Individual guppies differ in quantity discrimination performance across antipredator and foraging contexts

Abstract

The ability to discriminate between different quantities is useful to an animal since it allows adaptive decisions in several contexts. In humans, some individuals are generally better at solving different numerical and mathematical problems, but we currently ignore whether other species also show individual differences in quantitative abilities across different contexts. Aiming to investigate this possibility, we observed the performances of individual guppies (Poecilia reticulata) in an antipredator task that required the discrimination between shoals made of a different number of conspecifics (4 versus 6 fish) and, successively, in two foraging tasks that required the discrimination between different numbers of food items (4 versus 6 items) and food items with different sizes (0.67 ratio between the two surface areas). Overall, guppies achieved comparable performances in the discrimination of shoal size and food item size, but showed reduced accuracy in the discrimination between different numbers of food items. Performances of guppies were correlated between the discrimination of shoal size and food item size, suggesting the existence of individual differences in quantity discrimination abilities in different contexts in this species. Unexpectedly, this relationship was negative, and some guppies were better in the antipredator task, while others were better in the foraging task. Our results agree with the general trend of the literature on animals that suggests the existence of multiple cognitive functions whose activation are task specific, and also introduce the possibility that some of these functions are subject to constraints. In this work, we provided the first clear evidence of individual differences in the ability to solve quantity discriminations in a fish. Guppies were observed in three quantity discrimination tasks: recognising and joining the larger shoal of conspecifics among two options, a behaviour that confers protection from predators; selecting the larger number of food items between two sets; and selecting the food item with larger size. Guppies that were more accurate in the shoal size discrimination achieved lower scores in the food item size discrimination. Some individuals gain advantage from cognitive abilities that confer defence against predators, while other individuals from those abilities that improve foraging success.