Dermal modifications of the red lionfish, Pterois volitans.

Vertebrates have evolved flexible and hard dermal armor, but there is often a tradeoff between mobility and protection. Skeletal modifications include fish scales, the shells of tortoises and turtles, and the cranial projections that are found in marine iguanas and lionfish. Sexual dimorphisms of cranial structures are prominent in fishes; we hypothesized that cranial projections of Pterois volitans will change over ontogeny and are sexually dimorphic. The goal of this study is to quantify differences in the cranial armor of P. volitans over a range of sizes (juveniles to adults) to understand allometric growth and possible sexual dimorphisms using specimens from invaded ranges. We found no difference in the total number of cranial spines between sexes, suggesting that the number of cranial spines is not a sexually dimorphic trait in P. volitans. We found positive allometry for total cranial spine number, and length and width of the three largest cranial spines, with respect to the fish total length. Here, we also document another skeletal modification in P. volitans, which is the addition of spines on the caudal fin. Overall, these data show that P. volitans' develop robust dermal modifications as they grow larger, and we suggest that phenotypic plasticity of this species should be explored in their native and invaded ranges.