Invader population speeds up life history during c

Authors: PerArne Amundsen Erno Salonen Teuvo Niva Karl Øystein Gjelland Kim Præbel Odd Terje Sandlund Rune Knudsen Thomas Bøhn

Publish Date: 2012/01/20

Volume: 14, Issue: 7, Pages: 1501-1513

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Abstract

We explore the longterm developments in population biology and life history during the invasion and establishment of the fish species vendace Coregonus albula in a subarctic watercourse by comparing lifehistory traits and molecular genetic estimates between the source and the colonist population The two populations exhibited highly contrasting lifehistory strategies Relative to the source population the colonist population was characterized by slower somatic growth rates earlier sexual maturation at smaller individual size higher mortality rates and a shorter life span The two populations could also be significantly discriminated by the genetic markers Limited founder effects were detected from heterozygote deficit and reduced allelic richness in the colonist population but both populations were associated with relatively high genetic diversity The study reveals that the invasion into a new environment induced large changes in lifehistory strategy with typical rselected traits being more prominent in the colonist than in the source population We discuss the mechanisms that may explain the observed lifehistory differences between the source and the colonist population and argue that the accelerated life history of the colonist population represents an adaptive pioneer strategy aimed at fast population increase during colonization and establishmentInvasions may provide excellent opportunities to study basic processes in population biology and the plasticity of lifehistory traits Sakai et al 2001 Shea and Chesson 2002 and may be considered natural experiments in this respect often inducing ecological processes far more expeditious than those in undisturbed systems Sakai et al 2001 Few investigations have however addressed the population ecology and life history of the invading species during establishment Williamson 1999 The invasion of a species into a new environment may generate rapid changes in population biology lifehistory strategies and genetic structure of the invader eg Reznick and Ghalambor 2001 Lee 2002 Lambrinos 2004 Ecological and evolutionary processes may influence the development of the invader through 1 founder effects Tsutsui et al 2000 Dlugosch and Parker 2008 2 adaptations to the native ecological community with its new predator–prey relationships and competitive interactions Shea and Chesson 2002 Lockwood et al 2007 and 3 phenotypic adjustments to the new environment Sandlund 1992 Huey et al 2000 Based on these three often linked responses invading species may adopt a pioneer lifehistory strategy facilitating rapid population increase and expansion during the invasion process McMahon 2002 Ruesink 2005 A colonist population may therefore display a lifehistory strategy that is deviant from its source population but studies comparing population biology and lifehistory strategies of the source and colonist populations during an invasion are lackingThe present study addresses the invasion of a nonnative fish vendace Coregonus albula in the subarctic Inari–Pasvik watershed in northern Europe Vendace was introduced in Lake Inari Finland around 1960 Mutenia and Salonen 1992 established a dense population and colonised downstream lakes in the Pasvik watercourse Norway and Russia where the species was observed for the first time in 1989 Amundsen et al 1999 In Lake Vaggatem Norway in the upstream part of the Pasvik watercourse the invader rapidly became the dominant pelagic fish species Bøhn et al 2004 2008 Longterm investigations with annual sampling of vendace have been carried out in Lake Inari since 1985 Salonen 1998 2004 and in Lake Vaggatem since 1991 Amundsen et al 1999 Bøhn et al 2008 Here we perform a combined analysis of these timeseries in order to compare the population biology and lifehistory strategies of the source Lake Inari and colonist Lake Vaggatem populations of the invader species prior to and following the downstream invasion and establishment The genetic diversity variability and divergence between the two populations were also examined to evaluate whether any population differences were solely a consequence of phenotypic plasticity in life history traits or a combination of both phenotypic and genetic responsesMost fish species have indeterminate somatic growth trajectories and may show plasticity in growth rate and other lifehistory characteristics Stearns and Koella 1986 Wootton 1998 Plastic responses and selection on relevant traits may quickly modify phenotypes in periods of rapid population growth Reznick et al 1997 Hendry et al 2000 Vendace is a specialist with a narrow ecological niche in terms of food and habitat choice Svärdson 1976 Bøhn and Amundsen 2001 Kahilainen et al 2011 but is known to exhibit substantial variation in lifehistory parameters such as growth rate age and size at maturity individual fecundity and number of spawnings during their lifetime Sandlund 1992 Sarvala and Helminen 1995 Bøhn et al 2004 Hence following the invasion into a new environment vendace could potentially undergo rapid changes in lifehistory strategy We therefore hypothesized that the colonist and source population would exhibit distinct differences in population biology the colonist population having more rapid lifehistory characteristics including earlier sexual maturation reduced somatic growth and increased mortality rates due to larger reproductive investments representing phenotypic and adaptive responses facilitating the invasion of a new ecological environment

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