Temporal stability of niche use exposes sympatric Arctic charr to alternative selection pressures |
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Authors: | Rune Knudsen Anna Siwertsson Colin E Adams Monica Garduño-Paz Jason Newton Per-Arne Amundsen |
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Institution: | 1.Department of Arctic and Marine Biology,University of Troms?,Troms?,Norway;2.Scottish Centre for Ecology and the Natural Environment,University of Glasgow,Rowardennan, Glasgow,Scotland, UK;3.Facultad de Ciencias,Universidad Autónoma del Estado de México,Toluca, Estado de México,Mexico;4.NERC Life Sciences Mass Spectrometry Facility,SUERC,East Kilbride, Glasgow,Scotland, UK |
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Abstract: | There is now strong evidence that foraging niche specialisation plays a critical role in the very early stages of resource
driven speciation. Here we test critical elements of models defining this process using a known polymorphic population of
Arctic charr from subarctic Norway. We test the long-term stability of niche specialisation amongst foraging predators and
discuss the possibility that contrasting foraging specialists are exposed to differing selection regimes. Inter-individual
foraging niche stability was measured by combining two time-integrated ecological tracers of the foraging niche (each individual’s
δ13C and δ15N stable isotope (SI) signatures and their food borne parasite fauna) with a short-term measure of foraging niche use (stomach
contents composition). Three dietary subgroups of predators were identified, including zooplankton, gammarid and benthivore
specialists foragers. Zooplanktivorous specialists had muscle low in δ 13C, a high abundance of parasites transmitted from pelagic copepods, a smaller head, longer snout and a more slender body-form
than gammaridivorous specialist individuals which had muscle more enriched in δ 13C and high abundance of parasites transmitted from benthic Gammarus. Benthivorous individuals were intermediate between the other two foraging groups according to muscle SI-signals (δ13C) and loadings of parasites transmitted from both copepods and Gammarus. The close relationship between subgroups identified by stomach contents, time-integrated tracers of niche use (SI and parasites)
and functional trophic morphology (niche adaptations) demonstrate a long-term temporally stable niche use of each individual
predator. Differential habitat use and contrasting parasite communities and loadings, show differential exposure to different
suites of selection pressures for different foraging specialists. Results also show that individual specialisation in trophic
behaviour and thus exposure to different suites of selection pressures are stable over time, and thus provide a platform for
disruptive selection to operate within this sympatric system. |
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