The pattern of ovulation in females and effect of food restriction on male testicular development in the South African spiny mouse (Acomys spinosissimus)

Abstract

Reproduction is the process whereby an animal ensures the continuous existence of their genes in the population by procreation. Reproduction presents a series of obstacles for both males and females. Males have to ensure they are in peak physical condition in order to establish dominance and compete for the attention of the opposite sex. Females need enough energy to support their bodily needs whilst supplying energy to the growing foetuses and suckling young. The current thesis investigated the pattern of ovulation in female as well as the effect of photoperiod and food restriction on male gonadal development in wild caught South African spiny mice (Acomys spinosissimus) from the Limpopo province in South Africa by using faecal samples to measure hormone concentrations. A novel method, using faecal samples to monitor reproductive function in Acomys spinosissimus was validated during this study. It was shown that reproductive function can reliably be monitored in both sexes using enzyme immunoassays for 17-oxo-androgens in males and 20-oxopregnanes in females, respectively. Females were randomly assigned to one of three treatments. Seven females were housed completely separated from any male stimuli and represented the control group. The two experimental groups were each made up of seven females. The separated treatment was housed in visual and olfactory contact with intact males, separated by wire mesh. The paired treatment was housed with vasectomized males, allowing full contact between the two sexes. Females from all three treatment groups underwent normal follicular development with corpora lutea of ovulation recorded for one female from the control and one female from the paired treatment. Progesterone concentrations were compared between the different treatments using faecal hormone metabolite levels. The progesterone concentrations were not affected by the different treatments; however, the day of faecal sample collection influenced progesterone levels. The findings from the ovarian histology and faecal progestagens strongly suggest a spontaneous pattern of ovulation. To investigate the effects of photoperiod and food restriction, males were randomly assigned to one of four treatment groups. The first two groups, consisting of six males each, were subjected to a 14L: 10D (LD) photoperiod. Within the LD treatment, one group was fed ad libitum (NR) whilst the other group was subjected to a 10% food restriction (R). The remaining two cohorts were subjected to the same feeding regime as mentioned above, but they were kept on a 10L: 14D (SD) photoperiod. Male spiny mice exposed to a long photoperiod had significantly greater testes volume and seminiferous tubule diameters when compared to the males exposed to a short photoperiod. Total body fat did not differ significantly when compared between the different treatments. Males exposed to the long photoperiod also had significantly higher testosterone concentrations when compared to the males exposed to the short photoperiod. Feeding regime did not have any significant effect on any of the reproductive parameters investigated in this study. During this study it was concluded that Acomys spinosissimus is a spontaneous ovulator that is strongly photoperiodic with the availability of food resources enhancing the photoperiodic effect.