Biology subjects

Kajihara, H.

Publications and source records attributed to Kajihara, H..

2 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

From solitary to colonial with zooid miniaturization: ancestral-state reconstruction based on NGS data of stolidobranch ascidians

The size of organisms has consistently intrigued researchers across various disciplines in biology. However, the evolutionary process of zooid miniaturization in colonial animals remained an enigmatic topic. The family Styelidae, within the ascidian order Stolidobranchia, showcases a diverse spectrum of coloniality, positioning it as an ideal candidate for delving into the intricacies of colonial evolution. In this research, we inferred a phylogenomic relationship mainly within Styelidae using transcriptomes of a total of 42 ascidians; from 17 species sampled in Israel and Japan and transcriptome data from 25 species sourced from a previous study and a database. Through ancestral-state reconstruction, our analysis indicated a clear directional change: following the acquisition of coloniality, zooids tended to become progressively smaller. This miniaturization is likely an adaptive response, enabling organisms to swiftly colonize limited marine substrate. We formulated a mathematical model suggesting that zooid miniaturization, due to living space constraints, would result in a faster asexual cycle and accelerated expansion in a colony. Our data also suggested that coloniality evolved independently three times within Styelidae. Moreover, once colonial traits are established, they appear to be consistently preserved, underscoring their biological importance in the colonial lineage.

evolutionary biology↗