Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Asymmetry in fitness-related traits of later-generation hybrids between two invasive species.

Abstract

PREMISE: The importance of hybridization to invasion has been frequently discussed, with most studies focusing on the comparison of fitness-related traits between F1 hybrids and their parents and the consequences of such fitness differences. However, relatively little attention has been given to late-generation hybrids. Different fitness landscapes could emerge in later generations after hybrids cross with each other or backcross with their parents, which may play an important role in plant invasion and subsequent speciation. METHODS: In this study, artificial crosses were conducted to generate multiple generations, including F1, F2, and backcrosses between two invasive species: Cakile edentula (self-compatible) and C. maritima (self-incompatible). Putative hybrids were also collected in the sympatric zone and compared with their co-occurring parents for phenotypic and genetic differences. RESULTS: Genetic data provided evidence of hybridization happening in the wild, and phenotypic comparisons showed that natural hybrids had intermediate traits between the two species but showed more similarity to C. maritima than to C. edentula. The asymmetry was further identified in artificial generations for several phenotypic characters. Furthermore, backcrosses exhibited different patterns of variation, with backcrosses to C. maritima having higher reproductive output than their counterparts. CONCLUSIONS: Our results suggest that hybridization and introgression (backcrossing) in Cakile species is asymmetric and most likely to favor the proliferation of C. maritima genes in the mixed population and thus help its establishment, a finding that could not be predicted by characterizing F1 hybrids.