Blog written by Julia Zichello and Louise Bodt. Read the full manuscript here.
The European starling is one of the most wide-spread and successful invasive avian species in the world. Their native range extends across Europe and into Western Asia. Since the mid-1800’s, there have been multiple deliberate introductions of European starlings outside of their native range. Today, there are populations of starlings on every continent except Antarctica. Starlings are aggressive birds which travel sometimes in massive undulating flocks called murmurations. These birds are ubiquitous, industrious and downright hated. They destroy agricultural crops, spread diseases to livestock, fly into aircrafts and outcompete native birds. And yet, their outsized ability to establish and expand in novel environments, cannot — from an ecological or evolutionary perspective — be ignored.
Although there has been research investigating some of these invasive populations, our new dataset from North American starlings, combined with existing datasets from Australia, South Africa and the UK, allows us to compare mitochondrial diversity of starling populations across multiple continental distributions.
The story of the European starling in North America starts in 1890. Approximately 100 birds were brought to New York City’s Central Park between 1890 and 1891 by Eugene Schieffelin. This was part of an initiative by the American Acclimatization Society to bring all birds mentioned in Shakespeare to the US. The starling is mentioned only once in Shakespeare’s Henry IV. And over the last 130 years the starling population in North America has exceeded 200 million, over one-third of the global population. Several other introductions of starlings occurred in Australia and New Zealand in the mid-1800’s, in South Africa in the late 1800’s and in Venezuela and Argentina in the mid- to late-1900’s. These populations persist today and some continue to expand. These misguided introductions were undoubtedly ecologically destructive, and yet because of the scale, persistence, and repeatability they demonstrate, there is certainly a great deal to learn from these unfortunate experiments.
Here, we have presented the most geographically widespread analysis of starling population genetics to date. Our sampling from the United States (tissue samples provided from the USDA) combined with the existing datasets from Australia and South Africa and the native range allow us to compare genetic diversity and population dynamics among continents. We found that the US population shows signs that it is currently expanding, but does not show signs of any population structure. The lack of population structure could be due to the flexible patterns of seasonal migration that are exhibited in the North American population.
Additionally, the three invasive populations share only one mitochondrial haplotype with each other (see Venn diagram). This is consistent with three independent sub-samples of the mitochondrial diversity of the original native range. We also found that the mitochondrial diversity of the invasive populations in Australia, South Africa and the US are lower than that of the native range, as expected due to founder effects. However, this contributes to a broader understanding of how low genetic diversity is sometimes not an obstacle for evolutionary success (as has often been thought). Instead, perhaps behavioral and ecological plasticity are more primary factors in a species’ successful establishment in a new environment.
Invasive species offer a window into evolutionary processes over short timescales. The starling shows what can happen when a species is introduced to contrasting environments and independent populations are established from different founders. Because European starling invasions span multiple continents, comparisons of these populations can inform how subtle differences in founder populations and expansion rates affect present day patterns of diversity. The climatic variation across the different invasive regions here also provides another powerful variable to explore. Furthermore, studying a species with such a wide distribution across heterogenous environments (both ecologically and politically) has implications for conservation and invasive species management.
Birdwatchers leave them off their lists, ornithologists and farmers scoff at them and they present intricate and costly ecological challenges wherever they go. But they are — for better or worse— here, there and almost everywhere. Our paper represents intriguing insights into what the multiple European starling invasions across the world reveal about evolution and adaptive changes, and we will be engaging in future research on this unique, troublesome and complex avian system. Because, what is it about European starlings that made them such successful invaders again and again and again? That, is the question.