title: Latitudinal variation in sexual dimorphism in life-history traits of a freshwater fish.
abstract: Sexual dimorphism is common across the animal kingdom, but the contribution of environmental factors shaping differences between the sexes remains controversial. In ectotherms, life-history traits are known to correlate with latitude, but sex-specific responses are not well understood. We analyzed life-history trait variation between the sexes of European perch (Perca fluviatilisL.), a common freshwater fish displaying larger female size, by employing a wide latitudinal gradient. We expected to find sex-dependent latitudinal variation in life-history variables: length at age, length increment, and size at maturity, with females showing consistently higher values than males at all latitudes. We further anticipated that this gender difference would progressively decrease with the increasingly harsh environmental conditions toward higher latitude. We hypothesized that growth and length increment would decrease and size/age at maturity would increase at higher latitudes. Our results confirmed female-biased sexual size dimorphism at all latitudes and the magnitude of sexual dimorphism diminished with increase in latitude. Growth of both sexes decreased with increase in latitude, and the female latitudinal clines were steeper than those of males. Hence, we challenge two predominant ecological rules (Rensch's and Bergmann's rules) that describe common large-scale patterns of body size variation. Our data demonstrate that these two rules are not universally applicable in ectotherms or female-biased species. Our study highlights the importance of sex-specific differences in life-history traits along a latitudinal gradient, with evident implications for a wide range of studies from individual to ecosystems level.
authors.affiliation: Department of Environmental Sciences/Aquatic Sciences University of Helsinki Helsinki Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Estlander
authors.affiliation: Department of Environmental Sciences/Aquatic Sciences University of Helsinki Helsinki Finland.
authors.forename: Kimmo K
authors.initials: KK
authors.lastname: Kahilainen
authors.affiliation: Department of Environmental Sciences/Aquatic Sciences University of Helsinki Helsinki Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Horppila
authors.affiliation: Department of Environmental Sciences/Aquatic Sciences University of Helsinki Helsinki Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Olin
authors.affiliation: Natural Resources Institute Finland Jyväskylä Finland.
authors.forename: Martti
authors.initials: M
authors.lastname: Rask
authors.affiliation: Biological Centre Academy of Sciences of the Czech Republic Hydrobiological Institute České Budějovice Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Kubečka
authors.affiliation: Biological Centre Academy of Sciences of the Czech Republic Hydrobiological Institute České Budějovice Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Peterka
authors.affiliation: Biological Centre Academy of Sciences of the Czech Republic Hydrobiological Institute České Budějovice Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Říha
authors.affiliation: Department of Biology University of Eastern Finland Joensuu Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Huuskonen
authors.affiliation: Department of Environmental Sciences/Aquatic Sciences University of Helsinki Helsinki Finland.
authors.forename: Leena
authors.initials: L
authors.lastname: Nurminen
keywords: Bergmann's rule; Rensch's rule; growth; perch; sex; sexual maturity