Morphological divergence between three Arctic charr morphs - the significance of the deep-water environment - PubMed (original) (raw)

. 2015 Aug;5(15):3114-29.

doi: 10.1002/ece3.1573. Epub 2015 Jul 14.

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Morphological divergence between three Arctic charr morphs - the significance of the deep-water environment

Sigrid Skoglund et al. Ecol Evol. 2015 Aug.

Abstract

Morphological divergence was evident among three sympatric morphs of Arctic charr (Salvelinus alpinus (L.)) that are ecologically diverged along the shallow-, deep-water resource axis in a subarctic postglacial lake (Norway). The two deep-water (profundal) spawning morphs, a benthivore (PB-morph) and a piscivore (PP-morph), have evolved under identical abiotic conditions with constant low light and temperature levels in their deep-water habitat, and were morphologically most similar. However, they differed in important head traits (e.g., eye and mouth size) related to their different diet specializations. The small-sized PB-morph had a paedomorphic appearance with a blunt head shape, large eyes, and a deep body shape adapted to their profundal lifestyle feeding on submerged benthos from soft, deep-water sediments. The PP-morph had a robust head, large mouth with numerous teeth, and an elongated body shape strongly related to their piscivorous behavior. The littoral spawning omnivore morph (LO-morph) predominantly utilizes the shallow benthic-pelagic habitat and food resources. Compared to the deep-water morphs, the LO-morph had smaller head relative to body size. The LO-morph exhibited traits typical for both shallow-water benthic feeding (e.g., large body depths and small eyes) and planktivorous feeding in the pelagic habitat (e.g., streamlined body shape and small mouth). The development of morphological differences within the same deep-water habitat for the PB- and PP-morphs highlights the potential of biotic factors and ecological interactions to promote further divergence in the evolution of polymorphism in a tentative incipient speciation process. The diversity of deep-water charr in this study represents a novelty in the Arctic charr polymorphism as a truly deep-water piscivore morph has to our knowledge not been described elsewhere.

Keywords: Geometric morphometrics; incipient speciation; phenotypic diversity; profundal piscivore; resource polymorphism; salmonid.

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Figures

Figure 1

Figure 1

Color drawings showing the typical appearance of the three Arctic charr morphs from Skogsfjordvatnet: the littoral spawning omnivore morph (LO-morph), the profundal spawning piscivore morph (PP-morph), and the profundal spawning benthivore morph (PB-morph).

Figure 2

Figure 2

Landmark positions used in geometric morphometrics and measurements of linear morphological traits. Landmarks used for analyses of body shape: 1: Anterior point of the snout, 2: anterior extreme of bony orbit of the eye, 3: top of cranium at midpoint of eye, 4: top of cranium at posterior point of the bony opercle (5), 5: posterior point of the bony opercle, 6: dorsal insertion of pectoral fin, 7: anterioventral point of bony opercle, 8: anterior insertion of dorsal fin, 9: anterior base of adipose fin, 10: dorsal origin of caudal fin membrane, 11: posterior border of the hypural bones at the lateral midline, 12: ventral origin of caudal fin membrane, 13: anterior insertion of anal fin, and 14: anterior insertion of pelvic fin. Landmarks used for head shape: 1–7, and 15: Center of nostril, 16: top of cranium at midpoint of nostril (15), 17: anterior point of the upper jaw, 18: posterior point of the upper jaw, 19: ventral extreme of bony orbit of the eye, 20: dorsal extreme of bony orbit of the eye, 21: posterior extreme of bony orbit of the eye, 22: ventral point of intersection between the opercle and preopercle bones, 23: posterior point of intersection between the opercle and subopercle bones. Interlandmark distances used for linear morphological traits: caudal peduncle depth (CP): 10–12, body depth posterior (BSP): 9–13, body depth anterior (BDA): 8–14, postpelvic fin length (PPF): 11–14, head depth (HD): 4–7, head length (HL): 1–5, snout length (SL): 1–2, eye width (EW): 2–21, maxilla length (ML): 17–18.

Figure 3

Figure 3

Diet (prey abundance, %) of the three Arctic charr morphs; the LO-morph (green bars), the PB-morph (orange bars), and the PP-morph (blue bars) from Skogsfjordvatn.

Figure 4

Figure 4

Principal component analysis of body shape (PC1 and PC4) in three morphs of Arctic charr. Mean values for each morph are illustrated by the larger symbols. Graphical illustrations show body shape at each extreme value on both axes (PC1: 0.05 and −0.05, PC4: 0.025 and −0.025). The red dot illustrates the position of the pelvic fin on extreme values of PC4.

Figure 5

Figure 5

Principal component analysis of head shape (PC1 and PC2) in three morphs of Arctic charr. Mean values for each morph are illustrated by the larger symbols. Graphical illustrations show head shape at each extreme value on both axes (PC1: 0.09 and −0.09, PC4: 0.07 and −0.07). The red line indicates the size of the upper maxilla on extreme values of PC2.

Figure 6

Figure 6

Box plots of size-corrected linear traits for the three Arctic charr morphs; the littoral spawning omnivore morph (LO-morph), the profundal spawning piscivore morph (PP-morph), and the profundal spawning benthivore morph (PB-morph).

Figure 7

Figure 7

Box plots illustrating differences between morphs (LO, PB, and PP) in four head traits accounting for differences in head size (length).

Figure 8

Figure 8

Length (in cm) distribution of the three different morphs (LO-morph in green, PB-morph in orange and PP-morph in blue) in Skogsfjordvatn with alignment size at 19.5 cm given.

Figure 9

Figure 9

Mean and standard deviation for the three morphs of Arctic charr for PC2, 3, and 5 from a principal component analysis of body shape. Illustrations show the body shape associated with individual extreme values on PC2 (0.03 and −0.03), PC3 (0.03 and −0.03), and PC5 (0.025 and −0.025).

Figure 10

Figure 10

Mean and standard deviation for the three morphs of Arctic charr for PC3, PC4, and PC5 from a principal component analysis of head shape. Illustrations show the head shape associated with individual extreme values at 0.06 and −0.06 for all three PC axes.

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