Size Dependent Male Reproductive Tactic in the Two-Spotted Goby (Gobiusculus flavescens).

Area of Science:

• Behavioral Ecology
• Reproductive Biology
• Ichthyology

Background:

• The two-spotted goby (Gobiusculus flavescens) is a common North East Atlantic fish with a single breeding season.
• Males typically care for nests and raise multiple clutches.
• Previous studies indicate males are usually larger than females.

Purpose of the Study:

• Investigate male investment in testes and seminal duct glands (SDG) in relation to reproductive season timing and physical traits.
• Document reproductive tactic plasticity in a population with smaller-than-average males.
• Explore size-dependent shifts in male reproductive strategies.

Main Methods:

• Histological analysis of testes and seminal duct glands (SDG).
• Measurement of organ mass relative to body size.
• Comparison of reproductive investment across different male sizes and throughout the breeding season.

Main Results:

• A population of two-spotted gobies with smaller-than-average males was identified.
• Smaller males exhibited sneaker characteristics with larger testes and smaller SDG early in the season.
• Testes investment decreased significantly over the season, especially in smaller males, while SDG mass increased in smaller males.

Conclusions:

• Smaller males may shift from parasitic to nest-holding tactics during the breeding season.
• Reproductive tactics in G. flavescens are conditional and influenced by factors like mate availability and competition.
• Observed plasticity in SDG investment highlights the dynamic nature of male reproductive strategies.