Evolutionary origins of coordination: Physiological and molecular studies on sponges

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How nervous systems evolved is one of the enduring questions of evolutionary biology. Sponges are members of the Porifera, one of the earliest lineages of animals; they are filter feeders and are one of only two groups of multicellular animals that lack a nervous system, yet their genomes have many neuronal-type genes, and sponges have a range of coordinated behaviours in response to environmental stimuli. My students and I study how sponges coordinate behaviour to understand how sensory tissues and coordination systems may have given rise to neurons and nervous systems. In this program we address three questions: (1) Are `neural' molecules expressed and used in a sensory role in sponge tissues? (2) Are novel mechanisms used in sensory-coordination in sponges? and (3) What are the physical parameters that may have influenced early sensory system evolution? Using lab and field experiments we will study the genes, cells and molecules that exist in sponges and which work together to generate whole-body behaviours. 1) Using a sponge that can be grown in the lab - and which responds to stimuli by contracting in a stereotypical way that looks like a sneeze - we will use pharmacological studies to test how signals propagate across tissues. We will explore the triggers that cause contractions and those that prevent unwanted contractions to allow a coordinated behaviour. We will also map the sponge's tissues to better understand which parts are involved in sending and receiving the signals that cause contractions. 2) It is possible that animals evolved very different, unrelated, methods of coordinating their bodies. We will explore two new sensory systems in the sponge body to better understand whether these are quite novel, or whether they also retain roots shared with the animal tree. One such system is a photoreceptor or sponge eye, in a calcarous sponge. The other is a sponge 'nose' or flap of tissue that covers the inhalent openings preventing entry of unwanted particles. We will compare genes and molecules expressed in these structures with those in sensory organs in other animals. 3) How sponges respond and with what cells, tissues, and molecules, requires understanding what sponges respond to. In a third avenue we will investigate the range of environmental parameters that sponges respond to in their natural habitats. We will test whether presence or absence of food, oxygen, flow, light, or changes in temperature stimulate contractions in undisturbed sponges filmed in their habitat. We will also test the effect of specific parameters on sponges in tanks. Work will mostly be done at the University of Alberta, and at the west coast marine station, the Bamfield Marine Sciences Centre.