Prolific pioneers and reserved settlers. changes in the life-history of the western tubenose goby (Proterorhinus semilunaris) at different invasion stages.
The western tubenose goby is one of the most wide-spread invasive fish species in European freshwaters, though information of its life-history in relation to its invasion success is limited. We compared the reproductive traits, growth rate and condition of three populations that differed in their stage of invasion in its expanding range in the River Vistula: core - the oldest population established at the centre of the invasive range; intermediate - long established by downstream dispersal from the core area but continuously supplemented by drifting specimens; front - new population at the edge of the invasive range, upstream from the core area. Pronounced differences in life-history traits were found between the 'core' and the 'front' populations. The 'front' population displayed high investment in reproduction and had heavier gonads, higher fecundity, higher batch fecundity though smaller eggs than the 'core' population. The 'core' population was characterized by the lowest fecundity, the largest eggs, the highest condition after spawning, and the highest maximum age of males. The 'intermediate' population was intermediate between the 'front' and the 'core' populations regarding reproductive traits, but showed the highest growth rates. The life-history traits that varied most among populations were gonad weight, fecundity, gonado-somatic index, condition and growth in the first years of life. Inter-individual variability of life-history traits was lower in the front of the invasive range than in the core and intermediate area. The observed plasticity in life-history appears to favour production of large numbers of offspring in newly-colonized areas in the initial stages of invasion and at the edge of the expanding range. In longer-established populations, at the core of invasive range, a strategy for greater competitiveness under intra-specific competition appears to be favoured.