Pregnancy Rate and Conception Date in a Wild Population of Japanese Monkeys

Abstract

ABSTRACT. This study is the first to determine the conception dates of specific individuals and estimate the pregnancy rate of a wild population in Japanese monkeys. The conception dates estimated from the embryonic ages of 37 fetuses were distributed over 128 days between September 17 and January 23, with a mean conception date of November 19 (SD=29.2 days). A comparison of the mean conception dates among age groups showed a significantly delayed conception in the subadult animals (aged 4 to 5 years; December 5, n=8) than in the adult animals (aged 6 or more years; November 15, n=29; P<0.03). The mean pregnancy rate among animals aged 4 years or more in this local population was estimated to be 48.5% (32/66).

Small head size and delayed body weight growth in wild Japanese monkey fetuses after the Fukushima Daiichi nuclear disaster

“…Japanese monkeys in Fukushima City first conceive in fall when they were five years old and gave birth in spring when they were six years old 17 . Thus, we assumed that all the mothers we examined that conceived babies after the NPP disaster were continuously exposed to radiation from at the time of the disaster in 2011.…”

“…The Japanese monkeys in Fukushima City were seasonal breeders that bear young in March and April 17 . Accordingly, the fetuses collected in 2011 were almost fully developed at time of the NPP disaster.…”

“…Our research group studied the reproductive and nutritional status of the Japanese monkey population by performing autopsies on individuals captured and euthanized by Fukushima City 17 . These Japanese monkeys were the first wild primate population exposed to radiation as result of nuclear disaster.…”

Concentration of Radiocesium in the Wild Japanese Monkey (Macaca fuscata) over the First 15 Months after the Fukushima Daiichi Nuclear Disaster

“…They feed mainly on plant leaves and fruits, but also eat insects and other small animals [10]. In the Japanese monkey populations of Fukushima Prefecture, females aged 6 years or more give birth in the spring, with a birth rate of about 50% in adult females [11].…”

Low blood cell counts in wild Japanese monkeys after the Fukushima Daiichi nuclear disaster

“…The Japanese monkey, which is endemic to Japan, has a life span of more than 20 years3. In Japanese monkey populations in Fukushima City, adult females aged 5 years or higher are pregnant in the late fall and give birth in the spring4.…”