Biology subjects

Hellmann, J.

Publications and source records attributed to Hellmann, J..

5 recordsLinked to original sources

bioRxiv2026

Signatures of parallel evolution in sperm-mediated paternal effects in threespined sticklebacks

Transgenerational plasticity (TGP)- when parental environments influence offspring phenotypes - is ubiquitous across taxonomic groups and can have benefits for offspring beyond what is possible with developmental plasticity, particularly when selective pressures are high early in life. However, patterns of TGP vary widely across populations and species, and the evolutionary processes shaping this variation remain poorly understood. Here, we tested whether repeated evolutionary transitions result in parallel or population-specific evolutionary divergence in TGP relative to ancestral conditions. We examined sperm-mediated paternal effects across two ancestral marine and three derived freshwater populations of threespined stickleback fish (Gasterosteus aculeatus). We exposed fathers to dragonfly larvae (endemic to freshwater) or sculpin (endemic to all populations) predators and measured both paternal response to predators as well as antipredator behavior and growth in larval offspring. Fathers behaviorally responded to the presence of sculpin predators, but not dragonfly larvae. However, we found strong paternal effects in response to both predators in all populations. Further, the magnitude of TGP did not differ between marine and freshwater populations, suggesting that TGP does not become genetically accommodated as marine populations move into freshwater habitats. We found some evidence consistent with parallelism in both within and trans-generational plasticity: 1) personal exposure of larval stickleback to dragonfly larvae elicited strong antipredator responses in freshwater populations that were absent in marine populations, and 2) paternal predation exposure consistently increased offspring growth in marine populations while slowing growth in freshwater populations. In contrast, paternal effects altered offspring behavior in population-specific ways, with strong sex-specific effects of paternal exposure emerging in response to endemic predators. Adaptive evolution is a two-step process, in which heritable genotypic and phenotypic variation must first be present and then selected on. Therefore, high population-level variation in TGP suggests the capacity for rapid evolution of parental effects, while signatures of parallelism and sex-specific patterns suggest that TGP may evolve in targeted ways in response to ecological stressors.

evolutionary biology↗

bioRxiv2026

Chronic predation risk induces sex-specific effects in behavior but does not induce long-term oxidative damage

Predation is a strong environmental and selective pressure that can favour rapid and plastic shifts in behaviour and escape ability to increase an organisms immediate survival. However, maintaining antipredator responses under repeated predation stress can induce physiological costs to an organism from long-term exposure to elevated cortisol. We know little about how individuals balance this trade-off between short-term survival and longevity, including whether males and females balance this trade-off differently based on life history differences in reproduction, survival, and risk adversity. To assess sex differences in long-term behavioural responses and physiological costs to predation risk, we exposed threespine stickleback (Gasterosteus aculeatus) to visual cues of a live rainbow trout (Oncorhynchus mykiss) predator twice a week for 14 weeks, then measured stickleback antipredator behaviour and swimming performance 5 months later. To quantify potential long-term costs of behavioural adaptation, we measured relative telomere length as a proxy for long-term oxidative damage. We found strong sex specific effects in behaviour and swim endurance: males, but not females, altered their hiding behaviour and had shorter swim endurance in the first trial, suggesting overall lower activity. Surprisingly, we found no evidence for chronic predation shortening telomere length or hindering growth in body length. Overall, these results suggest that plastic responses can be dictated by the different life-history strategies for males and females, and suggest that individuals can maintain long-term changes in antipredator behaviour without costs to their physiological state. HighlightsO_LIChronic predator exposure produced persistent sex differences in space use and swim performance. C_LIO_LIPredator-exposed males altered their hiding strategy and showed reduced swim performance, while females showed no behavioural or performance differences. C_LIO_LIDifferences in swim times were restricted to the first trial and all individuals were exhausted by trial 3. C_LIO_LIRelative telomere length and growth in length did not differ between exposed and unexposed individuals. C_LI

ecology↗

bioRxiv2024

SMAS: Structural MRI-Based AD Score using Bayesian VAE

This study introduces the Structural MRI-based Alzheimers Disease Score (SMAS), a novel index intended to quantify Alzheimers Disease (AD)-related morphometric patterns using a deep learning Bayesian-supervised Variational Autoencoder (Bayesian-SVAE). SMAS index was constructed using baseline structural MRI data from the DELCODE study and evaluated longitudinally in two independent cohorts: DEL-CODE (n=415) and ADNI (n=190). Our findings indicate that SMAS has strong associations with cognitive performance (DELCODE: r=-0.83; ADNI: r=-0.62), age (DEL-CODE: r=0.50; ADNI: r=0.28), hippocampal volume (DEL-CODE: r=-0.44; ADNI: r=-0.66), and total grey matter volume (DELCODE: r=-0.42; ADNI: r=-0.47), suggesting its potential as a biomarker for AD-related brain atrophy. Moreover, our longitudinal studies suggest that SMAS may be useful for early identification and tracking of AD. The model demonstrated significant predictive accuracy in distinguishing cognitively healthy individuals from those with AD (DELCODE: AUC=0.971 at baseline, 0.833 at 36 months; ADNI: AUC=0.817 at baseline, improving to 0.903 at 24 months). Notably, over a 36-month period, SMAS index outperformed existing measures such as SPARE-AD and hippocampal volume. Relevance map analysis revealed significant morphological changes in key AD-related brain regions--including the hippocampus, posterior cingulate cortex, precuneus, and lateral parietal cortex--highlighting that SMAS is a sensitive and interpretable biomarker of brain atrophy, suitable for early AD detection and longitudinal monitoring of disease progression.

neuroscience↗

bioRxiv2024

Exercise-stimulated Resolvin Biosynthesis in Adipose Tissue is Abrogated by High Fat Diet-induced Adrenergic Deficiency

ObjectiveDiet-induced white adipose tissue inflammation is associated with insulin resistance and metabolic perturbations. Conversely, exercise (Exe) protects against the development of chronic inflammation and insulin resistance independent of changes in weight; however, the mechanisms remain largely unknown. We have recently shown that, through adrenergic stimulation of macrophages, exercise promotes resolution of acute peritoneal inflammation by enhancing the biosynthesis of specialized pro-resolving lipid mediators (SPMs). In this study, we sought to determine if exercise stimulates pro-resolving pathways in adipose tissue and whether this response is modified by diet. Specifically, we hypothesized that high fat diet feeding disrupts exercise-stimulated resolution by inhibiting adrenergic signaling, priming the development of chronic inflammation in adipose tissue (AT). Approach and ResultsTo explore the dietary dependence of the pro-resolving effects of Exe, mice were fed either a control or high-fat diet (HFD) for 2 weeks prior to, and throughout, a 4 wk period of daily treadmill running. Glucose handling, body weight and composition, and exercise performance were evaluated at the end of the feeding and exercise interventions. Likewise, catecholamines and their biosynthetic enzymes were measured along with AT SPM biosynthesis and macrophage phenotype and abundance. When compared with sedentary controls (Sed), macrophages isolated from mice exposed to 4 wk of exercise display elevated expression of the SPM biosynthetic enzyme Alox15, while whole AT SPM levels and anti-inflammatory CD301+ M2 macrophages increased. These changes were dependent upon diet as 6 wk of feeding with HFD abrogated the pro-resolving effect of exercise when compared with control diet-fed animals. Interestingly, exercise-induced epinephrine production was inhibited by HFD, which diminished expression of the epinephrine biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT) in adrenal glands. ConclusionTaken together, these results suggest that a diet high in fat diminishes the pro-resolving effects of exercise in adipose tissue via decreasing the biosynthesis of catecholamines. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=192 SRC="FIGDIR/small/608014v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1b508e7org.highwire.dtl.DTLVardef@5b9d8corg.highwire.dtl.DTLVardef@c46707org.highwire.dtl.DTLVardef@48083e_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2024

The transgenerational consequences of paternal social isolation and predation exposure in threespined sticklebacks

O_LIParents routinely encounter stress in the ecological environment that can affect offspring development (transgenerational plasticity: TGP); however, parents interactions with conspecifics may alter how parents respond to ecological stressors. C_LIO_LIDuring social buffering, the presence of conspecifics can reduce the response to or increase the speed of recovery from a stressor. This may have cascading effects on offspring if conspecifics can mitigate parental responses to ecological stress in ways that blunt the transmission of stress-induced transgenerational effects. C_LIO_LIHere, we simultaneously manipulated both paternal social isolation and experience with predation risk prior to fertilization in threespined stickleback (Gasterosteus aculeatus). We generated offspring via in-vitro fertilization to allow us to isolate paternal effects mediated via sperm alone (i.e., in the absence of paternal care). If social buffering mitigates TGP induced by paternal exposure to predation risk, then we expect the transgenerational effects of predation exposure to be weaker when a conspecific is present compared to when the father is isolated. C_LIO_LIOffspring of predator-exposed fathers showed reduced anxiety-like behavior and tended to be captured faster by the predator. Fathers who were socially isolated also had offspring that were captured faster by a live predator, suggesting that paternal social isolation may have maladaptive effects on how offspring respond to ecological stressors. Despite additive effects of paternal social isolation and paternal predation risk, we found no evidence of an interaction between these paternal treatments, suggesting that the presence of a conspecific did not buffer fathers and/or offspring from the effects of predation risk. C_LIO_LIOur results suggest that socially-induced stress is an important, yet underappreciated, mediator of TGP and can elicit transgenerational effects even in species that do not form permanent social groups. Future studies should therefore consider how the parental social environment can affect both within and trans-generational responses to ecological stressors. C_LI

animal behavior and cognition↗