Maternal androgens in black-headed gull (Larus ridibundus) eggs: consequences for chick development

Area of Science:

• Avian reproductive biology
• Maternal effects on offspring development
• Behavioral ecology

Background:

• Hatching asynchrony can disadvantage later-hatched chicks.
• Maternal androgens in egg yolks may influence offspring development and competitiveness.
• Previous evidence on this hypothesis is contradictory.

Purpose of the Study:

• To test if increased yolk androgens in later eggs enhance the competitive ability, growth, and survival of offspring.
• To investigate maternal strategies for maximizing reproductive output in black-headed gulls.

Main Methods:

• Experimental injection of black-headed gull eggs with oil or androgen solutions.
• Manipulation of clutch androgen levels to be constant or increasing with laying order.
• Comparison of embryonic development, chick growth, and survival rates.

Main Results:

• Androgen treatment accelerated embryonic development (earlier hatching) but did not affect hatching size.
• Androgen treatment enhanced chick growth, particularly in later-hatched chicks.
• Growth of first-hatched chicks was reduced when siblings received androgen treatment, indicating increased sibling competition.

Conclusions:

• Maternal transfer of varying yolk androgen concentrations is a mechanism to enhance the competitiveness of later-hatched chicks.
• This strategy helps mothers maximize reproductive success by optimizing offspring development and survival.
• Yolk androgens play a crucial role in mediating sibling competition and parental investment strategies.