Vachellia drepanolobium
| Whistling thorn | |
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Scientific classification 
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| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fabales |
| Family: | Fabaceae |
| Subfamily: | Caesalpinioideae |
| Clade: | Mimosoid clade |
| Genus: | Vachellia |
| Species: | V. drepanolobium
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| Binomial name | |
| Vachellia drepanolobium (Harms ex Sjöstedt) P.J.H.Hurter[2]
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| Synonyms | |
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Vachellia drepanolobium, more commonly known as Acacia drepanolobium or whistling thorn,[1] is a swollen-thorn acacia native to East Africa. The whistling thorn grows up to 6 meters tall. It produces a pair of straight spines at each node, some of which have large bulbous bases. These swollen spines are naturally hollow and occupied by any one of several symbiotic ant species. The common name of the plant is derived from the observation that when wind blows over bulbous spines in which ants have made entry and exit holes, they produce a whistling noise.[3]
Whistling thorn is the dominant tree in some areas of upland East Africa, sometimes forming a nearly monoculture woodland, especially on "black cotton" soils of impeded drainage with high clay content.[4][5] It is browsed upon by giraffes and other large herbivores. It is apparently fire-adapted, coppicing readily after "top kill" by fire.[6]
Whistling thorn is used as fencing, tool handles, and other implements. The wood of the whistling thorn, although usually small in diameter, is hard and resistant to termites.
Symbiosis with ants
Like other acacias, whistling thorns have leaves that contain tannins, which are thought to serve as deterrents to herbivory. Like all African acacias, they are defended by spines.
At a site in Kenya, three Crematogaster and one Tetraponera ant species compete for exclusive possession of individual whistling thorn trees: Crematogaster mimosae, C. sjostedti, C. nigriceps, and Tetraponera penzigi.[4][5] Ant species vary in their level of mutualism with whistling thorn trees. The most common ant symbiote (~ 50% of trees), C. mimosae, has the strongest mutualistic relationship, aggressively defending trees from herbivores while relying on swollen-spines for shelter and feeding from nectar produced by glands near the base of leaves. (See also: Crematogaster peringueyi.)
3-Octanone and 3-Octanol have been identified as the alarm pheromones of Crematogaster negriceps and C. mimosa used in defending their tree. These chemicals are components of the ant’s mandibular gland secretion.[14] Later analysis of the mandibular gland secretion of these ants and of C. sjostedti showed distinct differences in the 28 volatile compounds that were identified.[15]
Because the ants compete for exclusive usage of a given tree, some species employ tactics to reduce the chance of a hostile ant invasion. Crematogaster nigriceps ants trim the buds of trees to reduce their lateral growth, thereby reducing chances of contact with a neighbouring tree occupied by a rival colony. Tetraponera penzigi, the only species which does not utilise the nectar produced by the trees, instead destroys the nectar glands to make a tree less appealing to other species.
The symbiotic relationship between the trees and the ants appears to be maintained by the effects of browsing by large herbivores. At the site in Kenya, when large herbivores were experimentally excluded, trees reduced the number of nectar glands and swollen spines they provided to ants. In response, the usually dominant C. mimosae increased their tending of parasitic sap-sucking insects as a replacement food source. In addition, the number of C. mimosae-occupied trees declined while twice as many become occupied by C. sjostedti, a much less aggressive defender of trees. Because C. sjostedti benefits from the holes made by boring beetle larvae, this species facilitates parasitism of trees by the beetles. As a result, the mutualistic relationship between whistling thorn trees and resident ants breaks down in the absence of large herbivores, and trees become paradoxically less healthy as a result,[5] and become much more vulnerable should herbivores be reintroduced.[16]
Gallery
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Crematogaster nigriceps ants in defensive demeanor. Note the absence of leaves except at the swollen thorns. -
Vachellia (Acacia) drepanolobium -MHNT -
Vachellia (Acacia) drepanolobium seed pods. -
Vachellia (Acacia) drepanolobium. -
Vachellia (Acacia) drepanolobium growing in red volcanic soil on western slopes of Mount Kilimanjaro
References
- ^ . Retrieved 19 November 2021.
- hdl:10566/3454.
- ^ "Whistling Thorn". Archived from the original on 26 January 2008. Retrieved 2008-01-18.
- ^ a b
Young, T.P.; C.H. Stubblefield; L.A. Isbell (December 1996). "Ants on swollen-thorn acacias: Species coexistence in a simple system". Oecologia. 109 (1): 98–107. PMID 28307618.
- ^ a b c
Palmer, T.M.; M.L. Stanton; T.P. Young; J.R. Goheen; R.M. Pringle; R. Karban (January 2008). "Breakdown of an Ant–Plant Mutualism Follows the Loss of Large Herbivores from an African Savanna". Science. 319 (5860): 192–195. PMID 18187652.
- ^ Okello, Bell; T.P. Young; C. Riginos; D. Kelly; T. O'Connor (2008). "Short-term survival and long-term mortality of Acacia drepanolobium after a controlled burn". African Journal of Ecology. 46 (3): 395–401. .
- ^ "The Whistling Thorn". Retrieved 2008-01-18.
- .
- ISBN 978-0-88275-525-0.
- .
- PMID 12049231.
- PMID 28313462.
- ^ J.R. Goheen, and T.M. Palmer,"Defensive Plant-Ants Stabilize Megaherbivore-Driven Landscape Change in an African Savanna"[1], Current Biology,Available online 2 September 2010.
- ^ Wood, William F.; Chong, Berni (1975). "3-Octanone and 3-Octanol; Alarm Pheromones from East African Acacia Ants". Journal of the Georgia Entomological Society. 10: 332–334.
- .
- PMID 33822786.
External links
- Dressler, S.; Schmidt, M. & Zizka, G. (2014). "Acacia drepanolobium". African plants – a Photo Guide. Frankfurt/Main: Forschungsinstitut Senckenberg.