Anna Kearns with a specimen of the Cormorant from the American Museum of Natural History.
In the 1930s, renowned biologist Ernst Mayr became the first person to study Pacific Cormorants. He has made extensive records of the physical characteristics, behaviors and habitats of cormorants and other birds on Australia and its surrounding islands, proposing some basic concepts that could inform evolutionary research. Although there are significant differences between the islands, Mayr believes that the cormorants belong to the same species. Ernst Mayr has made great contributions to evolutionary biology, but like most scientists, he has had his own mistakes.
Anna Kearns of the Smithsonian Institution's Institute of Conservation Biology, a postdoc at the University of Maryland at Baltimore (UMBC), worked with co-supervisor Kevin Omland and colleagues to re-examine the relationship between Pacific cormorants on different islands using bird specimens that Mayr had used. The difference in this study is that Mayr mainly compared specimens "with the eyes", while Kearns used techniques such as DNA sequencing and spectrophotometry to quantitatively compare the feather color, brightness and saturation of birds, thus gaining a better understanding of the relationship between different island cormorants.
In a 2015 paper published in Conservation Genetics, Kearns noted that the cormorant, which lives on Norfolk Island, just east of Australia, is a separate species, while a new paper published this month in the Journal of Ornithology reports two other new species — one in the Solomon Islands and Bougainville, and the other in Fiji, Vanuatu and Samoa.
The new study shows that much about the biodiversity of birds is unknown. Omland, professor of biological sciences at UMBC and lead author of the paper, said: "Even for this well-studied bird, we don't know what its biodiversity unit is. Understanding these 'biodiversity units' is essential for species conservation, and when all the Pacific Cormorants and the Crimson Cormorants of mainland Australia are considered the same species (the smallest unit of biodiversity), the disappearance of birds on one or two islands will be unfortunate, but not necessarily have a large impact. However, if these birds were actually the only remaining members of an independent species, it would be a catastrophic loss.
"Anna's research shows that bird populations on these islands have very unique characteristics." Omland adds, "It's therefore extremely important to know what the biodiversity we want to conserve is. ”
The team's work showed that all Pacific partridges are descendants of the Australian population. But as small flocks of cormorants settled on remote islands, each island's population embarked on its own evolutionary path. Today, some island populations still maintain patterns of bright male feathers and dull female feathers, while on other islands both sexes have evolved bright (or dull) colors.
"Genetic data reveals that there are two distinct clades in all island populations from the common ancestor to today. Kearns said, "This means that these patterns have undergone multiple independent evolutions." ”
Kearns and Omland argue that these changes are more about random forces than with evolutionary adaptations. For example, the pattern in which an island population eventually forms may depend on the color of the individual who originally came to the island. In addition, in a very small population, the way genes are randomly distributed from generation to generation can have a significant impact — comparable to, or even greater than, the effects of natural selection.
Kearns said: "These birds live on many isolated islands in the Pacific Ocean, and sampling is extremely difficult, so there is not much comprehensive study of them." The study would not have been possible without these specimens collected by previous generations, nor would it have been possible to discover new species without modern technology. "Revealing the complex relationships between these partridges has increased understanding of the field and provided a reference for studying other island birds."