Female wallabies' presence sends males' testosterone soaring

London, April 16 (ANI): It's the presence of fertile females, not the season, that sends testosterone in male tammar wallabies soaring, a new study has found.

In the study, Marilyn Renfree of the University of Melbourne, Australia, and colleagues induced female tammar wallabies to come on heat out of season, and found males still experienced testosterone surges.

Adult female tammar wallabies mate once a year - at the end of January, just hours after giving birth. The fertilised embryo then lies dormant for months while the female lactates and tends to her current baby.

The embryo's development is reactivated in December, and as soon as it's born, the race to mate is on once more as oestrogen surges through the females for a few hours, making them highly receptive to male advances.

The female reproductive cycle is controlled during the first half of the year by suckling young, and in the second half by the hormone melatonin, which responds to the changing light levels of the seasons.

If young are removed from their pouch in the first half of the year or females are injected with melatonin in the second half, embryonic development restarts out of season.

Using both techniques, the researchers housed males with females primed to give birth out of season. Another group of males were housed with pregnant females due to give birth at the normal time.

By measuring blood testosterone levels in the males over breeding and non-breeding seasons, the researchers found that the hormone began increasing late in female pregnancy, with levels peaking just after birth, regardless of the time of year.

"This confirms that the male's reproductive state is dependent on a signal from females and it is not blocked through seasonal effects," New Scientist quoted Renfree as saying.

The signals could be 'a pheromone that the females are releasing, which could be from the urine, or pouch secretions, or both," she said, because 'males actively sniff the urogenital opening and the pouch of the expectant mothers'.

However, when the researchers presented male wallabies with swabs from the urogenital opening of females, some on heat, others off, to see which they preferred, the results were inconclusive.

The study has been published in the Journal Hormones and Behaviour. (ANI)