Testing the MEDALUS hillslope model

In the Mediterranean environment formative erosional and runoff events are sporadic, intense and infrequent. They are difficult to study, their effects difficult to anticipate and the impact of vegetational and climatic change, whether natural or human-induced, difficult to predict. For these reasons, modelling has to augment the traditional approaches. In the Mediterranean Desertification and Land Use research programme, models have been developed to look at these problems at the hillslope (MEDALUS model) and large catchment scale (MEDRUSH model). Such models are only as good as their capacity to replicate, to an acceptable level, the magnitude, pattern in space and time and character of real world processes. These models can be tested by (a) examining their logical structure and performance against synthetic or control data (primary level) (b) evaluating their behaviour against published empirical spatial and temporal data (secondary level) and (3) by direct comparison with field test data (real world validation).The MEDALUS catena model comprises atmospheric, plant growth, overland flow and erosion, and subsurface water redistribution components involving a number of important novel features especially for dryland environments. It produces vegetation biomass and storm event runoff and sediment yield for different positions over a hillslope at different times. It is here tested against plot data for events and vegetation, soil moisture, runoff, erosion and slope armouring for annual series over several years. The model is found to perform moderately well for runoff and very well for sediment yield for event-based simulations. The results for longer simulations, tested at the secondary level, perform well in comparison with responses cited in the literature.     

LDSO: a program to simulate pedigrees and molecular information under various evolutionary forces

Simulations are a major tool to evaluate new statistical methods and optimize experimental designs in the genomic era. However, this can only be achieved when the simulations are close enough to reality, as well as diverse enough to be realistic. For mapping studies, it is thus critical to re-create as much as possible the forces generating linkage (mutation, random drift, changes in population sizes, selection and pedigree structure) and the mechanisms producing trait genetic architecture (additivity, dominance, epistasis). We present here a computer program (ldso) simulating these phenomena. Optional outputs provide statistics on the linkage disequilibrium (LD) structure and the identity by descent between chromosomal segments, facilitating further data analyses. Furthermore, ldso enables the simulation of genomic data in known pedigrees, which sticks as precisely as possible to recent population history and structures of the long-range LD, allowing optimization of fine-mapping strategies.     

Soil enzymatic activities and microbial biomass in an integrated agroforestry chronosequence compared to monoculture and a native forest of Colombia

Large tracts of land in South American native forests have been converted to monoculture for livestock production which could negatively affect soils and environmental quality. A proposed management alternative is to use agroforestry systems, but little information is available on how they affect the soils. The objective was to assess the effect of a silvopastoral chronosequence in a tropical region of Colombia on soil microbiological and physico/chemical properties. The systems (three replications) were: monoculture grass conventional pasture (CP), native forest (F), and a silvopastoral system (SS) chronosequence with ages of 3 to 6 (SS₃), 8 to 10 (SS₈), or 12 to 15 (SS₁₂) years. Soil responses to these land management were determined by measuring soil chemical (total C and pH), physical (penetrometer resistance and bulk density), and microbiological properties (activities of ß-glucosidase, urease, and alkaline and acid phosphatase and microbial biomass). Because of differences in soil texture across management treatments, microbiological properties were normalized on organic C content basis. SS₁₂ showed the highest microbial biomass and enzyme activities on a per unit C basis and was consistently and significantly different from CP. Additionally, microbiological to C ratios were significantly affected by SS establishment age (P?相似文献   

Sperm competition and the evolution of sperm form and function in mammals

Sperm competition is a powerful selective force that has influenced many reproductive traits in males and females although additional evolutionary explanations may help to understand the diversity of mammalian reproduction. Sperm morphology varies considerably in mammals with extreme examples in several rodent lineages in which a wide range of sizes and complex head morphologies have been identified. Mammalian spermatozoa also differ in function, with swimming velocity and trajectory showing much divergence. Underlying processes mediating function have received little attention so far, but differences in timing and proportion of sperm undergoing capacitation or acrosomal exocytosis may be related to variation in signalling processes. Furthermore, energy required for sperm functions (such as motion, signalling and overall maintenance of cell integrity) can be produced and consumed, following different patterns among species and this could be the result of several selective forces. A more thorough understanding of the diversity in structure and function of sperm cells, and underlying selective forces, may help us develop better methods to assess them taking into account particulars and generalities of sperm form and performance. Such tests could then become more reliable in estimations of the impact of cryopreservation or effect of changes in the environment and their relevance for fertility.     

In Vivo and In Vitro Sperm Interaction with Oviductal Epithelial Cells of Llama

Sperm reservoirs in South American Camelids would be crucial for successful fertilization. Since ovulation occurs approximately 36 h after mating, the maintenance of the sperm viability in the oviduct waiting for the ovum is a critical reproductive event. Our study aimed at determining whether the isthmus or the utero tubal junction (UTJ) could function as a sperm reservoir in llama by means of in vivo and in vitro experiments. For the in vivo experiments, the oviducts of adult females with a dominant follicle bigger than 7 mm were examined for the presence of sperm at 6, 18, 24, 28 and 35 h after mating. The results using scanning and transmission electron microscopy showed ultrastructural differences between isthmus and UTJ with respect to (1) predominance of secretory cells in the UTJ and ciliated cells in the isthmus epithelium and (2) cytoplasmic bulbous projection of the secretory cells in the UTJ. Sperm adhered by a mucus‐like substance were seen only in the UTJ at 6, 18, 24 and 28 h post‐mating. Lack of sperm adhered to oviductal mucosa was observed around ovulation (35 h). In vitro experiments demonstrated higher ability of UTJ epithelial cell explants with respect to isthmus explants to bind sperm in a co‐cultured system. The anatomical features and the presence of a sperm bonding agent in the UTJ together with the in vitro differential binding of sperm to UTJ explants strongly suggest that both may be feasible mechanisms that facilitate sperm storage in this oviductal region in llama.     

Adaptation of ostriches to transport‐induced stress: Physiometabolic response

This study assessed the effects of five different transport periods on physiometabolic responses and gas exchange in ostriches. It included 138 ostriches that were assigned to five experimental groups. G₁ included 78 birds that were set aside as a reference group (RG). Each one of the four remaining experimental groups included 20 ostriches, which were transported in the following manner: G₁ on one occasion for a period of 1 h; G₂ on one occasion for 2 h; and G₃ on one occasion for 3 h; G_4a was made up of the ostriches from G₁ but they were shipped on a second occasion, for 2 h (making a total of 3 h); finally, G_4b was that same group, but after a third transport period, on this occasion during 3 h (for a total of 6 h). Groups G₂ and G₃ presented the most marked blood alterations (P < 0.05), including an increase in pH, hypocapnia (27.8 ± 0.80 mmHg), hypernatremia (171.75 ± 1.84 mmol/L), hypocalcemia (0.95 ± 0.03 mmol/L), and hyperglycemia (224.05 ± 3.94 mg/dL). Also, group G₃ presented the lowest hematocrit values (26.5 ± 0.47 HTC%). Therefore, transporting ostriches with no prior experience for 3 h caused the most pronounced physiometabolic changes.