Biology subjects

Koizumi, I.

Publications and source records attributed to Koizumi, I..

4 recordsLinked to original sources

bioRxiv2024

Mouth-attaching copepod Salmincola markewitschi reduces the body condition and growth of juvenile salmonid Salvelinus leucomaenis by decreasing host feeding activity: evidence from parasite removal experiment

Ectoparasitic copepods in the genus Salmincola Wilson, 1915 are considered harmful to host salmonids, yet experimental studies on whether and how these copepods affect hosts are critically limited. We evaluated the effects of the mouth-attaching Salmincola markewitschi Shedko and Shedko, 2002 on juvenile white-spotted charr Salvelinus leucomaenis (Pallas, 1814) using a parasite removal experiment where all individuals were artificially infected, and then parasites were removed in one group (i.e., treatment), while the copepods were left in another group (i.e., control). We hypothesized that the copepods reduce host feeding, thereby reducing host body condition and growth. The alternative hypothesis is that parasites do not change host feeding, or even increase because of the compensation for the negative effect. In this case, host condition and growth would not be reduced. The control group (parasite remained) had lower food consumption, body condition, and growth compared to the treatment (parasite removed). Thus, S. markewitschi negatively affected hosts by reducing host feeding, and no behavioral compensation was observed. It remains unknown, however, whether reduced feeding was due to impaired swallowing or physiological stresses caused by infections. Further experiments on gill- and body-surface-attaching Salmincola species could provide deeper insights into how these parasites influence host health.

ecology↗

bioRxiv2023

Does winterkill explain contrasting demographics of winter-breeding freshwater mussel populations in Ishikari River floodplain?

O_LIEnvironmental conditions bottlenecking species population demographics are less known in cold regions with harsh winters despite of global concerns of declining freshwater mussels (Unionidae). Few studies examined both cold and summer environments in attempts to promote habitat conservation of Unionidae species. C_LIO_LIWe identified the taxonomically confused Unionidae species using phylogenetic analysis with mtDNA (COI region) and tested the hypothesis that winter mortality is the main cause of contrasting population demographics and structures in floodplain lakes in northern Japan. Demographic surveys were conducted in two lakes, which contrasted in recruitment rates, over one year including 4-month ice-covered periods C_LIO_LIAlthough previous studies have identified freshwater mussels as introduced Anemina arcaeformis (Heude 1877) based on morphology, this study confirmed the focal species as potentially native Buldowskia iwakawai (Suzuki, 1939). High winter mortality (30-40%) of adult mussels was found, although the mortality did not significantly differ between the populations with contrasting recruitment. C_LIO_LISurprisingly, the annual mortality was much lower in juveniles (10%) than in gravid and nongravid adult individuals (40-75%). The main inter-population difference was attributed to the higher summer mortality of gravid females, but not juveniles and non-gravid individuals, in the population with low recruitment. C_LIO_LIThese results collectively suggest that summer hypoxia combined with physiological stresses on females in winter is a likely population growth-limiting mechanism. To prevent a chain of adult abundance decreases in winter and high mortality of gravid mussels and newly born juveniles in summer, improvements in summer habitat conditions are necessary, while winter conditions need to be considered simultaneously. Increases in water circulation rates and alleviations of hypoxic conditions is an option for short-term habitat improvement approach. The current study sheds light on the winter-mediated mortality of freshwater mussels in shallow eutrophic floodplain lakes and contributes to improved management strategies for degraded floodplain waterbodies. C_LI

ecology↗

bioRxiv2022

The role of geology in creating stream climate-change refugia along climate gradients

Identifying climate-change refugia is a key adaptation strategy for reducing global warming impacts. Knowledge of the effects of underlying geology on thermal regime along climate gradients and the ecological responses to the geology-controlled thermal regime is essential to plan appropriate climate adaptation strategies. The dominance of volcanic rocks in the watershed is used as a landscape-scale surrogate for cold groundwater inputs to clarify the importance of underlying geology. Using statistical models, we explored the relationship between watershed geology and the mean summer water temperature of mountain streams along climate gradients in the Japanese archipelago. Summer water temperature was explained by the interaction between the watershed geology and climate in addition to independent effects. The cooling effect associated with volcanic rocks was more pronounced in streams with less summer precipitation or lower air temperatures. We also examined the function of volcanic streams as cold refugia under contemporary and future climatic conditions. Community composition analyses revealed that volcanic streams hosted distinct stream communities composed of more cold-water species compared with non-volcanic streams. Scenario analyses revealed a geology-related pattern of thermal habitat loss for cold-water species. Non-volcanic streams rapidly declined in thermally suitable habitats for lotic sculpins even under the lowest emission scenario (RCP 2.6). In contrast, most volcanic streams will be sustained below the thermal threshold, especially for low and mid-level emission scenarios (RCP 2.6, 4.5). However, the distinct stream community in volcanic streams and geology-dependent habitat loss for lotic sculpins was not uniform and was more pronounced in areas with less summer precipitation or lower air temperatures. Although further studies are needed to understand underlying mechanisms of the interplay of watershed geology and climate, findings highlight that watershed geology, climate variability, and their interaction should be considered simultaneously for effective management of climate-change refugia in mountain streams.

ecology↗

bioRxiv2022

'Ripple effects' of urban environmental characteristics on cognitive processes in Eurasian red squirrels.

O_LIUrban areas are expanding exponentially, leading more wildlife species to reside and settle in this environment. Urban environmental characteristics, such as human disturbance or green coverage, have been shown to affect some cognitive abilities such as innovative problem-solving performance of wildlife species. However, an untested hypothesis is that due to the shared underlying cognitive mechanisms, these affected performances may induce a ripple effect, and continue to affect other related cognitive processes (the ripple effect hypothesis). C_LIO_LIWe tested this hypothesis by targeting two cognitive abilities, generalisation and memory, that overlap the cognitive mechanisms (learning and memory) of the original problem solving task in urban Eurasian red squirrels. These squirrels reside in 11 urban areas where they had previously repeatedly solved the original task (the innovators), and that their solving performance in the original task was affected by the selected urban environmental characteristics. We presented two established food-extraction tasks to the innovators to measure their performance in applying the learned successful solutions when solving a similar but novel problem (i.e., generalisation process) and recalling the learned solution of the original problem when solving the same task after an extended period of time (i.e., memory). C_LIO_LIOur results provide more detailed information to refine the hypothesis; the initial effects of urban environmental characteristics on the performance of the original task affect performance at individual level but not at population level. These affected performance includes individuals generalisation solving latency across successes as well as their first solving latency in the memory task. C_LIO_LIUrban environmental characteristics affect solving performance at both population and individual levels. Some environmental characteristics such as direct and indirect human disturbance affect the success of solving the generalisation task and the memory task at site level whereas other environmental characteristics such as green coverage affect the individuals solving latency in both tasks. C_LIO_LIOverall, our results support the ripple effect hypothesis, indicating that urban environmental characteristics have a more global impact on shaping cognitive performance than previously has shown, and thus provide a better understanding of the mechanism that supports wildlife in adapting to urban environments. C_LI

animal behavior and cognition↗