Some aspects of the reproduction, growth and development of the rice field rat, rattus argentiventer Robinson & Kloss ( rodentia: muridae)
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Date
1979-08
Authors
Yuet Ming, Lam
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Abstract
Studies on the rise field rat R.• argentiventer were carried
out in the double-dropped (Bumbong Lima, Bukit Merah, Permatang Pasir)
and the single-cropped (Kota Kuala Muda) rice fields. Its population
structure varied considerably throughout the year, greatly influenced
by the state of the crop and this was observed to be more pronounced
in the single cropped area. On the average females were caught more
frequently than males in the ratio, male to female, 1 t 1. 78. Young
rats predominate during and after the breeding seasons. Studies on
the reproductive conditions of males and females showed that the weight
of the rats on attaining sexual maturity was 140 gm (corresponding .
HBL-class 175 mm) and 60 gm (HBL-class 125 mm) for males and females,
respectively. Males in the single-cropped area attained a greater
size upon sexual maturity when compared to those of the double-cropped
areas but this difference was not observed in the females.
Reproduction of argentiventer was sharply bimodal in the
double-cropped rice fields and unimodal in the single-cropped rice field.
The breeding season was found to correspond very closely with the
reproductive and ripening phases of the paddy during which litters
were produced. The mean number of embryos per female was 11.04 and
12.50 in the double· 8lld single-cropped ar~as, respectively. Intra-uterine
mortality was 2.92 per cent in the double-cropped areas and 1.55 per
cent in the single-cropped area. The number of ova ovulated, number
of embryos and litter size were found to be positively correlated to
the size of the female. The distribution of embryos between the two
horns of the uterus were equal with no marked tendency for all to
develop on one side. Mean litter size was 10.33 and 10.38 in the
double and single-cropped areas, respectively. The most common litter
size in the doublepped areas was 9 and the more common litter
sizes in the single-cropped area were 11 and 12. The sex ratio in
litters from the double-cropped areas, male to female, was 1. : 1.41
and in the single-cropped area 1.04 : 1.
In the rice fields !• argentiventer was found to be r-selectecl,
typified by high reproductive rate, large litter size, early sexual
maturity and short life-span of usually less than a year. Tl\e
reproductive JOtential of females in the double-cropped areas .was
estimated to be 4. 9 times that of the single-cropped area and in the
double-cropped areas productivity was 81 young per female per year
compared ~ 17 in the single-cropped area.
Reproduction, growth and development of !.• argentiventer was
studied in the laboratory. Females were polyoestrous and bred throughout
the year.. The oestrous cycle was 4. 3 days and females exhibited pOStpartum
oestrus. Mean gestation period was 21.4 days. Mean litter size
was 7 and the sex ratio, male to female, was 1.09 : 1. The litter size
increased initially up to the 4th litter after which it declined gradually.
The average number of litters per female per year was 7 and mean number
of young per female per year was 50. Birth of the young was by head
or breech delivery.
~re-natal and post-natal growth and development of the young
was studied. Embryos were visible on the 6th day of gestation and
pregnancy could be determined by palpation on the 9th day. Growth
of the embryo was most rapid from 15-21 days gestation and embryos
could be sexed by anogenital distance from 18 days gestation onwards.
There was sexual dimorphism in the size of the young at birth and
subsequent growth and sexual maturity. Morphological and behavioural
changes were described from birth till 60 days of age. Males have
scrotal testes starting at 26 days of age but only became sexually
mature at 90 days old. Females have perforated vagina at a mean age
of 33 days and could conceive at a mean age of 49 days.
Growth characteristics of males and females were described
from birth to 24 months of age. Both male and female exhibited the
greatest growth (mm/day) in the first month after birth and the greatest
weight gain (gm/day) in the first two months after birth. A model·
for the growth of males and females in the laboratory from 1-44 weeks
was developed.
Description
Keywords
Rattus argentiventer Robinson & Kloss , (Rodentia: muridae)