What dynamics act in animal migrations and parasitic infections?

Newswise — Whether to find food, reproduce, reduce competition, escape predators or escape winter, migration is a survival mechanism for many animal species.  

Whether it is a mammal, a bird, a fish or an insect, the migrating animal is exposed to parasites in the habitats it frequents while being able to limit the risks of infection for itself and for its congeners. 

In order to establish the dynamics at work in parasitic migrations and infections, Professor Sandra Binning, from the Department of Biological Sciences at the University of Montreal, and her colleague Allison Shaw, from the University of Minnesota, carried out a review of empirical studies on the subject to then create a model that makes it possible to understand parasitic infections resulting from the migratory behaviors of certain species.

The fruit of their work, in which doctoral student Marie Levet from UdeM took part, was recently published in the journal Ecology Letters .

Migration in decline

The diversity and inherent complexity of migratory behaviors and their indispensable role in the ecology and survival of many species have been widely studied. However, animal migration is decreasing globally due to climate change and the destruction of many natural environments. 

“Solutions to mitigate these losses are clear – increasing environmental protection, maintaining ecological connectivity and reducing deforestation for example – but in many cases we lack data on the factors that promote or hinder migratory behavior in the first place,” explains Sandra Binning.

More or less virulent parasitic infections depending on migrations

Working together for 10 years, Sandra Binning and Allison Shaw have developed different theories about salvage migration – which can lead to recovery from parasitic infection – and how parasites can influence migration itself. 

And the review of studies that they carried out with the support of Marie Levet allowed them to make certain observations.  

“On the one hand, the majority of studies focus on the purpose of migration – such as reproduction or wintering – but they neglect the transit phases, although they are essential elements of the dynamics of migration. infection during host movements,” says Sandra Binning. 

On the other hand, they noted that there is a diversity of results depending on the studies. 

“In some cases, the intensity of infection in migrants is greater or less than that in non-migrating individuals of the same species, while in others it may be greater or less severe at as individuals migrate,” adds the field research expert.

Different types of migratory behavior

The review of studies revealed a wide diversity of migratory behaviors linked to parasites, some over long distances, others over shorter distances.  

These behaviors have been grouped into three main categories: scavenging migration, escape migration and elimination migration.  

Salvage migration allows the animal to recover from an existing infection, while in escape migration it leaves a contaminated environment. 

“For example, among large deer in Europe and North America, we see that they head towards more northern latitudes during the summer, which allows them to escape ticks that take up residence in the environments further south, or they move towards higher altitudes,” illustrates Sandra Binning. 

In the case of elimination migration, the individual is so infected that it cannot reach its destination, thus protecting other individuals of its species from contamination. 

The researchers also revealed a taxonomic bias in research in this area.  

“Mammals and birds are over-represented in studies compared to fish, reptiles and insects – which are much more numerous to migrate and whose migratory behavior has been little studied, with the exception of monarch butterflies,” continues Sandra Binning.  

She says it’s important to learn more about insect migrations because of the vital role they play in the food chain.

A predictive model to understand migration disruptions

The researchers thus developed a unified evolutionary model based on the data from their study review.  

“Our model combines mathematics and biology and is based on a more complex ecological approach, which notably integrates the distance traveled during migration, the intensity of parasite infection throughout migration and the number of individuals who do not migrate,” says Sandra Binning. 

Because it captures the complexity of movement patterns observed across a range of migratory species, this model “will be particularly useful to scientists who wish to more quickly predict changes in migratory movements, disease, and the changing environmental conditions we face.” we are increasingly confronted with,” she concludes.