Size-dependent selection on arrival times in sticklebacks: why small males arrive first

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• High-quality males typically arrive first at breeding areas, gaining reproductive advantages.
• This phenomenon is often attributed to phenotype-dependent costs and benefits of early arrival.

Purpose of the Study:

• To investigate the arrival order of males in threespine stickleback (Gasterosteus aculeatus).
• To determine the factors influencing arrival time and its relation to male quality and reproductive success.

Main Methods:

• Observed arrival order of males of varying sizes at breeding grounds.
• Conducted experiments to assess selection coefficients for territory maintenance and hatching success.
• Analyzed the impact of delayed arrival on large males' reproductive probability.

Main Results:

• Smaller threespine stickleback males arrived before larger males.
• Early arrival incurred costs due to high predation risk and selection against early territory establishment.
• Large males benefited from delayed arrival by reducing predation risk and increasing offspring production.
• Large males could displace smaller males from established territories, negating the disadvantage of late arrival.

Conclusions:

• Male arrival order is influenced by competitive ability, with smaller males arriving early to secure territories.
• Natural selection favors later arrival due to costs, while sexual selection favors early arrival in smaller males.
• Optimal arrival times are size-dependent, balancing predation costs with reproductive opportunities and competitive dynamics.