Northeastern Naturalist Vol. 21, No. 3 J. Alcock 2014 351 2014 NORTHEASTERN NATURALIST 21(3):351–356 The Scramble Competition Mating System of the Dark Fishfly (Nigronia serricornis) (Megaloptera: Corydalidae) John Alcock* Abstract - Nigronia serricornis (Dark Fishfly) males were observed patrolling the borders of a small stream in northern Virginia. They flew toward females perched low in streamside vegetation. The first male to reach a female mated with her. Later arrivals left after a brief inspection of the mating pair. The mating system of this species appears to be based on nonaggressive scramble competition for widely scattered receptive females. Copulation in this member of the Corydalidae was prolonged. Introduction Despite the fact that the larval forms of Nigronia serricornis (Say in Keating) (Dark Fishfly) are prey of sportfish, little has been published about adult behavior since Needham and Betten (1901:plate 27) presented a photograph of a mating pair in their book on the aquatic insects of the Adirondacks. Henry (1999) observed captive adult megalopterans and presented fragmentary reports on their behavior. Males of a South American member of the dobsonfly genus Corydalus use their mandibles in aggressive interactions with other males and to lift wings of females during courtship, which may be followed by a very brief copulation (Parfin 1952, Sublett 2011). Although males of the dobsonfly genus Platyneuromus have large mandibles, they do not appear to use them in aggressive encounters, nor do they use them to manipulate female wings, only lightly touching potential partners with their jaws (Contreras- Ramos 1999). Observed copulations by members of this genus are also brief. Evans (1972) noted that Neohermes californicus Walker (California Fishfly) males do not engage in precopulatory courtship of any kind but quickly copulate in an end-to-end position, a pattern similar to that shown by Needham and Betten (1901) for the Dark Fishfly. Evans (1972) observed Orohermes crepusculus (Chandler) males pursuing a flying female and assembling near a perched female in the evening. Other studies of megalopteran reproduction have not attempted to describe mating behavior per se, but have focused on the donation of spermatophores by males to their mates (e.g., Hayashi 1993, 1998, 1999) or life-history differences among species (Takeuchi and Hoshiba 2012). Here I provide a description of the mating system of the Dark Fishfly based on field observations made in northern Virginia. Field Site Description and Methods I observed the Dark Fishfly on ten mornings during 28 May–11 June 2013 at a small woodland stream that runs through Monterey Farm, located about 5 km (3 *School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501; j.alcock@asu. edu. Manuscript Editor: Jay Stauffer Northeastern Naturalist 352 J. Alcock 2014 Vol. 21, No. 3 mi) west of Marshall, VA. At various times between 0630 and 1030 EDT from 30 May to 11 June, I counted the number of males flying low upstream or downstream during a 5-minute period as they crossed the brook at a particular spot. During the morning from as early as 0630 to as late as 1200, I also walked a path along the stream for a distance of about 200 m searching for patrolling males and those interacting with perched females. Results Male patrolling behavior Males were common in the early part of the study. They either flew slowly and steadily in one direction or the other along the streambank or above the stream, occasionally bumping into grass inflorescences as they flew. At times, males landed in the abundant Poa pratensis L. (Kentucky Bluegrass) growing close to the stream and remained there for a while before resuming flight. Flying males appeared to ignore one another completely. The number of patrolling males varied from day to day; the greatest numbers were 16 (in the 5 minutes beginning at 0830 on 30 May) and 14 (in the 5 minutes beginning at 0730 on 1 June). By 1030, patrolling males crossing the count line were either absent or consisted of 1 or 2 individuals (on 6 days between 30 May and 11 June). I observed patrolling males flying past the count line as early as 0630 (on 30 May). By 4 June, male patrolling activity was low at all hours of the morning and I saw no males after this date. On 11 June at 1230, I observed a single female that flew upstream and then landed on a tree leaf over the water . Mating behavior I recorded a total of five matings during the study—one on each of five different mornings 29 May–4 June. In all cases, the female was perched no more than 15 cm above the ground. Two or more semi-hovering males approached each female; their flight was slowed because of the obstacles created by the vegetation near the female. In every instance, the first male to contact the female mated with her, and copulation occurred rapidly. The male crawled under the female’s wings before making genital contact with his upraised and curled abdomen, after which he turned to mate facing away from his partner while upside down (Fig. 1). All copulations occurred between 0742 and 0949. In every case, at least one other male reached the mating pair within a few minutes after copulation was initiated (Fig. 2); the second male approached the female closely but soon left. After 10 minutes, coupled pairs were no longer visited by other males. Copulation was prolonged—I inspected three copulating pairs at intervals and observed that mating lasted at least an hour, and in one case, the pair remained together for over two hours. Discussion The lengthy copulation of the Dark Fishfly differs from the brief matings reported for most other megalopterans with the exception of the California Fishfly (Evans Northeastern Naturalist Vol. 21, No. 3 J. Alcock 2014 353 Figure 1. A copulating pair of Nigronia serricornis (Dark Fishfly). The male is hanging from the abdomen of the female. Northeastern Naturalist 354 J. Alcock 2014 Vol. 21, No. 3 Figure 2. A mating pair of Nigronia serricornis (Dark Fishfly) approached by a male that arrived soon after copulation had begun. Northeastern Naturalist Vol. 21, No. 3 J. Alcock 2014 355 1972). Prolonged copulations have been hypothesized to be a form of mate guarding (Thornhill and Alcock 1983), but they may also be associated with the transfer of a large quantity of materials from the male to the female (Vahed et al. 2011, but see Rajyaguru et al. 2013). Some corydalids attach a spermatophore to the genital opening of the female (Hayashi 1993). However, I did not observe spermatophores on recently mated Dark Fishfly females . The mating system of the Dark Fishfly appears to be based on scramble competition, in which males race to be the first to reach a receptive, signaling female, almost certainly by detecting a sex pheromone released by unmated individuals. Cases in which several males arrived more or less simultaneously near a perched, immobile female represent instances of elevated pheromone detection ability—a character for which males are likely selected. The fact that recently mated females continued to attract males for a brief period suggests that the pheromone did not dissipate instantly upon copulation. Similar to some other animals, females of the species are scarce and dispersed and thus, difficult to find (e.g., Schwagmeyer 1988). The rarity with which I observed mating is consistent with a loss of receptivity by females following copulation, a factor that may contribute to the scarcity of mates and thus promote scramble competition among males (Barry et al. 2011). In this species, selection appears to have favored mobile males that cover a large area efficiently (Marmet et al. 2012) and can outrace competitors to potential mates rather than investing in costly weaponry that might enable some individuals to keep other males from gaining access to these females. Acknowledgments Jason Jannot and David Lenat directed me to Boris Kondratieff, who provided the Dark Fishfly identification. 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