Reproductive ecology of Dianthus inoxianus: A rare wild carnation with a specialized pollination system

Abstract

Plants with specialized pollination systems may be susceptible to reproductive failure when pollinator service is unpredictable. This can influence the selection of floral traits that promote outcrossing in the presence of pollinators and selfing in their absence. Limited evidence exists regarding the association between specialized pollination and reproductive assurance, necessitating further investigation. We studied the reproductive biology of Dianthus inoxianus, a rare Mediterranean carnation endemic to a semi-arid region in SW Spain. D. inoxianus exhibited protandrus flowers and additional phenotypic signs of specialization for nocturnal pollination. Nectar sugar concentration remains relatively constant throughout the day (average 33.4%), while the standing crop varies considerably (average 1.5 μL/flower), peaking in the late afternoon and early evening. Controlled hand pollinations revealed that D. inoxianus is fully self-compatible, with similar reproductive success in autogamous, geitonogamous, and allogamous crosses. However, a small proportion of bagged flowers exhibited autonomous selfing. To assess the impact of presumed nocturnal pollination, we studied reproductive fitness and flower visitors over five years in three populations. Over 210 h of pollinator censuses, the hawkmoth species Hyles livornica and Macroglossum stellatarum, which were mainly dusk-active, accounted for > 95% of flower visits. Fruit and seed set positively correlated with hawkmoth visitation rate across years and populations. Additionally, pollinator exclusion experiments demonstrated that reproduction relies predominantly on nocturnal pollinators. However, under natural conditions, D. inoxianus also showed a non-negligible degree of autonomous self-pollination, with fruit- and seed-set being equivalent in absence of pollinators or under diurnal pollinators. We found evidence of an ecologically specialized pollination system and capacity for autonomous selfing, a combination that may enable the persistence of this taxon in a markedly unpredictable pollination environment.