STH and schistosomiasis is one of the most cost-effective public health interventions.     

Pattern control in insect segments: superimposed features of the pattern may be subject to different control mechanisms

Summary The integument of an insect segment displays two distinct pattern features which are based on different properties of the constituent epidermal cells. Normally, the uniform orientation of epidermal cell polarities (polarity pattern) is strictly correlated with the sequence of differentiated cells (differentiation pattern). Here it is reported that in the integument of the cotton bug Dysdercus epidermal cells can adopt orientations that do not correlate with the pigmentation pattern and which are not compatible with the gradient model. The results indicate that different features of a composite pattern can be independently controlled.     

Alternative parasite development in transmission strategies: how time flies!

Among parasitic platyhelminths with complex life cycles, it has been well documented that transmission opportunities are the main forces shaping the diversity of life‐history traits and parasite developmental strategies. While deviations in the development pathway usually involve shortening of life cycles, their extension may also occur following perception of remaining time by parasites. Polystoma gallieni, the monogenean parasite of Hyla meridionalis, is able to trigger two alternative developmental strategies depending on the physiological stage of the tadpoles upon which larvae attach. The distribution and reproductive outputs of both resulting phenotypes were surveyed to address questions about the dynamics of transmission in natural environments. Because modifications in the completion of life cycles can have drawbacks which may perturb the dynamic equilibrium of the resulting host–parasite systems, experimental infestations were also performed to assess parasite–parasite interactions. Our results suggest that the bladder adult phenotype, which involves transmission between frogs and tadpoles, is supplied secondarily by the branchial phenotype which involves transmission between tadpoles and metamorphs. They also support the occurrence of finely tuned trade‐offs between hosts and parasites and highlight positive trends behind the extension of direct life cycles, in which host‐derived signals account for the remaining time to achieve parasitic transmission.     

Human macroecology: linking pattern and process in big‐picture human ecology

Humans have a dual nature. We are subject to the same natural laws and forces as other species yet dominate global ecology and exhibit enormous variation in energy use, cultural diversity, and apparent social organization. We suggest scientists tackle these challenges with a macroecological approach—using comparative statistical techniques to identify deep patterns of variation in large datasets and to test for causal mechanisms. We show the power of a metabolic perspective for interpreting these patterns and suggesting possible underlying mechanisms, one that focuses on the exchange of energy and materials within and among human societies and with the biophysical environment. Examples on human foraging ecology, life history, space use, population structure, disease ecology, cultural and linguistic diversity patterns, and industrial and urban systems showcase the power and promise of this approach.     

Apoplastic sugar may be lost from grape berries and retrieved in pedicels

In ripening grape (Vitis sp.) berries, the combination of rapid sugar import, apoplastic phloem unloading, and water discharge via the xylem creates a potential risk for apoplastic sugar to be lost from the berries. We investigated the likelihood of such sugar loss and a possible sugar retrieval mechanism in the pedicels of different Vitis genotypes. Infusion of D-glucose-1-¹³C or L-glucose-1-¹³C to the stylar end of attached berries demonstrated that both sugars can be leached from the berries, but only the nontransport sugar L-glucose moved beyond the pedicels. No ¹³C enrichment was found in peduncles and leaves. Genes encoding 10 sugar transporters were expressed in the pedicels throughout grape ripening. Using an immunofluorescence technique, we localized the sucrose transporter SUC27 to pedicel xylem parenchyma cells. These results indicate that pedicels possess the molecular machinery for sugar retrieval from the apoplast. Plasmodesmata were observed between vascular parenchyma cells in pedicels, and movement of the symplastically mobile dye carboxyfluorescein demonstrated that the symplastic connection is physiologically functional. Taken together, the chemical, molecular, and anatomical evidence gathered here supports the idea that some apoplastic sugar can be leached from grape berries and is effectively retrieved in a two-step process in the pedicels. First, sugar transporters may actively retrieve leached sugar from the xylem. Second, retrieved sugar may move symplastically to the pedicel parenchyma for local use or storage, or to the phloem for recycling back to the berry.

Grape berry pedicels may retrieve sugar that is lost via the xylem following apoplastic phloem unloading in the berries.     

A nested parasite species subset pattern in tropical fish: host as major determinant of parasite infracommunity structure

The number of monogenean gill parasite species associated with fish hosts of different sizes is evaluated for 35 host individuals of the West African cyprinid Labeo coubie. The length of host individuals explains 86% of the total variation in monogenean species richness among individuals. Larger hosts harbour more species than smaller ones. The existence of a hierarchical association of parasite species in individuals of L. coubie is demonstrated. Monogenean infracommunities on larger fish hosts consist of all species found on smaller hosts plus those restricted to the larger size categories, suggesting some degree of compositional persistence among host individuals. The findings provide strong support for an interpretation of the relationship between monogenean parasite species richness and host body size in terms of a nested species subset pattern, thus providing a new record of repetitive structure and predictability for parasite infracommunities of hosts.After 15/01/1995, ORSTOM, BP 165 97323 Cayenne cedex Guyane France     

Species of Echinococcus: pattern and process

Although classification and nomenclature within the cestode genus Echinococcus has, historically, been controversial, the past 20-30 years have provided a period of relative stability. Recent calls for taxonomic revision in the genus have therefore created something of a stir. In this article, Alan Lymbery and Andrew Thompson describe the reasons for the new controversy, and suggest that the problem can only be resolved by agreement on an appropriate species concept and on operational procedures for implementing that concept.     

Tannins and self-medication: Implications for sustainable parasite control in herbivores

Animals adapt to the variability of the external environment and to their changing internal needs not only by generating homeostatic physiological responses, but also by operating in the external environment. In this study, we determined whether sheep with a gastrointestinal parasite infection increased intake of a low-quality food containing a natural antiparasitic agent (tannins) relative to non-parasitized sheep. Four groups of lambs (n = 8 lambs/group) were assigned to a 2 × 2 factorial design with parasitic burden (P = parasites; NP = no parasites) and the offer of a supplement containing tannins (yes, no) as the main factors. Parasitized lambs ate more of the tannin-containing food than non-parasitized lambs for the first 12 days of the study, when parasite burdens were high, but differences became smaller and disappeared toward the end of the study when parasite burdens decreased. This result suggests the lambs detected the presence of internal parasites or associated symptoms and modified their ingestion of an antiparasitic agent as a function of need.