Re: WHAT IS THE EVOLUTIONARY ADVANTAGE .......?

jillery wrote:
On Feb 10, 1:00 pm, Friar Broccoli <elia...@xxxxxxxxx> wrote:
On Feb 10, 12:28 pm, jillery <69jpi...@xxxxxxxxx> wrote:





On Feb 10, 11:04 am, Friar Broccoli <elia...@xxxxxxxxx> wrote:

On Feb 10, 10:12 am, "Mike Dworetsky"

<platinum...@xxxxxxxxxxxxxxxxxxxx> wrote:
Friar Broccoli wrote:
On Feb 10, 3:13 am, "Mike Dworetsky"
<platinum...@xxxxxxxxxxxxxxxxxxxx> wrote:

I am quoting the following from you:

and the death of the adults
prevents competition for resources between young and old.

to give you an opportunity to think about it critically.

I'm not sure if you think I am right, wrong, or need to think
about it some more.

.

I can imagine two scenarios: The spawning adults live on, and
(being exhausted from their swim) eat lots of food that the
hatchlings would otherwise get to eat. Or, they die soon after
spawning, as now, and do not compete with their offspring for the
limited food available in the river environment.

This fails on two counts that I can see:

Secondarily: the fry won't hatch for many months after the eggs
have been laid, so the adults will be long gone and their effect
on the potential food supply long in the past at hatching.

Fundamentaly: Salmon spawning grounds contain from tens to many
thousands of individuals. Any benefit accrued would be primarily to
the offspring of others. In evolution there are no prizes for
preferently helping the offspring of others.

Thus, since the benefit would be extremely marginal and not
focused on your own offspring this argument makes no sense.

The first might seem good for the surviving adults, but at some
point they will have to go downstream, past the gauntlet of
predators, and out into the sea to feed and build up strength for
another spawn. Then they have to run another guantlet of
predators on the way back. If their chances of success the first
time was 10%, the second time it is 1% for a lifetime. The
majority of salmon eggs will be laid by fish doing it for the
first time.

I am not sure how to think about the second marginal advantage but
see two obvious problems anyway here:

Steelhead behave like other salmon but DO repeatedly spawn in
separate years. I presume they lay fewer eggs in each spawning so
they have enough resources to get back to the ocean, but could be
completely wrong about this. So the strategy is viable.

.

There are two kinds of steelhead, separated by where they sexually
mature. "Summer-run" steelheads sexually mature in the rivers and
lakes, and spawn the following spring. "Winter-run" steelheads
sexually mature in the ocean, and spawn shortly after migrating.
Apparently winter-run steelheads spawn in coastal streams, while the
summer-run steelheads restrict themselves to the more inland
streams. There are also populations that don't migrate at all, and
stay in freshwater year-round. I couldn't find anything that said so
explicitly, but my impression is these are separate populations and
rarely crossbreed. Is it possible there is also a difference in the
two populations as to their ability to survive multiple spawinings?

I don't know much about steelhead, having only caught one in my life
and in that case someone told me what it was at the end of the day. I
thought I'd just caught a regular salmon, although I noted that the
fight was very unusual.

I suspect I know about as much as you on this point, and from the same
sources, so neither of us can claim any superior authority.

Since salmon lay thousands of eggs, a second try would provide an
individual with a real reproductive advantage even at 100%. This is
especially the case since it is not uncommon for an entire run to
suffer mortalities well in excess of 99%. So if a female (or male)
contributed a second set of eggs that landed on a good year it
could easily increase it reproductive success by a factor of
hundreds.

.

However the main problem is the logic which suggests the salmon are
dying for the benefit of the group at the expense of their
individual success.

I don't see that as the main problem, as I don't see anybody using
that logic.

In context the phrase:

"and the death of the adults prevents competition for resources
between young and old."

appears to be presented as a benefit of Semelparity (see r norman's
comments and reference). For THAT reason for dying to be a benefit it
is a benefit to the entire population of upcoming juveniles in that
spawning ground. If this is not a group selection argument someone
will need to explain how this act benefits the offspring of a
salmon's own offspring.

IIUC r norman's comments contradict the notion that the salmon's death
is a matter of group selection. I don't see that semelparity
correlates with group selection, but with whether or not the parent's
death increases or decreases that parent's ability to pass on its
genes. Using that understanding as a base, and focusing on those
salmon that die after spawning, I interpret Mike Dworetsky's comment
different than you do. From the standpoint of the individual salmon,
what is the evolutionary benefit of surviving after they spawn? None,
because they put all they had into that one act of reproduction. That
other salmon manage multiple spawnings means they use a differerent
strategy, and that strategy doesn't apply to those salmon that use
semelparity.

Thanks, I wasn't trying to be cryptic, and it does appear that competition
for scarce resources isn't necessarily the reason for the die-off of the
adults, or at least certianly not the only reason. There appear to be many
different processes going on, all of which seem focussed on laying and
fertilizing one generation of eggs rather than the continued life of the
parents.

Does anyone know if the dead bodies of the parents provide nutrients in the
water that assist the young when the eggs hatch?

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

.

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