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Festschrifts can provide valuable vantage points for reflecting on a discipline’s evolution and future possibilities. This article honoring Devang Vipin Khakhar (DVK) offers such an opportunity─not through a comprehensive career review, but by examining one dimension of scholarly achievements through the lens of collaborative work spanning 40 years and three generations of researchers. Specifically, we review DVK’s contributions to our understanding of flowing granular materials across three domains: surface flows, mixing and segregation, and computational modeling. This retrospective traces the field’s evolution from early explorations of chaos and mixing in rotating tumblers to sophisticated analyses of flow kinematics and segregation in heaps. We use this opportunity to chart the emergence of granular mechanics as a predictive science. In addition, we look forward to identifying persistent challenges and emerging opportunities: modeling unconfined geometries with evolving boundaries, extending segregation theory across wide size-ratio regimes, addressing cohesive effects and particle breakage, and integrating multiscale computational approaches with machine learning. 

Like other contributions to this volume, the subject matter for this chapter sits at the intersection of major historical trends, the future trajectory of which is uncertain. There is a growing impact of humanity’s tools and techniques on natural systems. Climate change is only the most obvious and comprehensive example. Humans have long had significant impacts on the composition of species existing in a given ecosystem, but the trend is for greater domestication of previously wild environments, heightened challenges to the survival of wildlife and an increasing rate of species extinction. At the same time, the perception of ethical duties or responsibilities to the non- human world of living things has also undergone dramatic change. 

The influences of restitution coefficient, $e_n$ , interparticle friction, $\mu$ , and size ratio, $R$ , on gravity-driven percolation of fine particles through static beds of larger particles in the free-sifting regime ( $R\gtrsim 6.5$ ) remain largely unexplored. Here, we use discrete element method simulations to study the fine particle percolation velocity, $v_p$ , and velocity fluctuations, $v_{\mathrm{rms}}$ , for $7\le R\le 50$ and a range of $e_n$ and $\mu$ . Varying $e_n$ modulates the degree of particle excitation and thereby alters the nature of particle trajectories: at low $e_n$ , percolation is dominated by gravity, whereas increasing $e_n$ amplifies velocity fluctuations thereby reducing the mean percolation velocity. Increasing $\mu$ decreases $v_{\mathrm{rms}}$ but its influence on $v_p$ varies with $v_{\mathrm{rms}}$ , decreasing $v_p$ for low $v_{\mathrm{rms}}$ and increasing $v_p$ for high $v_{\mathrm{rms}}$ . Although the influence of size ratio is weaker, larger values of $R$ increase both $v_p$ and $v_{\mathrm{rms}}$ . We also assess the influence of different excitation mechanisms, specifically using static, randomly excited, and sheared beds, finding that an inverse correlation between $v_p$ and $v_{\mathrm{rms}}$ persists across all cases and is well-described by the Drude model, where increased scattering reduces mobility, when $v_{\mathrm{rms}}$ is large. However, for weakly excited particles with low $v_{\mathrm{rms}}$ , the Drude analogy breaks down. In this regime, we introduce a staircase-inspired model that accounts for the gravitationally dominated percolation behavior. These findings provide fundamental insight into the mechanisms governing percolation dynamics in porous media and granular systems. 

Abstract Larvae of the caddisfly Arctopsyche grandis BANKS build protective structures and spin silken capture nets in flowing water. Caddisfly H-fibroin, the major protein component of its silk fibers, has a blocky structure with repeating units defined as beginning with a [(SX)nE]m region followed by a G-rich spacer. Previous observation of H-fibroin allelic variation in haploid-resolved individuals led us to investigate allelic variation within two geographically close but separated natural populations of A. grandis. The genomes of 18 individuals were sequenced, and 34 haploid-resolved H-fibroin sequences were extracted. Twenty-four unique alleles were identified in 18 genomes, revealing the dynamic nature of the H-fibroin gene. H-fibroin length variations of up to 25% were tolerated. The major source of the length variations were large-scale deletions and insertions of entire [(SX)nE]m blocks. Small scale indel events were numerous, nonrandomly distributed, and constrained to a few types. One was a 44 residue indel comprising two (SX)nE motifs that split direct tandem repeats in [(SX)nE]m regions, changing m by ±2 without disrupting tertiary structure or block boundaries. The G-rich spacers are of two types, the first distinguished by repeating GLGPH pentapeptides. Indels within this spacer type occur as multiples of the GLGPH pentapeptide. The other category of G-rich spacer was confined to a narrow length distribution. Overall, the results demonstrate the rapid evolution of the caddisfly H-fibroin gene and the wide range of H-fibroin structural polymorphism tolerated in functional capture net silk. At the same time, the limited nature of the indels point to the critical structural features of H-fibroin. 

Abstract The Permian–Triassic mass extinction represents the most severe loss of biodiversity in Earth history and profoundly reorganized terrestrial ecosystems. On land, this crisis was followed by a marked floral turnover, with herbaceous lycophytes dominating Early Triassic vegetation. Here we show that these pioneer (so-called disaster) taxa that rapidly colonized stressed post-extinction environments, possessed specialized physiological traits that promoted survival under extreme conditions. Independent phylogenetic analyses show that Early Triassic lycophytes are closely related to modern Isoetales, a group characterized by exceptional ecophysiological flexibility. Their carbon isotope signatures resemble those of extantIsoetesthat use crassulacean acid metabolism (CAM) photosynthesis, indicating a similar physiological strategy in deep time. Coupling these results with climate simulations suggests that CAM photosynthesis could have conferred a substantial advantage under Early Triassic super greenhouse conditions. Together, our findings identify CAM physiology as a potential mechanism enabling plant survival and ecosystem recovery following Earth’s largest mass extinction. 

Abstract The acorn weevil Curculio nanulus (Coleoptera: Curculionidae) is a seed predator that lays its eggs inside developing acorns and hickory nuts in the western United States. The female weevil uses her elongated rostrum to excavate a hole into the seed, creating a protected site for oviposition. Natural history traits among Curculio species—such as host specificity and variation in larval diapause—suggest a dynamic evolutionary relationship with their host plants. These traits are best studied through a comparative genomic framework, but such analyses cannot currently be undertaken due to the lack of whole-genome assemblies for Curculio species. To address this gap, we generated a whole-genome assembly for C. nanulus using PacBio HiFi sequencing. The resulting assembly is ∼1.5 Gbp in length, with high contiguity (contig N50 = 7.7 Mbp) and gene completeness (BUSCO score: 98.97%). To enable comparative analysis, we also assembled the genome of the pecan weevil, Curculio caryae, using publicly available PacBio HiFi reads. For both species, we annotated repetitive elements and protein-coding genes and compared these features with those of other weevil genomes. Our results reveal a marked expansion of repetitive elements within Curculio and its close relatives. These genomic resources provide a foundation for investigating seed predation, co-speciation, and host-parasite evolutionary dynamics in Curculio and related taxa, as well as their impacts on forest ecology. 

Gene duplications are a major driver of molecular diversification and phenotypic evolution. Arthropod silk genes provide an excellent model for studying these processes due to their extensive internal repeats and rapid evolutionary rates. In Lepidoptera, the Fibroin heavy chain (fibH) gene encodes the primary structural protein for silk fibers, contributing largely to their mechanical strength. This inner fibroin core is surrounded by an outer coating composed primarily of sericins. Sericins are a group of highly repetitive, serine-rich proteins that modulate silk fiber properties. Although sericins in the domestic silkworm (Bombyx mori) have been associated with life stage-specific variation in silk characteristics, their evolution and function remain poorly understood. Here, we provide a detailed molecular characterization of sericin genes in the Luna moth (Actias luna) known for forming dense, robust, silk-woven cocoons. We identified eight sericin genes that (i) include two clusters of closely related paralogs, (ii) exhibit considerable variation in repeat number and amino acid composition, and (iii) display distinct gene expression patterns across life stages. A comparison of sericin genes between A. luna and three other moths of the superfamily Bombycoidea reveals evidence for convergent subfunctionalization. These findings suggest that sericin gene duplications enable dynamic shifts in silk composition both within and between species, potentially reflecting adaptive responses to ecological and functional demands. 

In 1939, Margery and Lorus Milne published a creative figure that illustrated the evolutionary history of caddisflies. Here, we pay tribute to that paper by generating a new figure in the style of the original, updated with our most recent knowledge of caddisfly evolution, informed by phylogenomic inference and a statistical treatment of ancestral states. Our analysis infers that the ancestral larval caddisfly was a free-living detritivore, living in flowing water. It spun a cocoon prior to pupation within a dome-shaped pupal shelter. In subsequent lineages, caddisflies evolved a variety of larval construction behaviors, which enabled unprecedented ecological diversification, allowing them to become one of the most diverse lineages of freshwater animals.