Patterns of Performance Variation Between Animal Hybrids and their Parents: A Meta-analysis

Abstract

Hybridization is a widespread phenomenon in animals, and hybrid heterosis/breakdown could be key processes determining the evolutionary dynamics of hybrids. Indeed, hybrids are not consistently disadvantaged compared to the parental lineages, as was historically assumed. Multiple processes could lead to performance differences between parental lineages and their hybrids. Despite many studies evaluated the performance of hybrids, a quantitative synthesis is required to assess the general pattern. Here we used meta-analytic and meta-regression approaches to quantify the fitness differences between parental lineages and their hybrids, and to identify possible processes that could lead to these differences. Specifically, we tested biological and methodological parameters that could determine differences in performance between hybrids and parental lineages. Hybrid performance was extremely variable across studies, being often significantly higher or lower compared to the mean performance of their parents. Nevertheless, the averaged hybrid performance was similar to the fitness of parental lineages, with differences across studies related to how performance was assessed. Genetic divergence between parental lineages, and the approach used to identify hybrids were the parameters most strongly related to variation in hybrid performance. Performance was lower for hybrids between distantly related lineages. Furthermore, study settings and the use of imprecise approaches for hybrid identification (e.g. morphology-based) can bias assessments of performance. Studies performed on wild populations and using genetic approaches for hybrid identification detected more often a decreased hybrid performance, compared to laboratory studies. We highlight the importance of appropriate settings for a realistic understanding of the evolutionary impacts of hybridization.

Ecological niche contributes to the persistence of the western × glaucous‐winged gull hybrid zone

“…Our study provides additional support for the importance of exogenous selection in maintaining the hybrid zone between glaucous-winged gulls and western gulls, with selection favoring hybrids over either parental species. We now know that hybrid fitness can be quite variable, and understanding the factors that affect hybrid performance is critical for predicting the evolutionary dynamics of hybrid zones (Curry, 2015;Muraro et al, 2022).…”

“…Our study provides additional support for the importance of exogenous selection in maintaining the hybrid zone between glaucous‐winged gulls and western gulls, with selection favoring hybrids over either parental species. We now know that hybrid fitness can be quite variable, and understanding the factors that affect hybrid performance is critical for predicting the evolutionary dynamics of hybrid zones (Curry, 2015; Muraro et al., 2022). The tension zone model permits hybrid zone movement in response to dispersal of the parental species, while the bounded superiority model predicts that hybrid zones will be stationary as long as the environmental gradient across the hybrid zone persists (Curry, 2015; Key, 1968; Moore, 1977).…”

Does hybridisation with an invasive species threaten Europe’s most endangered reptile? Genomic assessment of Aeolian lizards on Vulcano island

“…The low fitness of latergeneration hybrid offspring can be indirectly inferred from the apparent lack of later generation hybrids in our analyses. Negative effects of hybridisation are often manifested in later-generations, such as F2s and higher order hybrids (Edmands, 1999;Muraro et al, 2022). Nevertheless, the detection of a few individuals with backcross genetic signatures indicate that early-generation hybrids are not always sterile as previously proposed (Capula, 1993).…”

Hidden in the ocean: The importance of detecting hybridisation in pelagic and deep‐water fishes

“…Importantly, as much as there are countless cases of hybrids with higher fitness than in the parental species, the opposite is not uncommon and low‐fitness hybrids are also well documented (e.g. Muhlfeld et al, 2009; Muraro et al, 2022). The consequences of this may depend on the relative abundance of parental species or on the phylogenetic distance among parental species (Montanari et al, 2014).…”