The Impacts of Pregnancy on Cognition and Cell Proliferation in a Live‐Bearing Fish ( <scp> <i>Poeciliopsis gracilis</i> </scp> )

Pregnancy is a high-energy process which temporarily decreases cognitive function and affects the neurogenic capacity of the maternal brain. Pregnant females exhibit decreased performance in spatial memory tasks which has been linked to altered neurogenesis in the dentate gyrus of the hippocampus. While these processes are well-resolved for mammals, whether they are conserved across other, nonmammalian, live-bearing animal lineages without placentation remains enigmatic. Here, we test the relationship between pregnancy and cognition in the live-bearing fish Poecilipsis gracilis. Female P. gracilis are almost continuously pregnant after sexual maturation meaning that any cognitive deficits due to pregnancy may be constant throughout adulthood. To determine the consequences of this continuous pregnancy on maternal cognition, we compared the performance of pregnant and virgin females in two ecologically relevant cognitive assays, a spatial memory task and a reversal learning task. To further assess pregnancy-induced changes in brain plasticity, the brains of each female were then assessed using immunohistochemical staining for the neurogenic proliferation marker ki67. We found that pregnant females showed a decline in spatial learning performance, exhibiting more non-choice trials. Although pregnant females did not exhibit decreased cell proliferation in the hippocampal-analogous region of the brain, they did show decreased proliferation in the olfactory bulb and ventral telencephalon. Our results indicate that, just like in mammals, pregnancy in fish impacts female cognitive capacity and cell proliferation, even though those poeciliid fishes do not have a placenta.