Crematogaster sjostedti

Crematogaster sjostedti
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Crematogastrini
Genus:	Crematogaster
Species:	C. sjostedti
Binomial name
Crematogaster sjostedti Mayr, 1907

One of four ant species (also Crematogaster mimosae, Crematogaster nigriceps, Tetraponera penzigi) that live on Vachellia drepanolobium. This small arboreal ant assemblage, nesting in this dominant Africa savanna tree, have been the subject of intensive research by a large group of ecologists studying species interactions and species co-existence.

At a Glance

• Ant-plant specialist

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: -19.18333° to -19.18333°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

Afrotropical Region: Kenya, Mozambique, United Republic of Tanzania, Zimbabwe, Zimbabwe.

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Inhabits swollen thorns of Vachellia drepanolobium, a dominant tree in large expanses of African savanna and acacia woodland. This species and three other ants (Crematogaster mimosae, Crematogaster nigriceps, Tetraponera penzigi) that compete for the hollow thorn nesting sites have been the subject of some of the most intensive ecological research examining interactions between ants, acacias, and other elements, e.g., herbivory and fire, in places where this plant is abundant. Many of these studies have been carried out in Kenya's Mpala Research Centre and surrounding areas, all of which are part of the expansive Laikipia Plateau.

Crematogaster gerstaeckeri sjostedti is the dominant ant in the largest, oldest trees (>5 m in height). The ants are mutualists with the acacia trees. The trees provide nesting resources (domatia) and can produce extralfloral nectaries. The ants, in turn, protect the tree from herbivory. Rather than using the extrafloral nectaries as a food resource, as some of the other ants that are part of this arboreal community do, C. sjostedti appears to tend scale insects.

Explore Vachellia drepanolobium  Vachellia drepanolobium, more commonly known as Acacia drepanolobium or whistling thorn, 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. 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. In addition, whistling thorn acacias are myrmecophytes that have formed a mutualistic relationship with some species of ants. In exchange for shelter in the bulbous spines (domatia) and nectar secretions, these ants appear to defend the tree against herbivores, such as elephants and giraffes, as well as herbivorous insects. At a site in Kenya, three Crematogaster and one Tetraponera ant species compete for exclusive possession of individual whistling thorn trees: Crematogaster mimosae, Crematogaster sjostedti, Crematogaster nigriceps and Tetraponera penzigi (Young et al., 1996; Palmer et al., 2008). 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. 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 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 (Palmer et al., 2008) and become much more vulnerable should herbivores be reintroduced. References Palmer, T.M., Stanton, M.L., Young, T.P., Goheen, J.R., Pringle, R.M., Karban, R. 2008. Breakdown of an Ant–Plant Mutualism Follows the Loss of Large Herbivores from an African Savanna. Science 319(5860): 192–195 (doi:10.1126/science.1151579). Young, T.P., Stubblefield, C.H., Isbell, L.A. 1996. Ants on swollen-thorn acacias: Species coexistence in a simple system. Oecologia 109(1): 98–107 (doi:10.1007/s004420050063).

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• sjostedti. Crematogaster sjostedti Mayr, 1907b: 17 (w.) TANZANIA.
  • Type-material: syntype workers (number not stated).
  • Type-locality: Tanzania (“Deutsch-Ostafrika”): Usambara Mts, nr Tande, 1905-06 (Y. Sjöstedt).
  • Type-depositories: NHMW, NHRS.
  • Combination in C. (Crematogaster): Wheeler, W.M. 1922a: 844;
  • combination in C. (Acrocoelia): Emery, 1922e: 148.
  • Subspecies of gallicola: Forel, 1913a: 124 (in text); Forel, 1914d: 237; Santschi, 1914b: 94.
  • Subspecies of gerstaeckeri: Santschi, 1930b: 69; Santschi, 1935b: 270; Santschi, 1937a: 55; Santschi, 1937g: 76; Bolton, 1995b: 162; Hita Garcia, et al. 2013: 210.
  • Status as species: Wheeler, W.M. 1922a: 844; Emery, 1922e: 148; Santschi, 1928d: 65; Taylor & McGavin, 2020: 13.
  • Distribution: Kenya, Mozambique, Sudan, Tanzania.

References

• Sensenig, R. L., D. K. Kimuyu, J. C. Ruiz Guajardo, K. E. Veblen, C. Riginos, and T. P. Young. 2017. Fire disturbance disrupts an acacia ant–plant mutualism in favor of a subordinate ant species. Ecology. 98:1455-1464. doi:10.1002/ecy.1797
• Taylor, B., Agoinon, N., Sinzogan, A., Adandonon, A., Kouaguou, Y. N., Bello, S., Wargui, R., Anato, F., Ouagoussounon, I., Houngbo, H., Tchibozo, S., Todjihounde, R., Vayssieres, J.F. 2018. Records of ants (Hymenoptera: Formicidae) from the Republic of Benin, with particular reference to the mango farm ecosystem. Journal of Insect Biodiversity 8(1): 6-29 (doi:10.12976/jib/2018.08.1.2).
• Taylor, B., McGavin, G. 2020. Ants found on acacia of the genus Vachellia. Belgian Journal of Entomology 99: 1-47.