Insect visitation patterns in diploid Centaurea aspera and its related allotetraploid and triploid hybrids: Similar...

Polyploidy is key to plant evolution by contributing to speciation, diversification, and adaptability. However, the minority cytotype exclusion effect can limit the persistence of polyploids, which can be mitigated by reproductive barriers such as distinct insect visitation between cytotypes. In eastern Spain, the diploid C. aspera, its related allotetraploid C. seridis, and their sterile triploid hybrid C. ×subdecurrens coexist in contact zones. Here we assessed the diversity and behavior of insects visiting these Centaurea taxa, identified factors influencing insect visitation, and explored potential changes in visitor composition and frequency across taxa in the contact zone of El Saler (Valencia, Spain).

Five natural blocks (25-50 m²) on sand dunes, each with all three plant taxa in proximity, were monitored weekly when their flowering periods overlapped. Insect visitors were identified, and number of visits and of capitula were recorded. Linear modelling was used to identify factors predicting visit frequency and differences in insect composition among plant taxa.

Seventeen flying insect species visited Centaurea plants. The number of florets and the number of capitula were the strongest predictors of visit frequency, showing similar outcomes, rather than plant taxon or date. Although overall visitation rates did not significantly differ among plant taxa, insect assemblages varied. Centaurea seridis attracted a distinct set of insects compared to C. aspera and C. ×subdecurrens, with some insects displaying visitation biases at particular times.

Differences in insect assemblages suggest potential prezygotic barriers that could help C. seridis overcome minority exclusion, supporting its long-term establishment.