What insects can tell us about the origins of consciousness

How, why, and when consciousness evolved remain hotly debated topics. Addressing these issues requires considering the distribution of consciousness across the animal phylogenetic tree. Here we propose that at least one invertebrate clade, the insects, has a capacity for the most basic aspect of consciousness: subjective experience. In vertebrates the capacity for subjective experience is supported by integrated structures in the midbrain that create a neural simulation of the state of the mobile animal in space. This integrated and egocentric representation of the world from the animal’s perspective is sufficient for subjective experience. Structures in the insect brain perform analogous functions. Therefore, we argue the insect brain also supports a capacity for subjective experience. In both vertebrates and insects this form of behavioral control system evolved as an efficient solution to basic problems of sensory reafference and true navigation. The brain structures that support subjective experience in vertebrates and insects are very different from each other, but in both cases they are basal to each clade. Hence we propose the origins of subjective experience can be traced to the Cambrian.

Exploring the role of the physical marine environment in silver eel migrations using a biophysical particle tracking model

Both the American eel (Anguilla rostrata) and European eel (Anguilla anguilla) undertake long-distance migrations from continental waters to their spawning sites in the Sargasso Sea. Their migration routes and orientation mechanisms remain a mystery. A biophysical particle tracking model was used in this study to simulate their oceanic migration from two release areas: off the Scotian Shelf (Canada) and off the Irish continental shelf. Two plausible swimming-directed behaviours were considered for simulating two different migratory paths: true navigation to specific spawning sites and innate compass orientation towards the vast spawning area. Several combinations of swimming speeds and depths were tested to assess the effect of ocean circulation on resulting migratory pathways of virtual eels (v-eels), environmental conditions experienced along their oceanic migration, and energy consumption. Simulations show that the spawning area can be reached in time by constantly swimming and following a readjusted heading (true navigation) or a constant heading (compass orientation) even at the lowest swimming speed tested (0.2 m s−1) for most v-eels. True navigation might not be necessary to reach the spawning area. The ocean currents affect mainly the migration of American v-eels, particularly for swimming speeds lower than 0.8 m s−1. The ocean circulation increases the variability in the oceanic migration and generally reduces the efficiency of the v-eels, although positive effects can be possible for certain individuals. The depth range of diel vertical migration (DVM) significantly affects the total energy expenditure due to the water temperature experienced at the various depths. Model results also suggest that energy would not be a limiting factor as v-eels constantly swimming at 0.8 BL s−1 spent <25 and 42% of energy available for migration for American and European v-eels, respectively.

Ultrasonic Tracking of Homing Cutthroat Trout (Salmo clarki) in Yellowstone Lake

Displacement of 42 mature cutthroat trout (Salmo clarki) from their spawning tributaries to the open water of Yellowstone Lake in the summers of 1966 and 1968 and following them ultrasonically up to 13.5 hr and 11.8 km indicated that those that homed used a compass mechanism rather than search or true navigation to find shore and then followed the shoreline to the home stream. Vision was unnecessary for homing. For many of the fish whose movements showed no consistent pattern, the transmitters failed prematurely.Of 29 nonanesthetized trout tracked from a point northwest of their home streams, six moved generally eastward to shallow water, turned south, and followed the shoreline toward the home streams, three being followed all the way home. Six moved generally south or southeast and progressed toward their home streams entirely in open water, one being followed home. Three moved inappropriately for homing but were less than 2 km from the release point when tracking was ended. Fourteen moved randomly or did not move enough or were not tracked long enough to establish a pattern.Of five anesthetized-blinded trout, two moved eastward and then south along the shoreline, one moved south in open water, and the other two did not show a consistent pattern. Of four anesthetized-control trout, two moved eastward and then south along shore, one being followed home; one moved inappropriately and the other did not establish a pattern.Of four nonanesthetized trout tracked from a point southwest of their home stream, three moved east and then north along shore toward the home stream, one being followed home; the fourth moved north in open water.Current directions may have influenced the initial orientations.Swimming speeds ranged from 0.0 to 46.2 cm sec−1 in open water and from 8.5 to 82.3 cm sec−1 along shore. Average along-shore speed (36.6 cm sec−1) was greater than average open-water speed (22.9 cm sec−1). Blinded trout swam at about the same speeds (average 22.6 cm sec−1) as control trout (average 27.0 cm sec−1) and nonanesthetized trout (average 23.3 cm sec−1).