Intraspecific variation in resource use is not explained by population persistence or seasonality

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Generalist grazers often exhibit powerful (fast growth on rich resources) and efficient (better growth on poor resources) genotypes.
• A power-efficiency trade-off is hypothesized to maintain genetic diversity through variation in resource quality.

Purpose of the Study:

• To evaluate if a power-efficiency trade-off maintains genetic diversity in Daphnia pulicaria populations.
• To investigate if resource quality variation and population persistence patterns influence the distribution of powerful and efficient genotypes.

Main Methods:

• Sampling of six Daphnia pulicaria populations with varying persistence patterns (year-round vs. spring-only).
• Assessing growth rates of different genotypes on resource diets of varying quality.
• Analyzing shifts in clonal composition of persisting populations between spring and summer.

Main Results:

• No evidence for a power-efficiency trade-off was found; growth rates on rich and poor diets were positively correlated.
• Individuals from non-persisting populations were smaller but did not lack efficient clones.
• Clonal composition shifted seasonally in persisting populations, but not towards more efficient genotypes.

Conclusions:

• Population persistence patterns and seasonal resource quality shifts alone do not fully explain the maintenance of genetic variation in these Daphnia populations.
• The power-efficiency trade-off mechanism may not be the primary driver of genetic diversity in this system.
• More complex ecological or evolutionary factors likely contribute to maintaining genetic diversity in Daphnia pulicaria.