Some birds listen, instead of look, for mates
WEST LAFAYETTE, Ind. - Looks can be deceiving, but certain bird species have figured out that a voice can tell them most of what they need to know to find the right mate.
Andrew DeWoody, a Purdue University professor of genetics, found that the higher the pitch of a male bird's song, the more genetic diversity that bird has, making him a better mate for breeding. His study was published Wednesday (Dec. 2) in the early online edition of PLoS One.
"If you have a diverse set of genes, that can translate into physiological and morphological diversity as well," DeWoody said. "Animals that are heterozygous, or have genetic diversity, are often bigger, stronger or can run faster."
DeWoody and former Purdue graduate student Johel Chaves-Campos studied ocellated antbirds in the tropical forests of Central America. The antbirds survive by tracking army ants, which hunt in large swarms and are capable of killing just about anything in their paths. The birds flit ahead of the swarms and collect arthropods that flee for their lives.
"They wait at the front for the ants to flush out a grasshopper, for example," DeWoody said.
The antbirds have several calls, some to let fellow antbirds know where the army ants are heading, others to attract mates and still others that are defensive or aggressive to protect turf. DeWoody's research involved recording those calls and matching them to DNA samples of the birds. The results suggest that genetic diversity in antbirds affects their physical abilities to produce certain sounds.
"Our results are consistent with the idea that some sound frequencies are biomechanically difficult to produce. Males that are genetically diverse, and therefore expected to be in better physical condition, are able to produce sound frequencies that males with less genetic variation are unable to reach," Chaves-Campos said.
DeWoody said females can pick up on the pitch of the males' songs to decide which birds will make the best mates.
"Females may prefer to mate with males that hit the highest notes because their offspring will have more genetic diversity," DeWoody said. "Male calls could be honest indicators of their genetic diversity."
Antbirds also can use pitch information in disputes. For instance, a bird could decide not to escalate a conflict over territory if it decides the other bird is in better physical condition. The bird also could decide to intensify the conflict if it believes its opponent is weaker.
Funding for the research came from the National Science Foundation. Chaves-Campos said the next step is to show that the finding in antbirds holds true in other birds.
Yimen Araya-Ajoy, a graduate student from the University of Costa Rica, collaborated with DeWoody and Chaves-Campos on the research and was first author on the paper.
Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu
Sources: Andrew DeWoody, 765-496-6109, dewoody@purdue.edu
Johel Chaves-Campos, jchaves@purdue.edu
Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
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ABSTRACT
High-pitched Notes During Vocal Contests Signal Genetic Diversity in Ocellated Antbirds
Yi-men Araya-Ajoy, Johel Chaves-Campos, Elisabeth K.V. Kalko and J. Andrew DeWoody
Animals use honest signals to assess the quality of competitors during aggressive interactions. Current theory predicts that honest signals should be costly to produce and thus reveal some aspects of the phenotypic or genetic quality of the sender. In songbirds, research indicates that biomechanical constraints make the production of some acoustic features costly. Furthermore, recent studies have found that vocal features are related to genetic diversity. We linked these two lines of research by evaluating if constrained acoustic features reveal male genetic diversity during aggressive interactions in ocellated antbirds (Phaenostictus mcleannani). We recorded the aggressive vocalizations of radiotagged males at La Selva Biological Station in Costa Rica and found significant variation in the highest frequency produced among individuals. Moreover, we detected a negative relationship between the frequency of the highest pitched note and vocalization duration, suggesting that high-pitched notes might constrain the duration of vocalizations through biomechanical and/or energetic limitations. When we experimentally exposed wild radiotagged males to simulated acoustic challenges, the birds increased the pitch of their vocalization. We also found that individuals with higher genetic diversity (as measured by zygosity across 9 microsatellite loci) produced notes of higher pitch during aggressive interactions. Overall, our results suggest that the ability to produce high-pitched notes is an honest indicator of male genetic diversity in male-male aggressive interactions.