Salinity tolerance of three ostracode species (Crustacea:Ostracoda) of Iberian saline lakes

Laboratory experiments and field data were used to determine salinity tolerance limits of three ostracode species (Prionocypris aragonica, Eucypris mareotica and Heterocypris barbara) from Iberian saline lakes. Salinity tolerance appeared related to ionic composition and temperature. Implications for ostracode ecology and geographical distribution are evaluated.     

Evidence for Na+/H+ antiport inMethanospirillum Hungatei

The growth and methane formation ofMethanospirillum hungatei were inhibited by an inhibitor of Na⁺/H⁺ antiport amiloride. After addition of NaCl or LiCl, when the cells had a lower intracellular pH and were deenergized, they extruded protons into the external medium. The acidification of the external medium was stimulated by protonophores and inhibited by amiloride. These findings suggest the existence of an Na⁺/H⁺ antiport in the cytoplasmic membrane ofM. hungatei and its role in the energetics of methanogenic bacteria.     

Interactions among species with contrasting dispersal modes explain distributions for epiphytic lichens

Understanding how the biodiversity response to climate change will be modified at ecological scales, e.g. by species interactions, is a major challenge. Lichen epiphytes – the close interdependent relationship between a heterotrophic fungus and photosynthetic partner (photobiont) – are used here to explore how interaction regimes (between lichen species, and between lichens and their photobionts) explain distribution patterns along spatial climatic gradients. To do this we tested field evidence for the ‘core‐fringe hypothesis’, which proposes a facilitative interaction; sexually‐reproducing and spore‐dispersed lichens with a requirement for resynthesis with a compatible photobiont (Nostoc) are facilitated by the prior establishment of asexual lichens which disperse both the fungus and photobiont together. We used two closely related Nephroma species which differ in their reproductive mode – N. laevigatum (sexual spore‐dispersed) and N. parile (asexual) – and compared their occurrence along a bioclimatic gradient to local habitat factors, including the co‐occurrence of asexual lichens which have shared specificity for compatible Nostoc genotypes. The results showed that: 1) N. laevigatum is significantly more likely to occur on trees that have already been colonised by asexual lichens with shared specificity for Nostoc, supporting the core‐fringe hypothesis, while 2) N. parile is independent of this association (strengthening the core‐fringe hypothesis), with its response to a precipitation gradient modified by microhabitat factors. This positive test for the core‐fringe hypothesis demonstrates how interaction regimes can fundamentally alter expectations under climate change. There is an assumption that spore‐dispersed lichen species could more easily track their suitable bioclimatic space through fragmented habitat, compared to asexual species with larger and heavier propagules. However, the establishment of spore‐dispersed lichen epiphytes into new habitat may be limited by the dispersal rates of asexual species, which act as key facilitators.     

Dengue Virus RNA Structure Specialization Facilitates Host Adaptation

Many viral pathogens cycle between humans and insects. These viruses must have evolved strategies for rapid adaptation to different host environments. However, the mechanistic basis for the adaptation process remains poorly understood. To study the mosquito-human adaptation cycle, we examined changes in RNA structures of the dengue virus genome during host adaptation. Deep sequencing and RNA structure analysis, together with fitness evaluation, revealed a process of host specialization of RNA elements of the viral 3’UTR. Adaptation to mosquito or mammalian cells involved selection of different viral populations harvesting mutations in a single stem-loop structure. The host specialization of the identified RNA structure resulted in a significant viral fitness cost in the non-specialized host, posing a constraint during host switching. Sequence conservation analysis indicated that the identified host adaptable stem loop structure is duplicated in dengue and other mosquito-borne viruses. Interestingly, functional studies using recombinant viruses with single or double stem loops revealed that duplication of the RNA structure allows the virus to accommodate mutations beneficial in one host and deleterious in the other. Our findings reveal new concepts in adaptation of RNA viruses, in which host specialization of RNA structures results in high fitness in the adapted host, while RNA duplication confers robustness during host switching.     

Nature’s Palette: Characterization of Shared Pigments in Colorful Avian and Mollusk Shells

Pigment-based coloration is a common trait found in a variety of organisms across the tree of life. For example, calcareous avian eggs are natural structures that vary greatly in color, yet just a handful of tetrapyrrole pigment compounds are responsible for generating this myriad of colors. To fully understand the diversity and constraints shaping nature’s palette, it is imperative to characterize the similarities and differences in the types of compounds involved in color production across diverse lineages. Pigment composition was investigated in eggshells of eleven paleognath bird taxa, covering several extinct and extant lineages, and shells of four extant species of mollusks. Birds and mollusks are two distantly related, calcareous shell-building groups, thus characterization of pigments in their calcareous structures would provide insights to whether similar compounds are found in different phyla (Chordata and Mollusca). An ethylenediaminetetraacetic acid (EDTA) extraction protocol was used to analyze the presence and concentration of biliverdin and protoporphyrin, two known and ubiquitous tetrapyrrole avian eggshell pigments, in all avian and molluscan samples. Biliverdin was solely detected in birds, including the colorful eggshells of four tinamou species. In contrast, protoporphyrin was detected in both the eggshells of several avian species and in the shells of all mollusks. These findings support previous hypotheses about the ubiquitous deposition of tetrapyrroles in the eggshells of various bird lineages and provide evidence for its presence also across distantly related animal taxa.     

Induction and Characterization of Laccase in the Ligninolytic Fungus Pleurotus eryngii

Two protein bands with laccase activity were found after PAGE of culture liquid or mycelium extract of Pleurotus eryngii, grown on glucose–ammonium tartrate–yeast extract medium with and without inducers. A major and a minor laccase band were observed in the basal medium. The intensity of the major band (laccase I) did not change after the addition of inducers. However, the minor band (laccase II), characterized by higher electrophoretic mobility, was strongly induced by wheat–straw alkalilignin and vanillic and veratric acids. Laccase activity in the basal medium had an optimum pH of 4.5 and was stable from pH 3 to 10 during 24 h at room temperature. This enzyme had wide substrate specificity on hydroquinones, methoxy-substituted monophenols, and aromatic amines. In general, laccase activity was found only with compounds having a redox potential lower than 0.5 mV. The highest activity was obtained with methoxy- and methyl-substituted p-hydroquinones and aromatic diamines. Some activity also occurred with the aliphatic compound 3,5-cyclohexadiene-1,2-diol. Received: 22 April 1996 / Accepted: 29 June 1996     

Using variation partitioning techniques to quantify the effects of invasive alien species on native urban bird assemblages

Quantifying the impacts that invasive alien species (IAS) cause on affected systems is not an easy task. Here, we explore the application of variation partitioning techniques to measure and control for the effects of possible confounding factors when studying the impact that feral pigeons, European starlings, and house sparrows cause on native urban bird communities in Mexico. We argue that these IAS are provoking a severe impact on whole assemblages of native passerines only if (a) their marginal effect is statistically significant, (b) it remains so after partialling out other explanatory variables, and (c) is larger than (or similar to) the conditional effect of these covariates. We censused passerine bird assemblages and measured habitat variables in a number of greenspaces in three replicate study areas. Then, by means of partial redundancy analyses, we decomposed the total variability in bird data as a function of IAS, physical variables and vegetation data. In one of the study areas the marginal effect of IAS on native assemblages was significant, but the conditional effect was not. We conclude that this IAS effect was confounded with other explanatory variables. In the other study areas, no (marginal or partial) significant effect was found. Without invoking interspecific competition, our results support the opportunistic hypothesis, according to which IAS can exploit ecological conditions in modern cities that native species cannot even tolerate. Finally, apart from the Precautionary Principle, we found no scientific justification to control the abundance of the three IAS in our study areas.     

Ecological and social determinants of association and proximity patterns in the fission–fusion society of spider monkeys (Ateles geoffroyi)

Some social species exhibit high levels of fission–fusion dynamics (FFD) that improve foraging efficiency. In this study, we shed light on the way that FFD allows animal groups to cope with fluctuations in fruit availability. We explore the relative contribution of fruit availability and social factors like sex in determining association and proximity patterns in spider monkeys. We tested the influence of fruit availability and social factors on the association and proximity patterns using three-year data from a group of spider monkeys in the Yucatan Peninsula of Mexico. We identified subgroup members and estimated their Interindividual distances through instantaneous scan sampling. We evaluated fruit availability by monitoring the phenology of the 10 most important food tree species for spider monkeys in the study site. Social network analyses allowed us to evaluate association and proximity patterns in subgroups. We showed that association patterns vary between seasons, respond to changes in fruit availability, and are influenced by the sex of individuals, likely reflecting biological and behavioral differences between sexes and the interplay between ecological and social factors. In contrast, proximity patterns were minimally affected by changes in fruit availability, suggesting that social factors are more important than food availability in determining cohesion within subgroups.