Meeting Abstract
105.3 Sunday, Jan. 6 Visual ecology of two ephemeral pool crustaceans: phototaxis and light-orientation behavior of Triops (Branchiopoda: Notostraca) and Streptocephalus (Branchiopoda: Anostraca) LESSIOS, N*; RUTOWSKI, RL; COHEN, JH; Arizona State University; Arizona State University; University of Delaware nicolas.lessios@asu.edu
Triops and Streptocephalus are branchiopod crustaceans that are often found within the same ephemeral freshwater pools. Triops are mainly benthic foragers but also swim to the air-surface boundary in hypoxic conditions. They have two sessile compound eyes, as well as four median ocelli (naupliar eyes). Streptocephalus swim within the water column and are mainly suspension feeders. They have two stalked compound eyes and three median ocelli. Both lay desiccation-resistant eggs that also require light to resume development. This study aimed to characterize the light environment, phototactic response and dorsal light-orientation of Triops and Streptocephalus from the same pools (filled by monsoon rains in SE Arizona, USA). Irradiance measurements were taken over a depth gradient, and over time. Phototactic responses were observed within an acrylic chamber in the horizontal plane using a 500W Tungsten projector with interference filters to limit stimulus light to narrow bandwidths. Action spectra and phototaxis thresholds were obtained from ovisac-bearing adults for species of each genus, taken from the field and lab-reared. A distinct dorsal light reflex was observed by testing orientation in an acrylic chamber that simulates natural angular light distribution near the surface of an ephemeral pool. Statocysts have not been reported in branchiopod crustaceans, suggesting that light is a primary means of vertical orientation. Irradiance measurements were red-shifted with increasing depth, suggesting that vertical orientation could have a wavelength-specific component. Understanding the adaptive significance of eyes in Triops, Streptocephalus and other non-malacostracan crustaceans will help to infer transitions in eye evolution, and will illustrate the diversity of extant insect-crustacean sensory systems.
