Speciation: Birds of a feather...

Date:  March 26, 2019

Source:  Ludwig-Maximilians-Universität München

Carrion crows and hooded crows are almost indistinguishable genetically, and hybrid offspring are fertile. Ludwig-Maximilians-Universitaet (LMU) in Munich biologists now show that the two forms have remained distinct largely owing to the dominant role of plumage color in mate choice.

Crows have divided Europe between them. Western Europe is the realm of the soot-black carrion crow, while the eastern half of the continent is home to the hooded crow with its grayish black plumage. The boundary between the two populations -- or more precisely, the hybrid zone where the two meet -- is only 20-50 km wide, and in Germany it essentially follows the course of the River Elbe. This is the only stretch of territory in which both of these species are found and sucessfully mate with each other. The plumage of the fertile offspring of these pairings is intermediate in color between those of their parents. The sharp demarcation between the two populations, however, clearly indicates that gene flow across the hybrid zone is restricted, which implies that hybrids are at a selective disadvantage. "Defining speciation as the buildup of reproductive isolation, carrion crows and hooded crows are in the process of speciation," says LMU evolutionary biologist Jochen Wolf. He and his research team have now analyzed the genetic basis for the division of European crows into two populations. Indeed, the results of the study demonstrate that the old saying "birds of a feather flock together" really does apply in this instance: The only genes that differ significantly between the two variants are those involved in determining the color of the plumage. This suggests that each form preferentially mates with partners of the same color as themselves. The new findings appear in the journal Nature Ecology and Evolution.

Continued

Cardinals living in adjacent deserts are sharply distinct in genetics and song

New research investigates whether dialect differences might indicate new species

Date:  December 12, 2018

Source:  American Museum of Natural History

New research suggests that populations of the Northern Cardinal --one of the most ubiquitous backyard birds in the United States-- are undergoing speciation in two adjacent deserts. This study, which analyzed genetics and vocal behavior, gives clues about the early steps in bird speciation. The study is published in the journal Ecology and Evolution.

"In general, songs are really important for describing and identifying birds," said lead author Kaiya Provost, a comparative biology Ph.D. Candidate in the American Museum of Natural History's Richard Gilder Graduate School. "Most studies assume that differences in song are important in the process that gives rise to new bird species. But looking at speciation using both genetics and behavior in wild birds can be really difficult. We went out to test both of these spheres of biology on wild desert birds to look at the full story."

The researchers focused on Northern Cardinal populations in two deserts: the Sonoran Desert, which covers parts of Arizona, California, and Mexico; and the Chihuahuan Desert, which covers parts of Texas, New Mexico, Arizona, and Mexico. The deserts are separated by about 120 miles of high-elevation plains. Analysis on the DNA of the birds in these areas shows that the two populations have been separated for at least 500,000 years and possibly for as long as 1 million years, which "might be old enough for the speciation process to finish," Provost said.

In parallel, the researchers examined the song-related behavior of these populations. Songs play a crucial role in a bird's ability to attract and impress a potential mate. If two birds can't communicate with each other, for instance, by singing different types of songs, they are less likely to breed. Over time, populations that don't reproduce with each other will accumulate more and more genetic differences. As time goes on, these two processes can feed back into each other and lead the populations down the path of speciation.

To investigate, Provost and her collaborators--Brian Smith, an assistant curator in the Museum's Department of Ornithology, and William Mauck III, a researcher at the New York Genome Center--created a bird song experiment that they played in each desert. Each audio series contained four recordings of male birds: neighboring cardinals, cardinals from the same desert but a distance away, cardinals from the adjacent desert, and a control recording of a Cactus Wren.

In the Sonoran Desert, male cardinals reacted to the recorded songs from neighboring birds with aggression--flying around looking for the "intruder" and singing loudly. Songs from birds living further away, both from within the same desert and from the adjacent one, were ignored.

"We saw that the birds are really aggressive to songs by their next-door neighbors, as you would expect, but once there is enough distance between them, they don't understand the songs anymore," Provost said. "It's like if you speak Portuguese in Portugal, you can probably understand Spanish, and you might understand French, but if you keep going further and further away, eventually you'll hit German or Arabic--languages that are unfamiliar, that you can't parse."

Continued  

Darwin 2.0: New theory on speciation, diversity

Birds that are related, such as Darwin's finches, but that vary in beak size and behavior specially evolved to their habitat are examples of a process called speciation. It has long been thought that dramatic changes in a landscape like the formation of the Andes Mountain range or the Amazon River is the main driver that initiates species to diverge. However, a recent study shows that speciation occurred much later than these dramatic geographical changes. Researchers from LSU's Museum of Natural Science have found that time and a species' ability to move play greater parts in the process of speciation. This research was recently published in the print edition of Nature.

"The extraordinary diversity of birds in South America is usually attributed to big changes in the landscape over geological time, but our study suggests that prolonged periods of landscape stability are more important," said Robb Brumfield, LSU Museum of Natural Science director and Roy Paul Daniels professor in the Department of Biological Sciences, one of the lead authors.

Brumfield and his colleagues examined the genealogy of 27 species of birds in the most bio-diverse region in the world, the Neotropics, which extends from southern Mexico through Central America to southern Brazil and includes the Amazon rainforest.

Continued ...