Reproductive isolation in a native population of Petunia sensu Jussieu (Solanaceae)

Reproductive isolation was studied in four syntopic species of Petunia sens u Jussieu (Solanaccae) at a site in Rio Grande do Sul State, Brazil. Recipr ocal artificial crossing experiments confirmed that a genetic barrier exist s between Petunia (P. axillaris and P. integrifolia) and Calibrachoa (C. pa rviflora and C. heterophylla), and also between C. parviflora and C. hetero phylla. Petunia axillaris (white, nocturnally scented flower) is geneticall y compatible with the syntopic and allotopic P. integrifolia (coloured, uns cented flower). Reproductive isolation appears to be maintained by the two species having different pollinators: nocturnally active hawkmoths (Manduca contracta and M. diffissa subsp. petuniae) pollinate P. axillaris while a diurnally active bee (Hexantheda sp.) pollinates P. integrifolia. Flowers o f P. integrifolia exhibit diurnal opening and closing movements synchronous with the activity period of the bee. Other than a probable nectar robber ( a carpenter bee, Xylocopa augusti), no insect visited flowers of P. axillar is in the day. Amounts of floral nectar in P. axillaris and P. integrifolia were within the range of hawkmoth- and bee-pollinated flowers, respectivel y. Reproductive isolating mechanisms in the genus Petunia sensu Jussieu are discussed. (C) 2001 Annals of Botany Company.