Genetic differentiation between alternate-year cohorts of Xestia tecta (Lepidoptera, Noctuidae) in Finnish Lapland

Abstract

Several species in the noctuid genus Xestia exhibit periodic dynamics, with two coexisting cohorts flying in alternate years. The population dynamics and two-year life cycle of Xestia moths suggest that the two cohorts are more or less isolated in time. Typically one cohort is abundant and the other one is rare. Knowledge of the extent of isolation between the two cohorts is important to fully understand the population dynamics and the evolution of alternate-year flight in these species. We applied allozyme electrophoresis and mitochondrial genome sequencing to infer the extent of genetic differentiation among different cohorts of Xestia tecta (Hübner) within the same geographical area as well as between cohorts with opposite-phase flight pattern in different geographical regions. We found no evidence for substantial genetic differentiation and isolation between the even- and odd-year cohorts in eastern Lapland, nor between the cohorts in eastern and western Lapland. The most informative markers were the most polymorphic allozyme loci (Pgm and Mpi) and the AT-rich region in the mtDNA. However, owing to the generally low levels of genetic variation it was not possible to establish conclusively the degree of genetic isolation between the different cohorts. We discuss the implications of our results in relation to two different hypotheses which could account for this pattern: ongoing gene flow between different cohorts and recent common ancestry.

Testing biennialism in the butterfly Erebia palarica (Nymphalidae: Satyrinae) by mtDNA sequencing

“…The low genetic diversity as revealed by mtDNA data (Table 1) and the lack of variability in nuclear microsatellite loci (Cassel, 2002) are congruent with data from other narrowly distributed endemic taxa (Frankham, 1996). Low levels of mitochondrial and nuclear variation were also a handicap for Kankare et al . (2002) in their attempt to establish the degree of genetic differentiation between alternate‐year cohorts of another Lepidoptera.…”

Conservation implications of genetic variation between spatially and temporally distinct colonies of the endangered damselfly Coenagrion mercuriale

“…Given the emerging pattern of localised genetic differentiation in this species (Watts et al ., 2004a and Tables 2 and 3 in the present study), significant genetic differences would be expected to accumulate rapidly between cohorts if they were reproductively isolated. Similar to results obtained for populations of the plectopterans Pteronarcys proteus and Peltoperla tarteri (White, 1989; Schultheis et al ., 2002) and the lepidopteran Xestia tecta (Kankare et al . 2002), low levels of genetic differences were present between alternate‐year cohorts.…”

Use of forest corridors by boreal Xestia moths

“…exhibit a striking alternate-year periodicity in the study area with the vast majority of adults emerging in odd years (Mikkola 1976;Rost et al 2001). Their natural history (Vµrkonyi and Ahola 2001), population dynamics including interaction with hymenopteran parasitoids (Rost et al 2001;Vµrkonyi et al 2002), and population genetics (Kankare et al 2002) We studied three moth species, Xestia speciosa (Hübner), X. fennica (Brandt) [=rhaetica auct. nec Staudinger, 1871] (nomenclature after Kullberg et al 2001) and X. alpicola (Zetterstedt), which have somewhat dissimilar habitat preferences.…”