The evolution of defensive spines and warning coloration in porcupines and spiny rats

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Mariana Leyva, Biological Sciences, California State University, Long Beach, Long Beach, CA and Theodore Stankowich, California State University, Long Beach (CSULB)

Background/Question/Methods
A variety of mammals have specialized morphological defenses that help protect them from a wide range of predators. These defenses include body weaponry like armored plates (armadillos & pangolins), quills (porcupines), spines (hedgehogs), and noxious sprays (skunks). In addition to this, some mammals rely strongly on bold warning coloration to advertise these defenses. Morphological defenses may be favored by factors like body size and conspicuousness to predators, and may be correlated with activity, brain size, and/or metabolic rate. We are investigating the ecological and behavioral factors that favored the evolution of spines in three different families of Rodentia: Hystricidae, Erethizontidae, and Echimyidae. Modified spine measurements and coloration scores along with natural history data will be used to run phylogenetic comparative analysis tests to better understand the factors that may promote defensive evolution and warning coloration.
Results/Conclusions
Our statistical analyses show that there is a positive correlation between average spine volume and factors like body size and habitat openness for Hystricidae and Erethizontidae species, but no correlation for Echimyids. We can infer from our data that living in more open habitats or having a large body size can increase conspicuousness and in hand increase pressure predation. This situation may favor the need for more robust spines in porcupines (Hystricidae and Erethizontidae). We will continue to look these factors and other factors like activity, brain size, and warning coloration further using evolutionary phylogenetic analyses on R.