Obligate association of an oligolectic bee and a seasonal aquatic herb in semi-arid north-eastern Brazil

Abstract

Hydrocleys martii (Limnocharitaceae) is an annual aquatic herb common in ephemeral isolated ponds in semi-arid northe-astern Brazil. We studied pollination of H. martii, emphasizing reproductive success and association with oligolectic pollinators. The yellow flowers bear a central cone of staminodes that encloses the fertile stamens and four free carpels. The self-incompatible species depends on pollinators to set fruits. In 25 temporary water bodies in five Brazilian states, Protodiscelis palpalis bees (Colletidae, Paracolletinae) were the unique effective pollinators of H. martii and, in 18 of these, the sole flower visitors. Females of this narrowly oligolectic species show adapted behaviour to access the pollen chamber in the flower centre. Females removed more than 80% of the 480 000 pollen grains in only 2 h from the flowers but maintained a high visitation frequency almost until flower senescence. In this highly specialized plant-pollinator system, on average, 1.6% of the pollen grains reached the stigmatic surface and 9.6% remained uncollectible in the flowers. In the absence of P. palpalis, flowers set almost no seeds, indicating reproductive dependence on the oligolectic species. This pioneer pollination study of a species of Limnocharitaceae provides evidence of a close relationship of the family to species of Protodiscelis, their specific pollinators.