Attempting genetic inference from directional asymmetry during convergent hindlimb reduction in squamates

Loss and reduction in paired appendages are common in vertebrate evolution. How often does such convergent evolution depend on similar developmental and genetic pathways? For example, many populations of the threespine stickleback and ninespine stickleback (Gasterosteidae) have independently evolved pelvic reduction, usually based on independent mutations that caused reduced Pitx1 expression. Reduced Pitx1 expression has also been implicated in pelvic reduction in manatees. Thus, hindlimb reduction stemming from reduced Pitx1 expression has arisen independently in groups that diverged tens to hundreds of millions of years ago, suggesting a potential for repeated use of Pitx1 across vertebrates. Notably, hindlimb reduction based on the reduction in Pitx1 expression produces left‐larger directional asymmetry in the vestiges. We used this phenotypic signature as a genetic proxy, testing for hindlimb directional asymmetry in six genera of squamate reptiles that independently evolved hindlimb reduction and for which genetic and developmental tools are not yet developed: Agamodon anguliceps, Bachia intermedia, Chalcides sepsoides, Indotyphlops braminus, Ophisaurus attenuatuas and O. ventralis, and Teius teyou. Significant asymmetry occurred in one taxon, Chalcides sepsoides, whose left‐side pelvis and femur vestiges were 18% and 64% larger than right‐side vestiges, respectively, suggesting modification in Pitx1 expression in that species. However, there was either right‐larger asymmetry or no directional asymmetry in the other five taxa, suggesting multiple developmental genetic pathways to hindlimb reduction in squamates and the vertebrates more generally.     

Phosphorus Limitation in Boreal Forests: Effects of Aluminum and Iron Accumulation in the Humus Layer

Plant growth in boreal forests is generally considered to be predominantly nitrogen (N) limited, but forested groundwater discharge areas may be exceptions. In this study, we conducted tests to determine whether highly productive forested groundwater discharge areas generally differ from adjacent groundwater recharge areas in terms of humus chemistry and the availability of phosphorus (P) and N to plants. We investigated six forested sites, divided into groundwater discharge and adjacent groundwater recharge areas, in northern Sweden. The humus layers of the forested groundwater discharge areas were clearly distinguished from the adjacent groundwater recharge areas by having higher acid-digestible calcium (Ca) and/or aluminium (Al) and iron (Fe) content and higher organic P and N content. Soil solution inorganic N (NH₄ ⁺ and NO₃ ⁻) and pH were higher in the groundwater discharge areas than in the groundwater recharge areas. The organic P content showed a positive linear relationship to the Al and Fe content in the humus layer, indicating that organic P is associated with Al and Fe compounds in the humus. A plant bioassay using humus substrate from one groundwater discharge area and the adjacent groundwater recharge area found that plants grown in groundwater discharge area humus (with a high P-fixation capacity) increased their biomass upon P fertilization, whereas no growth response was found for N additions. By contrast, plants grown in humus from the groundwater recharge area did not respond to added P unless N was added too. This study suggests that groundwater discharge can affect the nutrient availability of N and P both directly, via increased P fixation due to the redistribution of Al and Fe, and indirectly, via the inflow of groundwater high in Ca and alkalinity, maintaining a high pH in the humus layer that favors in situ N turnover processes. Received 2 March 2001; Accepted 9 November 2001.     

Reduced leg blood flow during dynamic exercise in older endurance-trained men

It is currentlyunclear whether aging alters the perfusion of active muscles duringlarge-muscle dynamic exercise in humans. To study this issue, directmeasurements of leg blood flow (femoral vein thermodilution) andsystemic arterial pressure during submaximal cycle ergometry (70, 140, and 210 W) were compared between six younger (Y; 22-30 yr) and sixolder (O; 55-68 yr) chronically endurance-trainedmen. Whole body O₂uptake, ventilation, and arterial and femoral venous samples forblood-gas, catecholamine, and lactate determinations were alsoobtained. Training duration (min/day), estimated leg muscle mass(dual-energy X-ray absorptiometry; Y, 21.5 ± 1.2 vs. O, 19.9 ± 0.9 kg), and blood hemoglobin concentration (Y, 14.9 ± 0.4 vs. O, 14.7 ± 0.2 g/dl) did not significantly differ (P > 0.05) between groups. Leg bloodflow, leg vascular conductance, and femoral venousO₂ saturation were ~20-30%lower in the older men at each work rate (allP < 0.05), despite similarlevels of whole body O₂ uptake. At210 W, leg norepinephrine spillover rates and femoral venous lactateconcentrations were more than twofold higher in the older men.Pulmonary ventilation was also higher in the older men at 140 (+24%)and 210 (+39%) W. These results indicate that leg blood flow andvascular conductance during cycle ergometer exercise are significantlylower in older endurance-trained men in comparison to their youngercounterparts. The mechanisms responsible for this phenomenon and theextent to which they operate in other groups of older subjects deservefurther attention.

     

Interactive Effects Between Reindeer and Habitat Fertility Drive Soil Nutrient Availabilities in Arctic Tundra

Herbivores impact nutrient availability and cycling, and the net effect of herbivory on soil nutrients is generally assumed to be positive in nutrient-rich environments and negative in nutrient-poor ones. This is, however, far from a uniform pattern, and there is a recognized need to investigate any interactive effects of herbivory and habitat fertility (i.e., plant C/N ratios) on soil nutrient availabilities. We determined long-term effects of reindeer on soil extractable nitrogen (N) and phosphorus (P) and their net mineralization rates along a fertility gradient of plant carbon (C) to N and P ratios in arctic tundra. Our results showed that reindeer had a positive effect on soil N in the more nutrient-poor sites and a negative effect on soil P in the more nutrient-rich sites, which contrasts from the general consensus. The increase in N availability was linked to a decrease in plant and litter C/N ratios, suggesting that a shift in vegetation composition toward more graminoids favors higher N cycling. Soil P availability was not as closely linked to the vegetation and is likely regulated more by herbivore-induced changes in soil physical and chemical properties. The changes in soil extractable N and P resulted in higher soil N/P ratios, suggesting that reindeer could drive the vegetation toward P-limitation. This research highlights the importance of including both the elements N and P and conducting studies along environmental gradients in order to better understand the interactive effects of herbivory and habitat fertility on nutrient cycling and primary production.     

Global change‐driven effects on dissolved organic matter composition: Implications for food webs of northern lakes

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial–aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)—the messenger between terrestrial and lake ecosystems—with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change‐driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice‐out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.     

Extraction, amplification and characterization of wood DNA from dipterocarpaceae

A successful DNA extraction from wood yielding appropriate DNA quality for PCR amplification allows molecular genetic investigations of wood tissue. Genotypes, the origin of sampled material, and species can be identified based on an investigation of wood if suitable information on genetic variation patterns within and among species is available. Potential applications are in forensics and in the control of the timber and wood trade. We extracted DNA from wood of Dipterocarpaceae, a family that dominates rainforests and comprises many important timber species in Southeast Asia. Several different DNA isolation techniques were compared and optimized for wood samples from natural populations and from wood processing enterprises. The quality of the DNA was tested by spectrophotometry, PCR amplification, and PCR inhibitor tests. An average DNA yield of 2.2 μg was obtained per 50–100 mg of dried wood sample. Chloroplast DNA (cpDNA) regions of different length were amenable to PCR amplification from the extracted DNA. Modification of DNA isolation techniques by the addition of polyvinylpyrrolidone (PVP) addition up to 3.1% into lysis buffer reduced PCR inhibition effectively. In order to evaluate the extraction method, we analyzed leaves and wood from the same tree by PCR amplification, genotyping and sequencing of chloroplast microsatellites.     

Taxonomic aggregation does not alleviate the lack of consistency in analysing diversity in long‐term phytoplankton monitoring data: a rejoinder to Pomati et al. (2015)

相似文献   

The absolute dating of Upper Pleistocene subSaharan fossil hominids and their place in human evolution

In the evolution of anatomically modern man and his subspecies most specialists have concentrated on investigating geographical areas other than Africa as the possible area of origin.In this study 20 fossil hominids and associated faunal remains from South and East Africa were dated by microanalysis, radiocarbon, and amino-acid dating in order to see whether modern man appears later, was sympatric, or even predated Neandertal man.These dates indicate that anatomically modern man occurs sympatrically and possibly even predates the Rhodesian group of Neandertals in Africa. Modern man might also be contemporary to and possibly even predate the occurrence of Neandertal in Europe.This would indicate that modern man did not evolve from but possibly gave rise to the Neandertals as off-shoots.Two possibilities for the evolution of modern man are suggested. First, that Homo sapiens capensis evolved about 90,000 to 100,000 years ago from possibly Homo erectus by way of a “basic” Homo sapiens and later gave rise to Homo sapiens rhodesiensis, Homo sapiens afer, and possibly Homo sapiens palestinus around 50,000 years ago with Homo neanderthalensis and Homo sapiens capensis evolving separately from Homo erectus. In this case Homo neanderthalensis would be a different species from Homo sapiens which includes Homo sapiens capensis, Homo sapiens rhodesiensis, Homo sapiens afer, and possibly Homo sapiens palestinus.Secondly, Homo sapiens capensis evolved by way of a “basic” Homo sapiens with Homo sapiens rhodesiensis and Homo sapiens palestinus branching off from Homo sapiens capensis around 50,000 years ago. Before that, around 90,000 to 100,000 years ago Homo sapiens capensis evolved first and was then followed by Homo sapiens neanderthalensis from a “basic” Homo sapiens stock, but diverged. This means, all Neandertals, Homo sapiens capensis, Homo sapiens sapiens and Homo sapiens afer can be considered as subspecies of Homo sapiens.The author favors the first scheme since on relative dating grounds the existence of Neandertal man in Europe before the earliest date of Homo sapiens capensis and a “basic” Homo sapiens seems to be fairly well documented. Irrespective of either one of these possibilities, modern man evolved in Africa and seems to have migrated into Europe and other parts of the world.New absolute dating techniques are mentioned in detail like the new radiocarbon-collagen method and amino acid dating.