Linking recruitment to trophic factors: revisiting the Beverton--Holt recruitment model from a life history and multispecies perspective

The Beverton--Holt recruitment model can be derived from arguments about evolution of life history traits related to foraging and predation risk, along with spatially localized and temporarily competitive relationships in the habitats where juvenile fish forage and face predation risk while foraging. This derivation explicitly represents two key biotic factors, food supply (I) and predator abundance (R), which appear as a risk ratio (R/I) that facilitates modelling of changes in trophic circumstances and analysis of historical data. The same general recruitment relationship is expected whether the juvenile life history is simple or involves a complex sequence of stanzas; in the complex case, the Beverton--Holt parameters represent weighted averages or integrals of risk ratios over the stanzas. The relationship should also apply in settings where there is complex, mesoscale variation in habitat and predation risk, provided that animals sense this variation and move about so as to achieve similar survival at all mesoscale rearing sites. The model predicts that changes in food and predation risk can be amplified violently in settings where juvenile survival rate is low, producing large changes in recruitment rates over time.     

Selection for phenotypic plasticity in Rana sylvatica tadpoles

The hypothesis that phenotypic plasticity is an adaptation to environmental variation rests on the two assumptions that plasticity improves the performance of individuals that possess it, and that it evolved in response to selection imposed in heterogeneous environments. The first assumption has been upheld by studies showing the beneficial nature of plasticity. The second assumption is difficult to test since it requires knowing about selection acting in the past. However, it can be tested in its general form by asking whether natural selection currently acts to maintain phenotypic plasticity. We adopted this approach in a study of plastic morphological traits in larvae of the wood frog, Rana sybatica. First we reared tadpoles in artificial ponds for 18 days, in either the presence or absence of Anax dragonfly larvae (confined within cages to prevent them from killing the tadpoles). These conditioning treatments produced dramatic differences in size and shape: tadpoles from ponds with predators were smaller and had relatively short bodies and deep tail fins. We estimated selection by Anax on the two kinds of tadpoles by testing for non-random mortality in overnight predation trials. Dragonflies imposed strong selection by preferentially killing individuals with relatively shallow and short tail fins, and narrow tail muscles. The same traits that exhibited the strongest plasticity were under the strongest selection, except that tail muscle width exhibited no plasticity but experienced strong increasing selection. A laboratory competition experiment, testing for selection in the absence of predators, showed that tadpoles with deep tail fins grew relatively slowly. In the cattle tanks, where there were also no free predators, the predator-induced phenotype survived more poorly and developed slowly, but this cost was apparently not associated with particular morphological traits. These results indicate that selection is currently promoting morphological plasticity in R. sylvatica, and support the hypothesis that plasticity represents an adaptation to variable predator environments.     

Progression of human bone marrow stromal cells into both osteogenic and adipogenic lineages is differentially regulated by structural conformation of collagen I matrix via distinct signaling pathways

Adult human bone marrow stromal cells (BMSCs) containing or consisting of mesenchymal stem cells (MSCs) are an important source in tissue homeostasis and repair. Although many processes involved in their differentiation into diverse lineages have been deciphered, substantial inroads remain to be gained to synthesize a complete regulatory picture. The present study suggests that structural conformation of extracellular collagen I, the major organic matrix component in musculoskeletal tissues, plays, along with differentiation stimuli, a decisive role in the selection of differentiation lineage. It introduces a novel concept which proposes that structural transition of collagen I matrix regulates cell differentiation through distinct signaling pathways specific for the structural state of the matrix. Thus, on native collagen I matrix inefficient adipogenesis is p38-independent, whereas on its denatured counterpart, an efficient adipogenesis is primarily regulated by p38 kinase. Inversely, osteogenic differentiation occurs efficiently on native, but not on denatured collagen I matrix, with a low commencement threshold on the former and a substantially higher one on the latter. Osteogenesis on collagen I matrices in both structural conformations is fully dependent on ERK. However, whereas on native collagen I matrix osteogenic differentiation is Hsp90-dependent, on denatured collagen I matrix it is Hsp90-independent. The matrix conformation-mediated regulation appears to be one of the mechanisms determining differentiation lineage of BMSCs. It allows a novel interpretation of the bone remodeling cycle, explains the marked physiological aging-related adipogenic shift in musculoskeletal tissues, and can be a principal contributor to adipogenic shift seen in a number of clinical disorders.     

A PCR-based linkage map of Agrostis stolonifera and identification of QTL markers for dollar spot resistance

Creeping bentgrass (Agrostis stolonifera L.) is the most widely utilized cool-season turf species for intensively managed sports playing surfaces, including bowling greens and golf course putting greens, tees, and fairways. One of the biggest disease problems affecting creeping bentgrass is dollar spot disease caused by Sclerotinia homoeocarpa F.T. Bennett. Relative to traditional food crops, little attention has been paid to applying molecular technology to traditional creeping bentgrass breeding programs. The objective of this study was to develop a PCR-based linkage map of creeping bentgrass and identify quantitative trait loci (QTLs) associated with dollar spot resistance. Mapping populations segregating for dollar spot resistance were created, phenotyped for disease resistance, and genotyped for simple sequence repeat, conserved intron scanning primer, intron length polymorphism, and amplified fragment length polymorphism markers. As expected, 14 linkage groups (LGs) were detected for each parental map, covering a total of 1,424 and 1,374 cM for the 7418-3 and the L93-10 parental maps, respectively. A total of eight QTL regions (23 markers) for dollar spot resistance were observed for three isolates (Crenshaw, PRG, and UMass1) in our creeping bentgrass mapping populations. LGs 1, 4, and 5 contained at least two overlapping QTL regions to different isolates, indicating that these regions may play a significant role in dollar spot resistance. Identification of QTLs associated with disease resistance will help to facilitate marker-assisted selection in traditional creeping bentgrass breeding programs.     

An examination of the epiphytic nature of Gambierdiscus toxicus, a dinoflagellate involved in ciguatera fish poisoning

Twenty-four specimen of macroalgae were collected in nearshore waters of the island of Hawaii, identified, and maintained to examine how the epiphytic relationship between Gambierdiscus toxicus (isolate BIG12) varied among the macroalgal species. Gambierdiscus cells were introduced to Petri dishes containing 100 g samples of each macroalgal host, which were examined at two, 16, 24, and every 24–72 h thereafter, over a 29-day period. Gambierdiscus proliferated in the presence of some host species (e.g., Galaxaura marginata and Jania sp.), but grew little in the presence of other species (e.g., Portieria hornemannii). Gambierdiscus exhibited high survival rates (>99%) in the presence of Chaetomorpha sp., but died before the end of the experiment (after 21 days) with other host species (e.g., Dictyota and Microdictyon spp.). Gambierdiscus avoided contact with P. hornemannii, but averaged up to 30% attachment with other host species. The numbers of Gambierdiscus cells belonging to one of three classes (alive and attached; alive and unattached; and dead) were determined for each time point. The 24 algal hosts were grouped according to their commonalities relative to these three classes using a Bray-Curtis similarity index, similarity profile (SIMPROF) permutation tests, and Multi-Dimensional Scaling (MDS) analysis (PRIMER 6). The resultant six groupings were used to construct different Gambierdiscus growth profiles for the different algal hosts. Group A is characterized by a preponderance of unattached cells and high mortality rates. Groups B, C, E, and F also displayed high proportions of unattached cells, but mortality either occurred later (Groups B and C) or rates were lower (Groups E and F). Group D had the highest proportion of attached cells. Group E contained three out of the four chlorophyte species, while Group F contained the majority of the rhodophytes. Over 50% of the species in Group F are considered to be palatable, whereas Groups A, B, and C are composed of species that exhibit chemical defenses against herbivory. The results of this study coupled with previous findings indicate that Gambierdiscus is not an obligate epiphyte; it can be free-swimming and found in the plankton. The conditions that lead to changes between epiphytic and planktonic stages need to be better studied in order to determine how they affect Gambierdiscus growth and physiology, connectivity and dispersion mechanisms, and toxin movement up into the foodweb.     

The transcriptome of Toxoplasma gondii

Background  

Toxoplasma gondii gives rise to toxoplasmosis, among the most prevalent parasitic diseases of animals and man. Transformation of the tachzyoite stage into the latent bradyzoite-cyst form underlies chronic disease and leads to a lifetime risk of recrudescence in individuals whose immune system becomes compromised. Given the importance of tissue cyst formation, there has been intensive focus on the development of methods to study bradyzoite differentiation, although the molecular basis for the developmental switch is still largely unknown.     

Chromatin insulator bodies are nuclear structures that form in response to osmotic stress and cell death

Chromatin insulators assist in the formation of higher-order chromatin structures by mediating long-range contacts between distant genomic sites. It has been suggested that insulators accomplish this task by forming dense nuclear foci termed insulator bodies that result from the coalescence of multiple protein-bound insulators. However, these structures remain poorly understood, particularly the mechanisms triggering body formation and their role in nuclear function. In this paper, we show that insulator proteins undergo a dramatic and dynamic spatial reorganization into insulator bodies during osmostress and cell death in a high osmolarity glycerol–p38 mitogen-activated protein kinase–independent manner, leading to a large reduction in DNA-bound insulator proteins that rapidly repopulate chromatin as the bodies disassemble upon return to isotonicity. These bodies occupy distinct nuclear territories and contain a defined structural arrangement of insulator proteins. Our findings suggest insulator bodies are novel nuclear stress foci that can be used as a proxy to monitor the chromatin-bound state of insulator proteins and provide new insights into the effects of osmostress on nuclear and genome organization.     

Pathways of soil genesis in the Coast Range of Oregon, USA

Background and Aims

Soil chronosequences on marine terraces along the Pacific Coast of California and Oregon show evidence of podzolization, though soils ultimately evolve to Ultisols. It is not clear if this pathway of soil evolution can be extended to the humid, inland Oregon Coast Range.

Methods

We analyzed soil properties for a fluvial terrace chronosequence sampled along the Siuslaw River (Oregon, USA) about 50 km from the Pacific coast. The seven terraces ranged in age from <3.5 ky to nearly 1,000 ky.

Results

There was no evidence of early podsolization. Instead, evidence was found that andisolization starts early and occurs even in older soils when pedogenic iron accumulation and clay synthesis and illuviation dominate. Soils develop the morphology characteristic of Ultisols sometime between 20 and 70 ky, but high levels of oxalate extractable iron and aluminum satisfy criteria of an andic subgroup. Alfisols are not formed as an intermediary stage.

Conclusions

The lack of Spodosols inland is due to the inland shift from udic to ustic or xeric moisture regime, which favors summer drying and ripening of short-range order minerals rather than deep leaching or translocation. Other factors are higher pH, different organic chemistry and faster calcium cycling under the Douglas fir inland when compared to the Sitka spruce of the coastal terraces.     

EVOLUTIONARILY STABLE SEX RATIOS AND MUTATION LOAD

Frequency‐dependent selection should drive dioecious populations toward a 1:1 sex ratio, but biased sex ratios are widespread, especially among plants with sex chromosomes. Here, we develop population genetic models to investigate the relationships between evolutionarily stable sex ratios, haploid selection, and deleterious mutation load. We confirm that when haploid selection acts only on the relative fitness of X‐ and Y‐bearing pollen and the sex ratio is controlled by the maternal genotype, seed sex ratios evolve toward 1:1. When we also consider haploid selection acting on deleterious mutations, however, we find that biased sex ratios can be stably maintained, reflecting a balance between the advantages of purging deleterious mutations via haploid selection, and the disadvantages of haploid selection on the sex ratio. Our results provide a plausible evolutionary explanation for biased sex ratios in dioecious plants, given the extensive gene expression that occurs across plant genomes at the haploid stage.