Evolution of Defensive Armor and Sexual Weapons

Specialized morphological defenses and weaponry help prevent injury upon attack and/or improve one’s chances of finding a mate, and such traits are found in some members of nearly every animal group. Defenses usually take the form of thickened tough skin, hard armored shells or exoskeletons, sharp spines, noxious sprays, or toxic secretions. Clearly, some taxa invest a great deal in body armor while others favor other antipredator strategies (crypsis, aposematism, rapid escape, specialized refuge use) – we do not know what influences the evolution, maintenance, or diversity of morphological defenses.

Sexual weaponry like antlers, horns, and tusks that are used by males to win access to mates may be grown and used only seasonal or may carried permanently all year. Regardless of the duration, weapons like these are certainly costly to construct and maintain. It takes significant energy and material resources to construct a large antler or long tusk, and the fact that males are often the only sex to bear such structures, could set up different energetic allocation strategies for males and females.

For both armor and weaponry, we are interested in the factors that promote their evolution and effects they have on other aspects of morphology, life history, physiology, or behavior. We are interested in how certain antipredator behaviors and morphological characters evolve together, or how the presence of one influences the other. Currently, we are exploring the evolution of spines and armored plates across all mammal groups, the evolution of tusks in ungulates, and the biomechanical properties of dermal armor in armadillos and pangolins.

Working with preserved skins and skulls in natural history museum collections as well as books and photographs found online, this research uses phylogenetic analyses of antipredator behavior and physical defenses in hopes of discovering what morphological and environmental factors facilitate the evolution of antipredator behavior.