Interspecific aggression causes negative selection on sexual characters

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Zoology

Background:

• Interspecific aggression, often due to mistaken species recognition, is hypothesized to influence sexual character evolution.
• This hypothesis linking aggression to selection on secondary sexual characters has lacked direct empirical testing.

Purpose of the Study:

• To experimentally test if interspecific aggression imposes selection on secondary sexual characters.
• To investigate the role of interspecific aggression in driving character displacement between damselfly species.

Main Methods:

• Field experiment involving wild damselfly populations (Calopteryx virgo and Calopteryx splendens).
• Manipulated the presence of C. virgo males to assess their impact on survival selection of C. splendens wing spot size.
• Quantified male aggression based on wing spot size.

Main Results:

• Males of Calopteryx virgo exhibited increased aggression towards Calopteryx splendens males with larger wing spots.
• Experimental removal of C. virgo males altered directional survival selection on C. splendens wing spot size.
• In the absence of C. virgo, the relationship between C. virgo abundance and selection on wing spots disappeared.

Conclusions:

• Interspecific aggression can indeed exert negative selection on secondary sexual characters.
• This mechanism provides an alternative explanation for reinforcement and character displacement in sexually selected traits.
• Findings support the role of interspecific interactions in shaping species divergence.