Acacia-ant symbiosis

Acacia-ant symbiosis is the interaction between myrmecophilous Vachellia trees (ant acacias) and ants that nest on them (acacia ants). Obligate acacia ants dwell in the gall-like domatia within the swolen stipular spines of African or Central American ant acacia species, and they also take the food (nectar or Beltian bodies) offered by the tree. Some of them protect ant acacias from herbivores in return, hence mutualism; the others provide inadequate protection or none at all, hence weaker or non-mutualism. Facultative (non-obligate) acacia ants often nest on stems instead of in gall-like domatia, and tend to be non-mutualistic.^[1][2][3]

Africa

Acacia ants living in the gall-like domatia of Vachellia drepanolobium

Four acacia ant species are symbiotic with Vachellia drepanolobium: Crematogaster mimosae, C. nigriceps, and Tetraponera penzigi are obligate and mustualistic symbionts, whereas C. sjostedti is facultative and the least mustualistic, and it even facilitates attack on the tree by beetles.^[3]

Vachellia bullockii, V. burttii, V. bussei, V. elatior, V. erioloba, V. erythrophloea, V. luederitzii var. retinens, V. malacocephala, V. mbuluensis, V. myrmecophila, V. pseudofistula, V. seyal var. fistula, and V. zanzibarica are also known to have gall-like domatia,^[4] but their symbiotic ants are yet to be studied.

Central America

Pseudomyrmex ferruginea feeding on nectar produced by Vachellia cornigera (or V. sphaerocephala)

The following are 10 obligate and mutualistic acacia ants and their reported host plants in Central America:^[2]

• Pseudomyrmex ferruginea: Vachellia allenii, V. chiapensis, V. collinsii, V. cookii, V. cornigera, V. gentlei, V. globulifera, V. hindsii, V. janzenii, V. mayana, and V. sphaerocephala
• P. flavicornis and P. nigrocinctus: V. collinsii, V. cornigera, and V. hindsii
• P. janzeni: V. hindsii
• P. mixtecus and P. veneficus: V. collinsii and V. hindsii
• P. particeps: V. allenii
• P. peperi: V. chiapensis, V. collinsii, V. cornigera, V. gentlei, V. globulifera, and V. hindsii
• P. satanicus: V. melanoceras
• P. spinicola: V. collinsii, V. cornigera, and V. allenii

The obligate acacia ant with weak or non-mutualism include P. nigropilosus, P. simulans and P. subtilissimus.^[2]

Facultative acacia ants in Central America include P. boopis, P. gracilis, P. hesperius, P. ita, P. kuenckeli, P. opaciceps, Crematogaster and Camponotus species.^[2][5]

Some swollen-spine acacias in Central America are less dependent on acacia-ant mutualism and often unocuppied by obligate acacia ants without being significantly damaged by herbivores, e.g. V. cookii, V. globulifera, and V. ruddiae.^[5]

References

1. Palmer, T.M. (2023-06-05). "Acacia ants". Current Biology. 33 (11): R469 – R471. Bibcode:2023CBio...33R.469P. doi:10.1016/j.cub.2023.02.002. PMID 37279676.
2. Ward, P.S. (1993). "Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae)" (PDF). Journal of Hymenoptera Research. 2 (1): 117–168.
3. Palmer, T.M.; Young, T.P. (2017), Oliveira, P.S.; Koptur, S. (eds.), "Integrating Ecological Complexity into Our Understanding of Ant-Plant Mutualism: Ant-Acacia Interactions in African Savannas", Ant-Plant Interactions: Impacts of Humans on Terrestrial Ecosystems, Cambridge: Cambridge University Press, pp. 200–222, doi:10.1017/9781316671825.011, ISBN 978-1-107-15975-4, retrieved 2024-10-10
4. Lebrun, Jean-Pierre; Stork, Adélaïde L. (2008). Tropical African Flowering Plants: Ecology and Distribution. Vol. 3. Genève: Conservatoire et jardin botaniques de la Ville de Genéve. ISBN 978-2-8277-0114-8.
5. Janzen, D.H. (1974). "Swollen-Thorn Acacias of Central America". Smithsonian Contributions to Botany (13). Washington D.C.: Smithsonian Institution: 1–131. doi:10.5479/si.0081024X.13.