Mechanical damage to pollen aids nutrient acquisition in Heliconius butterflies (Nymphalidae)
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Neotropical Heliconius and Laparus butterflies 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 various Heliconius species and Laparus doris in 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 damaged Psychotria pollen, 72.04 ± 23.4% of damaged Psiguria/Gurania pollen, and 21.35 ± 14.5% of damaged Lantana pollen (numbers represent median ± first quartile). Damaged pollen grains showed deformed contours, inhomogeneous and/or leaking contents, or they were empty. Experiments with Heliconius and Laparus doris from a natural population in Costa Rica demonstrated that 200 min of pollen processing behaviour significantly increased the percentage of damaged pollen of Psychotria compared to pollen from anthers (P = 0.015, Z = −2.44, Mann–Whitney U-test). Examination of pollen loads from green house reared Heliconius butterflies resulted in significantly greater amounts of damaged Psiguria pollen after 200 min of processing behaviour compared to pollen from flowers (P < 0.001, Z = −4.583, Mann–Whitney U-test). These results indicate that pollen processing functions as extra oral digestion whereby pollen grains are ruptured to make the content available for ingestion.
KeywordsPollen feeding Extra oral digestion Heliconius Butterfly Lepidoptera
We are grateful to A. Demetz, T. Buchegger, S. Hufnagl for assistance in capturing butterflies, preparation of the pollen and counting pollen grains. Fieldwork was aided by the excellent facilities provided by the staff of the Tropical Research Station La Gamba (Costa Rica). The Costa Rican Ministerio del Ambients y Energia kindly granted research permits. We thank the Brackenridge Field Laboratory, University of Texas at Austin (USA) for logistic support as well as J. Bauder and J. Plant for editorial help. Funding was provided from the Austrian Science Fund (FWF project number P 18425 B03).
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