Latitude and altitude differentially shape life history trajectories between the sexes in non-anadromous brown trout

Abstract

We used two different approaches involving two organizational levels and spatial scales to explore altitudinal and latitudinal variation in life histories of non-anadromous brown trout Salmo trutta. First, we studied the factors influencing the maturation of individuals from populations in northern Spain. Second, we explored the effects of altitude (range 40–1,340 m) and latitude (range 40.6–61.7°N) on longevity, maximum length, length and age at maturity, and fecundity, comparing Spanish and Norwegian populations. Individual maturation was determined by length, age, and sex, and at a given size and age individuals were more likely to mature at higher altitudes. Brown trout lived longer but attained smaller sizes at higher latitudes. Both males and females matured at an older age with increasing latitude, but latitude affected their life-history strategies differentially. Males matured at smaller sizes with increasing latitude and altitude, which may indicate that their maturation threshold depends on the growth potentiality of the river since they compete with other males from the same population. The opposite effects were detected in females. Since female fecundity increases strongly with size there may be a size below which maturation has strong fitness costs. Brown trout are extraordinarily plastic, allowing persistence in a wide variety of environments. In the context of climate change, latitudinally based studies are important to predict potential effects of climate change, especially at the southern edge of species distribution.