Sprenger, A. | Search bioRxiv

bioRxiv2025

Cytogenetic constraints on hybridization: A meta-analysis investigating the role of chromosome number in monocot hybrid evolution using a newly developed tool, the ploidy deviation index (PDI).

Background and aimsHybridization is a major driver of plant diversity, yet the role of cytogenetic compatibility, particularly differences in chromosome number, remains poorly understood. Differences in parental chromosome number can present barriers to hybrid formation by disrupting meiotic stability, but the extent to which biological and ecological factors influence the chromosomal architecture of hybrids remains poorly quantified, especially in monocots. This study aims to investigate how chromosome number divergence interacts with biological and ecological factors to shape hybrid formation in monocots, using a novel quantitative metric, the Ploidy Deviation Index (PDI), to standardize comparisons of hybrid cytogenetic architecture. Material and methodsWe developed and applied the PDI, a continuous index quantifying chromosome-number deviation between a hybrid and its two parents, across approximately 200 hybrid cases with documented parental karyotypes. Hybrids were categorized as homoploid, uniparentally homoploid, intermediate, or polyploid based on their PDI values. We analyzed the distribution of PDI scores in relation to type of hybrid origin (natural vs. artificial), growth habit, size of the genus (a proxy for richness), and range of chromosome number within a genus (proxy for diversity). Comparisons across categories employed Anderson-Darling k-sample tests, multinomial logistic regression, and Mann-Whitney U tests to determine significance. Key resultsHomoploid hybrids were found to be the most frequent. We found no significant difference in PDI distributions between natural and artificial hybrids. Significant variation in PDI distributions was found among growth habits, with aquatic hybrids more likely to be homoploid and geophytic hybrids showing higher proportions of polyploidy. Intermediate hybrids were common in larger genera with broader chromosome-number ranges, whereas polyploid hybrids showed the highest PDI values in large and karyotypically diverse genera. ConclusionThese results challenge long-held assumptions that polyploidy dominates hybrid formation and reveal that homoploid and intermediate chromosomal configurations are common in monocots. The PDI framework offers a powerful, standardized approach for assessing cytogenetic constraints on hybridization, with implications for systematics, evolutionary biology, and conservation.

plant biology↗

bioRxiv2024

Personalized tDCS targeting visual motion area V5 modulates smooth pursuit initiation

Transcranial direct current stimulation (tDCS) for the modulation of ongoing eye movements provides an ideal model for investigating sensorimotor integration. Within neural networks subserving smooth pursuit eye movements, visual motion area V5 is a core hub to integrate visual motion information with oculomotor control. Here, we applied personalized tDCS explicitly targeting individual V5 in healthy human participants using algorithmic optimization informed by functional magnetic resonance imaging and combined electro- and magnetencephalography. We hypothesized subtle modulation of sensorimotor integration during pursuit and assessed the gain by personalized tDCS targeting V5, compared to personalized tDCS targeting the frontal eye field, as well as conventional normative tDCS over V5. Indeed, pursuit initiation was specifically delayed during personalized cathodal tDCS targeting right V5 indicating the involvement of distinct functional subregions of V5 in the initial sensorimotor integration of visual motion information with pursuit eye movements, but not the maintenance of ongoing pursuit. The results were well-controlled by anodal and sham tDCS, different pursuit tasks, finite-element simulations of individual electric fields, and by two additional control experiments, one that applied personalized tDCS targeting frontal eye field and another that applied normative tDCS over V5. Importantly, in contrast to personalized tDCS targeting FEF and normative tDCS over V5, personalized tDCS targeting V5 effectively modulated pursuit by adapting electric fields to individual anatomical and functional V5 properties. Our results provide evidence for the specific involvement of area V5 in sensorimotor integration during pursuit initiation and the ability of (targeted) tDCS to specifically introduce subtle modulation of the brain network underlying smooth pursuit eye movements. Further, our results indicate the potential of personalized tDCS to alter behavior as the main aspect of interest in human neuromodulation.

neuroscience↗