Bathymetric evolution of black corals through deep time

Area of Science:

• Marine Biology
• Evolutionary Biology
• Deep-Sea Ecology

Background:

• Deep-sea species are often assumed to evolve from shallow-water ancestors.
• The evolutionary history of deep-sea anthozoans, including black corals, remains largely unknown.
• Understanding the timing and drivers of deep-sea invasions is crucial for marine biodiversity research.

Purpose of the Study:

• To reconstruct the time-calibrated phylogeny of the order Antipatharia (black corals).
• To investigate the bathymetric evolutionary history and diversification patterns of black corals.
• To identify the ecological factors associated with the invasion of deep-sea habitats by black corals.

Main Methods:

• Phylogenetic analysis of 83 species within the order Antipatharia.
• Time-calibration of the phylogeny using molecular clock methods.
• Ancestral state reconstruction to infer evolutionary transitions and trait evolution.

Main Results:

• Extant black coral lineages first diversified in early Silurian (∼437 Ma) continental slope depths (250–3000 m).
• Subsequent radiations occurred into continental shelf (<250 m) and abyssal (>3000 m) habitats.
• Morphological adaptations for nutrient acquisition coincided with the colonization of new depths.

Conclusions:

• Black corals exhibit a deep-sea origin, contradicting the prevailing shallow-water ancestor hypothesis for deep-sea fauna.
• Continental slope habitats served as crucial 'source' regions for black coral diversification and subsequent dispersal.
• Conservation of slope ecosystems is vital to protect deep-sea biodiversity and evolutionary history.