NATURAL SELECTION ON HYDROID COLONY MORPHOLOGY BY INTRASPECIFIC COMPETITION

Area of Science:

• Evolutionary Biology
• Marine Ecology
• Genetics

Background:

• Colonial hydroids of the genus Hydractinia exhibit significant morphological variation.
• This morphological variation is known to influence intraspecific competitive ability.
• Intraspecific competition is frequent in natural settings, implying it's a key selective pressure.

Purpose of the Study:

• To investigate the genetic basis of morphological variation in Hydractinia.
• To test the hypothesis that intraspecific competition is a selective force on morphology.
• To examine the relationship between morphology, competitive ability, and population dynamics.

Main Methods:

• A replicated common garden experiment was conducted to assess the genetic basis of morphological traits.
• Two datasets were analyzed: pre- and post-competition samples from juvenile and adult populations.
• Correlative analyses examined the relationship between morphology frequency and observed intraspecific competition rates across eight populations.

Main Results:

• A genetic basis for morphological variation in Hydractinia was confirmed.
• Morphologies with lower competitive ability were less abundant in adult (post-competition) samples compared to juvenile (pre-competition) samples.
• The relative frequencies of different morphologies correlated with the observed rates of intraspecific competition within populations.

Conclusions:

• Intraspecific competition acts as a selective agent on genetically based morphological variation in Hydractinia.
• The direction of selection observed in this species challenges current predictions based on cross-taxa comparisons.
• Inferences about past selection pressures based solely on present-day correlations across species may be limited.