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INTRASPECIFIC VARIATION IN SEX ALLOCATION IN A SIMULTANEOUS HERMAPHRODITE: THE EFFECT OF INDIVIDUAL SIZE
Christopher W Petersen1, Eric A Fischer2
1College of the Atlantic, 105 Eden Street, Bar Harbor, Maine, 04609-1198.
Summary
In chalk bass, larger individuals invest more in reproduction with a female bias. This size-specific sex allocation is an adaptive response to mating success and sperm competition dynamics.
Area of Science:
- Evolutionary biology
- Reproductive strategies
- Behavioral ecology
Background:
- Simultaneous hermaphrodites exhibit variation in reproductive investment and allocation between male and female functions.
- Chalk bass (Serranus tortugarum) provide a model for studying size-dependent reproductive allocation and success.
Purpose of the Study:
- To investigate how individual size influences reproductive investment and sex allocation in chalk bass.
- To test predictions from a local-mate-competition (LMC) model regarding sex allocation strategies.
Main Methods:
- Estimating reproductive allocation and success in male and female functions for different-sized chalk bass.
- Analyzing gonadal data to assess investment in male and female gametes.
- Comparing empirical data with predictions from a quantitative LMC model.
Main Results:
- Reproductive investment increases with body size in chalk bass.
- A shift towards a stronger female bias in allocation occurs with increasing size.
- Spawning frequency remains constant across sizes, but larger individuals release more gametes per spawn.
- Model predictions for average male allocation closely match empirical data.
Conclusions:
- Size-specific shifts in sex allocation in chalk bass are an adaptive response to mating success and sperm competition.
- The findings support the LMC model's predictions regarding investment and allocation strategies.
- Reproductive strategies in simultaneous hermaphrodites are shaped by ecological factors like competition and mating systems.
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