Leagues of their own: sexually dimorphic features of meiotic prophase I

Meiosis is a conserved cell division process that is used by sexually reproducing organisms to generate haploid gametes. Males and females produce different end products of meiosis: eggs (females) and sperm (males). In addition, these unique end products demonstrate sex-specific differences that occur throughout meiosis to produce the final genetic material that is packaged into distinct gametes with unique extracellular morphologies and nuclear sizes. These sexually dimorphic features of meiosis include the meiotic chromosome architecture, in which both the lengths of the chromosomes and the requirement for specific meiotic axis proteins being different between the sexes. Moreover, these changes likely cause sex-specific changes in the recombination landscape with the sex that has the longer chromosomes usually obtaining more crossovers. Additionally, epigenetic regulation of meiosis may contribute to sexually dimorphic recombination landscapes. Here we explore the sexually dimorphic features of both the chromosome axis and crossing over for each stage of meiotic prophase I in Mus musculus, Caenorhabditis elegans, and Arabidopsis thaliana. Furthermore, we consider how sex-specific changes in the meiotic chromosome axes and the epigenetic landscape may function together to regulate crossing over in each sex, indicating that the mechanisms controlling crossing over may be different in oogenesis and spermatogenesis.

     

The effects of elevated temperature and dissolved ρCO2 on a marine foundation species

Understanding how climate change and other environmental stressors will affect species is a fundamental concern of modern ecology. Indeed, numerous studies have documented how climate stressors affect species distributions and population persistence. However, relatively few studies have investigated how multiple climate stressors might affect species. In this study, we investigate the impacts of how two climate change factors affect an important foundation species. Specifically, we tested how ocean acidification from dissolution of CO₂ and increased sea surface temperatures affect multiple characteristics of juvenile eastern oysters (Crassostrea virginica). We found strong impacts of each stressor, but no interaction between the two. Simulated warming to mimic heat stressed summers reduced oyster growth, survival, and filtration rates. Additionally, we found that CO₂‐induced acidification reduced strength of oyster shells, which could potentially facilitate crab predation. As past studies have detected few impacts of these stressors on adult oysters, these results indicate that early life stages of calcareous marine organisms may be more susceptible to effects of ocean acidification and global warming. Overall, these data show that predicted changes in temperature and CO₂ can differentially influence direct effects on individual species, which could have important implications for the nature of their trophic interactions.     

What is winter? Modeling spatial variation in bat host traits and hibernation and their implications for overwintering energetics

White‐nose syndrome (WNS) has decimated hibernating bat populations across eastern and central North America for over a decade. Disease severity is driven by the interaction between bat characteristics, the cold‐loving fungal agent, and the hibernation environment. While we further improve hibernation energetics models, we have yet to examine how spatial heterogeneity in host traits is linked to survival in this disease system. Here, we develop predictive spatial models of body mass for the little brown myotis (Myotis lucifugus) and reassess previous definitions of the duration of hibernation of this species. Using data from published literature, public databases, local experts, and our own fieldwork, we fit a series of generalized linear models with hypothesized abiotic drivers to create distribution‐wide predictions of prehibernation body fat and hibernation duration. Our results provide improved estimations of hibernation duration and identify a scaling relationship between body mass and body fat; this relationship allows for the first continuous estimates of prehibernation body mass and fat across the species'' distribution. We used these results to inform a hibernation energetic model to create spatially varying fat use estimates for M. lucifugus. These results predict WNS mortality of M. lucifugus populations in western North America may be comparable to the substantial die‐off observed in eastern and central populations.     

Stereospecificity of isopentenylpyrophosphate isomerase and prenyl transferase from pinus and citrus

Isopentenylpyrophosphate isomerases in cell-free extracts from Pinus radiata and from Citrus sinensis eliminate the C-4 pro-S proton from mevalonic acid.     

Tracking the Development of Muscular Myoglobin Stores in Mysticete Calves

For marine mammals, the ability to tolerate apnea and make extended dives is a defining adaptive trait, facilitating the exploitation of marine food resources. Elevated levels of myoglobin within the muscles are a consistent hallmark of this trait, allowing oxygen collected at the surface to be stored in the muscles and subsequently used to support extended dives. In mysticetes, the largest of marine predators, details on muscular myoglobin levels are limited. The developmental trajectory of muscular myoglobin stores has yet to be documented and any physiological links between early behavior and the development of muscular myoglobin stores remain unknown. In this study, we used muscle tissue samples from stranded mysticetes to investigate these issues. Samples from three different age cohorts and three species of mysticetes were included (total sample size = 18). Results indicate that in mysticete calves, muscle myoglobin stores comprise only a small percentage (17–23%) of conspecific adult myoglobin complements. Development of elevated myoglobin levels is protracted over the course of extended maturation in mysticetes. Additionally, comparisons of myoglobin levels between and within muscles, along with details of interspecific differences in rates of accumulation of myoglobin in very young mysticetes, suggest that levels of exercise may influence the rate of development of myoglobin stores in young mysticetes. This new information infers a close interplay between the physiology, ontogeny and early life history of young mysticetes and provides new insight into the pressures that may shape adaptive strategies in migratory mysticetes. Furthermore, the study highlights the vulnerability of specific age cohorts to impending changes in the availability of foraging habitat and marine resources.     

Continuing Bonds and Psychosocial Functioning in a Recently Bereaved Pet Loss Sample

Research has shown that pet loss can be a devastating and complex experience for some human survivors, yet this loss may not be fully recognized by friends, partners, or acquaintances as a significant bereavement. The objectives of the current study were to consider how continuing bonds (CB) expressions relate to psychosocial functioning and to identify perceived social constraints as well as areas of resilience associated with efforts to cope with recent pet loss. Through an anonymous online survey, participants (n = 4,336) who had lost a pet to death within the past year were recruited via bereavement support groups and associated websites across the US. Findings in this severely bereaved sample demonstrated the utilization of a wide range of CB (e.g., reflecting on fond memories, holding onto possessions), which were experienced as comforting or distressing to varying extents across the sample. In addition, social constraints were associated with more negative mental health and functional outcomes, while post traumatic growth was in some cases associated with lower mental health and functional complaints. Results are discussed in terms of similarities in patterns of bereavement in human and pet loss samples as well as the importance of considering likely idiosyncratic patterns of response to loss. For example, distress and comfort associated with different efforts to maintain a connection to a deceased pet may occur simultaneously. Given the cross-sectional nature of the current study, experimental and longitudinal research is recommended to determine whether increasing CB efforts experienced as comforting may be a potentially adaptive, growth-enhancing aspect of bereavement.     

Ploidy variation in multinucleate cells changes under stress

Ploidy variation is found in contexts as diverse as solid tumors, drug resistance in fungal infection, and normal development. Altering chromosome or genome copy number supports adaptation to fluctuating environments but is also associated with fitness defects attributed to protein imbalances. Both aneuploidy and polyploidy can arise from multinucleate states after failed cytokinesis or cell fusion. The consequences of ploidy variation in syncytia are difficult to predict because protein imbalances are theoretically buffered by a common cytoplasm. We examined ploidy in a naturally multinucleate fungus, Ashbya gossypii. Using integrated lac operator arrays, we found that chromosome number varies substantially among nuclei sharing a common cytoplasm. Populations of nuclei range from 1N to >4N, with different polyploidies in the same cell and low levels of aneuploidy. The degree of ploidy variation increases as cells age. In response to cellular stress, polyploid nuclei diminish and haploid nuclei predominate. These data suggest that mixed ploidy is tolerated in these syncytia; however, there may be costs associated with variation as stress homogenizes the genome content of nuclei. Furthermore, the results suggest that sharing of gene products is limited, and thus there is incomplete buffering of ploidy variation despite a common cytosol.     

Mycobacterium abscessus Morphotype Comparison in a Murine Model

Pulmonary infections with Mycobacterium abscessus (M. abscessus) are increasingly prevalent in patients with lung diseases such as cystic fibrosis. M. abscessus exists in two morphotypes, smooth and rough, but the impact of morphotype on virulence is unclear. We developed an immune competent mouse model of pulmonary M. abscessus infection and tested the differences in host inflammatory response between the morphotypes of M. abscessus. Smooth and rough morphotypes of M. abscessus were isolated from the same American Type Culture Collection strain. Wild type and cystic fibrosis mice were intratracheally inoculated with known quantities of M. abscessus suspended in fibrin plugs. At the time of sacrifice lung and splenic tissues and bronchoalveolar lavage fluid were collected and cultured. Bronchoalveolar lavage fluid was analyzed for leukocyte count, differential and cytokine expression. Pulmonary infection with M. abscessus was present at both 3 days and 14 days post-inoculation in all groups at greater levels than systemic infection. Inoculation with M. abscessus rough morphotype resulted in more bronchoalveolar lavage fluid neutrophils compared to smooth morphotype at 14 days post-inoculation in both wild type (p = 0.01) and cystic fibrosis (p<0.01) mice. Spontaneous in vivo conversion from smooth to rough morphotype occurred in 12/57 (21%) of mice. These mice trended towards greater weight loss than mice in which morphotype conversion did not occur. In the described fibrin plug model of M. abscessus infection, pulmonary infection with minimal systemic dissemination is achieved with both smooth and rough morphotypes. In this model M. abscessus rough morphotype causes a greater host inflammatory response than the smooth based on bronchoalveolar lavage fluid neutrophil levels.     

Genetic analysis reveals multiple cryptic invasive species of the hydrozoan genus Cordylophora

Understanding the patterns and dynamics of biological invasions is a crucial prerequisite to predicting and mitigating their potential ecological and economic impacts. Unfortunately, in many cases such understanding is limited not only by ignorance of invasion history, but also by uncertainty surrounding the ecology, physiology, and even systematics of the invasive taxa themselves. The invasive, colonial euryhaline hydroid Cordylophora has invaded multiple regions outside of its native Ponto-Caspian range. However, extensive morphological and ecological plasticity has prevented consensus on both species-level classification within the genus and the environmental conditions conducive to establishment. The goal of this research was to explore the invasive history and species composition of the genus Cordylophora through molecular analyses. We addressed both issues using DNA sequence data from two mitochondrial loci [the small subunit 16S rRNA and cytochrome c oxidase subunit I (COI)] and one nuclear locus (28S large nuclear rRNA), generated from 27 invasive Cordylophora populations collected throughout the global range of the taxon. Phylogenetic analysis and comparisons of genetic distances between populations suggest the presence of multiple cryptic species within the genus. This conclusion is further supported by the observation of significantly different habitat preferences between invasive lineages. Geographic distribution of lineages is consistent with the introduction of multiple lineages to some non-native regions, indicating that repeated introductions may contribute to the current global distribution of Cordylophora. Applying molecular and morphological analyses to additional populations of Cordylophora is likely to assist in clarifying the taxonomy of this genus and in providing a better understanding of the invasive history of this hydroid.