Biology subjects

Watanabe, Y. Y.

Publications and source records attributed to Watanabe, Y. Y..

3 recordsLinked to original sources

bioRxiv2026

Comparative analyses of tailbeat frequency and stride length reveal how regionally endothermic fishes cruise fast

Cruising speed is a key factor affecting prey-search efficiency and migration range in continuously swimming animals. Tunas and lamnid sharks (e.g., white sharks) have convergently evolved traits for high-speed cruising, including the ability to maintain slow-twitch, aerobic red muscle (RM) warmer than ambient water, known as RM endothermy. Despite their well-known high cruising speeds, kinematic features underlying their elevated speeds remain unclear. Swim speed is the product of tailbeat frequency (TBF; Hz) and stride length (SL, the absolute distance traveled per tailbeat; m). RM endothermy is expected to elevate TBF by enhancing muscle contraction performance. Furthermore, within RM-endothermic fishes, tunas and lamnid sharks may exhibit distinct kinematic features because of differences in caudal fin morphology and tailbeat amplitude. Here, we compiled kinematic parameters from 20 fish species, including five RM-endothermic species, measured in the wild using animal-borne sensors. Comparative analyses showed that, for a given body mass and water temperature, RM-endothermic fishes exhibited 1.9 times higher cruising speed and TBF than ectothermic fishes, while SL remained similar. Within RM-endothermic fishes, tunas exhibited 2.3 times higher TBF than similar-sized lamnid sharks, whereas lamnid sharks showed 1.7 times longer SL than similar-sized tunas. These results indicate that RM endothermy is generally associated with higher TBF, while significant kinematic differences remain between tunas and lamnid sharks. This divergence may be partly explained by the greater caudal fin area and tailbeat amplitude in lamnid sharks. It may also reflect contrasting skeletal types of teleosts and elasmobranchs, which potentially influence body stiffness and swimming kinematics.

animal behavior and cognition↗

bioRxiv2025

The Greenland shark genome: insights into deep-sea ecology and lifespan extremes

The Greenland shark (Somniosus microcephalus) is known for its slow metabolism and deep-sea habitat. It is considered the longest-lived vertebrate on Earth, with an estimated lifespan of 392{+/-}120 years. Despite its remarkable longevity and lifestyle, there have been no genomic studies on this species. Here, we report the first, chromosome-level assembly of the Greenland shark genome, which is 5.9 Gb in size with an N50 length of 233 Mb, and contains 37,125 predicted genes with a completeness score of 86.5%. We found that the copy numbers of three gene families (TNF, TLR, LRRFIP), which are involved in activating the NF-{kappa}B signaling pathway, are significantly increased in the Greenland shark compared to short-lived shark species. In the rhodopsin of this deep-sea dweller, we detected amino acid substitutions that result in spectral tuning for the so-called blue shift, suggesting adaptive evolution to dim-light vision. We also elucidate the dynamics of the effective population size (Ne) of the Greenland shark and its close relative, the Pacific sleeper shark (Somniosus pacificus). These genomic analyses offer new insights into the molecular basis of the exceptional longevity of the Greenland shark and highlight potential genetic mechanisms that could inform future research into longevity.

genomics↗

bioRxiv2021

Idea Paper: Effects of gonad type and body mass on the time required for sex change in fishes

Sex change is a well-known phenomenon in teleost fishes, and it takes several days to a few months depending on the species and direction of sex change. However, the underlying factors influencing the time required for sex change (TS) remain unclear. Given that the time for producing a new gonad largely determines TS, the gonad type (i.e., whether fish retain the gonad of opposite sex or not [delimited or non-delimited]) and metabolic rate are the ultimate determinants of TS. This study sought to test two hypotheses: (1) the delimited gonad shortens TS; and (2) TS scales with mass0.1-0.2, because the metabolic scaling exponent ({beta}) in fishes is 0.8-0.9 and biological times scale with mass1-{beta} in general. We compiled data on TS for 12 female-to-male and 14 male-to-female sex-changing species from the literature. Results of individual examinations of the effects of gonad type and mass were consistent with our hypotheses. However, upon simultaneous examination of the effects of gonad type and mass, these effects became unclear because of their strong multicollinearity. The compiled data for delimited and non-delimited gonads were biased toward the smaller and larger species, respectively, precluding us from being able to statistically distinguish between these effects. Small species with non-delimited gonads and large species with delimited gonads exist; however, their TS has not been measured with high temporal resolution thus far. Therefore, additional experiments on these species are required to statistically distinguish between, as well as to better understand, the effects of gonad type and mass on TS.

animal behavior and cognition↗