Re: The fungi did it

[don ohmes <d_ohmes@yahoo.com>]

If memory serves: R. Seymour writes that diffusion
coefficients were very high in dinosaur eggs (4x-100x
that expected for crocs) and proposes a humid nest
environment to prevent dessication... perhaps they
were very vulnerable to fungi infestation?

--- don ohmes <d_ohmes@yahoo.com> wrote:

> Any specific mention in the PDF of effects on eggs
> or
> hatchlings?
> 
> --- David Marjanovic <david.marjanovic@gmx.at>
> wrote:
> 
> > > An article from earlier this year which I just
> > came across:
> > >
> > > Casadevall, A. 2005. Fungal virulence,
> vertebrate
> > endothermy, and dinosaur
> > > extinction: is there a connection? Fungal
> Genetics
> > and Biology 42 (2):
> > > 98-106.
> > 
> > The prepublished online abstract was mentioned
> > onlist, and I contacted the 
> > author in a heroic ;-) attempt to prevent
> > publication. Arturo Casadevall was 
> > so kind as to send me a complete pdf so that I
> could
> > understand his points 
> > better. A short discussion ensued. In sum, it
> seems
> > plausible to me that the 
> > fungal spike, a known consequence of the impact,
> > could well have contributed 
> > to the extinction of dinosaurs and could even help
> > explain why dinosaurs 
> > were hit harder than mammals... even though it's
> > practically impossible to 
> > test.
> > 
> > > "Fungi are relatively rare causes of
> > life-threatening systemic disease in
> > > immunologically intact mammals despite being
> > frequent pathogens in 
> > > insects,
> > > amphibians, and plants.
> > 
> > Often the same species of mould can produce
> disease
> > in all those and more 
> > victims.
> > 
> > > Given that virulence is a complex trait, the
> > > capacity of certain soil fungi to infect,
> persist,
> > and cause disease in
> > > animals despite no apparent requirement for
> animal
> > hosts in replication or
> > > survival presents a paradox. In recent years
> > studies with amoeba, slime
> > > molds, and worms have led to the proposal that
> > interactions between fungi
> > > and other environmental microbes, including
> > predators, select for
> > > characteristics that are also suitable for
> > survival in animal hosts.
> > 
> > An interesting finding!
> > 
> > > Given
> > > that most fungal species grow best at ambient
> > temperatures, the high body
> > > temperature of endothermic animals must provide
> a
> > thermal barrier for
> > > protection against infection with a large number
> > of fungi.
> > 
> > Hurray! A selective advantage of endothermy plus
> > homeothermy! :-)
> > 
> > > Fungal disease is relatively common in birds but
> > most are
> > > caused by only a few thermotolerant species.
> [...]
> > > Deforestation and
> > > proliferation of fungal spores at
> > cretaceous­tertiary boundary suggests 
> > > that
> > > fungal diseases could have contributed to the
> > demise of dinosaurs and the
> > > flourishing of mammalian species."
> > 
> > If we assume that all dinosaurs were as
> susceptible
> > as modern birds to 
> > infections with large amounts of fungal spores.
> > 
> > >    - Fungal diseases are rare in endotherms
> > compared to ectotherms, 
> > > perhaps
> > > due to greater resistance.
> > 
> > First and foremost due to higher body temperature.
> > 
> > >    - Widespread deforestation after the K-T
> > boundary led to a sizable
> > > increase in fungi in the environment (all that
> > lovely dead vegetation to
> > > grow on), which would have resulted in greater
> > risk of infection from
> > > facultative parasites. (Note for the
> > phylogenetically-retentive: Fungi 
> > > seems
> > > to be used in this paper in the old sense of the
> > name, covering everything
> > > from slime moulds to oomycetes to fungi proper
> > :-S)
> > 
> > Really? Slime moulds and oomycetes don't infect
> > animals, do they? (And isn't 
> > there only one clade of the polyphyletic slime
> > moulds that is pathogenic at 
> > all?)
> > 
> > >    - Endotherms survive better than ectotherms
> > (see above), therefore 
> > > birds
> > > and mammals survive but ectothermic dinosaurs
> > don't.
> > 
> > Here there is a problem. I haven't been able to
> > convince Arturo of the 
> > evidence for widespread endothermy in nonavian
> > dinosaurs. (Should have 
> > mentioned sauropods, for instance.) Still, the
> > higher susceptibility of 
> > birds than mammals is interesting.
> > 
> > > Remember:
> > >    Lizards! Some one on the list recently
> pointed
> > out that there are more
> > > living species of lizard than there are mammals,
> > even leaving out the
> > > snakes, which are phylogenetically speaking an
> > idiosyncratic form of 
> > > lizard.
> > > So how come ectothermic lizards did so
> swimmingly?
> > Not to mention
> > > crocodiles, which aren't too different in size
> > from at least a smaller
> > > dinosaur.
> > 
> > Oh yes. I fear I forgot them, too. How easily do
> > they get fungal infections? 
> > What about turtles (which have a higher metabolic
> > rate -- they can't run 
> > away, so they can't thermoregulate as easily by
> > behaviour)?
> > 
> > >    No mention, of course, of all the marine
> > organisms
> > > that lost their place at the table.
> > 
> > Eh, all that mould isn't supposed to _replace_ the
> > impact. As we've read in 
> > Science a year or two ago, it's a _consequence_ of
> > the impact.
> > 
> > >    Perhaps saddest of all, this article received
> a
> > favourable editorial in
> > > the lastest issue of Mycological Research (under
> > the title "Did pathogenic
> > > fungi contribute to dinosaur extinction?"). It
> > concludes "While the
> > > hypothesis is difficult to test... The idea
> merits
> > floating in all basic
> > > mycology courses, where it is sure to generate
> > interest and debate".
> > 
> > By people who know even less about dinosaurs!?!
> :-S 
> > 
> > 
> 
>