We use South American weakly electric fish and Trinidadian killifish to investigate the effects of predation on adult neurogenesis and brain morphology. Previously, we examined the effect of predation on brain cell proliferation in wild-caught electric fish, Brachyhypopomus occidentalis in Panama. Fish exposed to higher levels of predation risk and tail injuries from predators showed decreased forebrain cell proliferation compared to fish with low levels of predation risk and intact tails. Brain cell proliferation decreased in the region of the brain that is homologous to the mammalian hippocampus. We further investigated the effect of predators by experimentally amputating the tails of Brachyhypopomus gauderio and Apteronotus leptorhynchus. Fish with amputated tails showed significantly reduced levels of brain cell proliferation than the control fish with intact tails, which parallels findings in the field.
Recently, we examined wild populations of killifish, Rivulus hartii in Trinidad, that lived in either predator abundant and predator-free streams. The ecology of these fish has been studied extensively, which enables us to understand brain growth and cell dynamics in the context of their environment and life history. We found that fish from predator abundant environments had much smaller brains than the predator-free populations. In addition, killifish that lived with predators had a much higher rate of cell proliferation. Neurogenesis was not regionally specific, but rather predation exposure enhanced neurogenesis across the brain.
We are currently examining the F1 offspring of the same wild caught populations of killifish. These lab-reared killifish were the offspring of wild-caught parents from streams of differing predation pressure. In this common garden study, we are testing if there is a genetic difference between killifish populations living in predator abundant and predator-free streams. The results from this study will allow us to attribute population differences in neurogenic rate to genetic differentiation or to the environment – i.e., the presence of predators.
Joshua Corbo, July 2018