Body mass evolution and diversification within horses (family Equidae)

Area of Science:

• Paleontology
• Evolutionary Biology
• Macroevolutionary Studies

Background:

• The horse family (Equidae) displays significant adaptive radiation, with a ~60-fold increase in body mass and high species diversity.
• Adaptive radiation patterns are often linked to niche competition driving increased taxonomic diversity and size disparity.
• Neutral macroevolutionary processes, like diffusion, can also increase disparity without necessarily increasing diversity.

Purpose of the Study:

• To quantify the contributions of diversity-driven and diffusion-driven mechanisms to size disparity in Equidae radiation.
• To clarify the role of species competition versus neutral processes in equine body size evolution.

Main Methods:

• Utilized a comprehensive database of Equidae species size estimates.
• Applied a common mathematical framework to analyze macroevolutionary patterns.
• Measured the relative influence of diversity and diffusion on changes in size disparity.

Main Results:

• Over 90% of the changes in size disparity within Equidae are attributable to macroevolutionary diffusion alone.
• Neutral diffusion processes were found to be the primary driver of increased size disparity.
• Species diversity was found to be weakly coupled with morphological disparity.

Conclusions:

• Macroevolutionary diffusion, a neutral process, is the dominant factor in equine body size evolution, not niche competition.
• Morphological disparity and species diversity may be weakly linked in macroevolutionary contexts.
• Large species can evolve solely through neutral macroevolutionary diffusion processes.