|
|
| |
| The diversification of bird nests and its association with bird evolution |
| |
|
|
| |
 |
|
|
Nests can protect birds’ eggs and chicks, and nest-construction might be one reason why birds survived the last mass extinction in Earth’s history, while their relatives, dinosaurs (or non-avian dinosaurs if we consider birds as dinosaurs), did not. Given the critical role of nests in avian biology, one might think that ornithologists already understand the evolution of bird nests very well. Surprisingly, this is not true. Our study provides the first comprehensive view of bird nest evolution across the avian phylogeny. The research results are published in the journal Nature Communications on May 14th, 2018.
Bird nests vary considerably from simple scratches on the ground, to platform nests floating on lake surfaces, to astonishingly elaborate nests hanging from tree branches. An often-asked question is how this nest diversity evolved? Interestingly, birds of the same species almost always build the same types of nests, and species of the same genus or even higher taxonomic ranks are often found to construct similar nests. For example, most pigeon species build flimsy, saucer-shaped nests, and thus people can easily distinguish a pigeon’s nest from those of other birds. However, it is still unclear whether the putative rule of nest resemblance between close relatives can be applied to all birds on Earth. The results of our study show that the answer is both “Yes” and “No”.
One critical but often overlooked point is that the bird nest is not one single character, but a combination of several ones. To have a functional nest, birds first need to select a site, and then construct a nest with a particular shape and attach it to a supporting object. Recognizing this point, we collected nest information for all 242 avian families in the world from literatures and analyzed the evolutionary paths for the three dimensions of nest characters – nest site, structure and attachment – separately. We found that the most recent common ancestor of all modern birds was likely to have laid eggs directly on the ground, similar to what ostriches and plovers do. Since then, its descendants have developed the wide range of nest structures, sites and attachments that we see clone royal oak 15500 today. However, we showed that these characters did not evolve together. While closely related birds often build similar nest structures, their nest sites can be very diverse. Nest attachment approaches rarely changed across the avian tree of life, and the most common approach is to attach a nest to a site with support from bottom (i.e., basal attachment). These findings suggest that similarity in nest structures may reveal the nesters’ evolutionary relationships; however, the evolution of nest site or attachment is too labile or inertial to reflect the evolutionary history of birds.
The three nest characters have different evolutionary paths, but our results revealed that they evolved interdependently. For example, birds could only build nests off the ground after they started to construct nests with structures other than simple scratches. The more elaborate attachment approaches, such as attaching the lateral parts of nests to reeds, evolved only in birds that could build cup- or dome-shaped nests.
Estimating the changes in nest characters along the avian tree of life, we show that the emergence of multiple novel nest characters contributed, at least partially, to two instances of large-scale, rapid evolution (i.e., adaptive radiation) in birds. The two adaptive radiations occurred after the K-T (Cretaceous-Tertiary) boundary by which dinosaurs died out due to dramatic climate change. The bursting diversification of bird nests might have resulted in current avian diversity on the planet. Therefore, when facing rapid climatic and environmental changes, the speed of nest character evolution can be a key for birds to survive in the future.
|
|
|
|
Previous | Next | Back to E-News| Send to Friend
|
