Conclusion
Understanding ecological mechanisms of diversification is challenging
(Ackermann et al., 2004). Divergence occurs along a continuum and in
early stages, such as in post-glacial lakes, morphological and dietary
variation may not always be features that are related (Bolnick et al.,
2020; Bolnick et al., 2007). The debate around diversification sequence,
(which diverges first, behaviour, morphology, or ecology?) highlights
the mosaic nature of intraspecific variation (Hendry et al., 2009a). In
this study, we asked whether among-individual diet variation could be
occurring within an ecotype by examining the fine-scale trophic
variation of an early stage of sympatric divergence of lake trout in
Great Bear Lake (i.e., postglacial, representing ~350
generations; Harris et al., 2015). Due to presumed homogeneity, few
studies have investigated dietary patterns and groupings within an
ecotype. Thus, this study provides evidence that among-individual
resource specialization can occur within an ecotype. The co-existence of
multiple generalist ecotypes in Great Bear Lake (Chavarie et al.,
2016a), combined with the individual specialization shown here in the
piscivorous generalist ecotype, expands our understanding of niche use
and expansion, plasticity, individual specialization, and intraspecific
diversity in evolutionarily young populations.
Rapid divergence within relatively few generations and among-individual
diet variation have both been demonstrated to be a strong driver of
population dynamics (Ashley et al., 2003; Bolnick et al., 2020; Fussmann
et al., 2007; Turcotte et al., 2011). In this study, the fine-grained
trophic patterns shown within this ecotype suggested that ecological
drivers (i.e., spatial variation, habitat use, prey diversity, and
abundance) could have important effects on plasticity expression in
early stages of divergence. Theory and experiments have demonstrated
that among-individual diet variation can increase stability within a
system (Agashe, 2009). Using a broad resource spectrum has been
identified as an adaptive strategy for fishes living in Arctic
environments, where food availability is patchily distributed and
ephemeral (Dill, 1983; Kassen, 2002; Smith et al., 2011). Thus, it is no
surprise that the trophic individual specialization within an ecotype
was discovered within a northern lake.