An international team of scientists led by the University of Sydney has confirmed a frenzied approach to the mating season is resulting in males ageing faster and dying earlier and in worse condition than their female counterparts, who prioritise body-maintenance over short-term reproductive success.
In the study population of red-sided garter snakes in North America:
- males undertake energetically expensive mating for 2-4 weeks a year;
- males don't eat and must compete with thousands of other males during the mating season;
- females stay at the orgy site for as little as one day, compared with up to 21 days for males; and
- snakes hibernate underground for eight months in their communal dens and emerge en masse in spring, to form large aggregations where males scramble to locate and mate with females.
The research is published today in the Royal Society journal Proceedings B.
The study measured telomere length, which is a biomarker of ageing, in male and female snakes. The team found that males are unable to maintain good body condition, and age faster than females. This is probably because males spend their energy on mating, instead of protecting against DNA and cellular damage associated with ageing. In contrast, females prioritise body condition and may be better able to repair cellular damage, leading to longer lives and future opportunities to reproduce.
Senior author at the University of Sydney Dr Christopher R Friesen, explained that the snakes made good use of the relatively short amount of time to procreate, having only four months a year to breed, feed and have babies.
"Although we believe that all females mate every year, they only stay at the den sites (where mating takes place) for a short period of one- to three days; much less than males, who remain for at least a week and up to 21 days, which seems to result in males ageing faster and dying earlier than females" Dr Friesen said.
"Females reproduce every other year, which depends on their stored fat/energy reserves. Our previous research has shown that females can store sperm for up to 15 months or more before she uses the sperm to fertilise her eggs!"
The paper reported: "The relationship between body condition and age differed strikingly between sexes, with females maintaining their body condition with age, while condition decreased with age in males."
In addition to prioritising self-preservation over sex, the female garter snakes studied in Manitoba, Canada, did not waste energy on looking after their babies postnatally, which is in line with the parenting approach of other snakes.
University of Sydney co-authors at the School of Life and Environmental Sciences are Dr Friesen, Nicky Rollings and Dr Camilla Whittington (Sydney School of Veterinary Science). Other researchers comprise: Prof Mats Olsson, Goteborgs Universitet; Prof Robert Mason, Oregon State University; Assoc Prof Heather Waye, University of Minnesota at Morris; Assoc Prof Randolf Krohmer, Saint Xavier University and Dr Emily Uhrig, Linköping University.
The paper, "Age-related sex differences in body condition and telomere dynamics of red-sided garter snakes", will be published in Proceedings B on 5 April 2017 at 0:01 GMT / 10:01am Australian Eastern Standard Time (AEST). URL after publication: http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2016.2146
University of Sydney web story – including video (will be live once the embargo lifts): http://sydney.edu.au/news-opinion/news/2017/04/05/sex-obsession-a-killer-for-male-snakes–research-footage-shows.html
YouTube video at https://www.youtube.com/embed/vPomv9iXtik
HIGH DEFINITION VIDEO/FOOTAGE available on request
Notes to Editors (additional research findings)
- Females reach sexual maturity at three years of age, while males are sexually mature at one or two years.
- Age and sex predicted body size: older animals were longer and females were significantly longer than males of the same age
- The results support the researchers' prediction that males experience greater telomere loss with age due to prioritisation of current reproduction over cellular maintenance and longevity. Overall, the decrease in both body condition and telomere length in males with age suggests that they senesce at an earlier age than females.