Phenotypic Divergence of Indigenous and Translocated Arctic Charr (Salvelinus alpinus) Populations in Maine
Author(s)Michaud, Wendy K.
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AbstractSelection on traits related to trophic ecology is recognized as an important contributing factor in adaptive divergence and speciation. For several freshwater fish species, including Arctic charr (Salvelinus alpinus), such selection is commonly reflected in relationships between diet, habitat use and phenotypic divergence. Trophic specializations that emerge have been extensively studied among sympatric forms, but much less is known of the extent of this type of divergence in allopatry. Trait differences among these forms are also thought to reflect thousands of years of evolution, making it difficult to examine root causes of such divergence in natural populations. Here, I address the hypotheses that selection on trophic characters is important to incipient stages of divergence and the maintenance of specialized forms in allopatry, using indigenous and recently translocated populations of Arctic charr in Maine. To address this, I compared aspects of body shape, gill raker morphology, growth, and diet among six populations, including one transplant and its ancestral source. This examination revealed the presence of at least three trophic forms among Maine charr, including a benthic specialist not previously identified in this region. Differences observed among these populations were analogous to those typical of trophic forms found elsewhere in sympatry, though perhaps less extensive in scale. Divergence between a translocated population and its source suggest some aspects of specialization are labile in contemporary time. In combination, these results indicate trophic ecology may play an important role in all stages of adaptive divergence, and niche stability may be important in maintaining trophic specializations over longer periods of time. In light of this new information, I also suggest that management plans for this species in Maine should seek to incorporate more information about such specialized forms, and should employ ecosystem based management to preserve forms within the unique contexts of their respective lake systems. Management approaches that fail to preserve lake community structure in situ are likely to result in either extinctions or revisions of specializations.