Evolution of reproductive isolation in a long-term evolution experiment with Drosophila melanogaster: 30 years of divergent life-history selection

Abstract

We ask if three decades and over 1 500 generations of divergent life history selection on age at reproduction has resulted in the evolution of reproductive isolation (RI) between laboratory populations of Drosophila melanogaster. We tested for premating, postmating-prezygotic and postzygotic reproductive isolation between 3 replicate population pairs. Large, evolved differences in body size between selection treatments suggested the potential for prezygotic barriers driven by sexual selection or physical incompatibilities between the sexes. Although a simple prediction would be preference for larger size, creating directional isolation, our results from individual mate choice trials indicate that populations from both selection treatments show a marked bias towards homotypic mate choice; indicative of prezygotic RI driven by sexual selection or sexual conflict. Hybridization between the focal populations resulted in the production of viable adult flies with intermediate size and developmental traits. We observed a suggestive but statistically non-significant trend of fitness decline in the F2 generation of hybrids, but no significant evidence suggesting the evolution of postmating-prezygotic or postzygotic RI. Our findings are in accord with extant literature that posits that premating RI evolves before postmating forms of RI.

Differentiating mechanism from outcome for ancestry-assortative mating in admixed human populations

“…Positive assortative mating (hereafter, assortative mating), wherein genotypic or phenotypic trait values are positively correlated between mates, has been empirically observed across animal species ( Jiang et al 2013 ). Theoretical and empirical studies have demonstrated the consequences of assortative mating for speciation and hybridization ( Kondrashov 1983 ; Otto et al 2008 ; Tung et al 2012 ; Schumer et al 2017 ; Kopp et al 2018 ; Powell et al 2021 ; Muralidhar et al 2022 ; Natola et al 2022 ; Smadja et al 2022 ; Robinson et al 2023 ), and for the distributions of traits within populations ( Wright 1921 ; Norris et al 2019 ; Kim et al 2021 ; Border et al 2022 ; Muralidhar et al 2022 ; Horwitz et al 2023 ).…”