Phylogenetic relationships, diversification and biogeography in Neotropical Brotogeris parakeets

Aim We present a molecular phylogenetic analysis of Brotogeris (Psittacidae) using several distinct and complementary approaches: we test the monophyly of the genus, delineate the basal taxa within it, uncover their phylogenetic relationships, and finally, based on these results, we perform temporal and spatial comparative analyses to help elucidate the historical biogeography of the Neotropical region. Location Neotropical lowlands, including dry and humid forests. Methods Phylogenetic relationships within Brotogeris were investigated using the complete sequences of the mitochondrial genes cyt b and ND2, and partial sequences of the nuclear intron 7 of the gene for Beta Fibrinogen for all eight species and 12 of the 17 taxa recognized within the genus (total of 63 individuals). In order to delinetae the basal taxa within the genus we used both molecular and plumage variation, the latter being based on the examination of 597 skin specimens. Dates of divergence and confidence intervals were estimated using penalized likelihood. Spatial and temporal comparative analyses were performed including several closely related parrot genera. Results Brotogeris was found to be a monophyletic genus, sister to Myiopsitta. The phylogenetic analyses recovered eight well‐supported clades representing the recognized biological species. Although some described subspecies are diagnosably distinct based on morphology, there was generally little intraspecific mtDNA variation. The Amazonian species had different phylogenetic affinities and did not group in a monophyletic clade. Brotogeris diversification took place during the last 6 Myr, the same time‐frame as previously found for Pionus and Pyrilia. Main conclusions The biogeographical history of Brotogeris implies a dynamic history for South American biomes since the Pliocene. It corroborates the idea that the geological evolution of Amazonia has been important in shaping its biodiversity, argues against the idea that the region has been environmentally stable during the Quaternary, and suggests dynamic interactions between wet and dry forest habitats in South America, with representatives of the Amazonian biota having several independent close relationships with taxa endemic to other biomes.     

Electrophysiological evidence for the autoregulation of β-cell secretion by insulin

Electrophysiological studies of cultured rat pancreatic β-cells using intracellular microelectrodes show that exogenous insulin over the range of 0.1–10.0 μg/ml inhibits the electrical activity due to 27.8 mM glucose in a dose-related manner. This inhibitory effect is manifested by a mean increase of the membrane potential from about ?20 to ?30 mV and inhibition of the manner of cells impaled showing spike activity from 60 to less than 10%. The inhibitory influence of insulin is rapid occuring within 5 min for the highest level used. The results provide evidence for a negative feedback role of insulin in regulating its own release.     

Orthotopic allotransplantation and autotransplantation of the baboon heart following 24-hr storage by a portable hypothermic perfusion system

A nonpulsatile perfusion apparatus, based on the air-lift pump principle, has been developed. Circulation of the perfusate, as well as oxygenation and maintenance of acid-base balance, is provided by the flow of a mixture of 97% oxygen and 3% carbon dioxide. The system is easily and entirely portable. Eleven baboons underwent orthotopic allotransplantation with donor hearts stored by continuous hypothermic (4-10 degrees C) perfusion for periods of up to 24 hr. Three were electively killed after 2 to 3 days; the remaining eight, immunosuppressed with methylprednisolone and either azathioprine or cyclosporin A, survived to rejection at between 10 and 49 days. Cardiac catheterization performed in six animals 7-14 days after allotransplantation showed virtually normal hemodynamic data. Three more baboons underwent heart excision and storage by hypothermic perfusion for 24 hr, and subsequent othotopic autotransplantation, the circulation of the baboon being maintained in the interim by an allograft. One animal survives 8 months later with hemodynamic data at cardiac catheterization differing little from that obtained before autotransplantation. This perfusion system has subsequently been used to store four human donor hearts prior to heterotopic transplantation.     

Inhibition by specific monosaccharides of interleukin 2-induced thymocyte proliferation

When rat thymocytes are cultured for 3 days in serum-free medium and are stimulated to divide by interleukin 2 (IL 2), concanavalin A, or sodium periodate oxidation, addition to the medium of 10–25 mMd-ribose, 2-deoxy-d-ribose, or N-acetyl-d-galactosamine inhibits by 40% or more the incorporation of [³H]thymidine. d-ribose and lectin-free IL 2 generated from sodium periodate oxidation of rat spleen cells were used to study the characteristics of this inhibition and to test possible mechanisms of inhibition. Viability of thymocytes cultured with d-ribose is similar to that of cells cultured without this sugar. In order to be inhibitory, d-ribose has to be added to the cultures within the first 24 hr, and the inhibition can be prevented if the sugar is removed 18–24 hr after the start of culture. d-Ribose does not block the absorption of IL 2 by unstimulated rat thymocytes or by concanavalin A-generated thymic or splenic blast cells. When thymocytes are cultured with d-ribose for 24 hr, inactivated with mitomycin C, and then cultured for 3 days with fresh mitogenically stimulated cells, [³H]thymidine incorporation into the latter is not altered. This suggests that the sugar does not generate suppressor cells or suppressor supernates. d-Ribose does not appear to be a general metabolic inhibitor since [³H]leucine incorporation into thymocyte proteins and the release of [³H]leucine into medium after a 2-hr. [³H]leucine pulse are not altered by d-ribose. Trivial or artifactual effects (nonspecific cytotoxicity, changes in thymidine transport, or changes in isotonicity of the culture medium) cannot explain the inhibition. A hypothetical mechanism of inhibition is discussed.     

Tropical niche conservatism as a historical narrative hypothesis for the Neotropics: a case study using the fly family Muscidae

Aim We evaluate the extent to which the tropical conservatism hypothesis can explain the evolutionary development of the Muscidae. Furthermore, we compare the geographical patterns of muscid phylogenetic structure with biogeographical regions that have been identified for Neotropical insects. Location Central and South America. Methods We modelled the geographic distributions of 658 species using Maxent and 19 environmental variables. A generic‐level supertree of the Muscidae was assembled using matrix representation with parsimony and used to map the geographic pattern of mean root distance (MRD), a metric of the relative evolutionary development of assemblages. Regression models (ordinary least squares and regression trees) were used to examine temperature and other environmental correlates of MRD to explore potential environmental drivers of muscid diversification. We used the regression tree results to recognize variable intervals that best explained MRD, and these intervals were mapped to recognize and compare with biogeographical regions of Neotropical insects. Results The geographic pattern of MRD was consistent with the tropical conservatism hypothesis: species in genera that diversified relatively early, as measured by their distance from the tree root, dominate lowland tropical South America, whereas species in genera that diversified more recently occupy extra‐tropical areas, sub‐Antarctic areas and the Andean highlands. Temperature was the strongest correlate of MRD. Three biogeographical regions were recognized and they coincided with two regions known for insects. Main conclusions Evolutionary responses of muscid flies to post‐Eocene climate change taking the form of an expansion of a tropical group into regions with colder climates may be fundamental to explaining their distribution in the Neotropics. Our biogeographical regions delimited by temperature and the phylogenetic metric, surrogates of the tropical conservatism hypothesis, were very similar to general insect patterns, supporting the ‘tropical origin and evolutionary response to climate cooling’ as a broadly based historical narrative for the Neotropics.     

Climate‐driven rampant speciation of the Cape flora

Aim To test whether the radiation of the extremely rich Cape flora is correlated with marine‐driven climate change. Location Middle to Late Miocene in the south‐east Atlantic and the Benguela Upwelling System (BUS) off the west coast of South Africa. Methods We studied the palynology of the thoroughly dated Middle to Late Miocene sediments of Ocean Drilling Program (ODP) Site 1085 retrieved from the Atlantic off the mouth of the Orange River. Both marine upwelling and terrestrial input are recorded at this site, which allows a direct correlation between changes in the terrestrial flora and the marine BUS in the south‐east Atlantic. Results Pollen types from plants of tropical affinity disappeared, and those from the Cape flora gradually increased, between 10 and 6 Ma. Our data corroborate the inferred dating of the diversification in Aizoaceae c. 8 Ma. Main conclusions Inferred vegetation changes for the Late Miocene south‐western African coast are the disappearance of Podocarpus‐dominated Afromontane forests, and a change in the vegetation of the coastal plain from tropical grassland and thicket to semi‐arid succulent vegetation. These changes are indicative of an increased summer drought, and are in step with the development of the southern BUS. They pre‐date the Pliocene uplift of the East African escarpment, suggesting that this did not play a role in stimulating vegetation change. Some Fynbos elements were present throughout the recorded period (from 11 Ma), suggesting that at least some elements of this vegetation were already in place during the onset of the BUS. This is consistent with a marine‐driven climate change in south‐western Africa triggering substantial radiation in the terrestrial flora, especially in the Aizoaceae.     

A new longirostrine dyrosaurid (Crocodylomorpha,Mesoeucrocodylia) from the Paleocene of north‐eastern Colombia: biogeographic and behavioural implications for New‐World Dyrosauridae

Abstract: Fossils of dyrosaurid crocodyliforms are limited in South America, with only three previously diagnosed taxa including the short‐snouted Cerrejonisuchus improcerus from the Paleocene Cerrejón Formation of north‐eastern Colombia. Here we describe a second dyrosaurid from the Cerrejón Formation, Acherontisuchus guajiraensis gen. et sp. nov., based on three partial mandibles, maxillary fragments, teeth, and referred postcrania. The mandible has a reduced seventh alveolus and laterally depressed retroarticular process, both diagnostic characteristics of Dyrosauridae. Acherontisuchus guajiraensis is distinct among known dyrosaurids in having a unique combination of craniomandibular characteristics, and postcranial morphology that suggests it may have occupied a more placid, fluvial habitat than most known Old‐World dyrosaurids. Results from a cladistic analysis of Dyrosauridae, using 82 primarily cranial and mandibular characters, support an unresolved relationship between A. guajiraensis and a combination of New‐ and Old‐World dyrosaurids including Hyposaurus rogersii, Congosaurus bequaerti, Atlantosuchus coupatezi, Guarinisuchus munizi, Rhabdognathus keiniensis and Rhabdognathus aslerensis. Our results are consistent with an African origin for Dyrosauridae with multiple dispersals into the New World during the Late Cretaceous and a transition from marine habitats in ancestral taxa to more fluvial habitats in more derived taxa.     

Morphological variability of Aulacoseira granulata (Ehr.) Simonsen (Bacillariophyceae) in the Lower Paraná River (Argentina)

In this paper we consider the morphological variation within a natural population of Aulacoseira granulata (Ehr.) Simonsen in relation to environmental factors. This species was dominant in the phytoplankton of the Lower Paraná River (Argentina) and exhibited seasonal fluctuations of cell dimensions. The mean cell diameter was directly correlated with the river water level and inversely with pH and nitrate concentrations, whereas cell length was directly correlated with transparency and nitrate concentration and inversely with suspended solids. This pattern was similar to that observed for filament length. The cell length : diameter ratio was inversely related to water level and discharge and directly related to pH, transparency, and nitrate concentration. Maximum diameters did not coincide with maximum lengths. A tendency to maintain cell volume throughout the annual cycle was observed, which probably relates to both buoyancy and photosynthetic capacity. These results associate the water ascendancy and the size recovery phases to discharge. Cells become smaller on the ebbing of the flood phase, and the decreasing depth increases the probability that the alga will be disentrained from the turbulent field. The loss during low water would act as a stimulus for auxosporulation, contributing to the production of large cells to start off the next population. Received: August 12, 2000 / Accepted: November 14, 2000