A second host species of the inquiline ant Leptothorax wilsoni.
Psyche 102:73-77, 1995.
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A SECOND HOST SPECIES OF THE INQUILINE ANT LEPTOTHORAX WILSON1
BY J. HEINZE, B. TRUNZER, K. LECHNER, AND D. ORTIUS Theodor-Boveri-Institut (Biozentrum der Universitat) LS Verhaltensphysiologie und Soziobiologie Am Hubland, D-97074 Wurzburg, FRG
The workerless parasitic ant, Leptothorax wilsoni, as yet known only from colonies of Leptothorax cf. canadensis, was found in five colonies of a second host species, Leptothorax sp. A (sensu Heinze and Buschinger, 1989) near Escoumins, Quebec. This is the first finding of an inquiline with more than one host species in the ant tribe Formicoxenini. In contrast to a previous statement, the palp formula of L. wilsoni is 4, 3.
The ant Leptothorax wilsoni was described from New England, Quebec, and New Brunswick (Heinze, 1989). Since then it has repeatedly been collected at the type locality, Mt. Monadnock in southern New Hampshire (Heinze unpubl.), and recently it was found also in Alberta and Montana (Buschinger and Schumann, 1994). L. wilsoni is an inquiline ant, i.e., a workerless social para- site, living in colonies of a large black Leptothorax (s.str.), which has been referred to as Leptothorax sp. B or, more recently, Lep- tothorax cf. canadensis (Heinze, 1994). Here we report on the occurrence of L. wilsoni in colonies of a second host species, Lep- tothorax sp. A, an as yet undescribed but well characterized taxon (e.g., Heinze and Buschinger, 1989; Heinze, 1991). In September 1994 and May 1995, we collected four colonies of L. wils mi in a pine-aspen- birch forest between Bergeronnes and Manuscript received 13 March 1995.
74 Psyche [VOI. 102
Fig. 1: Labium and maxillae of a Lepwhorax wilsoni queen from Escoumins, Quebec. The arrow points to the 4-segmented maxillary palp. Escoumins (Co. de Saguenay, Quebec), 4 km east of Cap Bon Dksir, on a road branching off route 138 to the north and leading to a garbage dump ("Depotoir"). A fifth colony was found approxi- mately 0.5 km north of the first site on rocky outcrops with scat- tered spruces and pines. Colonies nested in rotting sticks in partly shaded areas directly along the road, on a forest path, and on the edge of a rocky patch.
Of a total of 65 Leptothorax colonies collected in these two sites, 14 were L. cf. canadensis and 36 were L. sp. A, as deter- mined by the trapezoidal shape of their postpetiole in dorsal view, the length of the epinotal spines, and the electrophoretic migration velocity of several enzyme markers (e.g., Heinze, 1991). Three L. sp. A colonies contained each a gynomorphic, i.e., an originally normal, alate queen of L, wilsoni, 5, 10, and more than 50 host
19951 Heinze, Trunzer, Lechner & Ortius 75 workers, respectively, and brood. In both of the two remaining colonies, an "intermorphic," i.e., originally brachypterous L. wilsoni queen with 50 to 60 host workers and brood was found. L. wilsoni from the Escoumins sites did not differ conspicuously in morphology from specimens from Mt. Monadnock and Jasper National Park, though they were somewhat lighter in coloration. Specimens from Escoumins, Jasper, and Mt. Monadnock also share a very slowly migrating variant of the enzyme malate dehydroge- nase (MDH) not known from other Leptothorax (Heinze, 1991). Queen polymorphism in L. wilsoni was assumed on the basis of several short-winged "intermorphs" from Mt. Monadnock and one gynomorphic queen from Mt. du Lac des Cygnes in Quebec (Heinze, 1989). The co-occurrence of both queen morphs within a single population (and even within the same host colony) was only recently confirmed for a population in Alberta (Buschinger and Schumann, 1994). Our finding shows that both queen morphs co- occur also in Quebec.
Host queens have not been found in L. wilsoni colonies from other populations (Heinze, 1989 and unpublished; Buschinger and Schumann, 1994); however, in one colony from Escoumins, an intermorphic L. wilsoni queen and a gynomorphic L. sp. A queen occurred together. Dissection of the L. sp. A queen revealed the presence of sperm in the spermatheca and elongated ovaries, but neither developing eggs nor corpora lutea were found. The whitish coloration of the fat body and the ovarian development suggest that the L. sp. A queen was a young queen which had returned into the parasitized nest after mating without becoming fertile. In July 1988, at the Mt. Monadnock site a solitary queen of L. wilsoni was collected near a nest of Leptothorax sp. A. This find- ing was initially interpreted as an accidental mixing of a solitary L. wilsoni queen, searching for a L. cf. canadensis host colony after mating, and an unparasitized L. sp. A colony (Heinze, 1989). Our recent observations raise the possibility that on Mt. Monadnock L. wilsoni parasitizes both L. cf. canadensis and L. sp. A. However, all five fertile L. wilsoni queens known from Mt. Monadnock were found with L. cf. canadensis, though more than 70 colonies of L. sp. A and 100 colonies of L. cf. canadensis were checked. The occurrence of L. wilsoni in colonies of a second host species, L. sp. A, is especially surprising as workerless parasites
Heinze, Trunzer, Lechner & Ortius
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