Meeting Abstract
Metazoan respiratory systems are diverse, and the size and components of the respiratory system often scale with body size. Many vertebrates rely on gills and lungs for gas exchange, and the surface area and thickness of the respiratory barrier (gill or lung) is the primary limit to oxygen transport. Some organisms and life stages, however, rely on cutaneous gas exchange, which means that the respiratory surface (egg shell, skin, or cuticle) serves two primary functions: gas-exchange and structural support. The respiratory surface must be thin and porous enough to transport gases but strong enough to prevent buckling or tearing from external forces. Here, we tested whether surface area and thickness of the gas-exchange barrier together explain the limits to oxygen uptake in twelve species of sea spiders (pycnogonids); a group of animals that rely on cutaneous respiration. Respiratory surface area scaled with a lower exponent (b = 0.67) than that of endothermic and ectothermic vertebrates (b = 0.89 and b = 0.78, respectively, Gillooly et al., 2016), but cuticle thickness scaled with a higher exponent (b = 0.3) than endothermic and ectothermic vertebrate barrier thickness (b = 0.1 and b = -0.04, respectively). We hypothesize that the difference in scaling exponents reflects the unusual dual role of the sea spider cuticle in both structural support and gas exchange. In further contrast to vertebrates, the scaling of surface area and cuticle thickness in sea spiders did not match the scaling of metabolism (b = 0.9). To meet this mismatch, the diffusion coefficient of oxygen in cuticle scaled positively with body size (b = 0.11) reflecting that larger sea spiders have thicker but increasingly porous cuticle. NSF PLR- 1341485.
