Biology subjects

Izumi, S.

Publications and source records attributed to Izumi, S..

3 recordsLinked to original sources

bioRxiv2026

Size-invariant aerobic scope across ontogeny in a giant deep-sea scavenger

Aerobic scope is the aerobic metabolism left after maintenance costs are met, and it sets a simple limit on how much oxygen-dependent activity an animal can support. In many aquatic animals, this margin changes with body size because resting and active metabolic rates do not always scale in the same way. Large deep-sea scavengers are interesting in this respect because they live where food is sparse and unpredictable, but they must still move when carrion or food cues appear. We measured resting metabolic rate (RMR) and post-exercise peak oxygen consumption, here referred to as active metabolic rate (AMR), in the giant isopod Bathynomus doederleini across a body-mass range of 1.7-48.4 g using intermittent-flow respirometry at 10 {degrees}C. RMR and AMR both increased with body mass and had similar scaling exponents. As a result, factorial aerobic scope (FAS = AMR/RMR) did not change with body mass (median FAS = 2.83). A residual analysis also showed that mass-corrected RMR was not significantly related to mass-corrected AMR. Thus, individuals with relatively high maintenance metabolism did not necessarily have higher post-exercise aerobic capacity. These results show that exercise-induced aerobic scope was maintained across ontogeny in this deep-sea scavenger. They also show that body size and individual metabolic phenotype provide different information: body size explained the shared increase in RMR and AMR, whereas residual variation did not show a strong link between the two traits.

physiology↗

bioRxiv2025

Intraspecific differences in habitat depth in a deep-sea isopod, Bathynomus doederleini (Crustacea: Isopoda: Cirolanidae), off the west coast of Kyushu, Japan

The giant deep-sea isopod, Bathynomus doederleini, is a benthic scavenger distributed in the northwestern Pacific. Despite its ecological importance, little is known about its habitat use and intraspecific variation in body size in relation to depth. In this study, we examined the habitat depth, size structure, and distributional limits of B. doederleini off the western coast of Kyushu, Japan, using baited traps deployed at depths ranging from 151 to 821 m. A total of 1,152 individuals were collected, with the highest catch per unit effort (CPUE) observed between 300 and 500 m. CPUE declined sharply below 700 m, likely due to thermal constraints and interspecific competition. Body size distribution varied significantly with depth: minimum body size increased with depth, while maximum body size remained constant. Smaller individuals were more abundant in shallower, warmer waters, suggesting ontogenetic habitat segregation possibly driven by metabolic and competitive factors. No brooding individuals were captured, supporting previous findings that reproductive females avoid baited traps. These results suggest that B. doederleini forms a reproductively active population in the East China Sea, with ecological adaptations to thermal conditions and depth-related niche partitioning. This study highlights the importance of trap type and environmental gradients in understanding deep-sea species ecology.

ecology↗

bioRxiv2021

Cis-regulatory elements of the cholinergic gene locus in the silkworm Bombyx mori

Genes of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) are encoded in the same gene locus, called the cholinergic gene locus. They are essential in cholinergic neurons to maintain their functional phenotype. The genomic structure of the cholinergic gene locus is conserved among invertebrates to mammals. However, it is still inconclusive how cholinergic genes express only in cholinergic neurons in insects. In this study, we analyzed the upstream sequence of cholinergic gene locus in the silkworm Bombyx mori to identify specific cis-regulatory regions. We found multiple enhancer regions that are localized within 1 kb upstream of the cholinergic gene locus. The combination of promoter assays using small deletions and bioinformatic analysis among insect species illuminates two conserved sequences in the cis-regulatory region: TGACGTA and CCAAT, which are known as the cAMP response element and CAAT box, respectively. We found that dibutyryl-cAMP, an analog of cAMP, influences the expression of ChAT. Tissue-specific expression analysis of transcriptional factors showed potential candidates that control the cholinergic gene locus expression. Our investigation provides new insight into the regulation mechanism of cholinergic neuron-specific gene machinery in this lepidopteran insect.

molecular biology↗