Oviposition Resources, Territoriality and Male Reproductive Tactics in the Dragonfly Paltothemis Lineatipes (Odonata: Libellulidae)
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OVIPOSITION RESOURCES, TERRITORIALITY AND MALE REPRODUCTIVE TACTICS IN THE DRAGONFLY PALTOTHEMIS LINEATIPES (ODONATA: LIBELLULIDAE) by JOHN ALCOCK1) (Department of Zoology, Arizona State University, Tempe AZ 85287-1501, U.S.A.) (With1 Figure) (Acc.19-XII-1989) Introduction In resource defense polygyny, males guard patches of resources useful to females and thereby gain access to potential mates (EMLEN & ORING, 1977). For mating systems of this sort, it is reasonable to suppose that a male's reproductive success will be correlated with the quantity or qual- ity of resources that he defends. This is a key element, for example, of the polygyny threshold model of ORIANS (1969). Males monopolizing more materials could be expected to attract more females that wished to utilize these resources; the more females drawn to a resource patch, the more mates a male might acquire. Females in a diversity of vertebrates choose mates on the basis of the resources controlled by males (e.g. CRONIN & SHERMAN, 1976; KODRIC- BROWN, 1977; HOWARD, 1978; LENINGTON, 1980; SEARCY, 1982; READ, 1986; but for exceptions see LIGHTBODY & WEATHERHEAD, 1987; LEONARD & PICMAN, 1988). For a number of insects as well, females apparently evaluate key resources defended by males before selecting a mate (e.g. THORNHILL, 1976, 1981; SEVERINGHAUS et al., 1981; HUGHES & HUGHES, 1982; McLAIN, 1984; STEELE, 1986; SHELLY et al., 1987). However, experimental tests of the hypothesis that the quantity of resources under male control determines his mating success are rare. 1) This study was conducted at the Southwestern Research Station of the American Museum of Natural History with the assistance of the director Wade SHERBROOKE.My excellent field assistants were Scott ROBERTS,DONALD SEJKORA and David SPADAFORE; additional help was provided by Emily OGRINZ,SHEILA LYONS, Linda MORIWAKI,Donna SACHS,Christina SWARTZand Lisa TEODECKI.Funding was provided by NSF grant BNS-862 0352. 252 They include two studies of territorial damselflies whose males defend sites containing oviposition materials (ALCOCK, 1987a; WAAGE, 1987). Although the quantity of oviposition resources is not the only factor to influence male mating success in the damselfly Calopteryx maculata, it is an extremely important variable. Manipulations of the amount of floating plant material in a male's territory affect the number of females that come to the site and therefore the male's access to mates (ALCOCK, 1987a; WAAGE, 1987). The dragonfly Paltothemis lineatipes also appears to practice resource defense polygyny (ALCOCK, 1987b). In the Chiricahua Mountains of southeastern Arizona, males defend territories (usually 3 to 6 m long) that contain one or more patches of barely submerged fine gravel over which water is flowing moderately rapidly. Stream segments with stand- ing or weakly flowing water are not defended by males nor are these loca- tions used by ovipositing females. Males readily find potential egg-laying spots in their territories and carry receptive females in tandem there before mating. During the brief copulation, the male flies with his part- ner in a narrow arc back and forth directly over the oviposition resources, apparently displaying them to his mate. After copulation, females are released to lay their eggs, which they do by dipping the tip of the abdomen repeatedly into the water just above the gravel in places they select (often, but not always, at the spot where mating occurred). Thus, females potentially could assess the suitability of the oviposition materials in a male's territory prior to mating, or after mating but before ovipositing. Such an assessment would affect a male's fitness; females that refuse to oviposit in a male's territory generally mate again else- where before laying their eggs (ALCOCK, 1987b), probably subjecting the sperm of earlier mates to displacement or dilution. This paper reports the results of several experiments with P. lineatipes in which varying amounts of oviposition materials were added to male territories in order to test whether the quantity of these resources affected female reproductive behavior and the tactics adopted by males. Methods The study was conducted from 18 June to 9 July 1987, 2 to 26 June 1988, and 20 May to 9 June 1989 at the middle fork of Cave Creek in the Chiricahua Mountains of south- eastern Arizona. In each year, males along the same stretch of stream were captured, and each individual received a distinctive mark of Liquid Paper Typewriting Correction Fluid on its wing(s). In addition to the experiments described below, I gathered observational data to establish that males could identify potential oviposition sites in their territories. To do .