山本 俊昭

Thelazia callipaeda (Nematoda: Spirurida: Thelaziidae) parasitizes the eyes of dogs, cats, humans, and various wild mammals, and is transmitted by drosophilid flies. In Japan, T. callipaeda is considered an emerging parasite that has expanded its endemic region northward. However, reports of its detection in mammals other than domestic animals and humans are scarce. This study reports the detection of T. callipaeda in Japanese red fox (Vulpes vulpes japonica), masked palm civet (Paguma larvata), Japanese badger (Meles anakuma), Japanese black bear (Ursus thibetanus japonicus), raccoon (Procyon lotor), Japanese raccoon dog (Nyctereutes viverrinus), domestic dog (Canis lupus familiaris), domestic cat (Felis silvestris catus), and human. Of these, the Japanese red fox, masked palm civet, Japanese badger, and Japanese black bear have been reported as novel host records. Sequence analysis of the cytochrome c oxidase subunit I gene of T. callipaeda revealed two unique lineages specific to Japan, with no regional or host species differences. These results suggest a wide host range for T. callipaeda, highlighting the significant role of wildlife as a reservoir for this parasite in Japan.

Hair hormone analysis has received increasing attention in the fields of wildlife management and conservation over the last decade. However, few studies focused on sex steroid hormones, even though hair sex steroid hormone analysis has the potential to provide information on an individual's reproductive health, leading to a better understanding of animal reproductive biology and the assessment of individual and population health. Here, we tested the assay validation and examined whether hair progesterone concentration (HPC) differs between different sexes and age classes in the Asian black bear, Ursus thibetanus. We also investigated the effects of reproductive condition, age, and body condition index (BCI) on HPC to determine the utility of hair progesterone analysis in bears. The assay validation was reported in our study. We found a significantly higher HPC in adult females than in juvenile females and juvenile and adult males. In addition, we found no effects of age and BCI on HPC but a significant positive effect of reproductive condition, as the HPC in breeding adult females was significantly higher than in nonbreeding adult females. These results suggest that hair progesterone analysis has the potential to evaluate the reproductive condition of Asian black bears.

To clarify the effect of paternal life-history form and egg size on offspring life-history traits (e.g., growth and maturation) in masu salmon (Oncorhynchus masou), we studied an artificially fertilized population for 3 years using mark-recapture methods. The body size of offspring in early life was associated with egg size, but not paternal life-history form. By contrast, the growth rate of individuals during summer and winter seasons was not influenced by egg size or paternal life-history form. Movement within the tributary differed between males and females, with more females moving downstream during early life stages compared to males. However, the effects of egg size and paternal life-history form on the movement of offspring were not detected. Out of 192 males that remained in the tributary, 77 had relatively large body sizes and reached sexual maturity at one year old. The probability of maturation was associated with the body size in September, but not with paternal life-history form and egg size. We concluded that offspring life-history traits are profoundly influenced by environmental conditions, whereas they are slightly influenced by parental genetic effects.

Offspring growth is greatly influenced by both the maternal and paternal genotypes. However, although the effects of maternal genotype on offspring growth are recognised widely, ecological studies of the paternal genotype have not focused on the links with physiological traits, especially at the embryo stage. In this study, we conducted three experiments to determine the effects of two contrasting paternal life history traits (anadromous males, which return to their natal rivers for spawning after migrating to the sea, and resident males, which mature in rivers without migrating to the sea) on offspring growth during early life based on the metabolic rate in masu salmon Oncorhynchus masou. In the first experiment, metabolic rates of fertilised eggs were compared between 24 half-sibships. Results suggested that the metabolic rate of embryos was higher for the offspring of resident males than of anadromous males. In the second experiment, the body sizes of 133 half-sibships at the yolk-sac absorption stage were compared. The offspring from the resident males were larger, which could be related to metabolic rate differences at the embryo stage associated with paternal life history. In the third experiment, the differences in body size observed at the yolk-sac absorption stage were positively correlated with growth after 60 days of fry rearing. Our findings, taken together with previous demonstrations that faster-growing males tend to become younger resident males, are thus consistent with early growth and associated traits, such as metabolic rate, being heritable from the male parent to the offspring.