World's smallest primates live longer than thought

Mouse lemurs, the world's smallest primates that weigh a mere 30 to 80 grams, can live at least eight years in the wild - twice as long as some previous estimates, a new long-term study has found.
The research on brown mouse lemurs (Microcebus rufus) was led in Madagascar by biologist Sarah Zohdy, a post-doctoral fellow in Emory's Department of Environmental Sciences and the Rollins School of Public Health.
"It's surprising that these tiny, mouse-sized primates, living in a jungle full of predators that probably consider them a bite-sized snack, can live so long," said Zohdy, who conducted the research while she was a doctoral student at the University of Helsinki.

"And we found individuals up to eight years of age in the wild with no physical symptoms of senescence like some captive mouse lemurs start getting by the age of four," Zohdy said.
It is likely that starvation, predation, disease and other environmental stressors reduce the observed rate of senescence in the wild, Zohdy noted, but a growing body of evidence also suggests that captive conditions may affect mental and physical function.
The study determined ages of wild mouse lemurs in Madagascar's Ranomafana National Park through a dental mold method that had not previously been used with small mammals.

In addition to the high-resolution tooth-wear analysis for ageing, fecal samples underwent hormone analysis.

The researchers found no difference between the longevity of male and female mouse lemurs, unlike most vertebrates where males tend to die first.
"And even more interestingly, we found no difference in testosterone levels between males and females," Zohdy said.
"While elevated male testosterone levels have been implicated in shorter lifespans in several species, this is one of the first studies to show equivalent testosterone levels accompanying equivalent lifespans," Zohdy said.
Mouse lemurs in captivity live six times longer than mammals of similar body size, such as mice or shrews. Captive gray mouse lemurs (Microcebus murinus) can live beyond age 12. By age four, however, they can start exhibiting behavioural and neurologic degeneration.

In addition to slowing of motor skills and activity levels, reduced memory capacity and sense of smell, the captive four-year-olds can start developing gray hair and cataracts, Zohdy said.
The wild brown mouse lemurs in the study were trapped, marked and released during the years 2003 to 2010. A total of 420 dental impressions were taken from the lower-right mandibular tooth rows of 189 unique individuals. Over the course of seven years, 270 age estimates were calculated.
"We found that wild brown mouse lemurs can live at least eight years. In the population that we studied, 16 per cent lived beyond four years of age. And we found no physical signs of senescence, such as graying hair or cataracts, in any wild individual," Zohdy said.

The study is published in the journal PLOS ONE.