Biology subjects

Schroeder, L.

Publications and source records attributed to Schroeder, L..

18 recordsLinked to original sources

bioRxiv2026

Dysregulation of epithelial differentiation architecture underlies field cancerization in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) has exceptionally high recurrence rates, exceeding 50%, contributing to mortality and morbidity. This recurrence rate is proposed to be due to field cancerization, a phenomenon where tumor-adjacent "field" tissue that appears histologically normal harbors molecular changes that prime it for subsequent tumor growth. Current models attribute field cancerization to shared driver mutations between tumors and adjacent at-risk tissue, but this assumption has never been directly tested. To comprehensively characterize this phenomenon, we profiled patient-matched tumor, normal-adjacent field (NAF), contralateral normal, and blood samples from HPV-negative HNSCC patients using whole genome sequencing, targeted driver gene sequencing, single-nucleus multiome profiling, spatial transcriptomics and functional proliferation assays. While histologically normal NAF tissues did harbor expanded mutant clones, these mutations rarely overlapped with paired tumors and were not shared across patients, suggesting molecular features beyond mutations are altered in NAF. Single-cell multiomics revealed that NAF epithelium loses its normal organizational hierarchy: basal stem cell markers persist in differentiated cells, while terminal differentiation programs fail to activate, with reconfiguration of both gene regulatory networks and cell-cell interactions. Proliferating cells appeared in tissue layers normally restricted to post-mitotic cells, a pattern typically seen only in overt dysplasia. Within this disrupted hierarchy, a distinct epithelial state arose in NAF that expressed both normal epithelial and tumor-associated markers, which we localized to the parabasal layers using immunofluorescence and spatial transcriptomics. Together, our findings demonstrate that field cancerization operates through epithelial hierarchy disorganization that disrupts differentiation, generates cells with tumor-like features, and may create a permissive environment for the expansion of cancer-associated mutations, all within tissue that appears histologically normal.

cancer biology↗

bioRxiv2026

Oncomimetic β-catenin activity onset, duration and region defines aberrant intestinal development

In early intestinal carcinogenesis, adenoma formation is commonly initiated by loss-of-function mutations in a tumor suppressor that lead to oncoprotein gain-of-function, like in the tumor suppressor-oncoprotein pair APC-{beta}-catenin. Small intestinal organoids provide an in vitro system to study consequences of such mutations on tissue organization. However, conventional genetic manipulations do not allow precise control over the onset and duration of oncoprotein activity to study their influence on tissue transformation. Furthermore, homogenous tissues of clonal genetic models do not readily capture cellular interaction among mutated and neighboring wildtype tissue during early transformation. To mimic oncogenic activation of {beta}-catenin, we established a chemical-(opto)genetic approach to gain bio-orthogonal acute, spatial and temporal control over {beta}-catenin oncoprotein stability and relate oncoprotein levels to morphological development of mouse small intestinal organoids. We identified aberrant phenotypes that result from bio-orthogonally induced oncoprotein activity but persist even after oncoprotein depletion. Furthermore, local activation of oncomimetic {beta}-catenin activity within the stem cell niche leads to aberrant differentiation during homeorhesis and homeostasis, recapitulating early events of tissue transformation.

cancer biology↗

bioRxiv2026

Benchmarking ambient RNA removal across droplet and well-plate platforms reveals artificial count generation as a critical failure mode of scAR and CellClear

BackgroundAmbient RNA contamination is a pervasive artifact of single-cell and single-nucleus RNA sequencing (sxRNA-seq), yet no consensus exists on which computational removal tool performs best across experimental platforms. ResultsWe present a systematic benchmark of six tools: CellBender, DecontX, SoupX, scCDC, scAR, and CellClear - evaluated across six human-mouse cell line mixing (hgmm) datasets (1k-20k cells) providing partial ground truth, two droplet-based complex tissue datasets (PBMC scRNA-seq; prefrontal cortex snRNA-seq), and a well-plate-based dataset (BD Rhapsody WBC). Using inter-species counts as partial ground truth, we quantify sensitivity, specificity, precision, and removal consistency per tool. We further apply a count-integrity criterion quantifying gene-cell positions where corrected values exceed raw counts. This reveals that scAR and CellClear do not merely denoise but fundamentally restructure count matrices: CellClear replaces >93% of counts with values derived from matrix factorization, while scAR generates spurious cell types absent from uncorrected data, including three spurious coarse cell types in the BD Rhapsody dataset and up to eight novel cell types in the prefrontal cortex. CellBender and SoupX exhibit reliable contamination removal with minimal count distortion. DecontX and scCDC are the only tools operable on non-droplet platforms without raw count matrix access. Runtime benchmarking at atlas scale (up to 172,000 nuclei) further demonstrates that CellClear fails to scale. ConclusionsCount matrix integrity, not removal sensitivity alone, must be a primary criterion when selecting ambient RNA correction tools. We provide platform-specific recommendations and a decision framework to guide tool selection across experimental contexts.

bioinformatics↗

bioRxiv2025

Long-Term Intestinal Epithelial Remodeling Induced by Acute Protein-Energy Malnutrition

Protein-energy malnutrition (PEM) is a global health burden with lasting effects that extend well beyond the initial nutrient deficiency. To systematically investigate the long-term effects of a single episode of PEM on the structure and function of the intestinal epithelium and its associated microbiota, we employed a comprehensive multi-omics approach, including (spatial) transcriptomics, DNA methylation analysis, fecal metagenomics, and metabolomics. Our findings show that PEM persistently alters the intestinal epithelium by depleting Paneth cells and suppressing antimicrobial gene expression - changes linked to DNA methylation that persist despite dietary recovery. In germ-free mice, the sustained epithelial phenotype after was absent. We identified the microbial lipid metabolite 9-HODE and epigenetically deregulated PPAR-driven GDF15 expression as key molecular drivers of the persistent PEM-induced Paneth cell dysfunction. Targeting microbial lipid production and its link to the host GDF15 pathway could offer novel therapeutic strategies for long-term consequences of malnutrition and other Paneth cell-associated diseases.

immunology↗

bioRxiv2025

Capturing transient states of heterodimeric ABC transporter TM287/288 by Time-Resolved Small-Angle X-ray Scattering

Structures of the heterodimeric ABC transporter TM287/288 have been previously determined in several states indicating large conformational changes during its reaction cycle. However, for a complete description of the cycle, transient states (such as an occluded state) are still missing, as they are difficult to capture with static structural biology techniques. Here, we investigate the kinetics and accompanying structural changes in the course of the reaction cycle of full-length TM287/288 using time-resolved small-angle X-ray scattering, initiated by stopped-flow mixing. The use of active site mutants and state-specific sybodies/nanobodies enabled us to dissect the temporal events involved in the ATP-driven conformational cycle of TM287/288 and reveal a transient occluded state of this ABC transporter. Statement of SignificanceATP-binding cassette transporters are essential molecular machines that use the power of ATP binding and hydrolysis to move substances across cellular membranes. Here, we use time-resolved small-angle X-ray scattering combined with conformation-specific nanobodies to directly capture and assign different states to the heterodimeric ABC transporter TM287/288 in solution. Our findings advance our understanding of ABC transporter and demonstrate a broadly applicable method for dissecting the different molecular states in membrane proteins on a second-to-minute time scale. TOC figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/679171v2_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@b83fbaorg.highwire.dtl.DTLVardef@5fec81org.highwire.dtl.DTLVardef@1a022fdorg.highwire.dtl.DTLVardef@592c92_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2025

The chloroplast ionome shines new light on organellar Fe homeostasis

Annually, chloroplasts fix 258 billion tons of CO2 through photosynthesis. Photosynthesis and other biochemical pathways require specific amounts of metal ions in the organelle. Transport proteins in the plastid inner envelope maintain the organellar ion homeostasis. Despite substantial progress over the last decades, many genes encoding for plastid ion channels and ion carriers or their regulators remain unknown. To fill this knowledge gap, detailed information on the elemental composition of chloroplasts i.e., a plastid ionome, is needed. This will allow to compare mutants of transporter candidates with wild-types. Here, we provide quantitative descriptions of chloroplast ionomes from Arabidopsis thaliana, the metal hyperaccumulator Arabidopsis halleri, Pisum sativum, and Nicotiana benthamiana and analyze similarities and distinctions. Using A. thaliana, we show that plastid ionomes can be genetically manipulated. Chloroplasts of oligopeptide transporter3 (opt3)-deficient mutants contain 14-fold more iron, which they deposit into stromal FERRITIN. The removal of FERRITIN in opt3 mutants leads to a substantial decrease in plastid and leaf iron pointing to important signaling linked to the chloroplast ionome. Our study reveals that chloroplasts can be turned into large iron storages. Since crop biofortification to fight hidden hunger has become a global mission, this research provides groundwork to reach this goal.

plant biology↗

bioRxiv2025

2-Deoxy-D-glucose chemical exchange-sensitive spin-lock MRI of cerebral glucose metabolism after stroke in the rat

Rapid breakdown of cerebral glucose metabolism is a hallmark in stroke pathology. Metabolic activity delineates the penumbra from the infarct core, representing tissue that is potentially salvageable by therapeutic interventions. Tools to image dynamics of glucose and its spatial distribution could provide biomarkers of disease severity and of the success of therapeutic interventions. Here, we developed a new protocol to measure glucose metabolism in a rat model of stroke using chemical exchange-sensitive spin-lock (CESL) MRI of the glucose analog 2-deoxy-D-glucose (2DG). We further implemented a protocol that combines 2DG-CESL-MRI with perfusion and diffusion MRI to relate this new signal to established definitions of hypoperfused tissue, cytotoxic edema and the penumbra. We found that 2DG-CESL-MRI provides a biomarker of disturbed glucose metabolism after stroke with high effect size. This is the first study to investigate CESL MRI of 2DG in the context of metabolism imaging in rodent stroke.

neuroscience↗

bioRxiv2024

Hexokinase 1-mediated plant immunity under abiotic stress depends on chloroplast positioning

Molecular networks involved in the responses of plants towards environmental changes are multifaceted and affect diverse metabolic and signalling pathways. Under challenging environmental conditions, such as low temperatures and high light intensities, plants need to immediately adjust their metabolism to prevent irreversible tissue damage, e.g., caused by reactive oxygen species. Regulation of photosynthesis and carbohydrate metabolism plays a crucial role in this stress response. Here, we analysed mutants of Arabidopsis thaliana, which were affected in either central enzymatic activities of carbohydrate metabolism, in chloroplast positioning or in a combination of both. Plants were exposed to a treatment of combined cold and elevated light. While mutants with deficiencies in sucrose (spsa1) or starch (pgm1) metabolism showed affected metabolic pathway regulation under abiotic stress, Hexokinase 1 mutants (hxk1) showed a severe growth phenotype with lesions and pale areas on leaf tissue. In a double mutant, which combined deficiencies in Chloroplast Unusual Positioning 1 (CHUP1)-mediated chloroplast positioning and HXK1 (chup1 x hxk1), this growth phenotype vanished resulting in wild type-like plants. Transcriptome analysis revealed a significantly affected immune response of hxk1 plants, which was suppressed in the double mutants. Our findings provide evidence for a role of HXK1 as a positive regulator of the plant immune response. Finally, we suggest that, due to its potential role as a negative regulator of plant immunity, CHUP1 deficiency counteracted the reduced immunity of hxk1 in the double mutant which rescued the plants. Future studies might now reveal whether deficiencies in CHUP1 function and/or transcription represent a conserved strategy to increase plant immunity under abiotic stress.

plant biology↗

bioRxiv2023

Temperature acclimation of photosynthesis and carbohydrate metabolism are related to the geographical origin of Arabidopsis thaliana

Acclimation is a multigenic trait by which plants adjust photosynthesis and metabolism to cope with a changing environment. Here, natural variation of photosynthetic and metabolic acclimation was analyzed in response to low and elevated temperature. For this, 18 natural accessions of Arabidopsis thaliana, originating from Africa and Europe, were grown at 22{degrees}C before being exposed to 4{degrees}C and 34{degrees}C for cold and heat acclimation, respectively. Amounts of carbohydrates were quantified together with their subcellular distribution across plastids, cytosol and vacuole. Linear electron transport rates (ETRs) were determined together with maximum quantum efficiency of photosystem II (Fv/Fm) for all growth conditions and under temperature fluctuation. Under elevated temperature, residuals of ETR under increasing photosynthetic photon flux densities were found to significantly correlate with the longitudinal gradient of the geographic origin of accessions indicating a naturally occurring east-west gradient of photosynthetic acclimation capacities. Further, in heat acclimated plants, vacuolar fructose amount was found to positively correlate with longitude while plastidial and cytosolic amounts were found to be negatively correlated. Plastidial sucrose concentrations were found to positively correlate with maximal ETRs under fluctuating temperature indicating a stabilizing role within the chloroplast. In summary, our findings revealed specific subcellular carbohydrate distributions which contribute differentially to photosynthetic efficiencies of natural Arabidopsis thaliana accessions across a longitudinal gradient. This sheds light on the relevance of subcellular metabolic regulation for photosynthetic performance in a fluctuating environment and supports the physiological interpretation of naturally occurring genetic variation of temperature tolerance and acclimation.

plant biology↗

bioRxiv2023

Enamel proteins reveal biological sex and genetic variability within southern African Paranthropus

The evolutionary relationships among extinct African hominin taxa are highly debated and largely unresolved, due in part to a lack of molecular data. Even within taxa, it is not always clear, based on morphology alone, whether ranges of variation are due to sexual dimorphism versus potentially undescribed taxonomic diversity. For Paranthropus robustus, a Pleistocene hominin found only in South Africa, both phylogenetic relationships to other taxa 1,2 and the nature of intraspecific variation 3-6 are still disputed. Here we report the mass spectrometric (MS) sequencing of enamel proteomes from four ca. 2 million year (Ma) old dental specimens attributed morphologically to P. robustus, from the site of Swartkrans. The identification of AMELY-specific peptides and semi-quantitative MS data analysis enabled us to determine the biological sex of all the specimens. Our combined molecular and morphometric data also provide compelling evidence of a significant degree of variation within southern African Paranthropus, as previously suggested based on morphology alone 6. Finally, the molecular data also confirm the taxonomic placement of Paranthropus within the hominin clade. This study demonstrates the feasibility of recovering informative Early Pleistocene hominin enamel proteins from Africa. Crucially, it also shows how the analysis of these proteins can contribute to understanding whether hominin morphological variation is due to sexual dimorphism or to taxonomic differences. We anticipate that this approach can be widely applied to geologically-comparable sites within South Africa, and possibly more broadly across the continent.

evolutionary biology↗

bioRxiv2023

The biological activity of bacterial rhamnolipids is linked to their molecular structure

Biosurfactants are amphiphilic compounds of microbial origin with a wide range of industrial applications. Rhamnolipids (RLs) offer a broad range of potential applications as biosurfactants in industry and agriculture. Several studies report a high capacity for controlling different plant pests and pathogens and consider RLs as promising candidates for bio-based plant protection agents. RLs are a class of glycolipids consisting of one (mRLs) or two (dRLs) rhamnose moieties linked to a single or branched {beta}-fatty acid. Due to the diversity of RLs, so far little is known about the relation between molecular structure and biological activity. Engineering the synthesis pathway allowed us to differentiate between the activities of mixtures of pure mRL and of pure dRL congeners and elaborated HPLC techniques further enabled to analyse the activity of single congeners. In a model system with the plant Arabidopsis thaliana and the plant-parasitic nematode Heterodera schachtii we demonstrate that RLs can significantly reduce infection, whereas their impact on the host plant varies depending on their molecular structure. While mRLs reduced plant growth even at low concentration, dRLs showed no or a beneficial impact on plant development. In addition, the effect of RLs on plant H2O2 production was measured as an indicator of plant defense activity. Treatment with mRLs or dRLs at a concentration of 50 ppm increased H2O2 production. Lower concentrations of up to 10 ppm were used to stimulate plants prior to a treatment with water or flagellin (flg22), a bacterial inducer of plant defense responses. At 10 ppm both mRLs and dRLs fostered an increased response to flg22. However, mRLs also led to an increased response to water, the non-inducing negative control, indicating a generally elevated stress level. Neither mRLs nor dRLs induced expression of plant defense marker genes of salicylic acid, jasmonic acid and ethylene pathways within a 1 hour and 48 hours treatment. Due to the negative effect of mRLs on plants further studies were concentrated on dRLs. Treatment of pre-parasitic infective juveniles of H. schachtii revealed that dRLs did not increase mortality even at a very high concentration of 755 ppm. In order to analyse the effect of single dRL congeners nematode infection assays were performed. While dRL congeners with a C10-C8 acyl chain increased nematode infection, dRLs with C10-C12 and C10-C12:1 acyl chains reduced nematode infection even at concentrations below 2 ppm. Plant growth was not reduced by C10-C8 dRLs, but by C10-C12 and C10-C12:1 dRLs at concentrations of 8.3 ppm. H2O2 production was increased compared to the water control upon treatment with C10-C8 dRLs at a concentration of 200 ppm, while C10-C12 and C10-C12:1 dRLs triggered the same effect already at 50 ppm. Our experiments show a clear structure-effect relation. In conclusion, functional assessment and analysis of mode of action of RLs in plants require careful consideration of their molecular structure and composition.

molecular biology↗

bioRxiv2023

Drivers of plant diversity, community composition, functional traits and soil processes along an alpine gradient in the central Chilean Andes

High alpine regions are threatened but understudied ecosystems that harbor diverse endemic species, making them an important biome in which to test the role of environmental factors in driving functional trait-mediated community assembly processes. In a high mountain system in the central Chilean Andes, we tested hypotheses about the drivers of plant community diversity, functional composition and soil processes along an elevation gradient. We surveyed vegetation and spectroscopic reflectance (400-2400 nm) to quantify taxonomic, phylogenetic, functional, and spectral diversity at five sites from 2400 m to 3500 m elevation. We characterized soil attributes and processes by measuring water content, carbon and nitrogen, and net nitrogen mineralization rates. At high elevation, colder temperatures led to a reduction in available soil nitrogen, while at warmer, lower elevations, soil moisture was lower. Metrics of taxonomic, functional, and spectral alpha diversity peaked at mid-elevations, while phylogenetic species richness was highest at low elevation. Leaf nitrogen followed global patterns of increasing leaf nitrogen with colder temperatures, a pattern consistent at the community level as well as within individual species. The increase in leaf nitrogen, coupled with shifts in taxonomic and functional diversity associated with turnover in lineages, indicate that the ability to acquire and retain nitrogen in colder temperatures may be important in plant community assembly in this range. Such environmental filters have important implications for forecasting shifts in alpine plant communities under a warming climate.

ecology↗

bioRxiv2020

Comparative study of four SARS-CoV-2 Nucleic Acid Amplification Test (NAAT) platforms demonstrates that ID NOW performance is impaired substantially by patient and specimen type.

The advent of the COVID-19 pandemic in the United States created a unique situation where multiple molecular diagnostic assays with various indications for use in the detection of SARS-CoV-2 rapidly received Emergency Use Authorization by the FDA, were validated by laboratories and utilized clinically, all within a period of a few weeks. We compared the performance of four of these assays that were being evaluated for use at our institution: Abbott RealTime m2000 SARS-CoV-2 Assay, DiaSorin Simplexa COVID-19 Direct, Cepheid Xpert Xpress SARS-CoV-2 and Abbott ID NOW COVID-19. Nasopharyngeal and nasal specimens were collected from 88 ED and hospital-admitted patients and tested by the four methods in parallel to compare performance. ID NOW performance stood out as significantly worse than the other three assays despite demonstrating comparable analytic sensitivity. Further study determined that the use of a foam nasal swab compared to a nylon flocked nasopharyngeal swab, as well as use in a population chronically vs. acutely positive for SARS-CoV-2, were significant factors in the poor comparable performance.

microbiology↗

bioRxiv2020

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position of chloroplasts changes due to a changing light regime. Chloroplast avoidance and accumulation response under high and low light, respectively, are well known phenomena, and deficiency of chloroplast movement has been shown to result in photodamage and reduced biomass accumulation. Yet, effects of chloroplast positioning on underlying metabolic regulation are less well understood. Here, we analysed photosynthesis together with metabolites and enzyme activities of the central carbohydrate metabolism during cold acclimation of the chloroplast unusual positioning 1 (chup1) mutant of Arabidopsis thaliana. We compared cold acclimation under ambient and low light and found that maximum quantum yield of PSII was significantly lower in chup1 than in Col-0 under both conditions. Our findings indicated that net CO2 assimilation in chup1 is rather limited by biochemistry than by photochemistry. Further, cold-induced dynamics of sucrose phosphate synthase differed significantly between both genotypes. Together with a reduced rate of sucrose cycling derived from kinetic model simulations our study provides evidence for a central role of chloroplast positioning for photosynthetic and metabolic acclimation to low temperature.

plant biology↗

bioRxiv2020

Cold acclimation has a differential effect on leaf vascular bundle structure and carbon export rates in natural Arabidopsis accessions originating from southern and northern Europe

Acclimation to low but non-freezing temperature represents an ecologically important process for Arabidopsis thaliana but also for many other plant species from temperate regions. Cold acclimation comprises and affects numerous molecular and physiological processes and the maintenance of sugar supply of sink tissue by photosynthetically active source tissue is preliminary for plant survival. Here, we analysed the correlation of changes in vascular bundle structure at the leaf petiole and sucrose exudation rates before and after cold acclimation. We compared six natural Arabidopsis accessions originating from southern and northern Europe. Photosynthetic capacities, i.e. maximum and effective quantum yield of photosystem II, revealed a significant effect of condition but not of genotype. Only for northern accessions we observed a highly significant negative correlation between leaf sucrose exudation rates, xylem and petiole cross section areas. Further, only for northern accessions we observed a significant increase of vascular bundle and leaf petiole cross section area during cold acclimation. In contrast, variance of cross section areas of cold acclimated southern accessions was strongly reduced compared to control plants while mean areas remained similar under both conditions. In summary, our findings suggest that natural Arabidopsis accessions from northern Europe significantly adjust sink strength and leaf vascular bundle structure to stabilize plant growth and photosynthesis for survival under low and freezing temperature.

plant biology↗

bioRxiv2018

A stable, high refractive index, switching buffer for super-resolution imaging

dSTORM super-resolution imaging relies on switching buffers to enable dye molecules to enter and exit a metastable dark state. Current buffers have a very limited shelf life of approximately 1 day and poorly match sample refractive index, impacting negatively on measurement reproducibility and image fidelity. We present a buffer based on chemical, rather than enzymatic, oxygen scavenging which exhibits dramatically improved stability, switching speed, contrast, and index matching.

biophysics↗

bioRxiv2018

Tryptophan recovers sensitivity to cell membrane stress in Saccharomyces cerevisiae

Sodium dodecyl sulfate is a detergent that disrupts cell membranes, activates cell wall integrity signaling and restricts cell growth in Saccharomyces cerevisiae. However, the underlying mechanism of how sodium dodecyl sulfate inhibits cell growth is not fully understood. Because deletion of the MCK1 gene leads to sensitivity to sodium dodecyl sulfate, we implemented a suppressor gene screening revealing that the TAT2 tryptophan permease rescues cell growth to sodium dodecyl sulfate-treated{Delta} mck1 cells. Therefore, we questioned the involvement of tryptophan in the response to sodium dodecyl sulfate treatment. In this work, we show that{Delta} trp1 cells have a disadvantage in the response to sodium dodecyl sulfate compared to auxotrophy for adenine, histidine, leucine or uracil. While also critical in the response to tea tree oil, TRP1 does not avert growth inhibition due to other cell wall/membrane perturbations that activate cell wall integrity signaling such as calcofluor white, Congo Red or heat stress. This implicates a distinction from the cell wall integrity pathway and suggests specificity to membrane stress as opposed to cell wall stress. We discover that tyrosine biosynthesis is also essential upon sodium dodecyl sulfate perturbation whereas phenylalanine biosynthesis appears dispensable. Finally, we observe enhanced tryptophan import within minutes upon exposure to sodium dodecyl sulfate indicating that these cells are not starved for tryptophan. In summary, our results expose a functional link between internal tryptophan levels and tryptophan biosynthesis in the response to plasma membrane damage.

cell biology↗

bioRxiv2017

Evolutionary Processes Shaping Diversity Across The Homo Lineage

Recent fossil finds have highlighted extensive morphological diversity within our genus, Homo, and the co-existence of a number of species. However, little is known about the evolutionary processes responsible for producing this diversity. Understanding the action of these processes can provide insight into how and why our lineage evolved and diversified. Here, we examine cranial and mandibular variation and diversification from the earliest emergence of our genus at 2.8 Ma until the Late Pleistocene (0.126-0.0117 Ma), using statistical tests developed from quantitative genetics theory to evaluate whether stochastic (genetic drift) versus non-stochastic (selection) processes were responsible for the observed variation. Results show that random processes can account for species diversification for most traits, including neurocranial diversification, and across all time periods. Where selection was found to shape diversification, we show that: 1) adaptation was important in the earliest migration of Homo out of Africa; 2) selection played a role in shaping mandibular and maxillary diversity among Homo groups, possibly due to dietary differences; and 3) Homo rudolfensis is adaptively different from other early Homo taxa, including the earliest known Homo specimen. These results show that genetic drift, and likely small population sizes, were important factors shaping the evolution of Homo and many of its novel traits, but that selection played an essential role in driving adaptation to new contexts.

evolutionary biology↗