A Dolichoderus taschenbergi queen found in a polygynous colony of D. plagiatus (Hymenoptera: Formicidae).
Psyche 102:147-150, 1995.
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A DOLZCHODERUS TASCHENBERGI QUEEN FOUND IN A POLYGYNOUS COLONY OF D. PLAGIATUS
LS fur Verhaltensphysiologie und Soziobiologie Am Hubland, D-97074 Wurzburg, Germany
Very little is known about colony founding strategies and social organization of the four North American species of the ant genus Dolichoderus. I here report the finding of a Dolichoderus taschen- bergi queen in a colony of D. plagiatus, which suggests parasitic colony founding may occur occasionally in Dolichoderus taschen- bergi. In addition, the colony contained three reproductively active queens of D. plagiatus, indicating that this species is facultatively polygynous.
The ant genus Dolichoderus Lund is represented by four species in North America (Creighton, 1950): mariae Forel, plagiatus Mayr, pustutatus Mayr, and taschenbergi Mayr. Except for studies by Kannowski (1959, 1967) on the flight activities of these species and a review by Johnson (1989) of their distribution and nest sites, very little is known about the life histories of North American Dolichoderus. Several authors (Wheeler, 1905a; Cole, 1940; Carter, 1962a, b; Wheeler and Wheeler, 1963) have described below-ground nest structures and leaf litter nests for all four North American Dolichoderus. D. plagiatus is considered to be monogy- nous (Kannowski, 1967) and nuptial flights are known to occur between mid June and July (Kannowski, 1959). Among the 12 colonies censused by Kannowski (1967), one colony contained two queens, which, however, he did not dis- sect. The majority of the D. plagiatus colonies investigated by Manuscript received 4 March 1995.
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Kannowski (1967) were monogynous, and the single polygynous colony found was interpreted as either a consequence of pleometrotic colony foundation (primary polygyny) or the adoption of young mated queens (secondary polygyny). The latter possibil- ity has been considered unlikely because of the observed nuptial flight activities of this species, which disperses the females from their mother colony and the high intraspecific aggressiveness of the workers, which would make the adoption of nonrelatives impossi- ble (Kannowski, 1959; 1967).
In the present note I report some new aspects concerning the nest sites and social organization of Dolichoderus taschenbergi and D. plagiatus. Voucher specimens are deposited in Harvard University's Museum of Comparative Zoology. During a collecting trip to Maine, USA, in September 1994, a colony of Dolichoderus plagiatus was found in a dead oak twig (from a dwarf tree of Quercus alba) on the ground. This report of a colony in dead wood and of others found on Mt. Monadnock, New Hampshire and Mt. Cadillac, Mt. Desert Island, Maine (Jiirgen Heinze, pers. comm.) and of arboreal D. pustulatus in Florida and Georgia (Johnson, 1989) suggests that nest sites of Dolichoderus species are more diverse than previously reported. The exact location of the nest was on the southeastern slope of Mt. Battie at an elevation of 330m in Camden Hills, Knox County, Maine. The colony contained 3 dealate queens, 2 alate queens, approximately 80 workers, and 1 worker pupa. Overwintering without brood seems to be typical for Dolichoderus plagiatus, D. pustulatus (Kannowski, 1967), and the European Dolichoderus quadripunctatus (Torossian, 1968). The two alate queens may have eclosed too late to take part in a nuptial flight and therefore remained in the mother colony for overwintering. The dissection of all three dealate D. plagiatus queens revealed that they all had filled spermathecae and developed ovaries, each ovary containing 14 ovarioles and several yolky oocytes. Surpris- ingly, mingled among the D. plagiatus specimens was a dealate queen of Dolichoderus taschenbergi.
During the few days following collection the members of the host colony never exhibited any kind of aggressive behavior
towards the foreign queen. In contrast, the D. plagiatus workers clustered around the D. taschenbergi queen as they did around the dealate queens of their own species, forming little subunits in the collection-tube. It thus appears that the alien queen was as attrac- tive to the workers as their own queens. On the second day after collection the D. taschenbergi queen was observed grabbing a D. plagiatus worker behind her neck without any counterreaction of the other colony members. About 10 minutes later the worker was decapitated and was later removed by a conspecific worker. Unfortunately the D. taschenbergi queen did not survive the transport to the laboratory and further observa- tions could not be made.
Even though this is not very strong evidence, these observations might suggest that D. taschenbergi queens occasionally use a para- sitic mode of colony founding, with D. plagiatus serving as host species.
Temporary social parasitism is a well known phenomenon espe- cially in the subfamily Formicinae (Holldobler and Wilson, 1990). In the subfamily Dolichoderinae, however, it is rare. Ants of the genus Bothriomyrmex have long been believed to be the only tem- porary social parasites in this group (Forel, 1906; Santschi, 1906), founding their nests in colonies of the genus Tapinoma. Buren, Nickerson, and Thompson (1975) deduced temporary social para- sitism from the finding of mixed nests of two Dorymyrmex species, now called Dorymyrmex medeis and D. bureni, (Trager, 1988). The parasitized species, D. plagiatus, appears to be facultatively polygynous, as three co-occurring reproductively active queens have been found in this colony. As stated by Kannowski (1959; 1967) there are two possible mechanisms by which polygyny might occur. Firstly, conspecific queens can either be adopted into established colonies (secondary polygyny), which seems to be likely for D. plagiatus as even heterospecific queens are sometimes adopted. Secondly, primary polygyny could arise through pleometrotic colony foundation. But this is a rather rare phenome- non in ants (Holldobler and Wilson, 1977). Further investigations will be needed to show if polygyny in D. plagiatus and temporary social parasitism in D. taschenbergi are common phenomena.
This study was supported by a DFG-grant He.162312-2 to Jiir- gen Heinze. Prof. Dr. B. Holldobler, Dr. J. Heinze, Dr. K, Fiedler, and an anonymous reviewer made helpful comments on an earlier draft of this manuscript. I also wish to thank Stefan Cover for the species determination.
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