Discrete prey availability promotes foraging segregation and early divergence in Arctic charr, Salvelinus alpinus

Abstract

Many animal species show individual foraging specialisms when potential prey requires prey-specific foraging strategies. Arctic charr are often found as benthic (macroinvertebrate) or pelagic (plankton) foraging specialists. Here, we tested specifically if given a choice of prey with different characteristics individuals would specialise in a single prey type and if individuals would chose prey based on their expressed trophic morphology, in a laboratory experiment and in a field observation. When offered a choice of benthic and pelagic prey most individuals (73%) showed that 100% fidelity to a single foraging source. Naïve individuals (not previously exposed to natural prey) with more robust head and mouth shape were more likely to forage on a benthic prey source (chironomids). In contrast, individuals with a more fusiform body, larger eye, but more slender head shape were more likely to specialise on pelagic prey (Artemia). Field observations of a natural population of Arctic charr from Loch Doine identified specialists foraging on either plankton or macrobenthos (on the basis of stomach contents) and some generalists. Morphological analysis showed that significant differences in shape reflecting recent foraging history. These results support the hypothesis that the availability of discrete, different prey types results in discrete foraging specialisms which in turn may result in the expression of discrete alternative phenotypes through subsequent plastic ontogenetic process. We conclude that this provides a partial explanation for why ecologically driven evolution processes are particularly prevalent in fishes from post-glacial lake systems.

Similar patterns of individual niche use are revealed by different time‐integrated trophic tracers (stable isotopes and parasites)

“…Similar patterns of shape variation with benthivore individuals having a more robust head shape compared to zooplanktivore individuals are known from Arctic charr (Knudsen et al 2007;Garduño-Paz & Adams 2010) and other fish populations (e.g., Robinson & Parsons 2002;Puebla 2009). Within the population, individuals with a blunt snout and a deep, more robust head typically ate more benthos (especially Gammarus), had high d 13 C values (i.e., benthic signatures) and correspondingly a high number of Gammarus-transmitted parasite species and concurrently also a low abundance of Diphyllobothrium spp.…”

Are phenotypic traits useful for differentiating among a priori Coregonus taxa?

“…Crucially, most of the traits used in the key of Kottelat & Freyhof (2007) are known to be affected by environmental pressures. Morphological traits such as head measurements can be modified by physical habitat and foraging behaviour (Adams et al , 2003; Garduño‐Paz & Adams, 2010) and such patterns seen between fishes that specialize in utilizing divergent resources are repeatable across fish taxa (Robinson & Wilson, 1994; Smith & Skúlason, 1996). In addition, there is often a growth effect on morphology (allometry) in fishes, which suggests that body proportions are not good diagnostic traits as they change over the life of an individual (Svärdson, 1950).…”

Intraspecific Morphological Variation in Two Common Marine Fish Species from South Africa

“…Mouths are usually downturned in benthic feeders, terminally placed in pelagic feeders, and upturned in surface feeders [21,22]. Benthic morphs usually display a more robust body shape with a broad rounded snout, whereas pelagic morphs usually exhibit a more fusiform slender body [23,24]. Individuals that feed on the benthos benefit from increased feeding efficiency associated with the broad rounded snouts and downturned mouths [1,21].…”