Meeting Abstract

8.3  Thursday, Jan. 3  Exoskeletal isometry in adult terrestrial arthropods LEASE, H.M.*; WOLF, B.O.; Univ. of New Mexico, Albuquerque; Univ. of New Mexico, Albuquerque hlease@unm.edu

Most terrestrial vertebrates devote an increasing fraction of their body mass to skeleton as they increase in size. This is because skeleton provides structural support against the stress of weight�and as body size increases, the weight-supporting capacity of endoskeleton increases more slowly than body weight. What do animals that �wear� their skeleton on the outside of their body do? To investigate this, we determined the exoskeletal mass across several orders of magnitude of body size in >600 adult terrestrial arthropods (286 species; primarily insects) in order to assess how exoskeletal mass scales with body mass. Tissues were stripped from exoskeletons using high molar sodium hydroxide, and exoskeletal mass was compared to dry body mass. Our results show that exoskeleton scales to the first power in both insects and spiders, and therefore both large and small terrestrial arthropods devote a similar fraction of their body mass to exoskeletal structures. In addition, we show that differences in arthropod life history strategy and phylogenetic history can cause variation in support structure scaling. For example, 1) insects generally invest more in exoskeleton than do spiders, but spiders exhibit a stronger mass dependence for this relationship; 2) holometabolous insects invest more in exoskeleton than hemimetabolous insects; and 3) exoskeletal mass tends to be greater in non-flyers than in flyers. Finally, we discuss the implications of arthropod exoskeletal isometry (slope = 1) with respect to the positive allometry (slope > 1) of support structures in most other systems (vertebrates, plants, and buildings).