In research significant for endangered marsupial breeding programs, researchers have found that the healthier a female wallaby, the more likely she is to have a son.

According to research led by postdoctoral fellow Dr Kylie Robert at The University of Western Australia's School of Animal Biology, less robust female wallaby mothers are more likely to have daughters.

Published recently online in the Royal Society's journal Biology Letters, Dr Robert's project, in which her team worked with 32 tammar wallaby mothers from Tutanning Nature Reserve, shows that the sex of offspring depends on the health of mothers.

Dr Robert suggests this could be because stronger males have more mating success, while females will be mated regardless of their condition.  After swapping the wallaby babies that were less than 100 days old -  so that mothers birthing sons raised daughters and vice-versa, and keeping a control group of mothers raising their own offspring - the researchers monitored the wallabies for more than a year.

"All cross-fostering was performed with offspring of equivalent developmental stages to avoid problems owing to changes in milk composition over the course of lactation," Dr Robert said.

"After the cross-fostering, the females were transported to UWA's Native Animal Facility, where, before being released into their new enclosures, the females were examined to ensure the pouch young had successfully reattached to the teat."

"We measured offspring survival and body size at weaning and maternal body mass and condition over the course of lactation."

The study is important for breeding programs as animals bred in captivity are usually in good condition and therefore most often produce males.

"If we could uncover the physiological signals that prompt the birth of a male or a female we could optimise the sex ratio for successful breeding programs," Dr Robert said. 

Media references

Dr Kylie Robert  (+61 4) 47 898 864
Janine MacDonald (UWA Public Affairs)  (+61 8)  6488 5563 / (+61 4) 32 637 716