CP evolution (serious stuff this time, guys!)

Fernando Rivadavia Lopes (ferndriv@cat.cce.usp.br)
Thu, 15 Jun 1995 19:38:31 -0300 (EST)


First of all, I'd like to say welcome! It's good to hear from
you again!

> great interest, although at times it seems to drift into the bizarre. I
> would like to discuss several topic in regards to evolution. 1. Some of
> the discussion leads one to think that Drosera are thinking of ways to
> evolve to fill various nitches. My understanding of evolution (any
> evolution) is that random variations occur through time. If these
> variations increase the plants (or whatever) ability to reproduce (and
> grow to maturity to reproduce again) then it is beneficial and will
> result in the spread of the plant. Anything else doesn't count.

Again it seems like Jan or I were misinterpreted somewhere. I
guess I can talk on Jan's behalf too, so we're sorry if any of us sounded
Lamarckian along the way. I assure you we never believed Drosera just woke
up one day and said "hey, let's evolve!" Maybe you missed the beginning of
the discussion.

> As for the variations in evolution rates between Australia and South
> America. It doesn't have all that much to do with climate as you can find
> areas with similar climates on both continents. What has happened is
> that Drosera in Australia have randomly developed a method to live and
> grow in dryer area (possibly multiple times - suggested by pygmy Drosera
> and tuberous Drosera). This has opened up vast new area (nitches) for
> colonization by species which randomly adapt to use these generally
> underutilized areas.

First of all, though these climates might be similar today, they
cover areas which in the past had totally different climates, among each
other. Thus, the climates which preceded mediterranean in SW Australia were
different from the ones which preceded this climate in other parts of
the world and affected the (if any) local Drosera in different ways.
Second, for a "normal" Drosera to evolve into a pygmy or tuberous
Drosera, it must've taken a few million years at least until all the
necessary mutations arose by chance and were established in the
populations. These mutations were certainly very numerous, but why would
they only occur in SW Australia? Since mutations occur by chance,
wouldn't a mutation have the same chance of occuring in any Drosera, in
some gene common to all Drosera? The odds would be absurdly and
impossibly high if we imagine that the numerous mutations which resulted
in tuberous and pygmy Drosera could've also occured in Drosera in
S.America, but didn't "by chance". As Jan and I discussed previously, we
believe there was some exterior force which was either causing more
mutations (and thus increasing the chances of more useful mutations
appearing randomly) or was more efficiently selecting the mutations
which appeared randomly in the ancestral Drosera populations in Australia.
Jan an i seem to have come to an agrement, believing that the
inconsistency of the climates in Australia millions of years ago was
responsible for the local Drosera evolution. The difference between the
dry stresses on Drosera living in Australia and South America is that in
S.America it would only be acting on the plants growing in the
transitional habitats (between their ideal wet habitats and the drier
habitats around these) while in Australia the dry stress would not only
be acting on the peripheral members of a population, but on the
populations as a whole, since dry and wet seasons were more irregular.
We can imagine this inconsistency in dry/wet seasons permitting
the ancestral Drosera populations to boom during an exceptionally humid
year and then be reduced to a tiny number of individuals during a drought
the following year. Thus a larger number of plants would be exposed to
the dry stresses and if a mutation occured in an individual which
favored the survival in drier conditions, then the chances would be
increased of this individual being exposed to dryness, surviving it, and
spreading its genes around the population the next season.
So assuming the chances of mutations occuring were the same for
the S.American and Australian ancestral Drosera, the evolution of the
Australian species would thus be a result of the larger number of
individual Drosera which in the past were exposed to droughts, as
compared to S.America where mostly the peripheral plants in a Drosera
population are usually exposed to dry stresses. The mutations favoring
survival in dry conditions thus also occured in S.America, but more often
(than in Australia) in plants growing in "ideal" habitats, where these
new mutations would have no use and thus be lost.

> 2. As for suggesting that because an area has more species of Drosera
> (or any other taxa) than another that it is then the area of origin is
> wrong. This can easily be seen if you look at the evolution of the genus
> Nepenthes. It only means that the most recent evolution of that taxa,
> Drosera in this case, has occurred in that particular area (Australia in
> this case).

Sorry, but more misunderstanding. I clearly understood that that
was exactly what Jan said. The large number of Drosera in Australia COULD
mean that that's where they originated, but does not exclude other

Fernando Rivadavia
Sao Paulo, Brazil

P.S. Hey Jan, if it does seem like we've come to an agreement, how
about a joint article reuniting our conclusions and speculations?