A case of reversed sexual size dimorphism in a polygynous small mammal, Apodemus flavicollis (Rodentia: Muridae) [Prípad obráteného veľkostného pohlavného dimorfizmu u ryšavky žltohrdlej Apodemus flavicollis (Rodentia: Muridae)]
Kristína Trubenová, Martina Jurčovičová, Ľudovít Kocian
In the present study we analysed the occurrence and magnitude of sexual size dimorphism (SSD) in body weight and length of Apodemus flavicollis. We studied three different populations living at two localities in Slovakia: a lowland deciduous forest representing an optimal habitat (Sur Nature Reserve, Bratislava); and a mountain mixed forest representing a habitat close to margin of the distribution range of the studied species (Osobita Nature Reserve, West Tatra Mts.). The male-biased SSD in both body weight and length seems to be a general pattern in the studied species, which is in agreement with the expectation for a species with polygynous mating system. However, in the year 2004 we registered a case of a female- biased SSD at the mountain locality. In this year females were larger and males smaller than during all the other years of study at this locality. We expect that during this year of an exceptionally high population density on the locality, the reversed SSD could have been a result of two different, mutually acting selection pressures: selection favouring smaller males and selection favouring larger females. Our study provides evidence that both body weight and length in A. flavicollis show plasticity in terms of adapting to changes in the short term, which can consequently influence patterns of sexual size dimorphism.