The effect of experimental hybridization on cognition and brain anatomy: Limited phenotypic variation and transgression in Poeciliidae

Abstract

Hybridization can promote phenotypic variation and often produces trait combinations distinct from the parental species. This increase in available variation can lead to the manifestation of functional novelty when new phenotypes bear adaptive value under the environmental conditions in which they occur. While the role of hybridization as a driver of variation and novelty in traits linked to fitness is well recognized, it remains largely unknown whether hybridization can fuel behavioural novelty by promoting phenotypic variation in brain morphology and/or cognitive traits. To address this question, we investigated the effect of hybridization on brain anatomy, learning ability, and cognitive flexibility in first-and second-generation hybrids of two closely related fish species (Poecilia reticulata and P. wingei). Overall, we found that F1 and F2 hybrids showed intermediate brain morphology and cognitive traits compared to parental groups. Moreover, as phenotypic dispersion and transgression was low for both brain and cognitive traits, we suggest that hybridization is not a strong driver of brain anatomical and cognitive diversification in these Poeciliidae. To determine the generality of this conclusion, hybridization experiments with cognitive tests need to be repeated in other families.

Expansion of learning capacity elicited by interspecific hybridization

“…Although the evolutionary significance of interspecies hybridization on learning and cognitive functions remains elusive, genetic incompatibilities in F 1 hybrids might lead to cognitive impairments ( 23 ). As a result, interspecies hybridization does not always positively influence the adaptation of cognitive and learning capacities in F 1 individuals ( 24 , 73 ). Moreover, it is important to recognize that “expanded learning” in interspecies hybrids does not necessarily denote adaptive and improved functionality across all domains.…”

“…Therefore, hybridization serves as a notable evolutionary driver, generating phenotypic diversity across many species (19,21). While numerous studies have focused on morphological and physiological traits in F 1 hybrids in comparison with their parental species, a few studies have examined the potential alterations in latent cognitive abilities, such as memory and learning (22)(23)(24)(25). Specifically, research on vocal learning in interspecies hybrids remains scarce.…”