Effect of photoperiod on the breeding season of the marsupial possum Trichosurus vulpetula

Abstract

The production of young by three groups of eight possums, housed in a natural, a short-day (10 h light:14 h dark) and a long-day (14 h light:10 h dark) photoperiod was monitored for 24 months to determine the role of photoperiod on the occurrence and duration of the breeding season. Possums were housed in each of the three light regimens on 22 November. The possum has a gestation duration of 17.5 days. Removal of the newborn young leads to ovulation approximately 9 days later and birth 26 days later. Repeated removal of pouch young was used to determine the duration of the breeding season. Possums in a natural photoperiod showed two breeding seasons for the 2 year observation, from March to October of each year. Over the same 2 year period, there were three breeding periods in possums in short-day and long-day photoperiod. A comparison of the timing of the first breeding season showed that short-day photoperiod brought the breeding season forward by 2 months and long-day photoperiod delayed it by 2.5 months. The total number of months in which births occurred was the same for natural and short-day photoperiod (16 out of 24 months) and less for long-day photoperiod (11 months). Fertility in the three groups was also examined. Within each group, there was no change in fertility with consecutive seasons. However, fertility, whether expressed as births per possum per month for each breeding period or births per possum for the total observation period, was higher (P < 0.05) in possums in natural photoperiod (total of 9.0 ± 1.2 births per possum) than in short-day (6.5 ± 1.9 births per possum) or long-day (3.8 ± 1.2 births per possum) photoperiod. It was concluded that photoperiod is important in the timing of breeding season, in the fertility of breeding possums and, possibly, in the duration of breeding seasons, but that it does not determine the occurrence of the breeding season.