Fruit-eating lemurs are one of the most important dispersers of seeds in Madagascar. But at least 17 species of Malagasy lemurs have gone extinct within the past few thousand years. According to a comprehensive new study published in Proceedings of the National Academy of Sciences this week, the extinction of lemurs would have huge negative effects on the health of Madagascar’s forests.
Having been isolated for so long, the island of Madagascar is home to a huge diversity of animals that aren’t found elsewhere. Lemurs have a variety of feeding strategies, and the fruit eaters (or frugivores) among them have complex relationships with native plants. Previous work with radiocarbon dating revealed that the majority of giant lemurs went extinct after human activity intensified on the island around 1,700 years ago. Based on tooth morphology, dental wear, and isotope analyses, researchers know that many of these extinct lemur lineages played important seed-dispersing roles. And all of them were much bigger than the lemurs we have today.
To investigate the evolutionary history of diet in Madagascar’s lemurs, Yale’s Sarah Federman and colleagues analyzed genomic data, gape sizes, and dietary strategies of living and extinct lemurs, as well as the effects those losses had on plant survival. They found that the extinction of large-bodied lemurs significantly decreased the number of large-seed dispersers in Madagascar.
The team also identified several "orphaned" large-seeded plants: These don’t have any animal dispersers anymore, and their seeds were likely consumed and spread by extinct lemurs. The evolutionary trend toward larger seeds – which may have once contributed to the success of these Malagasy trees – may now expedite their decline. The plants persist for now thanks to their long generation times and seed dispersal by rodents and strong winds during cyclones. However, since large lemurs are more efficient seed dispersers, the long-term survival of these plants are in danger.
Furthermore, the researchers also identified lemur species alive today that occupy dispersal niches that are both unique and essential. Several of them are critically endangered species, such as the black-and-white ruffed lemur (Varecia variegata) pictured below. To enjoy the large seeds of Canarium trees (pictured to the right), they hold the fruit in their cheeks and use the cusps of their teeth to scrape the flesh off before swallowing it whole. The seeds are subsequently passed during the course of the lemurs' daily movements. Dispersing away from the parent trees enhances gene flow and reduces competition among related individuals, and the extinction of these lemurs would jeopardize the future of large-seeded plant lineages.
A black-and-white ruffed lemur (Varecia variegata). Sarah Federman
Image in the text: Canarium fruit. Sarah Federman