Predicted impact of barriers to migration on the Serengeti wildebeest population

The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration--even without causing habitat loss--could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti.     

Models for the continuous culture of microorganisms under both oxygen and carbon limiting conditions

Two models for predicting the behavior of cultures of microorganisms under both oxygen and carbon limiting conditions have been evlauated on a chemostat growing Candida utilis on a glycolysis suppressing glycerol medium. The work indicated that parameter values obtained under wholly oxygen limiting or wholly carbon limiting conditions successfully predict the behavior of the chemostat under the wide range of flow and substrate concentration conditions tested. Both models are satisfactory and hence it is deduced that the simpler one may be used with confidence. It was found that Monod kinetics were applicable to the growth rate dependence on oxygen concentration but that Contois kinetics were superior for the corresponding dependence on carbon substrate concentration.     

Autism and intellectual disability are differentially related to sociodemographic background at birth

Background

Research findings investigating the sociodemographics of autism spectrum disorder (ASD) have been inconsistent and rarely considered the presence of intellectual disability (ID).

Methods

We used population data on Western Australian singletons born from 1984 to 1999 (n = 398,353) to examine the sociodemographic characteristics of children diagnosed with ASD with or without ID, or ID without ASD compared with non-affected children.

Results

The profiles for the four categories examined, mild-moderate ID, severe ID, ASD without ID and ASD with ID varied considerably and we often identified a gradient effect where the risk factors for mild-moderate ID and ASD without ID were at opposite extremes while those for ASD with ID were intermediary. This was demonstrated clearly with increased odds of ASD without ID amongst older mothers aged 35 years and over (odds ratio (OR) = 1.69 [CI: 1.18, 2.43]), first born infants (OR = 2.78; [CI: 1.67, 4.54]), male infants (OR = 6.57 [CI: 4.87, 8.87]) and increasing socioeconomic advantage. In contrast, mild-moderate ID was associated with younger mothers aged less than 20 years (OR = 1.88 [CI: 1.57, 2.25]), paternal age greater than 40 years (OR = 1.59 [CI: 1.36, 1.86]), Australian-born and Aboriginal mothers (OR = 1.60 [CI: 1.41, 1.82]), increasing birth order and increasing social disadvantage (OR = 2.56 [CI: 2.27, 2.97]). Mothers of infants residing in regional or remote areas had consistently lower risk of ASD or ID and may be linked to reduced access to services or under-ascertainment rather than a protective effect of location.

Conclusions

The different risk profiles observed between groups may be related to aetiological differences or ascertainment factors or both. Untangling these pathways is challenging but an urgent public health priority in view of the supposed autism epidemic.     

Receptor expression and oxidase activity in human neutrophils: Regulation by granulocyte-macrophage colony-stimulating factor and dependence upon protein biosynthesis

Incubation of human bloodstream neutrophils with 50 u/ml recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) primed the respiratory burst (as assessed by fMet-Leu-Phe stimulated luminol-dependent chemiluminescence) and resulted in a rapid (within 15 min) upregulation of expression of CD11b and CD18 (as measured by FACS analysis). This rapid priming and modulation of receptor expression was not inhibited by cycloheximide and hence appeared to be independent ofde novo protein biosynthesis. When neutrophils were incubated for up to 5 h in culture, the fluorescence distributions of CD11b and CD18 declined indicating the loss of expression of these receptors as the neutrophils aged, but in rGM-CSF treated suspensions receptor expression was maintained. When neutrophils were incubated in the presence of cycloheximide, they progressively lost their ability to generate reactive oxidants in response to fMet-Leu-Phe so that by 5 h incubation with this inhibitor they could only generate about 25% of the oxidative response stimulated in untreated cells, and the expression of CD16 and CD18 was grossly impaired. Similar effects were observed in rGM-CSF treated suspensions except that cycloheximide required longer incubation times (typically 4–5 h) before impairment of function or receptor expression occurred. These data show thatde novo protein biosynthesis is required for both the maintenance of neutrophil function and also for the continued expression of some plasma membrane receptors.Abbreviations fMet-Leu-Phe N-formylmethionyl-Leucyl-Phenylalanine - rGM-CSF recombinant granulocyte-macrophage colony-stimulating factor - FITC fluorescein isothiocyanate conjugate - Luminol 5-amino-2,3-dihydrophthalazine-1,4-dione     

Association of a missense mutation in the bovine leptin gene with carcass fat content and leptin mRNA levels

Previously, we have shown that alleles of the BM1500 microsatellite, located 3.6 kb downstream of the leptin gene in cattle, were associated with carcass fat measures in a population of 154 unrelated beef bulls. Subsequently, a cytosine (C) to thymine (T) transition that encoded an amino acid change of an arginine to a cysteine was identified in exon 2 of the leptin gene. A PCR-RFLP was designed and allele frequencies in four beef breeds were correlated with levels of carcass fat. The T allele was associated with fatter carcasses and the C allele with leaner carcasses. The frequencies of the SNP alleles among breeds indicated that British breeds have a higher frequency of the T allele whereas the continental breeds have a higher occurrence of the C allele. A ribonuclease protection assay was developed to quantify leptin mRNA in a separate group of animals selected by genotype. Animals homozygous for thymine expressed higher levels of leptin mRNA. This may suggest that the T allele, which adds an extra cysteine to the protein, imparts a partial loss of biological function and hence could be the causative mutation.     

Predicting spatially heterogeneous invasive spread: Pyracantha angustifolia invading a dry Andean valley in northern Argentina

Biological Invasions - Understanding the drivers of invasive species spread is key to designing optimal management programmes for controlling them. Population models, parameterized from demographic...     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Identifying Extrinsic versus Intrinsic Drivers of Variation in Cell Behavior in Human iPSC Lines from Healthy Donors

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