Genetic study investigates adder declines

Researchers are investigating adder populations in southern England to see if they are suffering from genetic bottlenecking. This can occur when populations become too small, and low gene flow means they are not enriched by sharing of mutations between numerous individuals.

Most conservationists report that adders are undergoing worrying and rapid declines in Britain, probably due to multiple causes. Habitat loss, damage and fragmentation are certainly major factors that result in populations becoming small and isolated.

Adders are often impacted by scrub removal, and accidental damage such as hibernaculum destruction. As such work tends to take place during the winter while adders are hibernating, this can wipe out whole populations. Localised damage is often caused by conservation work by land managers and sanctioned by statutory bodies.

Adders are not a vagile species like the grass snake. When they undergo extinction, they rarely recover. Fragmented and isolated populations may also face genetic problems. Low genetic diversity in isolated populations can lead to 'inbreeding depression', making populations vulnerable to birth defects, low fertility, and general lack of fitness.

Researchers at the Institute of Zoology in London are working with Oxford University and Natural England to study adder populations this spring. The researchers are studying smaller populations with fewer than 10 individuals, and larger ones with 20-30 individuals.

Natural England and the other research partners are funding the fieldwork and staff costs. The laboratory costs are being funded by a £1000 grant from the British Herpetological Society. The project officer, Nigel Hand, is currently catching and swabbing adders across England. The results should tell us in due course whether the adder is at risk from inbreeding effects.