Unravelling reproductive resilience and genetic characteristics of Cistus heterophyllus subsp. carthaginensis and their role in limiting recruitment on natural populations

Abstract This study compares reproduction and genetic traits of Cistus heterophyllus subsp. carthaginensis in two Iberian Peninsula populations (Murcia and Valencia), alongside C. albidus , the main competitor responsible for hybridisation in these populations. The former taxon is critically endangered (IUCN CR), justifying the conservation efforts. Thermal time, base temperature, hydrotime, base water potential, and seed longevity (through accelerated ageing) were used to assess competitiveness during germination. Six pollination treatments evaluated reproductive success in both populations. Three molecular markers analysed the phylogenetic affiliation of the populations. The Valencian population showed a stronger competitive response than C. albidus in temperature and water stress tests, while the Murcian seeds exhibited intermediate behaviour, reflecting their hybrid genetic traits. Longevity tests revealed higher P50 values in the hybrid population, suggesting potential hybrid vigour. Reproductive success was higher in the Murcian population, also associated to its hybrid nature; both populations exhibited low but positive self- compatibility. Our findings indicate that the germinative phase does not drive the regression of C. heterophyllus in Spain, compared to the advance of C. albidus . Instead, reduced fruit and seed production, linked to very low genetic variability, contribute to this regression.