| Summary: | Resource polymorphism and phenotypic differentiation is common in vertebrates as they adapted to local environments. Selection acts on the morphology, behavior and/or physiology of organisms increasing the efficiency of local resource use. Different resources use may lead to population diversification which in turn may result in emergent of distinct morphs within species even to speciation. Many ecological factors could promote divergence such as level of complexity and size of a lake, food availability, inter- and intraspecific competition and predation pressure. Different age classes, sexes and individuals within a population can exploit different resources with resulting ecological specialization which may lead to sexual dimorphism or population divergence. A model species in investigating morphological and behavioral divergence is threespine stickleback as it has undergone multiple adaptive radiations since the end of the Pleistocene period (10.000- 15.000 years ago) showing complex morphology, behavior and life history, and inhabits a wide range of aquatic habitat (small ponds, larger lakes, rivers). Specifically, behavioral differences have been revealed in spatial and social learning, response to predators and anti-predator behavior, and social behavior.In Iceland two distinct stickleback morphs have been described in neovolcanic lakes, the lava and mud morph which show morphological, behavioral adaptations to the distinct mud and lava habitats. The lava sticklebacks live predominantly in spatially structured lava substrate and they feed mainly on benthic invertebrates that are hosted in the numerous holes and crevice that the complex lava substrate provides while the mud sticklebacks are better adapted to pelagic prey and they are equally likely to forage on benthic prey and plankton. Behavioral differences were also described between the two morphs in anti-predator behavior most likely affected by the very different structural complexity of their habitats. In this study behavioral and morphological ...
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