The relative importance of refugia in determining the drift and habitat selection of predaceous stoneflies in a sandy-bottomed stream

Patch structure in sandy, compared to rocky streams, is characterized by isolated snags that can only be colonized by drifting. By measuring drift from patches (snags) of various quality we determined the factors that influence habitat selection and drift of the predaceous stoneflies Acroneuria abnormis and Paragnetina fumosa. The presence of refugia (loose bark and leaf packs) was more important than hunger level and modified the effects of increased predator densities and aggressive interactions. Stoneflies concentrated to 8x natural densities with access to refugia remained longer on snags than a single stonefly without access to refugia. During periods of activity, refugia were defended with larger stoneflies always displacing smaller nymphs. During long periods of inactivity, two and sometimes three nymphs would rest side-by-side sharing the same refuge. Hunger level (starved versus satiated stoneflies), an indirect measure of a predator's response to prey availability, had no significant effect on drift or habitat selection regardless of the presence of refugia. Stonefly predators had a uniform distribution while their prey were clumped. Drift was deliberate and almost always delayed until night, usually at dusk or dawn. An examination of previous research plus the results of this study suggest that non-predatory intra- and interspecific interactions can be an important mechanism causing drift in streams.     

Gene duplication and divergence produce divergent MHC genotypes without disassortative mating

Genes of the major histocompatibility complex (MHC) exhibit heterozygote advantage in immune defence, which in turn can select for MHC‐disassortative mate choice. However, many species lack this expected pattern of MHC‐disassortative mating. A possible explanation lies in evolutionary processes following gene duplication: if two duplicated MHC genes become functionally diverged from each other, offspring will inherit diverse multilocus genotypes even under random mating. We used locus‐specific primers for high‐throughput sequencing of two expressed MHC Class II B genes in Leach's storm‐petrels, Oceanodroma leucorhoa, and found that exon 2 alleles fall into two gene‐specific monophyletic clades. We tested for disassortative vs. random mating at these two functionally diverged Class II B genes, using multiple metrics and different subsets of exon 2 sequence data. With good statistical power, we consistently found random assortment of mates at MHC. Despite random mating, birds had MHC genotypes with functionally diverged alleles, averaging 13 amino acid differences in pairwise comparisons of exon 2 alleles within individuals. To test whether this high MHC diversity in individuals is driven by evolutionary divergence of the two duplicated genes, we built a phylogenetic permutation model. The model showed that genotypic diversity was strongly impacted by sequence divergence between the most common allele of each gene, with a smaller additional impact of monophyly of the two genes. Divergence of allele sequences between genes may have reduced the benefits of actively seeking MHC‐dissimilar mates, in which case the evolutionary history of duplicated genes is shaping the adaptive landscape of sexual selection.     

Interactions between fire and introduced deer herbivory on coastal heath vegetation

The coastal heathlands of the Royal National Park are impacted by both fire and herbivory by introduced deer, and to date these two factors have been dealt with independently in the management of natural areas. In recent years, there has been increasing recognition for a more integrated approach to manage these two disturbance agents. Fire and its role in Australian heathlands are well known, while impacts from introduced deer and the combined effects of fire and introduced deer are still poorly understood. In this study, we investigated the effects of fire and Javan rusa deer (Cervus timorensis) on both vegetation cover and floristics. The percentage cover of plants at different height layers and the presence/absence of individual species were recorded at sites representing two different burn histories (1993/1994 and 2000/2001) and deer presence or absence. Fire significantly reduced vegetation cover at low (<50 cm) and intermediate heights (50–100 cm), while deer presence affected grasses and sedges, and low vegetation at more recently burnt sites. Rusa deer also affected composition of the plant species assemblages, but no such effect was found for fire. Understanding the influence of each disturbance factor independently and together in the heathlands will be critical for implementing a more robust framework for future management.     

Impact of Ramadan intermittent fasting on cognitive function in trained cyclists: a pilot study

This study assessed selected measures of cognitive function in trained cyclists who observed daylight fasting during Ramadan. Eleven cyclists volunteered to participate (age: 21.6±4.8 years, VO₂max: 57.7±5.6 ml kg⁻¹·min⁻¹) and were followed for 2 months. Cognitive function (Cambridge Neuropsychological Test Automated Battery (CANTAB), Reaction Time index (RTI) and Rapid Visual Information Processing (RVP) tests) and sleep architecture (ambulatory EEG) were assessed: before Ramadan (BR), in the 1st week (RA1) and 4th week of Ramadan (RA4), and 2 weeks post-Ramadan (PR). Both cognitive tests were performed twice per day: before and after Ramadan at 8-10 a.m. and 4-6 p.m., and during Ramadan at 4-6 p.m. and 0-2 a.m., respectively. Training load (TL) by the rating of perceived exertion (RPE) method and wellness (Hooper index) were measured daily. If the TL increased over the study period, this variable was stable during Ramadan. The perceived fatigue and delayed onset muscle soreness (DOMS) increased at RA4. Sleep patterns and architecture showed clear disturbances, with significant increases in the number of awakenings and light sleep durations during Ramadan (RA1 and RA4), together with decreased durations of deep and REM sleep stages at PR. RTI (simple and multiple reaction index) reaction and movement times did not vary over the study period. The RVP test showed reduced false alarms during Ramadan, suggesting reduced impulsivity. Overall accuracy significantly increased at RA1, RA4 and PR compared to baseline. At RA4, the accuracy was higher at 0-2 a.m. compared to 4-6 p.m. Despite the observed disturbances in sleep architecture, Ramadan fasting did not negatively impact the cognitive performance of trained cyclists from the Middle East.     

Immunocompetent cells in the chicken. II. Synergism between thymus cells and either bursa or bone marrow cells in the humoral immune response to sheep erythrocytes

Newly hatched F₁ hybrid chicks isogenic for the strong B histocompatibility locus were rendered immunologically incompetent by cyclophosphamide treatment and x-irradiation. They were then injected intravenously with thymus, bone marrow, or bursa cells together with sheep erythrocytes (SE) and received another iv injection of SE 3 days later. Splenic plaque-forming cells (PFC) and serum hemagglutinins were assayed 7 days after transfer. At donor ages of 14–26 days, cells from thymus (T) and bone marrow (BM) showed synergism when injected together, as indicated by a significantly higher geometric mean of PFC per recipient spleen in the BM + T group than in the BM group. The response of the T group was extremely low. With thymus and bursa cells from 6- to 28-day-old donors, significant synergism was demonstrated in 3 of 9 individual experiments. However, almost all the other 6 experiments showed marked differences in the same direction, and the combined probability for all experiments was < 0.001. The most striking demonstration of thymus + bursa synergism was made in 2 experiments using 1-week-old donors. Bone marrow cells from 1-week-old donors failed to cooperate with thymus, as did BM cells from older bursectomized agammaglobulinemic donors. This suggests that B cells from bone marrow originate in the bursa. Thymus-bursa cooperation was somewhat difficult to demonstrate in individual experiments using donors over 1 week of age, owing to the occurrence of some responses with bursal cells alone and to variability of response within bursa or bursa + thymus recipient groups. Synergism between thymus and bursa cells was more consistently demonstrable when irradiated normal spleen or low doses of bone marrow cells were added. These additions led to an increased response and a lowered coefficient of variation in the thymus + bursa recipient groups. The ‘third’ cell type needed for optimal response by the thymus and bursa cells together was tentatively identified as a macrophage.