Biology subjects

Otieno, M.

Publications and source records attributed to Otieno, M..

4 recordsLinked to original sources

bioRxiv2026

Nocturnal pollination services as an ecological safety net for papaya production in a tropical biodiversity hotspot

Pollination is of key importance for tropical agriculture, yet a bee-centred perspective often overlooks the critical role of nocturnal insects in pollination services. We evaluated the relative contributions of diurnal and nocturnal pollinators to papaya yields on subsistence farms in the Taita Hills, Kenya, a globally important biodiversity hotspot. We combined flower visitor observations with five experimental treatments: open pollination, wind-only (closed), hand pollination, and temporal exclusions for day-only and night-only services. Our results reveal complete temporal niche partitioning between diurnal bees and nocturnal hawkmoths (Sphingidae). We found that diurnal and nocturnal pollinators provide additive, rather than redundant, services, contributing to papaya fruit set and weight to a similar extent. Despite these contributions, supplementary hand-pollination experiments indicated a significant yield gap (36.9% lower fruit set), suggesting substantial pollinator limitation. While landscape-scale factors had no significant effects, nocturnal pollinators responded positively to organic management, whereas diurnal visitors did not. This indicates that local habitat quality and ecological intensification are more critical for sustaining specialised pollinators than landscape composition. Our study highlights the vital role of nocturnal insects as an ecological safety net and emphasises that their conservation through local organic practices is essential for securing yield quantity and quality in tropical papaya farming systems.

ecology↗

bioRxiv2026

A Polygenic Route to Thermal Melanism and high-elevation adaptation in Honey Bees

Thermal melanism, whereby darker pigmentation occurs in colder environments, is a widespread adaptive pattern, yet its genetic and physiological basis in eusocial insects remains poorly understood. East African honey bees (Apis mellifera) occupy steep elevational gradients in which highland populations are darker, larger, and more cold tolerant than lowland conspecifics. Here, we integrated population genomics, structural variation, reciprocal translocations, and functional genomics to dissect the basis of elevational melanism in honey bees. 139 workers from five East African mountain systems were sampled and phenotyped, and whole-genome resequencing was performed. A genome-wide association study identified 977 SNPs significantly associated with abdominal pigmentation, with a single pronounced peak at the ebony ortholog AmEbony on chromosome CM009931.2. Allelic variation at AmEbony formed three genetic clusters that closely tracked a continuous pigmentation gradient, and 77 highly divergent SNPs (DXY = 1) almost perfectly discriminated dark from light bees. Two large inversions (r7, r9), previously linked to high-elevation adaptation, were detected across additional mountain systems and were enriched in dark, highland genomic backgrounds, but did not replace AmEbony as the primary pigmentation locus. Reciprocal highland-lowland translocations revealed lineage-specific yet convergent expression shifts along detoxification/immune, chemosensory, proteostasis, and cuticle axes. CRISPR/Cas9-mediated disruption of AmEbony in A. m. carnica altered pigmentation and induced coherent changes in head transcriptomes, notably in odorant-binding and redox-related modules. Our results demonstrate that thermal melanism in a eusocial pollinator is governed by a top-heavy polygenic architecture centered on AmEbony, linking mechanistically naturally segregating pigmentation alleles to gene regulatory reprogramming and high-elevation adaptation.

evolutionary biology↗

bioRxiv2026

Octopaminergic signaling contributes to thermal adaptation to elevation in African honey bees (Apis mellifera)

Adaptation to local environments enables species to thrive in diverse and challenging habitats. Steep elevational gradients provide a compelling natural adaptation laboratory, because abiotic conditions change progressively over short geographical differences. Given that elevation can strongly reshape physiology and behavior of insects, neuromodulatory systems offer a promising lens through which to examine elevation-specific adaptation. We challenged the hypothesis that adaptation to elevation involves octopaminergic signaling in honey bees (Apis mellifera), an important pollinator species occupying different elevations along East African mountains. We collected foragers from two distinct elevations at Mount Kenya (1,150 m and 1,900 m above sea level) and analyzed elevation-dependent changes in octopaminergic signaling. Tissue-specific analysis revealed a striking upregulation of all three octopamine {beta} receptor genes in the thoracic flight muscles and elevated octopamine brain concentrations at high elevation. Expression differences in the brain and fat body were rather modest. We subjected CRISPR/Cas9-mediated octopamine {beta}2 receptor knockouts to cold stress to study the function of octopaminergic signaling in thermoregulation. Loss of AmOAR{beta}2 reduced both the slope and amplitude of heating phases, indicating altered thermogenic dynamics. Together, these results identify the octopaminergic system as a central neuromodulatory regulator of thermogenic performance across elevations in honey bees. More broadly, our study highlights how modulation of conserved aminergic signaling pathways can shape physiological resilience to environmental gradients, pointing to a general mechanism by which insects adapt to changing thermal landscapes. Highlights- Bees from high and low elevation differ in expression of octopamine {beta} receptor genes and octopamine brain concentrations - CRISPR/Cas9-mediated octopamine receptor knockout alters thermogenic behavior - Octopaminergic signaling emerges as a key neuromodulator in thermal adaptation to elevation in honey bees Significance statementAnimals living along mountain gradients must cope with rapidly changing temperatures, yet the mechanisms enabling this adaptation remain poorly understood. We show that honey bees from higher elevations have increased brain octopamine levels and enhanced expression of octopamine receptors in heat-producing flight muscles. Using gene editing, we demonstrate that disrupting one key receptor alters how bees generate heat under cold stress. These findings identify octopamine signaling as a central regulator of thermogenesis and reveal a mechanism by which insects adjust to colder environments. More broadly, our results highlight how conserved neuromodulatory systems can fine-tune physiological performance, offering insight into how insects may respond to changing climates and expanding environmental extremes.

physiology↗

bioRxiv2019

Liver-Chip: Reproducing Human and Cross-Species Toxicities

Nonclinical rodent and non-rodent toxicity models used to support clinical trials of candidate drugs may produce discordant results or fail to predict complications in humans contributing to drug failures in the clinic. Here we applied microengineered Organ-on-Chip (Organ-Chip) technology to design rat, dog, and human Liver-Chips containing species-specific primary hepatocytes interfaced with liver sinusoidal endothelial cells, with or without Kupffer cells and hepatic stellate cells, cultured under physiological fluid flow. The Liver-Chips detected diverse phenotypes of liver toxicity including hepatocellular injury, steatosis, cholestasis, and fibrosis as well as species-specific toxicities when treated with tool compounds. Multi-species Liver-Chips may provide a useful platform for prediction of liver toxicity and inform human relevance of liver toxicities detected in animal studies to better determine safety and human risk.\n\nOne Sentence SummaryMicroengineered Organ-Chip technology has been used to design rat, dog and human Liver-Chips that recapitulate species-specific liver toxicities.

pharmacology and toxicology↗