Body form differences between the Enos Lake species pair of threespine sticklebacks (Gasterosteus aculeatus complex)

Abstract

Two ecologically and morphologically divergent species of the Gasterosteus aculeatus (threespine stickleback) species complex occur in Enos Lake, Vancouver Island, British Columbia. The limnetic species swims in open water most of the time and feeds on plankton, and the benthic species lives near the shore in a structurally complex environment where it eats larger benthic prey. Based on design criteria inferred from hydrodynamic considerations, from other fishes, or from other populations of Gasterosteus, and on ecological differences between the two species, we expected that limnetic sticklebacks would have a more fusiform body, longer pectoral fins and snout, and larger eyes. Although some of these expected differences had been observed in a previous study of this species pair, others were verified for the first time in this study. Shape divergence between our samples results both from allometric trends coupled with differences in overall mean size and from size-free shape differences. Standard length is a poor proxy for general size (i.e., the first principal component of the morphometric variables) because several major features which differ between the species are dorsoventrally oriented. The marked morphometric divergence between these species has probably evolved within about the past 13 000 years, since deglaciation of Vancouver Island.

Ecological morphology of lacustrine threespine stickleback Gasterosteus aculeatus L. (Gasterosteidae) body shape

“…With these observations, it has been argued that the evolution of deep body profiles in stickleback is the consequence of selection for increased burst performance for either evading predators (Taylor & McPhail, 1986) or littoral foraging (Taylor & McPhail, 1986;Baumgartner, Bell & Weinberg, 1988). Both hydromechanical theory and the results of this study do not support the predation hypothesis (see above).…”

Ecomorphology of the eyes and skull in zooplanktivorous labrid fishes

“…Although a number of previous studies have concluded that zooplanktivores have enlarged eyes (McPhail 1984;Strauss 1984;Baumgartner et al 1988;Pankhurst 1989;Hulsey et al 2007;Cooper and Westneat 2009;Goatley and Bellwood, 2009), at least one previous analysis of Sebastes rockfishes did not (Ingram and Shurin 2009). It appears then that enlarged eyes are not a universal adaptive visual specialization of zooplanktivores.…”

“…One of the classic findings is that zooplanktivores have larger eyes than other fish (Fryer and Iles 1972;Davis and Birdsong 1973;Dullemeijer and Barel 1977;McPhail 1984;Strauss 1984;Baumgartner et al 1988;Pankhurst 1989;Hart and Gill 1994;Kassam et al 2003;Hulsey et al 2007;Cooper and Westneat 2009;Goatley and Bellwood 2009). The functional reasoning for this is provided by predictions from physiological optics.…”

Morphometric and meristic variation in Galician threespine stickleback populations, northwest Spain

“…The most remarkable example of such differentiation was found in Enos Lake, where the presence of two sympatric ecotypes or species was described: 'limnetics', with longer bodies, a larger pair of pectoral fins and a larger number of gill rakers, and 'benthics', with robust bodies and a smaller number of gill rakers (McPhail 1984). These general trends are thought to be the result of adaptation for better exploitation of divergent trophic resources (Lavin & McPhail 1986, Baumgartner et al 1988, Klepaker 1993, Kristja´nsson et al 2002. Elongated shallow bodies are a common pattern to many fishes, including stickleback, that predominately forage in open-water zones (Lavin & McPhail 1986, Cawdery & Ferguson 1988, Walker 1996, Rolda´n et al 2000, Kristja´nsson et al 2002.…”