Biology subjects

Johnsen, S.

Publications and source records attributed to Johnsen, S..

4 recordsLinked to original sources

bioRxiv2026

Global adaptation to climate change in the twilight zone revealed by shared signals of selection in mesopelagic lanternfishes

Rapid accumulation of greenhouse gases threatens humanity and global diversity. The oceans absorb 30% of anthropogenic carbon emissions annually, but adaptation to climate change by the biotic components of this sink are poorly understood. Lanternfishes (Myctophiformes) are the most abundant vertebrates on the planet by biomass and the dominant mesopelagic vertebrate consumers, thus crucial components of the global carbon cycle. However, it is unknown whether lanternfishes are adapting to global warming and ocean acidification (OA). We hypothesized that warming and OA would act as major shared selective forces across diverse oceanic environments and that disparate taxa would respond in parallel through shared genetic pathways. We used whole-genome sequencing to test this hypothesis by identifying shared signals of selection across lanternfishes from multiple sites in the Atlantic and Pacific spanning three genera (Benthosema glaciale, Triphoturus mexicanus, and Diaphus theta). Across all species we found evidence of expansion from a population bottleneck possibly corresponding to the last glacial maximum and effective population sizes of only 5 million, suggesting substantial reproductive skew and spatially restricted populations. We successfully identified 34 candidate genes experiencing strong shared selection pressure across all taxa in both oceans. 81% of these candidate genes were consistent with adaptations to warming and OA, including a heat-shock protein (HSP70) and genes related to skeletal development, calcium homeostasis, and biomineralization. 14 out of 34 candidate genes are also known from experimental climate change studies to be involved in the response to hypoxia, altered pH, and thermal stress. We found significant gene ontology enrichment within these candidates for otolith morphogenesis, a major component of OA adaptation in fishes. This study provides a new approach for studying climate change adaptation at a global scale and our results imply widespread shared adaptive responses of marine species to climate change.

evolutionary biology↗

bioRxiv2026

Serpin-Driven Green Camouflage and NIR Fluorescence in Frogs

Animals have evolved multiple strategies to generate optical traits and coloration. While most amphibians rely on a three-dimensional arrangement of chromatophores in the skin, hundreds of arboreal frog species achieve leaf-like green color through a different mechanism involving reduced pigmentation, subcutaneous biological mirrors, and high concentrations of the blood-derived pigment biliverdin. Although biliverdin is rapidly excreted in most vertebrates, hylid and centrolenid frogs can retain it through the binding to a serpin-family protein (BBS). Here we show that BBSs bind biliverdin with high affinity (Kd < 10 nM), comparable to hormone-receptor interactions. This interaction alters biliverdins spectral signature in ways that resemble those of green-leaf pigments. BBSs from different species exhibit distinct biophysical properties, accounting for interspecific differences in color saturation and hue. Unlike most serpins in vivo, BBS of the glassfrog Teratohyla pulverata is naturally cleaved, yielding a highly thermostable, thermodynamically favored protein, without loss of affinity. Using custom-designed hyperspectral photoacoustic tomography (PAT), we demonstrate that BBS is widely distributed throughout the body, contributing to whole-body color and camouflage. Furthermore, we show that BBSs emit near-infrared (NIR) fluorescence (>700 nm) rendering these frogs fluorescent in a spectral region where biological tissues are largely transparent. Together, BBSs shed light on serpin evolution, protein thermostability, amphibian color diversity, and the development of NIR molecular probes.

biochemistry↗

bioRxiv2022

Heart cockle shells transmit sunlight for photosynthesis using bundled fiber optic cables and condensing lenses

Many animals convergently evolved photosynthetic symbioses. In bivalves, giant clams (Cardiidae: Tridacninae) gape open to irradiate their symbionts, but heart cockles (Cardiidae: Fraginae) stay closed because sunlight passes through transparent windows in their shells. Here, we show that heart cockles (Corculum cardissa and spp.) use biophotonic adaptations to transmit sunlight for photosynthesis. Heart cockles transmit 11-62% of photosynthetically active radiation (mean=31%) but only 5-28% of potentially harmful UV radiation (mean=14%) to their symbionts. Beneath each window, microlenses condense light to penetrate more deeply into the symbiont-rich tissue. Within each window, aragonite forms narrow fibrous prisms perpendicular to the surface. These bundled "fiber optic cables project images through the shell with a resolution of >100 lines/mm. Parameter sweeps show that the aragonite fibers size ([~]1{micro}m diameter), morphology (long fibers rather than plates), and orientation (along the optical c-axis) transmit more light than many other possible designs. Heart cockle shell windows are thus: (i) the first instance of fiber optic cable bundles in an organism to our knowledge; (ii) a second evolution, with epidermal cells in angiosperm plants, of condensing lenses for photosynthesis; and (iii) a photonic system that efficiently transmits useful light while protecting photosymbionts from UV radiation.

evolutionary biology↗

bioRxiv2018

Orienting to Polarized Light at Night-Matching Lunar Skylight to Performance in a Nocturnal Beetle

For polarized light to inform behaviour, the typical range of degrees of polarization observable in the animals natural environment must be above the threshold for detection and interpretation. Here we present the first investigation of the degree of linear polarization threshold for orientation behaviour in a nocturnal species, with specific reference to the range of degrees of polarization measured in the night sky. An effect of lunar phase on the degree of polarization of skylight was found, with smaller illuminated fractions of the moons surface corresponding to lower degrees of polarization in the night sky. We found that South African dung beetle Escarabaeus satyrus (Boheman, 1860) can orient to polarized light for a range of degrees of polarization similar to that observed in diurnal insects, reaching a lower threshold between 0.04 and 0.32, possibly as low as 0.11. For degrees of polarization lower than 0.23, as measured on a crescent moon night, orientation performance was considerably weaker than that observed for completely linearly-polarized stimuli, but was nonetheless stronger than in the absence of polarized light.\n\nSummary StatementA degree-of-polarization threshold for orientation behaviour is reported for nocturnal dung beetle Escarabaeus satyrus in the context of measurements showing changes in the degree of polarization of skylight with lunar phase.

animal behavior and cognition↗