UHI Research Database pdf download summary Phenotypic and resource use partitioning amongst sympatric, lacustrine brown trout, Salmo trutta Verspoor, Eric; Adams, Colin E.; Greer, R.; Piggott, Camilla; Hooker, Oliver ; Newton, Jason Published in: Biological Journal of the Linnean Society Publication date: 2018 Publisher rights: Copyright © 2018, Oxford University Press The re-use license for this item is: CC BY-NC The Document Version you have downloaded here is: Early version, also known as pre-print The final published version is available direct from the publisher website at: 10.1093/biolinnean/bly032 Link to author version on UHI Research Database Citation for published version (APA): Verspoor, E., Adams, C. E., Greer, R., Piggott, C., Hooker, O., & Newton, J. (2018). Phenotypic and resource use partitioning amongst sympatric, lacustrine brown trout, Salmo trutta. 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Sep. 2021 1 Phenotypic and resource use partitioning amongst sympatric, 2 lacustrine brown trout, Salmo trutta (Linnaeus). 3 4 CAMILLA V. H. PIGGOTT1, ERIC VERSPOOR2, RON GREER3, OLIVER HOOKER1, 4 JASON 5 NEWTON5 and COLIN E. ADAMS1 6 1Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow, 7 Rowardennan, Glasgow, G63 0AW, Scotland, U.K. 8 2The Rivers and Lochs Institute, University of the Highlands and Islands, Inverness, U.K. 9 3The Old Armoury, Blair Atholl, Scotland, UK 10 4 PR Statistics, 6 Hope Park Crescent, Edinburgh Scotland, UK 11 5 NERC Life Sciences Mass Spectrometry Facility, SUERC, East Kilbride, UK 12 13 Running header: Polymorphism in brown trout 14 Key words: polymorphism, speciation, divergence, evolution, ecotypes 15 16 17 Corresponding Author: Colin Adams. Scottish Centre for Ecology & the Natural Environment, 18 IBAHCM, University of Glasgow, Rowardennan, Glasgow, G63 0AW, Scotland, U.K. 19 Tel: 01360870512 E-mail: [email protected] 20 21 22 23 ABSTRACT 24 Divergence into discrete foraging specialist morphs living in sympatry is relatively well 25 described in lacustrine fishes of the Salmonidae. Although piscivorous forms of Salmo trutta 26 have been widely reported, other trophic foraging specialists are strangely rarely recorded 27 amongst Salmo species. Microsatellite and mitochondrial genetic data segregated Salmo 28 trutta collected from Loch Laidon, Scotland, into four distinct genetic groups. Three groups 29 analysed in this study showed significant differences in body shape, stomach contents, 30 muscle stable isotope signature, gill raker length and spacing, and habitat use. We conclude 31 that the three genetically defined groups comprise: a generalist foraging morph, a pelagic- 32 feeding specialist morph and a profundal macrobenthos feeding morph. The features 33 distinguishing these morphs however, show a degree of overlap. This appears to be only the 34 second record of invertebrate resource use partitioning associated with expression of 35 alternative morphologies in sympatry this species and the first report of a profundal feeding 36 morph. Why such polymorphisms are generally rare in Salmo species still remains unclear, 37 however potential explanations are discussed. 38 39 KEYWORDS: ecotypes – evolutionary – divergence – polymorphism - Salmonidae 40 41 INTRODUCTION 42 The patterns of structuring of phenotypes and genotypes found within a single species in 43 the wild have the potential to provide insights into the very beginnings of the evolutionary 44 processes that may ultimately result in new species (Snorrason & Skulason, 2004). Complex 45 intraspecific structuring is now relatively well documented in many freshwater fishes 46 (Fevolden et al., 2012). It is particularly prevalent amongst fishes from the northern 47 hemisphere that live in freshwater lakes that were glaciated during the Quaternary period 48 (Skulason & Smith, 1996). Where intraspecific structuring occurs between unconnected 49 waters, it is generally thought to be the result of differential selection pressures operating at 50 a local population level (Garant, Forde & Hendry, 2007); the effects of phenotypic plasticity 51 responding to differing local environmental conditions (Adams, Woltering, & Alexander, 52 2003b); the random effects of genetic drift (Frazer & Rusello, 2013); or some combination of 53 these (Adams & Huntingford, 2004; Alexander & Adams, 2004). In a number of places 54 however, the pattern of intraspecific structuring exhibits greater complexity and therefore 55 more complex explanations for the processes resulting in its formation are likely to be 56 required. 57 Such situations offer opportunities to explore more deeply, early evolutionary processes 58 (Smith & Skulason, 1996; Skulason, Snorrason & Jonsson, 1999). One such situation is where 59 a single waterbody supports two or more clearly defined alternative phenotypic and/or 60 genotypic groups from a single species. Amongst fishes there have been a number of 61 reports of sympatric morphs, ecotypes or forms, particularly, although not solely, from 62 lake-dwelling species (Pakkasmaa & Piironen, 2001; Adams et al., 2016). Where such 63 sympatric morphs exist, evidence of distinct ecological differences between them is also 64 commonly reported (Skulason & Smith, 1995; Skulason et al., 1999; Jonsson & Jonsson, 65 2001). Most frequently, sympatric phenotypic polymorphisms manifest as divergence across 66 the littoral – pelagic habitats (Knudsen et al., 2006) or less frequently across littoral – 67 profundal habitats (Hooker et al., 2016). Such polymorphisms are recognised as an 68 important evolutionary step towards the emergence of new species (Maynard Smith, 1966; 69 Dieckmann & Doebeli, 1999; Snorrason & Skulason, 2004) 70 Amongst the fish genera that are commonly found in recently glaciated fresh waters, there 71 is considerable documented evidence of a common pattern of sympatric polymorphism 72 exhibiting partitioning of feeding resources by foraging specialists (Table I). Such patterns 73 are widely reported amongst fishes of the Salmonidae family (Skulason & Smith, 1995) 74 (Table I). Amongst species of the Salmo genus, piscivorous specialist forms, usually living in 75 sympatry with littoral benthos feeders, are relatively widely reported in Salmo trutta 76 (Hughes et al., 2016). However discrete and sympatric foraging specialisations across the 77 available invertebrate foraging resources now widely reported for other salmonid genera is 78 rarely reported in Salmo (Behnke, 1972). 79 This study describes a rarely reported phenotypic and ecological divergence of three or four 80 serendipitously discovered sympatric populations in the brown trout, Salmo trutta L. 1758. 81 Originally resolved by population genetic analysis (Verspoor et al., submitted), this study 82 tests the following hypotheses, that: 83 1) S. trutta categorised into the three distinct genetic groups are also morphologically 84 segregated. 85 2) Distinct genetic groups exhibit different foraging ecologies. 86 3) Variation in morphology and foraging ecology are linked. 87 88 METHODS 89 STUDY SITE AND SAMPLING METHOD 90 Loch Laidon (56° 39’ 56.65” N, 004° 40’ 4.6667” W) is an oligotrophic lake 283 m above sea 91 level on Rannoch Moor, Perthshire, Scotland. The lake is approximately 8 km long, 4 km2 in 92 area, with a maximum depth of 39 m and a mean depth of 10.7 m (Murray & Pullar, 1910). 93 The catchment is dominated by open heather (Ericaceae) moorland (McLeod, et al., 2005; 94 Shilland, et al. 2011). Campbell (1979) reports S.trutta, Atlantic salmon Salmo salar (L. 95 1758), perch Perca fluviatilis (L. 1758) and Arctic charr Salvelinus alpinus (L. 1758) in Loch 96 Laidon. The contemporary status of this latter species however is uncertain as it has not 97 been collected during recent sampling there (see Verspoor et al. submitted). 98 As a full fish sampling protocol is presented elsewhere (Verspoor et al. submitted) only 99 pertinent details are presented here (Table S1). S. trutta were collected from Loch Laidon 100 during May 2008 using both benthic and pelagic Nordic pattern gillnets, which are non- 101 selective for salmonids between 45 and 495 mm (fork length) (Appelberg et al., 1995). 102 Bathymetric data (Murray & Pullar, 1910) were used to define a random stratified sampling 103 design for four habitats: benthic littoral (< 6m water depth); benthic sub-littoral (6 – 20 m 104 depth); benthic profundal (defined as >20 m depth) and the pelagic habitat, (sampled with a 105 6m deep floating net set from the surface above ca 30 m deep water). All nets were 106 deployed over one night; all S. trutta caught, were killed on