Biology subjects

Parker, G.

Publications and source records attributed to Parker, G..

6 recordsLinked to original sources

bioRxiv2026

Overlapping flower and pollen production in two imperiled pitcher plants raises conservation challenges

Balancing sexual reproduction with vegetative growth poses challenges for many plants. Additionally, reproductive effort, such as production of pollen or flowers, is not always correlated with numbers of viable and germinable seeds. Energetic tradeoffs like these can be particularly fraught for imperiled species and might be especially complicated in landscapes with a possibility of interspecific hybridization. In this multi-year study, we track the reproductive effort, flowering phenology, and reproductive output of two interfertile Sarracenia (pitcher plants). We show that reproductive effort varies among years and sites, and that production of pollen and flowers does not always result in higher seed output. We demonstrate that phenological overlap in the timing of flower production and pollen viability could enable hybridization, and that the more imperiled taxon produces fewer seeds per flower. Results have implications for conservation of these pitcher plants, management of hybridization in these and other systems, and general principles of reproductive allocation.

ecology↗

bioRxiv2025

Regional adaptation to mosquito vectors shapes Plasmodium falciparum populations

Transmission of Plasmodium falciparum through mosquitoes represents the most severe population bottleneck in the parasites life cycle, yet the genetic basis of parasite-vector compatibility remains poorly understood. Here, we show that mosquito species-specific transmissibility depends on allelic variation in multiple P. falciparum genes expressed during midgut invasion, beyond the well-studied Pfs47. Using an allelic replacement strategy, we targeted highly geographically differentiated SNPs in P. falciparum that match regional variation in vector community composition. Transmissibility was compared across four mosquito species representing distinct geographic ranges (An. gambiae, An. stephensi, An. minimus, and An. albimanus). Two of five tested polymorphisms showed increased oocyst and sporozoite burdens in sympatric parasite-vector combinations compared to allopatric ones. Both substitutions occurred in ookinete micronemal proteins, CTRP and WARP, within von Willebrand factor A domains, suggesting that regional allelic variation modulates Plasmodium-vector compatibility by altering midgut adhesion interactions. These findings reveal that vector compatibility is a polygenic trait shaped by molecular interactions across several loci. Understanding this complexity refines models of parasite adaptation and can inform the design of transmission-blocking interventions effective across diverse vector-parasite combinations.

microbiology↗

bioRxiv2024

Viral and bacterial plant pathogens suppress antiviral defense against flaviviruses in their insect vectors

A positive, single-stranded RNA virus member within the Flavivirus genus was identified and characterized infecting Myzus persicae. This new insect-specific virus (ISV), Myzus persicae flavivirus (MpFV), is 23,236 nucleotides in length and encodes a large polyprotein from a single open reading frame. Analysis of conserved domains showed that helicases, NS3-proteases, Fts-J methyltransferase, and an RNA-dependent RNA polymerase are present in the coded polyprotein. Aphid-infecting ISVs have been reported to interact with plant viruses within the vector, modulating its titer and manipulating aphid behavior and morphology. Small RNA (sRNA) profile analysis of the M. persicae sRNA profile demonstrated that the circulative plant virus, potato leafroll virus (PLRV), modified the aphid antiviral immunity against MpFV. Abundant sRNA reads matching MpFV were detected when aphids were fed on healthy plants, sucrose diet, and potato virus Y-infected plants. In contrast, no MpFV reads were detected in aphids that had acquired PLRV from infected plants or artificial diet sachets containing purified virions. While the titer of M. persicae densovirus (MpDNV) was previously reported to be regulated by expression of the PLRV silencing suppressor protein P0, P0 had no effect on MpFV titer in the aphid. MpFV was transmitted 100% vertically to the offspring, and exhibited tissue tropisms for the body rather than the head. By artificial diet assays, other aphid species, including Aphis gossypii (cotton aphid), Schizaphis graminum (greenbug aphid), Rhopalosiphum padi (bird cherry-oat aphid), and R. maidis (corn leaf aphid), acquired the MpFV. These findings further support the idea that PLRV suppresses aphid immunity against ISVs, suggest the existence of at least two distinct pathways for PLRV-induced aphid immune system modulation. To test whether other circulative plant pathogens suppress insect anti-viral immunity against insect-specific flaviviruses, we quantified the small RNA response of Diaphorina citri, vector of "Candidatus Liberibacter asiaticus" (CLas) associated with citrus greening disease and showed that CLas also suppresses D. citri anti-viral immunity against D. citri-like flavivirus (DcLFV). These data reveal an evolutionary conserved, unexpected role for diverse circulative plant pathogens in modulating anti-viral immunity in hemipteran vectors.

microbiology↗

bioRxiv2023

Major axes of variation in tree demography across global forests

The future trajectory of global forests is closely intertwined with tree demography, and a major fundamental goal in ecology is to understand the key mechanisms governing spatial-temporal patterns in tree population dynamics. While historical research has made substantial progress in identifying the mechanisms individually, their relative importance among forests remains unclear mainly due to practical limitations. One approach is to group mechanisms according to their shared effects on the variability of tree vital rates and to quantify patterns therein. We developed a conceptual and statistical framework (variance partitioning of Bayesian multilevel models) that attributes the variability in tree growth, mortality, and recruitment to variation in species, space, and time, and their interactions, categories we refer to as organising principles (OPs). We applied the framework to data from 21 forest plots covering more than 2.9 million trees of approximately 6,500 species. We found that differences among species, the species OP, proved a major source of variability in tree vital rates, explaining 28-33% of demographic variance alone, and in interaction with space 14-17%, totalling 40-43%. The average variability among species declined with species richness across forests, indicating that diverse forests featured smaller interspecific differences in vital rates supporting the theory that the range of vital rates is similar across global forests. Decomposing the variance in vital rates into the proposed OPs showed that taxonomy is crucial to predicting and understanding tree demography on large forest plots. A focus on how variance is organized in forests can facilitate the construction of more targeted models with clearer expectations of which covariates might drive a vital rate. This study therefore highlights the most promising avenues for future research, both in terms of understanding the relative contributions of groups of mechanisms to forest demography and diversity, and for improving projections of forest ecosystems.

ecology↗

bioRxiv2022

Quantifying dynamic facial expressions under naturalistic conditions

Facial affect is expressed dynamically - a giggle, grimace, or an agitated frown. However, the characterization of human affect has relied almost exclusively on static images. This approach cannot capture the nuances of human communication or support the naturalistic assessment of affective disorders. Using the latest in machine vision and systems modelling, we studied dynamic facial expressions of people viewing emotionally salient film clips. We found that the apparent complexity of dynamic facial expressions can be captured by a small number of simple spatiotemporal states - composites of distinct facial actions, each expressed with a unique spectral fingerprint. Sequential expression of these states is common across individuals viewing the same film stimuli but varies in those with the melancholic subtype of major depressive disorder. This approach provides a platform for translational research, capturing dynamic facial expressions under naturalistic conditions and enabling new quantitative tools for the study of affective disorders and related mental illnesses.

neuroscience↗

bioRxiv2018

Uncovering a role for the dorsal hippocampal commissure in episodic memory

The dorsal hippocampal commissure (DHC) is a white matter tract that provides inter-hemispheric connections between temporal lobe brain regions. Despite the importance of these regions for learning and memory, there is scant evidence of a role for the DHC in successful memory performance. We used diffusion-weighted MRI (DW-MRI) and white matter tractography to reconstruct the DHC across both humans (in vivo) and nonhuman primates (ex vivo). Across species, our findings demonstrate close consistency between the known anatomy and tract reconstructions of the DHC. Anterograde tract-tracer techniques also highlighted the parahippocampal origins of DHC fibers in nonhuman primates. Finally, we derived Diffusion Tensor MRI (DT-MRI) metrics from the DHC in a large sample of human subjects to investigate whether inter-individual variation in DHC microstructure is predictive of memory performance. The mean diffusivity of the DHC was correlated with performance in a standardised episodic memory task; an effect that was not reproduced in a comparison commissure tract - the anterior commissure. These findings highlight a role for the DHC in episodic memory, and our tract reconstruction approach has the potential to generate further novel insights into the role of this previously understudied white matter tract in both health and disease.

neuroscience↗