Seasonal variation in the composition of fish assemblages in small Amazonian forest streams: evidence for predictable changes

1. The effects of seasonal inundation on the biology of fishes on floodplains of large Amazonian rivers are well studied. However, the small seasonal changes in headwater streams are generally considered to have little effect on fish assemblages. 2. In this study, we analysed seasonal changes in the species composition and abundance of fish in small Amazonian forest streams. We sampled fish with hand and seine nets in headwater streams in a 10 000 ha terra‐firme forest reserve near Manaus, Brazil. Each stream was surveyed at the end of the 2005 dry season, at the beginning of the 2006 rainy season and at the beginning of the 2006 dry season, by means of a standardized sampling effort. 3. The numbers of individuals and species caught were higher in the dry season, but rarefaction analyses indicated that greater species numbers could have been due simply to the larger number of individuals caught. 4. Between the dry and rainy season, the direction of changes in species composition in multivariate space varied among sites, especially for quantitative (abundance) data. However, the observed variation among sites was the less than expected if the directions of change were random. 5. Fish assemblages in the second dry season were more similar to those in the previous dry season than expected if changes in species composition among seasons were random. This indicates that a general seasonal pattern in fish assemblages can be detected, despite the existence of some erratic site‐specific changes. 6. Most of the species that showed large seasonal variations in density occupy temporary ponds during the rainy season, when much of the valley is inundated and pond networks form adjacent to streams. Short‐duration lateral migrations to these ponds may play an important role in the seasonal fish‐assemblage dynamics in Amazonian headwater streams. 7. Our results contrast with previous studies on small Amazonian streams, which have found little seasonal change in fish assemblages, and highlight the importance of the abundance of common species as an indicator of general fish assemblage structure in biological monitoring programmes.     

The use of structural reduction in phylogenetic reconstruction of decapods and a phylogenetic hypothesis for 15 genera of Majidae: testing previous larval hypotheses and assumptions

Summary

Using larval data of zoeae from selected genera of majids, we determined tree topologies, levels of homoplasy, and frequencies of reduction under three different assumptions of character argumentation: ordered reduction events, unordered reduction events, and outgroup comparison. Under each assumption we provided a phylogenetic hypothesis for some majid genera and evaluated the assumption that structural reduction can be assumed a priori as a criterion to infer character transformation polarity in phylogenetic reconstruction of decapods. The results indicate that the a priori assumption of “reduction” as the derived condition is not justified because under this assumption, reduction is not always maintained throughout the resulting phylogenetic hypothesis. Furthermore, we also found that this criterion fails to provide the most parsimonious explanation of the data set. Therefore, we reject the use a “reduction=derived” criterion to infer polarity in phylogenetic reconstruction. Phylogenetic analysis using outgroup comparison provided a phylogenetic hypothesis with a better fit and a lower frequency of reduction events. However, we found that statements of homology may be problematic when the number of larval stages in the outgroup differ from those of the ingroup. To overcome this problem, we suggest that, in the absence of evidence for developmental homology, all larval stages should be considered as potential homologues. Using this approach to homology of larval stages, we provide a new phylogenetic hypothesis for 15 genera of majids based on larval morphology. Within Majidae, representative members of Majinae formed a highly nested monophyletic group with the following topology: ((Jacquinotia+Notomithrax) (Leptomithrax+Maja)). In contrast, the Oregoniinae (Hyas+Chionoecetes) formed a basal monophyletic group. Contrary to established ideas for the monophyly of Inachinae, Macrocheira is basal to the Oregoniinae. Other taxa did not form monophyletic groupings based on classical assignment to subfamilies.     

Modelling past and present geographical distribution of the marine gastropod Patella rustica as a tool for exploring responses to environmental change

A climate envelope approach was used to model the distributions of the intertidal gastropod Patella rustica , to test the robustness of forecast responses to climate change. The model incorporated variables that were likely to determine the abundance and the northern range limit of this species in the NE Atlantic. The model was built using classification and regression tree analysis (CART) trained with historical distribution data from the mid 1950s and a set of corresponding climatic and oceanographic variables. Results indicated air and sea temperature, in particular during the reproductive and settlement periods, as the main determinants of the Atlantic distribution of P. rustica . The model was subsequently fed with contemporary climatic data and its output was compared with the current distribution and abundance of P. rustica , assessed during a 2002–2003 survey. The model correctly hindcasted the recent collapse of a distributional gap in northern Portugal, as well as an increase in abundance at locations within its range. The predicted northward expansion of the northern range limit did not occur because the absence of the species was confirmed in a survey encompassing the whole Atlantic French coast up to Brest. Stretches of unsuitable habitat too long to be overcome by dispersal are the likely mechanism controlling the northern limit of the distribution of this intertidal species.     

Systematics and evolutionary relationships of the mountain lizard Liolaemus monticola (Liolaemini): how morphological and molecular evidence contributes to reveal hidden species diversity

The delimitation of species is a major issue in systematic biology and has been a re-emerging discipline in the last decade. A number of studies have shown that the use of multiple data sets is critical for the identification of cryptic species, particularly in groups with complex evolutionary histories. Liolaemus monticola is a montane lizard species distributed in central Chile (32°–42°S), with four described subspecies in a latitudinal gradient from north to south: L. m. monticola , L. m. chillanensis , L. monticola ssp. and L. m. villaricensis . In order to test the systematic status and phylogenetic relationships of the taxa included in the L. monticola group, we analysed morphological (morphometric and meristic) and molecular (allozyme and mitochondrial DNA) data sets. The results of the morphological analyses showed that meristic variables correctly assigned individuals with higher accuracy than did morphometric characters. The results of the analyses of allozyme data revealed eight diagnostic loci that are evidence for significant differences among the four L. monticola subspecies. Phylogenetic analyses with mitochondrial DNA data, including additional species, showed that the L. monticola group is polyphyletic. We postulate that the four current subspecies represent independent evolutionary lineages and must be raised to the specific level as L. monticola , L. chillanensis and L. villaricensis . The taxonomic status of the unnamed L. monticola ssp. remains unresolved, although we provide a preliminary proposal.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 635–650.     

Effect of Source-to-sink Ratio on Partitioning of Dry Matter and14C-photoassimilates in Wheat during Grain Filling

Increasingly, wheat (Triticum aestivumL.) is being grown intropical environments, but there is inadequate information aboutthe physiological processes limiting yield. In this investigation,the source:sink ratio was manipulated to examine the performanceof source-sink interactions after anthesis and the factor(s)limiting grain filling in tropical conditions. Plants of threewheat cultivars, Cuba C-204, Candeias and IAC-60, were artificiallymodified to give different source:sink ratios. The treatmentswere: I, Control; II, all spikelets on one side of the spikeremoved; III, all spikelets removed except the four centralspikelets of the spike; and IV, flag leaf blade removed. Thedistribution of dry matter between kernels and stem internodeswas analysed at harvest in all three cultivars. Partitioningof¹⁴C-photoassimilates was measured on three occasions afteranthesis in the cultivar Cuba C-204. Modifications of source:sinkratio led to different patterns of allocation of dry matterbetween cultivars and sowing dates. The reduction in sink sizein treatment II produced no significant change in the mass pergrain in the January sowing, but this was enhanced in two cultivarsin the November sowing. In treatment III, both mass per grainand translocation of¹⁴C-photoassimilates declined, apparentlydue to feedback inhibition of photosynthesis. The participationof stem reserves in grain filling and the existence of genotypicdifferences in response to availability of photoassimilateswere corroborated. The pattern of partitioning of dry matterobserved in plants in this investigation suggests a source limitation,particularly during the November sowing. This pattern differedmarkedly from that in other studies, most of which have beenmade in temperate areas.Copyright 1999 Annals of Botany Company Photoassimilates, sink, source, partitioning, grain filling, wheat.     

Action Mechanisms of the Secondary Metabolite Euplotin C: Signaling and Functional Role in Euplotes

ABSTRACT. Among secondary metabolites, the acetylated hemiacetal sesquiterpene euplotin C has been isolated from the marine, ciliated protist Euplotes crassus, and provides an effective mechanism for reducing populations of potential competitors through its cytotoxic properties. However, intracellular signaling mechanisms and their functional correlates mediating the ecological role of euplotin C are largely unknown. We report here that, in E. vannus (an Euplotes morphospecies that does not produce euplotin C and shares with E. crasssus the same interstitial habitat), euplotin C rapidly increases the intracellular concentration of both Ca²⁺ and Na⁺, suggesting a generalized effect of this metabolite on cation transport systems. In addition, euplotin C does not induce oxidative stress, but modulates the electrical properties of E. vannus through an increase of the amplitude of graded action potentials. These events parallel the disassembling of the ciliary structures, the inhibition of cell motility, the occurrence of aberrant cytoplasmic vacuoles, and the rapid inhibition of phagocytic activity. Euplotin C also increases lysosomal pH and decreases lysosomal membrane stability of E. vannus. These results suggest that euplotin C exerts a marked disruption of those homeostatic mechanisms whose efficiency represents the essential prerequisite to face the challenges of the interstitial environment.     

Polyethism and nestmate recognition in the alarm reaction of Atta leaf-cutting ants

Abstract.  Ethological studies are conducted under laboratory conditions using workers of Atta sexdens sexdens and Atta opaciceps collected from field colonies to investigate the mechanisms involved in the alarm response and intra-specific recognition in leaf-cutting ants. Hexane extracts from the heads of gardeners and generalist workers elicit higher levels of alarm response in foragers from the same colony than do mandibular gland extracts from foragers and soldiers, indicating that gardeners, generalists and foragers are primarily responsible for the production of alarm pheromone. Foragers subjected to extracts from non-nestmates exhibit significantly greater alarm responses than are induced by similar extracts derived from nestmate workers, suggesting that the alarm pheromone may have a role in nestmate recognition.     

Plant trait responses to grazing – a global synthesis

Herbivory by domestic and wild ungulates is a major driver of global vegetation dynamics. However, grazing is not considered in dynamic global vegetation models, or more generally in studies of the effects of environmental change on ecosystems at regional to global scale. An obstacle to this is a lack of empirical tests of several hypotheses linking plant traits with grazing. We, therefore, set out to test whether some widely recognized trait responses to grazing are consistent at the global level. We conducted a meta‐analysis of plant trait responses to grazing, based on 197 studies from all major regions of the world, and using six major conceptual models of trait response to grazing as a framework. Data were available for seven plant traits: life history, canopy height, habit, architecture, growth form (forb, graminoid, herbaceous legume, woody), palatability, and geographic origin. Covariates were precipitation and evolutionary history of herbivory. Overall, grazing favoured annual over perennial plants, short plants over tall plants, prostrate over erect plants, and stoloniferous and rosette architecture over tussock architecture. There was no consistent effect of grazing on growth form. Some response patterns were modified by particular combinations of precipitation and history of herbivory. Climatic and historical contexts are therefore essential for understanding plant trait responses to grazing. Our study identifies some key traits to be incorporated into plant functional classifications for the explicit consideration of grazing into global vegetation models used in global change research. Importantly, our results suggest that plant functional type classifications and response rules need to be specific to regions with different climate and herbivory history.