Reward magnitude determines reinforcement learning efficiency

Conventional animal learning experiments deliberately keep reward sizes small to maximize behavioral repetitions, but this approach may artificially limit how fast animals can learn. Researchers tested mice across five different behavioral tasks to see how reward size affects initial learning, finding that unusually large rewards dramatically sped up learning. This improvement appeared through two distinct mechanisms: better within-session performance and stronger across-session retention, alongside greater overall engagement with the task. Measuring dopamine release in the ventral striatum revealed that both the duration and intensity of dopamine signals scaled directly with reward size. When the researchers artificially prolonged dopamine reward responses using optogenetics, they replicated many — though not all — of the advantages conferred by large rewards. The results suggest that animals are capable of learning far more efficiently than classical studies implied, and that dopamine encodes absolute reward magnitude to drive task engagement.

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A deep-time landscape of plant cis-regulatory sequence evolution

Identifying conserved noncoding sequences (CNSs) in plants is notoriously difficult because these regulatory regions evolve rapidly, genomes undergo whole-genome duplications, and comparative datasets have been limited. Researchers developed Conservatory, a computational tool that uses local gene-order context and iterative sequence alignments to link CNSs to their target genes across evolutionary time. Applying this to 284 plant species spanning 300 million years, they catalogued roughly 2.3 million CNSs, with over 3,000 predating the origin of flowering plants. The oldest CNSs cluster near developmental regulatory genes, and experimentally disrupting CNSs near HOMEOBOX genes caused pronounced developmental defects. The analysis also revealed several evolutionary principles: while the spacing between CNSs shifts over time, their relative order is maintained; chromosomal rearrangements can rewire CNS-gene pairings; and ancient CNSs tend to be retained in duplicate gene copies but are frequently lost together in groups or repurposed into lineage-specific regulatory elements.

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Long-distance genetic relatedness in megalithic central Europe

Researchers examined ancient DNA from 203 people buried across six megalithic tomb complexes in Late Neolithic central Europe, comparing individuals associated with two archaeologically distinct cultures: the Western Funnel Beaker and Wartberg groups. Despite their cultural differences, genomic analysis showed these populations were genetically indistinguishable. Strikingly, close biological relatives — including first- and second-degree kin — were found buried at sites up to 225 km apart, pointing to regular long-distance movement between communities. The burial sites served as communal grounds that were not reserved for biological family members, suggesting that social or fictive kinship shaped who was interred together. The lack of strong genetic links to other European megalithic populations further implies that the monumental building tradition spread through cultural exchange rather than population movement or biological connectivity across the continent.

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Biogeographic processes underlying global patterns of plant diversity

Using a dated phylogeny covering more than 300,000 plant species combined with ancestral biogeographic modeling, researchers mapped the evolutionary processes responsible for today's uneven distribution of plant life across the globe. They found that local speciation within regions dominates, accounting for roughly 78% of biogeographic events, with the Neotropics alone responsible for 37% of that in-situ diversification. Cross-realm dispersal was less common, representing about 16% of events, though it played a meaningful role in shaping plant communities across the Eastern Hemisphere. Extinction was the rarest process overall but was disproportionately concentrated in East Asia. The results back the tropical conservatism hypothesis: most plant lineages arose in tropical environments and have only recently colonized temperate zones, where insufficient time and strong biome fidelity have kept diversity comparatively low.

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