title: Mechanical damage to pollen aids nutrient acquisition inHeliconiusbutterflies (Nymphalidae).
abstract: NeotropicalHeliconiusandLaparusbutterflies actively collect pollen onto the proboscis and extract nutrients from it. This study investigates the impact of the processing behaviour on the condition of the pollen grains. Pollen samples (n= 72) were collected from proboscides of variousHeliconiusspecies andLaparus dorisin surrounding habitats of the Tropical Research Station La Gamba (Costa Rica). Examination using a light microscope revealed that pollen loads contained 74.88 ± 53.67% of damagedPsychotriapollen, 72.04 ± 23.4% of damagedPsiguria/Guraniapollen, and 21.35 ± 14.5% of damagedLantanapollen (numbers represent median ± first quartile). Damaged pollen grains showed deformed contours, inhomogeneous and/or leaking contents, or they were empty. Experiments withHeliconiusandLaparus dorisfrom a natural population in Costa Rica demonstrated that 200 min of pollen processing behaviour significantly increased the percentage of damaged pollen ofPsychotriacompared to pollen from anthers (P= 0.015,Z= -2.44, Mann-WhitneyU-test). Examination of pollen loads from green house rearedHeliconiusbutterflies resulted in significantly greater amounts of damagedPsiguriapollen after 200 min of processing behaviour compared to pollen from flowers (P< 0.001,Z= -4.583, Mann-WhitneyU-test). These results indicate that pollen processing functions as extra oral digestion whereby pollen grains are ruptured to make the content available for ingestion.
authors.affiliation: Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Harald W
authors.initials: HW
authors.lastname: Krenn
authors.affiliation: Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Monika J B
authors.initials: MJ
authors.lastname: Eberhard
authors.affiliation: Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Eberhard
authors.affiliation: Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Anna-Laetitia
authors.initials: AL
authors.lastname: Hikl
authors.affiliation: Department of Palynology and Structural Botany, Faculty of Life Sciences, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
authors.forename: Werner
authors.initials: W
authors.lastname: Huber
authors.affiliation: Brackenridge Field Laboratory and Section of Integrative Biology, University of Texas, Austin, TX 78712, USA.
authors.forename: Lawrence E
authors.initials: LE
authors.lastname: Gilbert
keywords: Butterfly; Extra oral digestion; Heliconius; Lepidoptera; Pollen feeding