Phenotypic plasticity or speciation? A case from a clonal marine organism

Area of Science:

• Marine Biology
• Genetics
• Ecology

Background:

• Clonal marine organisms display significant morphological variation.
• This variation can stem from environmental factors or genetic divergence due to disrupted gene flow.
• The gorgonian Eunicea flexuosa, a widespread Caribbean octocoral, exhibits extensive morphological variation.

Purpose of the Study:

• To investigate the morphological variation in Eunicea flexuosa populations.
• To differentiate between eco-phenotypic and genetic influences on morphology.
• To analyze population genetics using mitochondrial and nuclear genes.

Main Methods:

• Reciprocal transplants of colonies across depth gradients.
• Analysis of 14 morphological characters.
• Population genetics analysis of mitochondrial and nuclear genes.

Main Results:

• Significant morphological differences were observed across 12 locations in southwest Puerto Rico.
• Two distinct morphotypes, shallow (< 5 m) and deep (> 17 m), were identified based on depth distribution.
• Reciprocal transplants revealed gradual morphological changes, but no overlap with resident morphologies, suggesting limited phenotypic plasticity.
• Genetic analysis indicated two independent evolutionary lineages correlated with distinct morphologies and non-overlapping plasticity.

Conclusions:

• Eunicea flexuosa represents a complex of at least two distinct genetic lineages with specific habitat adaptations.
• These lineages exhibit narrower distributions and more rigid phenotypic plasticity than previously described.
• Misidentification of this species complex can lead to overestimations of distribution, abundance, and tolerance.