Sex and age-biased nematode prevalence in reptiles
Rising testosterone levels in male slow worms at breeding season may make them more susceptible to infections, say NERC-funded scientists.
The study, published in Molecular Ecology, looked into whether nematodes – parasites like roundworms - affect more male or more female slow worms.
They found that more male slow worms contracted the parasite overall, and that this was even higher during the breeding season – the first example of testosterone suppressing a slow worm's immune system.
'Slow worms are a common reptile in the UK, but there's not many studies so we don't know much about them,' says Dr David Brown of Cardiff University, lead researcher on the study.
The team had been looking into the slow worms' diet using molecular tools to analyse the animals faeces for DNA to determine which species they'd been eating. During this study they noticed that there were also lots of parasitic worms in the faeces.
'If you're not a taxonomist it's really difficult to identify parasitic species as many of them look very similar so we wanted to prove we could develop a tool to make screening or monitoring parasitism in species easier,' Brown says.
'I collected the faecal samples for the diet study by pulsating the animal until it defecated in my hand. Using DNA analysis to investigate diet is quite a cheap, simple, non-invasive process so I wondered if I could use it to look at parasitism as well,' he says.
Testosterone is known to act as an immunosuppressant, so the team were expecting to find that the males were more susceptible to the parasite. But they were surprised to find that the samples collected in April had more parasites than those collected later in the year.
'The samples collected later on had more equal numbers of parasites between the males and females,' explains Brown. 'April is their breeding season so the theory is that during breeding season the slow worms have more testosterone, which can surpress their immune system and make the animal more susceptible.'
While nematodes are known to be a parasite the researchers aren't sure what damage they cause to the worms during breeding season.
'The larger, older slow worms are less likely to have the parasite. This is either because they've built up immunity or because the parasite is killing them and removing them from the population so we're not finding them. If the latter is the case then it suggests longer term detriment, but this study can't confirm that,' says Brown.
The team are now hoping to study a different species of nematode that also affects the slow worm to better understand the relationship between the two types of parasite and find out if contracting one makes the animal more likely to contract the other.
This story is republished courtesy of Planet Earth online, a free, companion website to the award-winning magazine Planet Earth published and funded by the Natural Environment Research Council (NERC).