Floral visitation in the Australian native shrub genus Acrotriche R.Br (Ericaceae): an abundance of ants (Formicidae)

Abstract

AbstractThe genus Acrotriche is a group of predominantly winter flowering Australian native plants with small flowers that use a unique method of secondary pollen presentation. The mating system of one species has been determined as requiring transfer of pollen from one plant to another to enable effective pollination and floral conformity in other species suggests similar breeding systems. Previous authors have suggested non‐flying mammal pollination for members of the genus based on floral traits and reports of floral consumption; however, this hypothesis does not stand up to scrutiny. Acrotriche floral traits can also be interpreted as indicative of crawling invertebrate pollination. The identification of floral visitors and their potential for pollination has not been conducted previously for any Acrotriche species. To identify potential pollinators, the floral visitors to six different species of Acrotriche were observed throughout an entire 24 h period at a range of sites throughout South Australia. Ants were identified as the most common and abundant floral visitors for all Acrotriche species. Ant pollination is considered rare due to the negative effects that ant secretions can have on pollen viability. To determine these effects in relation to Acrotriche, pollen germination experiments were undertaken after contact with the integument of several ant species. Reductions in pollen viability varied between plants and ant species but in all experiments viable pollen remained after ant contact. These results, along with observed behaviour of ant visitors, indicate that ants may contribute to pollination in Acrotriche.