Re: The fungi did it

[don ohmes <d_ohmes@yahoo.com>]

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 
> 
>