An isolated population of fourhorn sculpins (Myoxocephalus quadricornis, family Cottidae) in a hypersaline high arctic Canadian lake

Abstract

Freshwater sculpins probably evolved from marine ancestors which entered bodies of water such as proglacial lakes or lakes which were gradually isolated from the sea by isostatic rebound . Sculpins in fresh water lakes (Myoxocephalus thompsoni [Girard]) lack cephalic horns and live well below a depth of 10 m . Those in the sea (Myoxocephalus quadricornis [Linnaeus]) typically live above 10 m and possess a well developed set of four cephalic horns . The sculpins in Garrow Lake, North West Territories, are intermediate between the marine and fresh water forms with respect to their depth distributions and their cephalic horns (spines) . As a consequence, Garrow Lake, which separated from the sea some 3000 years ago, serves as an excellent `laboratory' for studying evolutionary changes in this sculpin . The age of the lake was based on carbon-14 dates of the fossil pelecypods from raised beaches around the lake and from observations of rates of isostatic rebound in the area as reported by Dickman &Ouellet 1983 andPage et al. 1984 . During the last 3000 years, the surface waters of Garrow Lake have freshened and its sculpins have apparently adapted to this top down freshening by occupying a depth where the salinity of the lake approaches that of sea water. As a result, the sculpin population in Garrow Lake lives deeper than the sculpin population in the nearby Garrow Bay . Thus, the deeper dwelling Garrow Lake sculpins appear to be less vulnerable to avian predation than their shallow water dwelling marine ancestors . It is hypothesized that reduced avian predation of the Garrow Lake sculpin population is associated with the observed reduction in their cephalic horns which impart a certain degree of disruptive colouration and disruptive pattern outline allowing the shallow dwelling marine species to blend in with its background in a manner which appears to make it less visible to avian predators .It is unfortunate that the three thousand year old Garrow Lake sculpin population is now endangered by mine tailings entering the lake from the nearby Cominco Ltd . mine. The entire food chain of the lake appears to have been severely impacted by lead and zinc mine tailings entering Garrow Lake at a rate of 100 metric tonnes per hour .

Vision and Foraging in Cormorants: More like Herons than Hawks?

“…They are known to forage on both pelagic and benthic fish species [7], [10]. Cormorant populations in Greenland and Iceland are known to forage mainly on sculpins ( Myoxocephalus ) [6], [12], which are a group of cryptically coloured benthic fish with a disruptive outline pattern that may have evolved in response to avian predation pressure [13]. Given their ability to prey upon pelagic and cryptic benthic prey, and a high capacity to accommodate their eye's optical system to compensate for the loss of corneal refractive power upon immersion [3], [14]–[16], it is reasonable to expect that cormorants have a visual system well adapted to function in water and that, as in aerial predatory birds, vision is the primary sense that guides their foraging.…”

Some like it deep: Intraspecific niche segregation in ruffe (Gymnocephalus cernua)

“…The numbers of analysed fish are shown above the bars segregation along the littoral-profundal gradient has been widely reported for salmonids (e.g. Harrod et al, 2010;Klemetsen, 2010;Muir et al, 2015) but, to the best of our knowledge, not previously reported for percids or predominantly benthivorous fishes, although some gobies and sculpins can inhabit lake profundal zones (Dickman, 1995;Ruzycki & Wurtsbaugh, 1999;Walsh et al, 2007). The pronounced differences in physical and biological properties of the different lake habitats are commonly considered as the main environmental drivers of niche specialisation within fish populations (e.g.…”

“…Eloranta, Knudsen, & Amundsen, ; Quevedo, Svanbäck, & Eklöv, ). However, to the best of our knowledge, no previous studies have investigated the potential of benthivorous fishes for intraspecific niche segregation along a littoral–profundal resource axis, although some predominantly littoral species of sculpins and gobies do occasionally inhabit the lake profundal zone (Dickman, ; Ruzycki & Wurtsbaugh, ; Walsh, Dittman, & O'Gorman, ). Moreover, improved understanding of how lake community and ecosystem properties affect trophic ecology of ruffe will be necessary for future monitoring and evaluation of potential impacts of this highly invasive species on recipient ecosystems (e.g.…”

“…Eloranta, Quevedo, Svanb€ ack, & Ekl€ ov, 2009). However, to the best of our knowledge, no previous studies have investigated the potential of benthivorous fishes for intraspecific niche segregation along a littoral-profundal resource axis, although some predominantly littoral species of sculpins and gobies do occasionally inhabit the lake profundal zone (Dickman, 1995;Ruzycki & Wurtsbaugh, 1999;Walsh, Dittman, & O'Gorman, 2007).…”

Adaptive Evolution of Nearctic Deepwater Fish Vision: Implications for Assessing Functional Variation for Conservation

“…It is also a more recent addition to freshwater environments, invading freshwater just prior to the beginning of the Pleistocene glaciation ( Kontula and Väinölä 2003 ) after diverging from its marine sister species, the fourhorn sculpin ( Myoxocephalus quadricornis ). The most striking difference between these 2 species is the lack of cephalic horns in the deepwater sculpin, hypothesized to have been lost due to a decreased need for camouflage from aerial predators ( Dickman 1995 ). Both ciscoes and deepwater sculpin colonized many of the same postglacial lakes following the last glacial maximum ( Sheldon et al 2008 ; Turgeon et al 2016 ), but deepwater habitats are evolutionary novel ecological niches for both species.…”