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Thread: Discussion about Lake Trout, The Ice Age, Dall Sheep, Zoogeography and More

  1. #1

    Default Discussion about Lake Trout, The Ice Age, Dall Sheep, Zoogeography and More

    I've always been fascinated by the ice age and theories about how the ice age affected the spread of species over the continents. I'm sure some of you have heard about the theory/hypothesis about Dall Sheep and their current locations today correlating with the past locations of the ice sheets over Alaska. Interestingly, I have also been reading about lake trout distribution and how their current range almost perfectly matches the maximum extent of the ice sheets over North America during the ice age.

    My question is to anyone with expert knowledge on the subject is; why do the ranges overlap so well? What is the significance of the two overlapping ranges? I am assuming that the ice sheets had something to do with the creation of the large oligotrophic lakes that the lake trout thrive in, but what or how did the lake trout survive on top of, underneath, or in the middle of gigantic ice sheets? That part just doesn't make sense to me. It makes sense that after the ice sheets started melting, that the meltwater produced lakes that the lake trout took refuge in, but how did they get in or on the ice to begin with? Did they live in the outwash plains at the terminal ends of glaciers? Did they live in ice-dammed lakes like Glacial Lake Missoula and Glacial Lake Ahtna? If so, wouldn't they all die when the dammed lakes burst open, causing massive floods? I realize nobody was there to witness these events, or at least there are no historical records of these events taking place so any explanation would be purely speculative, but I just thought that maybe somebody with expert knowledge on the local geology might know of some plausible explanations that have been proposed. If so, I would love to hear a good explanation. Thanks.

  2. #2
    Member DannerAK's Avatar
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    The article and selected text below might help to answer some of your questions:

    http://www.fishfactor.tv/documents/L...%20strains.pdf

    "The early details of lake trout evolution will likely remain unknown. The close relationship
    between lake trout distribution and formerly glaciated areas (Lindsey, 1964; Scott and
    Crossman, 1973) suggests that fossil remains preceding the Wisconsinan glaciation were
    destroyed long ago by advancing glaciers. However, the roughly coincident divergences
    of the three subgenera of Salvelinus (Salvelinus, Cristivomer, and Baione) approximately 2
    to 3 million years ago (Behnke, 1972, 1980; Grewe et al., 1990; Phillips et al., 1992) indicate
    a short burst of evolutionary diversification and selection, potentially in response to major
    environmental or biotic pressures. The placement of lake trout in its own subgenus (Cristivomer)
    indicates the extent of its divergence from other charr species in response to
    Pleistocene events (Behnke, 1972).
    The nature of glacial disturbances makes it impossible to reconstruct the complete
    Pleistocene history of lake trout. Each glaciation effectively bulldozed continental landscapes
    under a wall of ice, wiping clean the geologic and biologic traces of preceding
    events. Because of this, the exact number of Pleistocene glaciations in North America is
    uncertain, with estimates ranging between 4 and 20 cycles (Pielou, 1991; Dawson, 1992;
    Gunn and Pitblado, Chapter 1, this volume). Each of these undoubtedly had major impacts
    on the distribution and genetic structure of lake trout, based on the speciesí present
    distribution in relation to glacial coverage (Figure 2.1). During each glacial interval, fish
    populations were extirpated or displaced, in some cases by thousands of kilometers. Those
    fish that survived were limited to a handful of refugial habitats along the periphery of
    the ice sheets."
    "The North wind is cold no matter what direction it's blowing"

  3. #3

    Default

    Quote Originally Posted by DannerAK View Post
    The article and selected text below might help to answer some of your questions:

    http://www.fishfactor.tv/documents/L...%20strains.pdf

    "The early details of lake trout evolution will likely remain unknown. The close relationship
    between lake trout distribution and formerly glaciated areas (Lindsey, 1964; Scott and
    Crossman, 1973) suggests that fossil remains preceding the Wisconsinan glaciation were
    destroyed long ago by advancing glaciers. However, the roughly coincident divergences
    of the three subgenera of Salvelinus (Salvelinus, Cristivomer, and Baione) approximately 2
    to 3 million years ago (Behnke, 1972, 1980; Grewe et al., 1990; Phillips et al., 1992) indicate
    a short burst of evolutionary diversification and selection, potentially in response to major
    environmental or biotic pressures. The placement of lake trout in its own subgenus (Cristivomer)
    indicates the extent of its divergence from other charr species in response to
    Pleistocene events (Behnke, 1972).
    The nature of glacial disturbances makes it impossible to reconstruct the complete
    Pleistocene history of lake trout. Each glaciation effectively bulldozed continental landscapes
    under a wall of ice, wiping clean the geologic and biologic traces of preceding
    events. Because of this, the exact number of Pleistocene glaciations in North America is
    uncertain, with estimates ranging between 4 and 20 cycles (Pielou, 1991; Dawson, 1992;
    Gunn and Pitblado, Chapter 1, this volume). Each of these undoubtedly had major impacts
    on the distribution and genetic structure of lake trout, based on the speciesí present
    distribution in relation to glacial coverage (Figure 2.1). During each glacial interval, fish
    populations were extirpated or displaced, in some cases by thousands of kilometers. Those
    fish that survived were limited to a handful of refugial habitats along the periphery of
    the ice sheets."
    Good read DannerAK. That actually explains a lot. Especially the part about the lake trout surviving along the periphery of the ice sheets in large melt water basins and then expanding their range to occupy new lakes created by the retreating ice sheets. I am still confused about some things though. In particular why does mitochondrial DNA seem to suggest that there was originally six or more separate populations located along the periphery and then they converged with the retreating ice sheet, but then later on in the article it seems to suggest that originally their was a genetic bottleneck, which lead to a decrease in genetic diversity. If so, where and when did this genetic bottle neck occur? Was it before the ice age? What mechanism would cause the genetic bottleneck. It seems like the ice sheet would have produced an opposite effect of a bottleneck, caused by separation of the populations (allopatric speciation). At least from my limited understanding of genetics and biology.

  4. #4
    Member Ak Laker Hunter's Avatar
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    They followed river streams in cold rivers from melting glaciers.Than hey big deep Lake just like ocean but less Sharks. Lol
    Got to look good even in defeat. IMAGE is everything.

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