"Long before it's in the papers"
January 27, 2015


Family tree traces evolution of mysterious birds

Oct. 14, 2014
Courtesy of Cornell University
and World Science staff

They’re some of the bright­est, loud­est, oddest-looking, least-understood birds. Some have bulb­ous crests, long fleshy wat­tles, or Elvis-worthy pom­padours in ad­di­tion to elec­tric blue, deep pur­ple, or scream­ing or­ange feath­ers. 

A male An­de­an Cock-of-the-rock (Rupi­cola pe­ru­viana), a mem­ber of the Co­tin­ga fam­i­ly. (Jer­ry Thomp­son/Wiki­me­dia Com­mons)

But thanks to a com­pre­hen­sive new ev­o­lu­tion­ary “tree of life” gen­er­at­ed for the trop­i­cal co­tin­ga family of South Amer­i­ca, sci­en­tists say the door is now open to new dis­cov­er­ies about the more than 60 spe­cies in this amaz­ingly di­verse group.

“Our study pro­vides com­pre­hen­sive in­sight in­to how nearly all the co­tin­ga spe­cies are re­lat­ed to each oth­er go­ing all the way back to their com­mon an­ces­tor,” said Jake Berv, a doc­tor­al stu­dent in ev­o­lu­tion­ary bi­ol­o­gy at Cor­nell Uni­vers­ity in Ith­aca, N.Y. “No pre­vi­ous at­tempts to un­der­stand the ev­o­lu­tion­ary his­to­ry of this group have in­clud­ed ge­net­ic sam­ples from nearly all the ex­ist­ing spe­cies.”

The study is pub­lished in the jour­nal Mo­le­cu­lar Phy­lo­gen­et­ics and Evo­lu­tion.

Berv be­gan se­quenc­ing DNA sam­ples and com­pil­ing da­ta in late 2010 while work­ing as a lab tech­ni­cian at Yale Uni­vers­ity with co-author Rick Prum, an ex­pert on co­tin­gas. Un­der­standing how one spe­cies is re­lat­ed to anoth­er with­in this group al­lows sci­en­tists to trace the ev­o­lu­tion of spe­cif­ic traits and be­hav­iors.

Berv and Prum have al­ready started to do that. They wanted to learn if the ev­o­lu­tion of differently-col­ored males and fe­males in this bird group (called sex­u­al di­mor­phism) is di­rectly linked to a breed­ing sys­tem in which males have mul­ti­ple mates (called poly­g­y­ny). 

A male Spangled Co­tin­ga (Greg Hume/Wiki­me­dia Com­mons)

Dar­win the­o­rized that the in­creased ev­o­lu­tion­ary pres­sures re­lat­ed to po­ly­g­y­ny spurred the de­vel­op­ment of col­or dif­fer­ences be­tween the sexes. This ap­pears to be true for many spe­cies—but not the co­tin­gas, bi­ol­o­gists say. When Berv and Prum ex­am­ined pat­terns of ev­o­lu­tion for these two traits across their new tree of life, it turned out they did­n’t per­fectly match up. 

But the in­ves­ti­ga­tors said such pres­sures, known as sex­u­al se­lec­tion, seem to have played a role in the ev­o­lu­tion of non-plumage gen­der dif­fer­ences in some co­tin­ga spe­cies. “In one case, the Scream­ing Piha, the males and fe­males look alike but the male sings one of the loud­est songs on the plan­et,” said Yale’s Prum. 

“One of the big­gest an­a­lyt­i­cal dif­fer­ences be­tween what we’ve done and past work is that we used a ‘spe­cies tree’ ap­proach, which is po­ten­tially more ac­cu­rate than what is typ­ic­ally ap­plied to ge­net­ic da­ta,” Berv said. “We ran our da­ta through more tra­di­tion­al types of anal­y­ses as well, and all of them strongly sup­ported a con­sist­ent ev­o­lu­tion­ary ‘tree of life.’”

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They’re some of the brightest, loudest, oddest-looking, least-understood birds. Some have bulbous crests, long fleshy wattles, or Elvis-worthy pompadours in addition to electric blue, deep purple, or screaming orange feathers. But thanks to a comprehensive new evolutionary “tree of life” generated for the tropical cotinga family of South America, scientists say the door is now open to new discoveries about the more than 60 species in this amazingly diverse group. “Our study provides comprehensive insight into how nearly all the cotinga species are related to each other going all the way back to their common ancestor,” said Jake Berv, a doctoral student in evolutionary biology at Cornell University in New York. “No previous attempts to understand the evolutionary history of this group have included genetic samples from nearly all the existing species.” Berv began sequencing DNA samples and compiling data in late 2010 while working as a lab technician at Yale University with co-author Rick Prum, an expert on cotingas. Understanding how one species is related to another within this group allows scientists to trace the evolution of specific traits and behaviors. Berv and Prum have already started to do that. They wanted to learn if the evolution of differently-colored males and females in this bird group (sexual dimorphism) is directly linked to a breeding system in which males have multiple mates (polygyny). Darwin theorized that the increased evolutionary pressures related to polygyny spurred the development of color differences between the sexes. This appears to be true for many species—but not the cotingas, biologists say. When Berv and Prum examined patterns of evolution for these two traits across their new tree of life, it turned out they didn’t perfectly match up. But the investigators said such pressures, known as sexual selection, seems to have played a role in the evolution of non-plumage gender differences in some cotinga species. “In one case, the Screaming Piha, the males and females look alike but the male sings one of the loudest songs on the planet,” said Yale’s Prum. “One of the biggest analytical differences between what we’ve done and past work is that we used a ‘species tree’ approach, which is potentially more accurate than what is typically applied to genetic data,” Berv said. “We ran our data through more traditional types of analyses as well, and all of them strongly supported a consistent evolutionary ‘tree of life.’”