Evolutionarily labile responses to a signal of aggressive intent

Area of Science:

• Ethology
• Evolutionary Biology
• Animal Behavior

Background:

• Males of numerous swordtail species exhibit vertical bar pigment patterns.
• These bars serve crucial roles in both courtship displays and aggressive (agonistic) interactions between males.
• Bar expression intensifies during aggression and diminishes in subordinate individuals, functioning as a conventional threat signal.

Purpose of the Study:

• To investigate the role of vertical bars as threat signals in swordtail fish.
• To compare the aggressive responses of four swordtail species to barred and barless visual stimuli.
• To determine the evolutionary lability of signal perception versus signal expression in aggressive interactions.

Main Methods:

• Utilized mirror image stimulation to present conspecific males with their own reflections.
• Manipulated the presence or absence of vertical bars on the mirror images.
• Recorded and analyzed the aggressive behavioral responses of males from four distinct swordtail species.

Main Results:

• A significant correlation was found between the genetic basis for bar development and the presence of a behavioral response to bars.
• The nature of the aggressive response evoked by the bar signal varied considerably across the four studied swordtail species.
• The study identified the first documented instance of closely related species displaying contradictory responses to the same aggressive signal.

Conclusions:

• The perception and behavioral response to the aggressive signal (bars) are evolutionarily more flexible than the signal itself.
• While the aggressive intent conveyed by the bars remains consistent, the specific behavioral reactions have diverged among species.
• This highlights the dynamic nature of signal evolution, where receiver responses can change independently of signal meaning.