Temporal stability of individual feeding specialization may promote speciation

Abstract

Summary 1.Inter-individual differences in trophic behaviour are considered important in the disruptive selection process for resource specialization and may represent an early phase in the evolution of polymorphism and adaptive radiation. Here, we provide evidence of high stability of individual trophic niches of a fish predator from a 15-year study. 2. Individual resource specialization was investigated by combining data from analyses of stomach contents (recent trophic niche), trophically transmitted parasites (long-term niche) and trophic morphology (niche adaptations) from single specimens of a postglacial fish (Arctic charr) population sampled from contrasting pelagic and littoral habitats. 3. Based on the relationships between morphology, parasites and diet, high inter-individual temporal consistency of narrow niches (zooplanktivorous vs. benthivorous) was evident through the ontogeny of the charr, indicating low degree of switching both in habitat utilization and feeding strategy of individual fish. Co-occurrence of differently specialized behavioural phenotypes was sustained over multiple generations. 4. The stable long-term habitat and feeding specializations may represent an important initial step in an adaptive radiation process, and our findings suggest a case of sympatric speciation into two incipient forms diverging along the littoral-pelagic resource axis.

Temporal stability of niche use exposes sympatric Arctic charr to alternative selection pressures

“…An ability to withstand the effects of a specific, restricted group of parasite larvae may then allow a specialist predator to exploit a potentially infected prey group without accumulating the high costs associated with defense against a more diverse range of parasite types (Lafferty et al 2000). Thus it is highly likely that parasites are causing parasite-mediated differential selection pressures amongst the three specialist charr foragers in Fjellfrøsvatn and that these and other identified differential selection pressures have remained consistent for at least 2 decades (see also Knudsen 2010).…”

“…For the ontogenetic effect of phenotypic plasticity to modify the expressed phenotype, individuals should retain their niche specialisms over a period close to the generation time. For disruptive selection to result in evolutionary divergence, resource specialisms need to be expressed in a population over multiple generations (see Woo et al 2008;Knudsen et al 2010). Secondly, for disruptive selection to operate, organisms occupying separate ecological niches need to be exposed to different selection pressures, disruptive selection could result in alternative expressed phenotypes of resource specialists (Abrams 2006;Doebeli et al 2007).…”

“…The Arctic charr in Fjellfrøsvatn, Northern Norway show discrete trophic specialisation related to macro-habitat segregation Knudsen et al 2007Knudsen et al , 2010. This trophic specialisation exposes individuals with different specialisms to different burdens of specific trophic transmitted parasite species ), which could act as strong parasite-mediated selection forces on the host populations (Maan et al 2008;Matthews et al 2010).…”

Divergent growth patterns between juveniles of two sympatric Arctic charr morphs with contrasting depth gradient niche preferences

“…This morph-pair is shown to have divergent trophic niches (e.g. habitat choice), which are stable over seasons including the long (*6 months) winter period, and across years (Klemetsen et al 2003b;Knudsen et al 2006Knudsen et al , 2010Amundsen et al 2008;Amundsen and Knudsen 2009). The differences in growth related to temperature can be explained as the LO-morph is a trophic generalist, utilising all habitats and dietary resources through their ontogeny (Knudsen et al , 2011Amundsen et al 2008) and experiencing large temperature fluctuations through the year.…”

Tracking niche variation over millennial timescales in sympatric killer whale lineages

“…The reliability of the optimized tree was estimated using 100 bootstrap replicates. To allow a heuristic visualization of lineage sorting based on trophic position, d 15 N isotopic values were treated as continuous characters and their ancestral state for these characters was inferred using Mesquite v. 2.75 [48], with the 'Trace Character Over Trees' module applying the parsimony reconstruction method.…”