Stable isotope analysis indicates microalgae as the predominant food source of fauna in a coastal forest stream,south‐east Brazil

Abstract: Stable isotope studies of food webs in floodplains, large rivers, mangroves, and seagrasses have shown that, although a large proportion of the biomass may come from higher plants, microalgae provide a disproportionate amount of carbon assimilated by metazoan consumers. Evidence is building that this may also be the case for streams, especially those in the tropics. At the level of individual consumer species we also see that the apparent diet may not be reflected in the carbon assimilated. Tropical streams commonly have omnivore‐detritivore species that potentially show this phenomenon. We tested these concepts in four moderately shaded sites in a stream in well‐preserved Atlantic rainforest at Ilha Grande, Rio de Janeiro. We sampled aquatic insects, shrimps and fish as well as potential terrestrial and aquatic primary food sources. Carbon stocks from terrestrial sources predominated over carbon of algal origin (>99% of total). The primary sources of carbon showed distinctly different isotopic signatures: terrestrial sources had δ¹³C values close to ?30‰, microalgae were ?20‰ and macroalgae were ?25‰. All fauna had δ¹³C values consistent with a carbon source derived from microalgae. Baetid mayflies and atyid shrimps exert a strong grazing pressure on periphyton and organic sediments but appear to assimilate predominantly microalgae. The palaemonid shrimp Macrobrachium olfersi also ingests large amounts of detritus of terrestrial origin, but apparently assimilates animal prey with algal δ¹³C signatures. These results support the growing view that tropical stream food chains are primarily algal based.     

The bite force of the largest fossil rodent (Hystricognathi,Caviomorpha, Dinomyidae)

Blanco R.E., Rinderknecht, A. & Lecuona, G. 2011: The bite force of the largest fossil rodent (Hystricognathi, Caviomorpha, Dinomyidae). Lethaia, Vol. 45, pp. 157–163. An exceptionally well‐preserved skull of the largest fossil rodent Josephoartigasia monesi allows the first analysis of the bite mechanics of this group of South American giant rodents. In this study, we reconstructed the main anatomical features of the skull of this Pliocene rodent, relating them to the bite force at incisors. Bite force was estimated using three different techniques. Two methods suggest that bite forces at incisors of around 1000 N were possible for these mammals. However, the incisors seem to be stronger than expected for this bite force implying that the bite forces may have been greater than 3000 N. We consider three hypotheses: allometric effects, teeth digging or defence against predators, to explain our results. □Bite force, Dinomyidae, incisors, largest rodent, Pliocene.     

Costs versus risks: Architectural changes with changing light quantity and quality in saplings of temperate rainforest trees of different shade tolerance

Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome‐mediated stem elongation in response to changes in red : far red ratio, while shade‐tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old‐growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade‐tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.     

Geographical pattern of genetic variation in the Robertsonian system of Mus musculus domesticus in central Italy

The Robertsonian (Rb) system of Mus musculus domesticus in central Italy consists of three Rb races (CD, 2 n  = 22; CB, 2 n  = 22; ACR, 2 n  = 24), and additional Rb populations with new metacentrics have recently been reported. The aim of the present paper is to provide insight into the process of house mouse raciation in this area. Here we present new data concerning the geographical distribution of mtDNA haplotypes (control region sequence) in the three Rb races and in the surrounding standard populations. The presence of exclusive clades in all the three Rb races supports the idea of a past fragmentation event and a subsequent period of isolation. However, comparison of mtDNA polymorphism between Rb and standard races, and the shape of the mismatch distribution within the races, does not reveal any clear sign of a strong reduction in population size, at this geographical scale, related to race formation.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 395–405.     

Mutational analysis of the <Emphasis Type="Italic">GLA</Emphasis> gene in Mexican families with Fabry disease

Fabry disease (FD) is a lysosomal storage disorder, which develops due to a deficiency in the hydrolytic enzyme, α-galactosidase A (α-Gal A). Alpha-Gal A hydrolyzes glycosphingolipid globotriaosylceramide (Gb3), and an α-Gal A deficiency leads to Gb3 accumulation in tissues and cells in the body. This pathology is likely to involve multiple systems, but it is generally considered to affect primarily vascular endothelium. In this study, we investigated mutations in the GLA gene, which encodes α-Gal A, in Mexican families with FD. We included seven probands with FD that carried known mutations. We analysed pedigrees of the probands, and performed molecular screening in 65 relatives with the potential of carrying a GLA mutation. Five mutations (P40S, IVS4 ⁺⁴, G328V, R363H, R404del) were detected in seven unrelated Mexican families with the classic FD phenotype. Of the 65 relatives examined, 42 (64.6%) had a GLA gene mutation. In summary, among seven Mexican probands with FD, 65 relatives were at risk of carrying a known GLA mutation, and molecular screening identified 42 individuals with the mutation. Thus, our findings showed that it is important to perform molecular analysis in families with FD to detect mutations and to provide accurate diagnoses for individuals that could be affected.     

Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus

Herbivory and water shortage are key ecological factors affecting plant performance. While plant compensatory responses to herbivory include reallocation of biomass from below‐ground to above‐ground structures, plant responses to reduced soil moisture involve increased biomass allocation to roots and a reduction in the number and size of leaves. In a greenhouse study we evaluated the effects of experimental drought and leaf damage on biomass allocation in Convolvulus demissus (Convolvulaceae), a perennial herb distributed in central Chile, where it experiences summer drought typical of Mediterranean ecosystems and defoliation by leaf beetles and livestock. The number of leaves and internode length were unaffected by the experimental treatments. The rest of plant traits showed interaction of effects. We detected that drought counteracted some plant responses to damage. Thus, only in the control watering environment was it observed that damaged plants produced more stems, even after correcting for main stem length (index of architecture). In the cases of shoot : root ratio, relative shoot biomass and relative root biomass we found that the damage treatment counteracted plant responses to drought. Thus, while undamaged plants under water shortage showed a significant increase in root relative biomass and a significant reduction in both shoot : root ratio and relative shoot biomass, none of these responses to drought was observed in damaged plants. Total plant biomass increased in response to simulated herbivory, apparently due to greater shoot size, and in response to drought, presumably due to greater root size. However, damaged plants under experimental drought had the same total biomass as control plants. Overall, our results showed counteractive biomass allocation responses to drought and damage in C. demissus. Further research must address the fitness consequences under field conditions of the patterns found. This would be of particular importance because both current and expected climatic trends for central Chile indicate increased aridity.     

Parapatric hybridization in the chromosomal speciation of the house mouse

Chromosomal races of the house mouse ( Mus domesticus ) occur extensively in Italy. The present paper reports results of studies on a hybrid zone in Central Italy on a chromosomal race with a 2 n = 22 karyotype and surrounding populations with a standard 2 n = 40 karyotype. Karyotypic and morphometric patterns of variation in this area are discussed in an attempt to contribute to an understanding of the chromosomal speciation in this species. Data are compared, where possible, with other findings on the same hybrid zone. Finally, it is suggested that changes in behavioural traits (inter-male aggression and female socio-sexual preferences) may help in promoting complete genetic isolation.     

Effect of Source-Sink Manipulations on the Crassulacean Acid Metabolism of Kalanchoe pinnata

The effect of manipulations of the sink-source at the above-groundlevel and girdling of source leaves was measured in 4-month-oldplants of the CAM species Kalancho pinnata (Lam.) Pers. At thisage plants developed five pairs of leaves. The upper fourthand fifth leaf pairs were not fully expanded and behaved ascarbohydrate sinks. Removal of the developing leaves induceda progressive accumulation of glucans and sugars in the matureleaves. The titratable acidity increased during the second weekbut accumulation was less than in the control plants three tofour weeks after sink removal. Similar, but more rapid, resultswere observed in mature leaves with girdled petioles. Up tothe second night after girdling dark CO₂ fixation increased,but decreased steadily afterwards. CAM Phase 4 (afternoon CO₂fixation) however, was more sensitive to girdling, being reducedby 38% on the first day, and disappearing completely 3 d aftergirdling. The glucan and sugar contents of girdled leaves increasedcontinuously after treatment, but day-night changes ceased completelyon the fifth day. Girdling also caused a considerable increasein chloroplast area, with up to 80% of their internal spaceoccupied by starch grains, leading to grana distortion. In girdledleaves, or in source leaves in plants lacking aerial carbohydratesinks, dawn-dusk changes in titratable acidity started to decreasewhen the leaf glucan content exceeded 1·0 mol equivalenthexoses kg^–1 dry weight. Increased sink strength throughshading of all leaves except one source leaf did not affectits CAM activity. The titratable acidity and non-structuralcarbohydrate content of the shaded mature leaves was reducedby around 55%. Removal of all the mature source leaves acceleratedthe maturation process of sink leaves, increasing titratableacidity at dawn and synthesis of glucans during the light period.The results support the hypothesis that CO₂ fixation in a CAMplant is controlled by accumulation of glucans in chloroplasts. Key words: CAM, glucan accumulation, sink-source ratio, CO₂ fixation     

Genetic diversity analysis and conservation implications for the Iberian threatened populations of the irano-turanian relict Krascheninnikovia ceratoides (Chenopodiaceae)

Krascheninnikovia ceratoides (L.) Gueldenst. (Chenopodiaceae) is an irano‐turanian steppe plant with a striking geographical vicariance between the western Mediterranean and the central Asian regions. Its westernmost populations are located in the north‐east part of the Iberian Peninsula, in the narrow middle Ebro and Alfambra valleys, where they are threatened and have been catalogued as ‘vulnerable’. Genetic diversity and structure was studied in 150 individuals from five populations of these two valleys using inter‐simple sequence repeats (ISSR). A total of 121 informative bands allowed the identification of 150 genotypes. Nei's genetic diversity found in all natural populations (h = 0.448) was higher than that of other geographical restricted species. Analysis of molecular variance and spatial correlations analyses showed a strong genetic differentiation among populations (35.88%) and among valleys (22.33%). The unweighted pair‐group method of arithmetical averages and Neighbour‐joining clusterings further demonstrated a substructure of two population cores within the Ebro valley. Our genetic data suggest that the high levels of genetic diversity and the strong genetic structure found among the northern Iberian populations and ranges of K. ceratoides might result from the summed effects of its tetraploidy, its outbreeding nature, and its success in colonizing newly altered areas. However, the ISSR data might also reflect the existence of an ancient wider distribution range of the plant in the Iberian Peninsula coupled with a more recent history of habitat fragmentation. Different management conservation guidelines are recommended for this plant after our genetic analysis: a microreserve of approximately 2 km² is proposed for the highly threatened population of Osera (Ebro valley), whereas seed collection strategies and occasional population reinforcements are suggested for the remaining populations. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 419–429.     

Carbon Dioxide Exchange, Soluble Carbohydrates and Acid Accumulation in a Fructan Accumulating Plant: Fourcroya humboldtiana Treal.

Fourcroya hunboldtiana Treal. (Agavaceae) is a rosette plantwhich accumulates fructans and shows active CAM metabolism undernatural conditions. Daily changes in titratable acidity wererelated to leaf age and degree of leaf inclination. Nocturnalacidification rates of 15 mmol H+ g–1 fresh weight h–1were measured under natural conditions and no recycling of respiratoryCO₂ could be detected. Fructans of low molecular weight apparentlyconstituted the only source for the synthesis of substrate forCO₂ fixation. Acidification was accounted for by the amountof external CO₂ fixed and the reduction in fructan content duringthe night. The maximum degree of polymerization of fructansas shown by differential extraction in alcoholic solutions ofdecreasing concentration, changed during the CAM cycle, at theend of the night period maximum degree of polymerization wasaround 24, while in the late afternoon the degree of polymerizationincreased up to 43. Key words: Fourcroya humboldtiana Treal., fructans, CAM metabolism