An annual, three-week frenzy of non-stop sexual activity without eating is connected to shorter lives and degraded bodies in male garter snakes, a University of Sydney-led study has shown.

While the males invest tremendous energy in this process, which involves thousands of snakes at a time, females spend just a few days at the mating site, before they slither off to feed after months of hibernation.

While these divergent sex strategies are not new to scientists, the connection they have with cellular and genetic health is now more clearly understood.

The researchers found a correlation between the stressful male reproductive strategy and a shortening of their telomeres, which are protective DNA caps at the end of chromosomes.

The females studied, in Manitoba, Canada, live longer, maintain healthier bodies and grow about 30 per cent longer on average than males.

"Males experience greater telomere loss with age due to prioritisation of current reproduction over cellular maintenance and longevity," said the study, which was published on Wednesday in Proceedings B of the Royal Society.

Research into telomere length in humans suggests some correlation with ageing and disease risks, including for some cancers and multiple sclerosis. 

Christopher Friesen, an author of the study from the University of Sydney, said: "We really don't know if shortened telomeres cause disease states or if they are a by-product of disease and ageing.

"The more we study different species, then we can start understanding what telomeres really do."

Beata Ujvari is a senior lecturer in biology at Deakin University, whose work on Northern Territory water pythons was cited in the Sydney University study. She was "cautious to generalise the findings to other species", but agreed that "stress levels potentially increase telomere attrition".

She said that the study was important for understanding species survival in challenging environments as climate change accelerates.

The red-sided garter snakes live in an extremely cold environment. After emerging from eight months' hibernation during the bitter Canadian winters, the males form huge "mating aggregates" of thousands of snakes.

The study says: "Courtship [is] energetically expensive and males may lose 10 per cent of body mass during weeks of mate-searching, courtship and mating."

Dr Friesen said: "Because of the pattern of emerging from hibernation, the males come out first and stay for longer," typically up to three weeks, he said.

"The males are really stressed out. They are fasting during their most energetically expensive task. It would be like someone running several marathons in a row without eating," he said.

The images of thousands of writhing snakes are no doubt unsettling to some, but Dr Friesen said the animals are completely harmless - "they're like cute little puppies", he said.

"You worry about hurting them, the males are so out of it searching for females they don't even notice you until you're foot is right there."

The males gather as each female emerges from hibernation, attracted by her pheromones.

"A single female can have up to 100 males trying to mate with her," Dr Friesen said.

The researchers thought that such widely different reproductive strategies would be reflected in different telomere lengths, and they were right.

"There are statistically significant difference in total telomere length between the sexes," Dr Friesen said.

"Females sustain that length over time as the male's diminish. This suggests females are actually spending energy to maintain telomere length."

As females get older, they get bigger and their litter size increase. Dr Friesen said that this means evolution is going to select for females to live longer so they can get the pay-off of larger litters, up to 40 or 50 snakes. 

Dr Friesen said if their hypothesis is right then they should see differences in garter snake populations further south.

"Where aggregates are smaller and winters shorter, we should see males living longer and their telomeres not shortening as much," he said.

"Now we need to go out and validate this with other populations to see if our hypothesis stands up to scrutiny."