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Predation impacts brain allometry and offspring production in female guppies (Poecilia reticulata)

Survivorship under predation exerts strong selection on reproductive traits as well as on brain anatomy of prey. However, how exactly predation and brain evolution are linked has not been resolved as current empirical evidence is inconclusive. This may be due to predation pressure having different effects across life stages and/or due to confounding factors in ecological comparisons of predation pressure. Here, we used adult guppies (Poecilia reticulata) to experimentally test the impact of a period of strong predation on brain anatomy and reproduction of surviving individuals. We compared the survivors to control fish, which were exposed to visual and olfactory predator cues but could not be predated on, and found that predation impacted the relative size of female brains. This effect was dependent on body size as larger female survivors showed relatively larger brains, while smaller survivors showed relatively smaller brains when compared to control animals. There were no differences in male relative brain size between the treatments, nor for any specific relative brain region sizes for either sex. Moreover, survivors produced more offspring, but did not show shorter interbrood intervals than controls. Our results corroborate the important, yet complex, role of predation as an important factor behind variation in brain anatomy.