Avian gut passage reduces seed exit costs in Sorbus aucuparia (Rosaceae) as measured by a diametral compression test
Torbjørn R. Paulsen A C , Ommund Lindtjørn A , Nils Roar Gjerdet B and Göran Högstedt AA Department of Biology, University of Bergen, Postboks 7800, N-5020 Bergen, Norway.
B Department of Oral Sciences — Biomaterials, University of Bergen, Årstadveien 17, N-5009 Bergen, Norway.
C Corresponding author. Email: torbjorn.paulsen@bio.uib.no
Functional Plant Biology 33(4) 401-406 https://doi.org/10.1071/FP05279
Submitted: 21 November 2005 Accepted: 6 February 2006 Published: 3 April 2006
Abstract
Reduced seed exit costs have been suggested to explain advanced seedling emergence and increased seedling growth in Sorbus aucuparia L. (Rosaceae; rowan) following Turdus spp. (Turdidae; thrush) gut passage. In the present study, seed coat tension strength of Turdus merula L. (Turdidae; blackbird) gut-passed and non-ingested control seeds were tested with a diametral compression test. Both maximum load (N) and work (mJ) required for opening the seeds were reduced in gut-passed seeds, although scanning electron microscopy showed no visible differences in seed coat surface structure between treatments. In addition, gut passage increased dry seed weight by 0.64 mg (22%), weight of hydrated seeds by 0.62 mg (16%) and width of hydrated seeds by 0.1 mm (9%). Absorption causing the seed coat to yield more easily to the germinating seedling is proposed as an explanation for the reduction in seed exit costs. For the emerging seedling, the time and force needed to open the seed coat was reduced, thus lowering dispersal and germination costs of S. aucuparia.
Keywords: endozoochory, frugivory, gut passage, seed mass, seedling emergence.
Acknowledgments
We thank the Faculty of Mathematics and Natural Sciences and the Faculty of Dentistry, University of Bergen, for making this study possible, Alf Tore Mjøs and Terje Lislevand for skillful field assistance, Irene Ohlen Moldestad, Odd Johan Lundberg, Erik Severin Erichsen and Teresa Cieplinska for technical assistance, and Glenn Hellekjær, Knut Helge Jensen, Per Harald Salvesen and two anonymous reviewers for valuable comments on earlier versions of the manuscript. Permission to capture and cage birds was granted by the Norwegian Directorate for Nature Management (ref. 2003 / 5458 ARTS-VI-ID).
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