The Role of Extrafloral Nectar Amino Acids for the Preferences of Facultative and Obligate Ant Mutualists |
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Authors: | Marcia González-Teuber Martin Heil |
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Affiliation: | 1.Department of General Botany–Plant Ecology,University of Duisburg-Essen,Essen,Germany;2.Departamento de Ingeniería Genética,CINVESTAV-Irapuato,Irapuato,México |
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Abstract: | Plants in some 300 genera produce extrafloral nectar (EFN) to attract ants as a means of indirect defence. Among Mesoamerican
Acacia species, obligate myrmecophytes produce EFN constitutively to nourish symbiotic ant mutualists, while non-myrmecophytes induce
EFN secretion in response to herbivore damage to attract non-symbiotic ants. Since symbiotic Acacia ants entirely depend on the host-derived food rewards while non-symbiotic ants need to be attracted to EFN, this system allows
comparative analyses of the function of EFN components in ant nutrition and attraction. We investigated sugar and amino acid
(AA) composition in EFN of two myrmecophytes (Acacia cornigera and Acacia hindsii) and two related non-myrmecophyte species (Acacia farnesiana and Prosopis juliflora). AA composition allowed a grouping of myrmecophytes vs. non-myrmecophytes. Behavioural assays with obligate Acacia inhabitants (Pseudomyrmex ferrugineus) and non-symbiotic ants showed that AA composition affected ant preferences at high but not at low AA/sugar ratios. Most
interestingly, behavioural responses differed between the two types of ants tested: Symbiotic ants showed a clear preference
for higher AA concentrations and preferred nectar mimics with those four AAs that most significantly characterised the specific
nectar of their Acacia host plant. In contrast, non-symbiotic ants distinguished among nectars containing different sugars and between solutions
with and without AAs but neither among nectars with different AA/sugar ratios nor among mimics containing different numbers
of AAs. Our results confirm that both AAs and sugars contribute to the taste and attractiveness of nectars and demonstrate
that the responses of ants to specific nectar components depend on their life style. AAs are a chemical EFN component that
likely can shape the structure of ant–plant mutualisms. |
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Keywords: | Acacia Ant– plant interaction Pseudomyrmex Mutualism Nectar |
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