Mating habits, dispersal and postglacial range expansion of Nigronia serricornis (Say) (Megaloptera: Corydalidae)

Historical events, e.g. Pleistocene glaciation, play an important role in shaping the current genetic population structure of a species. Glacial advances force organisms into refugia, while retreats make new habitat available for colonization. The rate and extent of recolonization is influenced by life history, especially dispersal ability. Nigronia serricornis (Say) (Corydalidae: Megaloptera) is an important indicator species of high water quality whose adults are reportedly "poor fliers". Little is known about dispersal ability in this species, and nothing about its population structure.; Detailed observations of mating and dispersal and measurements of tethered and untethered flight revealed that males took short (<10m), slow (0.72m/s), looping flights, but remained in the channel valley. Prior to mating, females were disinclined to flight. After oviposition, females either dispersed nearby at low height (3--5m), or flew high (18--24m) perpendicular to the river and out of the channel valley. Petersen (1974) observed 2 oviposition events, making it likely that "high flying" females are responsible for between-drainage dispersal.; It was hypothesized that fragmentation and isolation-by-distance would be evident in the genetic population structure, due to poor dispersal ability. Using sequence data from a 630-base fragment of cytochrome oxidase I (COI), nested clade phylogeographical analysis (NCPA) was performed to determine the patterns of genetic diversity and the effects of post-glacial range expansion (PGRE). Haplotype diversity was significantly negatively correlated with latitude (R2 = 0.475, p = 0.002), as seen in other species experiencing PGRE in eastern North America. The 68 unique COI haplotypes recovered were distributed into 6 major clades. A rapid range expansion arose from Tennessee colonizing Indiana, Illinois, Wisconsin, Michigan, and Ontario. Evidence was found for two contiguous range expansions: Pennsylvania into New York and North Carolina along the coast to Maine. Points of secondary contact were identified in New York and Ohio. The remaining clades showed no significant phylogeographic relationship according to the NCPA. The distribution of one of these clades, however, followed pre-glacial drainages. Fragmentation and isolation-by-distance were rampant throughout the range of the species, corroborating the conclusion of poor dispersal ability. Low levels of genetic diversity and poor dispersal make N. serricornis susceptible to anthropogenic population fragmentation.