Evolutionary disequilibrium and activity period in primates: a bayesian phylogenetic approach

Area of Science:

• Primate evolution
• Paleontology
• Behavioral ecology

Background:

• Activity period is crucial for understanding primate origins and adaptations.
• Lemurs exhibit diverse activity patterns, including nocturnal, diurnal, and cathemeral (24-hour) lifestyles.
• The evolutionary history of cathemerality in lemurs is debated, with hypotheses suggesting recent transient states versus ancient stable strategies.

Purpose of the Study:

• To reconstruct the evolutionary history of activity period in primates using phylogenetic methods.
• To test the evolutionary disequilibrium hypothesis regarding cathemerality in lemurs.
• To investigate the activity period of ancestral primates and key subgroups.

Main Methods:

• Bayesian phylogenetic analyses were employed to infer ancestral states of activity period.
• Reconstructions were performed at critical nodes within the primate evolutionary tree.

Main Results:

• The most recent common ancestor of Eulemur was reconstructed as cathemeral approximately 9-13 million years ago, supporting cathemerality as a stable strategy.
• Strong evidence supports a nocturnal ancestor for all primates, strepsirrhines, and lemurs.
• Diurnality was favored for the ancestor of simian primates, while haplorrhine ancestor reconstructions were equivocal.

Conclusions:

• Cathemerality in lemurs appears to be an ancient and stable evolutionary strategy, challenging the evolutionary disequilibrium hypothesis.
• The ancestral primate was likely nocturnal.
• Further research is needed to fully understand the evolution of cathemerality in lemurs.