This is a practice called "brooding parasitism", in which animals secretly leave eggs for another species to feed. Although there are parasitic parasites in birds, fish and insects, their mechanisms of action are different. Usually for birds, when the bird is not paying attention, this parasite will lay eggs in another nest. Rhododendron is the most famous example of hatching parasites and the source of the word cuckold. Incubation parasitism is often called evolutionary arms race, in which competing species constantly develop new adaptability to confront each other. In the case of hatching parasites, this usually means that its eggs will evolve more like those of its owners; For a parasitic bird, this means that its eggs will evolve into eggs that don't look like its parasitic parasites. ?
Parasitism is not uncommon in the animal kingdom, and Spottiswood is one of the most important experts in the world. However, becoming an expert will not reduce any challenges in finding eggs. As Spottiswoode told Sharon, "One of the most difficult challenges for people who study hatching parasites is to find enough parasite eggs and chickens. You must try to find many host nests and some of them. Those are parasitic on what you have learned. "
Fortunately, there are many talented nest seekers in the local area who are willing to help.
"For us, this is still a kind of * * *," Spottiswood explained. "Every time you see the parasitic nest in the host egg, there is a beautiful parasitic egg inside-this is something I will never get tired of. It is really gratifying to see the beautiful adaptation formed by natural selection for hundreds of thousands of years. "
Spottiswood has a good reason to wander around the bird's house. Spottiswoode, together with Professor Michael Sorenson of Boston University, led an international genetic research group to study how a parasitic bird hides its eggs and makes them similar to those of many other birds. For more than a century, scientists have been puzzled by this mystery, but researchers have successfully determined that the evolutionary arms race is the culprit.
"We believe that genetically controlled chromosomes exist in all female birds," Spottiswood explained. "This is not a chromosome dedicated to this function. In birds, females have Z chromosomes unique to females, just as males in humans have Y chromosomes unique to males. So among humans, of course, men are XY and women are XX. In birds, the male is ZZ and the female is ZW, so there is a chromosome passed from the mother to the daughter as a more or less complete copy, without any gene flow from the father. "
She added: "The broader problem we are trying to solve here is how different individuals of a single hybrid species have evolved special adaptability to parasitize different host species, even if they mate randomly, no matter what host species the male or female is raised by."
In a study published in the Proceedings of the National Academy of Sciences, scientists explained that maternal genetic factors can prevent cuckoos from accidentally inheriting the wrong imitation genes from their fathers raised in different hosts. This seems to be an evolutionary advantage-to some extent-but the author points out that once their hosts realize what they are doing, it will also make it more difficult for these species to evolve backwards. One of the reasons is that many birds are adapting to the fact that their eggs have many colors and patterns, providing birds with "features" that distinguish these eggs from intruders.
However, how did birds first produce such magical colorful eggs? Is it the only reason to stop hatching parasites?
"Of course, this is a question suitable for Easter," Spottiswood told Sharon. "We have some good answers, but we don't have a complete explanation, and there are still many mysteries. Usually, camouflage is the reason for the different colors of eggs. Camouflage is very important. Nesting predation and visual directional predators are very common, especially those that breed in the open air, such as those that breed on the ground, and other species. Some species have excellent eggs and are very interested in adapting to a specific environment. "
However, this does not explain the color of each egg. Spottiswood pointed out that some scientists speculated that birds that evolved to lay blue eggs did so to protect their embryos from ultraviolet radiation. In addition, birds may want to sign their eggs for reasons unrelated to hatching parasitism.
"In the case of great diversity within species, just like Easter eggs-you are coloring your eggs and they are painted in different colors-the driving force of diversity seems to be self-identification," Spottiswood mused. "We see this in birds that breed in groups, such as birds that nest on cliffs ... for example, they are very different among individuals. In this case, if you pull back from the cliff, you must know yourself. "
If there is a more appropriate declaration to sum up the spirit of Easter, I can't think of one.