Return of the elephants seals: From a few to thousands

At the start of the 20th century, northern elephant seals were on the brink of being wiped out by hunting. ‘Genetic analyses suggest that the population was likely reduced to fewer than 25 animals at that time,’ explains Professor Dr Joseph Hoffman, lead author of the study and head of the Evolutionary Population Genetics group at Bielefeld University. Such drastic population declines can squeeze out a species’ genetic diversity, increasing the risk of inbreeding and threatening its survival. The population of northern elephant seals has since recovered to around 225,000 individuals. The study published in the journal ‘Nature Ecology and Evolution’ examines how this near-extinction event impacted the species’ genetic diversity and health.

Adaptability at risk

For their analyses, the researchers combined genetic data, health records, modelling of population sizes and genetic simulations. Their findings suggest that the severe population decline led to the loss of many beneficial and harmful genes from the northern elephant seal’s gene pool. This pattern was not observed in the closely related southern elephant seal, which did not experience such a drastic decline.

‘The highly reduced genetic diversity, including the loss of beneficial gene copies, may impair the ability of northern elephant seals to cope with future environmental changes, including those caused by anthropogenic climate change, changes to the species’ habitat, or even natural threats such as disease outbreaks,’ warns Professor Dr Kanchon K. Dasmahapatra from the University of York, UK, who is the senior author of the study.

Surprising results on inbreeding

All individuals of a species carry some harmful mutations, though their effects are usually hidden. However, inbred individuals may face health issues as these mutations become exposed. ‘We looked at several key health traits in these seals, including body weight, blubber thickness and disease susceptibility. To our surprise, we found no signs of health problems related to inbreeding,’ Joseph Hoffman says. ‘We believe the severe population decline may have eliminated many harmful mutations.’

Significance for species conservation

‘Our study illustrates how a species’ unique population history shapes its genetic diversity,’ says Dasmahapatra. The findings offer important insights for species conservation and ecosystem management. Hoffman adds: ‘Our research underscores the importance of understanding a species’ history when planning conservation strategies. Each species responds differently to threats, so individualized approaches are essential.’