Find articles by Minami W. This article has been cited by other articles in PMC. Abstract The raccoon Procyon lotor , indigenous to North America, has naturalized in Japan as an invasive alien species, having been introduced into the country in the s. In Hokkaido, the northernmost island of Japan, feral raccoons have been increasing in number and spreading throughout the island. The age at the onset of puberty for raccoons is important for estimating individual lifetime reproductive success and population growth.
The present study investigated the timing of and potential factors affecting the onset of puberty in male raccoons in Hokkaido. External characteristics and histology of testes were studied in male feral raccoons and in 1 captive juvenile.
For the majority of feral yearling raccoons, prepubertal development began in May, and spermatozoa production began in October prior to their second mating season.
However, some larger juveniles attained puberty during the juvenile period. The captive juvenile, which was fed throughout the winter, attained puberty only 11 months after birth. These results suggest that if male raccoons can achieve enough body growth before the first mating season, puberty can be attained early.
In both juveniles and yearlings, spermatozoa production was only observed after autumn. This timing coincided with the recrudescence of seasonally active spermatogenesis in adult males. Therefore, attaining puberty in male raccoons appears to require both adequate body nutrient development and several environmental factors that control seasonal testicular changes. Procyon lotor, Puberty, Raccoon, Reproduction, Spermatogenesis The raccoon Procyon lotor is a mammal indigenous to North America that has naturalized in Japan as a result of escape from captivity and irresponsible releases since the s [ 1 ].
In Hokkaido, the northernmost island of Japan, feral raccoons have been increasing in number and spreading throughout the island [ 1 , 2 ]. An eradication program has been conducted under the Invasive Alien Species Act, which came into force in as a response to agricultural damage, adverse effects on biodiversity, and the possibility of zoonotic infection.
However, controls have not yet been successful. For effective population control, gathering basic biological information, particularly concerning reproductive characteristics in the wild, is crucial. Raccoons are promiscuous seasonal breeders. In Hokkaido, the mating season for raccoons is from January to March, and considering an approximately day gestation, litters are born between March and May [ 2 ], which is similar to the timing in North America [ 3 , 4 , 5 ].
Age at the onset of puberty is critical for determining individual lifetime reproductive success, and ultimately, age at puberty influences population growth [ 6 ]. Therefore, the timing of puberty is an essential factor affecting population growth [ 7 ]. Puberty in male animals is defined by Lincoln [ 8 ] as the period when accessory organs and secondary sexual characters develop under the influence of the testes and the animal first becomes fertile.
The timing of puberty in male raccoons varies among populations in North America. In Illinois, more than half of juveniles have the ability to produce spermatozoa during the first mating season [ 4 ]. In Alabama [ 3 ], Michigan [ 5 ] and North Dakota [ 9 ], males reach puberty during the second mating season as yearlings. Such differences might be caused by the surrounding environment, such as climate, temperature, light, and season, as well as food availability [ 11 ]; however, the timing of the onset of puberty is not known for male raccoons in Hokkaido.
We studied the timing of puberty and identified possible triggers of the onset of prepubertal development in male raccoons by examining changes in testicular developmental using both feral and captive raccoons in Hokkaido. Materials and Methods Animals We collected carcasses of feral male raccoons that were euthanized in the eradication program in west-central Hokkaido from May to March Fig. In total, male raccoons under 2 years old were employed for this study Table 1.
Raccoon carcasses were weighed, body lengths were measured, and the extrusibility of the penis was checked. The left testis was weighed, and the long diameter, short diameter and thickness were measured; the testis was then immediately fixed for about 12 h in Bouin's solution for histological observation.
The lower jaws were boiled, and then the lower canine teeth were removed for age determination.