In a message dated 7/6/00 8:58:28 AM Pacific Daylight Time,
joao.magalhaes@fundp.ac.be writes:
> >>Even species such as Desmognathus that live less than 15
> >>years do not show signs of increased mortality with age (in fact, they
> >>show decreased mortality after adulthood is reached).
> >
> >Do you have a cite for this?
>
> Finch's "Longevity, Senescence, and the Genome", pag 219.
I looked at all the data in Finch's book and I don't
think they properly address the presence of aging in
ectothermic vertebrates. The problem is that almost
all the studies cited were field studies, and all
the organisms had very high rates of extrinsic
mortality. If the extrinsic mortality is high, you
can't detect aging even when it's there. I note
that in the one case where Finch provides data (the
three turtle species) the curves show a distinct increase
in mortality rate over time. I expect it's not significant,
but I wonder whether the authors used the maximum
likelihood methods you need to really sort these things
out.
My plan for investigating aging in temporary habitat
shrimp is on hold for exactly this reason - I can't get
the extrinsic mortality rate down to appropriately low
levels. When I looked at mortality curves from another
student in the lab, I saw the same thing as with the turtles-
an increase in mortality with time, although it was
significant in this case.
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