Above: Previous studies found that Neotropical mannikins (white-collared pictured) evolved one of the fastest limb muscles on record to support their acrobatic courtship display. Now, the same team have shown how this modification played an instrumental role in the evolution of the genus Manacus

RECENT RESEARCH INTO a genus of colourful Neotropical birds suggests that a particular muscle has influenced the evolution of four distinct species.

Previous research carried out by biologist Matthew Fuxjager at the Wake Forest University in North Carolina, found that during its elaborate courtship dance, the male white-bearded mannikin (Manacus manacus) uses a muscle called the scapulohumeralis caudalis – said to be one of the fastest limb muscles of any vertebrate – to make a unique “roll-snap” movement at high speeds undetectable to the human eye. 

Now, in his latest study, Mr Fuxjager and Wake Forest doctoral student Meredith Miles looked at how the  Manacus mannikins (Aves: Pipridae) last shared a common ancestor roughly 300,000 years ago, before splitting into four species: white-bearded (M. manacus), golden-collared (M. vitellinus), white-collared (M. candei) and orange-collared (M. aurantiacus). 

Using the findings from the previous study, the team went on to examine not only how a small group of birds evolve, but how they behave overall and how a particular muscle in these organisms performs. Mr Fuxjager travelled to Panama and Costa Rica to measure how fast the mannikin’s scapulohumeralis caudalis expands and contracts when stimulated. Next the team compared recordings of the mannikin roll-snap sound display to note variations in speed and duration among species.

According to Mr Fuxjager, the patterns show that changes in physiology led to alterations in behaviour and then the evolution of four mannikin species.

He explained: “The ability of this muscle to develop different speeds has shaped the way these mannikin have evolved – it allowed for one species to become two, and two to become four. This is some of the first work that shows how this happens.”

Muscle speed differed significantly among the species with golden-collared mannikin producing the fastest roll-snaps, white-bearded and white-collared mannikin both producing intermediate speed roll-snaps, and orange-collared mannikin producing the slowest roll-snaps.

Mr Fuxjager added: “The study of superfast muscles such as the bearded mannikin’s scapulohumeralis caudalis may inform research into how diseases such as ALS [motor neurone disease] attack muscles in humans.”

The recent study was funded by the National Science Foundation. Findings were published in the journal eLIFE. 


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