ZSL

Written by Jenny Tse-Leon, Head of Conservation & Impact, Froglife

A new study published today by ZSL’s Institute of Zoology, the University of Cambridge and Froglife highlights important implications for conservation of translocating adders. 

Researchers studying an adder population in eastern England found that a population formed by the release of seven individuals managed to establish a population despite low genetic diversity – although there may have been an additional, unlicenced translocation at a later date. DNA samples found the genetic signature of the translocated snakes in the population, indicating that the translocation has been successful over the long term. However, there was also evidence of reduced genetic diversity, likely due to the small number of animals involved in the translocation.

The study was initiated after the 2015 discovery of a stillborn clutch of five adders still in their amniotic sac, raising the question of inbreeding in the population. Genetics samples of the stillborn clutch were collected as part of the Garden Wildlife Health project, a national wildlife disease surveillance scheme.

Analysis found that the clutch sampled was likely fathered by more than one male. However, the reasons behind stillbirth could still be genetic, as well as environmental maternal effects.

Despite being given some protection by the Wildlife and Countryside Act, adders can still be moved to new sites (translocated) without the need for this to be recorded or monitored – meaning very little is known about its impacts on adders. The population in this study was known to come from the introduction of seven adders from a development site 20km away, eighteen years previously, to a reserve now managed by Froglife.  This provided a rare opportunity to study the impacts of a small translocation on the resulting population – making it one of few, long-term genetic based studies following an adder translocation.  

Adder populations in the UK are severely declining, particularly small populations, due to habitat loss, habitat fragmentation, human disturbance and consequentially inbreeding as populations become increasingly isolated.  While misconceptions about adders have led to their persecution, these snakes are not dangerous if left alone and are an important and culturally relevant part of the UK’s natural heritage.

Professor Trent Garner, researcher as ZSL’s Institute of Zoology said: “Adders are declining in numbers across Western Europe, and we need a better understanding how translocations could be used to reverse these declines and restore their numbers. Population genetics can be used to understand the more long term outcomes of translocations in terms of reproduction and population growth. Careful management and ongoing monitoring are key to ensuring future populations are genetically healthy and able to grow and flourish.”

Since managing the reserve, Froglife has carried out annual reptile surveys showing a supposedly healthy and likely expanding population resulting from this translocation.  This study found however that the adder population has a low genetic diversity in comparison with published data from similar sized adder populations which is typical for a bottleneck in the population history.  The cause of the stillbirth clutch might have been a result of maternal fitness, which could either be a result of inbreeding or another factor such as disturbance from dog walkers, mountain bikers and trampling of vegetation.  Whatever the reason, female adders often have only one litter in their lifetime, so the loss of the whole clutch can have a significant genetic and demographic impact on a population, especially an isolated population with low genetic diversity.  In this study the loss of four females in the clutch is significant in a population already showing a relatively low proportions of females.  It highlights the need for protection of small populations in particular and ensuring connectivity between different populations.

“The discovery of a clutch of stillborn adders was very worrying however the outcomes of the research are reassuring for this population. The study shows the value of long-term monitoring and the need for ongoing funding to enable this to happen. It would also not have been possible without the support of our committed volunteers.” Jenny Tse-Leon, Head of Conservation and Impact at Froglife.