Fin modules: an evolutionary perspective on appendage disparity in basal vertebrates.

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Phylogenetics

Background:

• Fishes exhibit remarkable diversity in fin number, structure, shape, and size.
• Understanding the evolutionary history of fish appendages is crucial for explaining this disparity.
• Fin modularity is proposed as a key factor in fin evolution and the development of new fins.

Purpose of the Study:

• To investigate fin disparity in fishes from a phylogenetic perspective.
• To analyze the presence/absence and number of median and paired fins across fish orders.
• To test hypotheses of fin modularity in fish evolution.

Main Methods:

• Mapping of fin characters onto a phylogenetic supertree of fish orders.
• Comparative analysis of fin configurations across major fish groups (agnathans, chondrichthyans, actinopterygians).
• Assessment of character distribution non-independence for fin pairs.

Main Results:

• Fin disparity in agnathans arises from the sequential addition of novel fins.
• Chondrichthyan fin disparity is mainly due to median fin losses.
• Actinopterygian fin disparity involves fin losses, new fins (e.g., adipose), and duplications; pectoral/pelvic and dorsal/anal fins show non-independent evolution.

Conclusions:

• Pectoral/pelvic fins and dorsal/anal fins represent distinct evolutionary modules.
• The dorsal/anal fin module is nested within a broader median fins module.
• Findings link developmental, variational, and evolutionary modularity in fish fins.