Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

Growth of Isolated Amastigotes of Trypanosoma cruzi in Cell-Free Medium1

Amastigotes of Trypanosoma cruzi were purified from overlays of infected Vero cell cultures by centrifugation over a discontinuous gradient of metrizamide. Pure amastigote preparations were usually recovered from the pellet under the layer of specific gravity 1.086. The isolated amastigotes grew in cell-free ML-15HA medium. Growth rate for the different strains of T. cruzi were in the order Y > Tulahuan > CL. The generation time of amastigotes in ML-15HA medium was 16.8, 18.0, and 26.4 h for the Y, Tulahuen, and CL strains, respectively, in the presence of 5% CO₂) and 16.8, 31.2, and 36.4 h, respectively, in the absence of CO₂. Intracellular amastigotes did not differ ultrastructurally from amastigotes from either the density-gradient fractionation or culture in cell-free medium.     

Evolution of Dendrocolaptes platyrostris (Aves: Furnariidae) between the South American open vegetation corridor and the Atlantic forest

The open vegetation corridor of South America is a region dominated by savanna biomes. It contains forests (i.e. riverine forests) that may act as corridors for rainforest specialists between the open vegetation corridor and its neighbouring biomes (i.e. the Amazonian and Atlantic forests). A prediction for this scenario is that populations of rainforest specialists in the open vegetation corridor and in the forested biomes show no significant genetic divergence. We addressed this hypothesis by studying plumage and genetic variation of the Planalto woodcreeper Dendrocolaptes platyrostris Spix (1824) (Aves: Furnariidae), a forest specialist that occurs in both open habitat and in the Atlantic forest. The study questions were: (1) is there any evidence of genetic continuity between populations of the open habitat and the Atlantic forest and (2) is plumage variation congruent with patterns of neutral genetic structure or with ecological factors related to habitat type? We used cytochrome b and mitochondrial DNA control region sequences to show that D. platyrostris is monophyletic and presents substantial intraspecific differentiation. We found two areas of plumage stability: one associated with Cerrado and the other associated with southern Atlantic Forest. Multiple Mantel tests showed that most of the plumage variation followed the transition of habitats but not phylogeographical gaps, suggesting that selection may be related to the evolution of the plumage of the species. The results were not compatible with the idea that forest specialists in the open vegetation corridor and in the Atlantic forest are linked at the population level because birds from each region were not part of the same genetic unit. Divergence in the presence of gene flow across the ecotone between both regions might explain our results. Also, our findings indicate that the southern Atlantic forest may have been significantly affected by Pleistocene climatic alteration, although such events did not cause local extinction of most taxa, as occurred in other regions of the globe where forests were significantly affected by global glaciations. Finally, our results neither support plumage stability areas, nor subspecies as full species. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 801–820.     

Skull morphology and functionality of extant Felidae (Mammalia: Carnivora): a phylogenetic and evolutionary perspective

Felids morphology and ecological role as hypercarnivores are quite constant, despite considerable body size variation among species. Skull morphological and functional features of 34 extant cat species were evaluated under a phylogenetic framework of the Felidae. Twenty skull measurements were analysed through Principal Component Analysis to assess the species morphofunctional spaces. Force indexes were obtained from static equilibrium equations to infer jaw mechanics. Correlations between morphological, functional, and ecological traits were tested by phylogenetically independent contrasts. In spite of the general cat‐like pattern, specific features on the skulls allowed differentiation among groups. Acinonyx jubatus, for instance, showed a shorter and shallower temporal fossa than other big cats, and their bite functionality is marked by an increased contribution of the masseteric system. A morphofunctional dichotomy between Neotropical and Eurasian/African small cats was detected, and is associated with the major transversal axes of the skulls. According to the contrast analyses, the skull size is correlated with the bite force and prey size, but it is uncorrelated with the variations on jaw mechanics (from temporalis or masseter muscle optimizations). Also, there was no correlation between functional differences on jaw muscles and the ratio of prey weight to cat weight. The efficiency of the jaw apparatus among cats is quite consistent; therefore, the different evolutionary trends of jaw mechanics seem to be caused by the casuistic fixation of phenotypical variations, rather than by specific adaptative selections. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 414–462.     

Systematics of the spider genus Metabus O. P.-Cambridge, 1899 (Araneoidea: Tetragnathidae) with additions to the tetragnathid fauna of Chile and comments on the phylogeny of Tetragnathidae

The spider genus Metabus (Tetragnathidae) previously included nine species: the type M. gravidus O. P.-Cambridge, 1899 – junior synonym of Leucauge ocellata (Keyserling) – from Central America and eight species from Chile. In this paper, the classification of the Metabus species-complex is revised, and two new genera, with three new species and five new combinations, are described. Allende gen. nov. is created for four Chilean species not congeneric with the type of Metabus : the type A. puyehuensis sp. nov. , A. patagiatus (Simon) comb. nov. , A. nigrohumeralis (F. O. P.-Cambridge) comb. nov. and A. longipes (Nicolet) comb. nov. Further additions to the Chilean fauna are under the new genus Mollemeta gen. nov. – created for M. edwardsi (Simon) comb. nov. – and three new species of Chrysometa : C. acinosa sp. nov. , C. levii sp. nov. and C. maitae sp. nov. Metabus now includes four species: M. ocellatus (Keyserling) comb. nov. , M. debilis (O. P.-Cambridge) comb. nov. , M. ebanoverde sp. nov. and M. conacyt sp. nov. All of these species were included in a phylogenetic analysis of 38 tetragnathid and 12 orbicularian outgroup terminals scored for 105 morphological and behavioural characters. The results suggest that Metabus as previously circumscribed is polyphyletic. The phylogenetic relationships within tetragnathids are briefly discussed. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 285–335.     

Tradeoffs Between Irradiance Capture and Avoidance in Semi-arid Environments Assessed with a Crown Architecture Model

Plants in arid environments cope with stress from excessiveirradiance by physiological photoprotection of the photosyntheticapparatus and by structurally reducing the leaf area exposedto the sun (structural photoprotection). We assessed the ecologicalrelevance of structural photoprotection in two plants of contrastingarchitecture co-occurring in a semi-arid environment, usingthe three-dimensional canopy model YPLANT. We compared the roleof crown geometry in avoiding excessive radiation, analysedthe costs of structural photoprotection in terms of reductionof potential carbon gain, and compared these costs with thosedue to seasonal constraints of photosynthesis and tissue ageing.The results of the model simulations indicated that canopy architectureofStipa tenacissima(a tussock grass) andRetama sphaerocarpa(aleafless leguminous shrub) minimized the risk of overheatingand photo-oxidative destruction of the photosynthetic apparatuswith steeply oriented foliage and moderate self-shading. Butthis structural photoprotection imposed an increased cost interms of potential carbon gain. Diurnal and seasonal patternsof light interception by the crown of these plants translatedinto a simulated potential carbon gain only half that of anequivalent, horizontal photosynthetic surface. This reductionin potential carbon gain, due to irradiance avoidance, was similarto that imposed by water shortage.S. tenacissima,which ceasesphotosynthetic activity during periods of drought, exhibitedmore structural avoidance of irradiance thanR. sphaerocarpa,whichremains active throughout the year. This illustrates the influenceof the capacity of plants to utilize light for carbon fixationon the trade-offs between irradiance capture and avoidance.Structural avoidance of excessive radiation efficiently preventsthe risk of damage by intense irradiance, has no special maintenancecosts, and is biomechanically cheaper than enhanced light harvestingby a horizontal canopy, which points to structural photoprotectionas a very effective strategy to cope with high irradiance stressin poor and adverse habitats.Copyright 1999 Annals of BotanyCompany Canopy model, functional architecture, irradiance avoidance, light harvesting, photoinhibition, photoprotection, photosynthesis model, plant architecture,Retama sphaerocarpa,semi-arid environment,Stipa tenacissima,structural photoprotection.     

Assimilatory Sulfate Reduction by the Hemoflagellate Leishmania tarentolae1

SYNOPSIS. Continuous growth of one cell line (UCI variant) of Leishmania tarentolae was achieved in the absence of organic sulfur. These cells were able to use sodium sulfate, and, to a limited extent, sodium sulfite as their sole sulfur source and could utilize methionine sulfoxide in place of L-methionine. A related cell line (RU variant) was unable to grow in organic sulfate-free media nor could these cells utilize methionine sulfoxide. UCI promastigotes incorporated significant amounts of ³⁵S sodium sulfate; killed cells did not take up the label. ³⁵S incorporation was inhibited by sodium molybdate (5 × 10^?4 M), sodium arsenite (5 × 10^?4 M), 2,4-dinitrophenol (1 × 10^?4 M), or KCN (5 × 10^?4 M). RU promastigotes did not incorporate significant amounts of ³⁵S sodium sulfate. Thin layer chromatographs of protein hydrolysates from UCI cells incubated in ³⁵S sodium sulfate revealed several radio opaque spots, one of which had chromatographic properties of cystine. UCI variants of L. tarentolae were therefore capable of assimilatory sulfate reduction whereas RU cells lacked this ability.