The characteristics of highly effective parasites

Song Thrush

The Song Thrush was one species that likely brought avian malaria parasites to New Zealand when it was introduced from Europe over 100 years ago. Credit: Rohan Clarke

Biologists have documented, for the first time, the traits that allow parasites, which can have devastating impacts on native wildlife populations, to successfully invade new lands and species.

In research published today in the journal Ecology Letters, scientists from Monash University, The Zoological Society of London, The University of Adelaide and a number of universities in Europe, looked at thriving bird malaria parasites in New Zealand to determine their origins and the characteristics that led to their success. 

Over three summers, the researchers collected small samples from various native and introduced birds across northern New Zealand and screened the DNA from each sample for avian malaria parasites. Further molecular detective work allowed the individual strains of avian malaria to be identified with certainty and compared to a global database of all known avian malaria parasites.

Results showed that the most successful invaders were generalists - able to infect a broad range of host species and exist in a variety of geographical conditions in their native range. They were also found to be very common in hosts in their native range.

This combination of traits allowed parasites to hitch a ride with their hosts, survive the move within the host to the new land, spread to exotic species and thrive in new conditions.

Dr Rohan Clarke of Monash University's School of Biological Sciences said the study filled a gap in knowledge at a time when the spread of exotic species, including parasites, to new areas increasingly threatened biodiversity. 

"There has been remarkably little research into avian malaria in Australia and New Zealand, yet these findings demonstrate the potential to provide insight into the spread and establishment of parasites that is of global significance," Dr Clarke said. 

Lead author Dr John Ewen of the Zoological Society of London said results would be helpful in understanding how parasites spread, with often destructive consequences.

"These findings will help us understand the what, when and how of exotic parasite introductions globally," Dr Ewen said. 

Dr Clarke said New Zealand was an ideal location for the study because it has an extensive history of human facilitated bird introductions from Europe.

“By comparing parasite strains collected in New Zealand with those in the global database we were able, for the first time, to test hypotheses about both the origins and characteristics of successful invaders,” Dr Clarke said.