[Taxacom] Long distance dispersal of Amborella's ancestors

Tue Dec 11 09:49:19 CST 2018

What this shows is that there is no 'probably' at all. Chance dispersal
theory requires the invention of a means for which there is no actual
evidence and for the extinction of an endemic elsewhere. While Carlquist
might assert that the flora (and of course fauna, including giant ghost
moths
where gravid females are incapable of flying very far and cannot not glide)
"must have
arrived by long-distance dispersal" there is no 'must have' at all. Its all
based on a supposition, and one that is not required and while one can
assert
such origins for one taxon it does not explain others and ends up creating
puzzling enigmas and paradoxes. If this is what biogeography is all about
then
that is OK for those who want that. The vicariance alternative is supported
by biogeographic and tectonic evidence and does not create such problems.

Below is an excerpt on Amborella from Head's paper for those interested.
The reference to dispersal of the sister group into New Caledonia
is just range expansion after the original allopatry - by ordinary
ecological
means, not chance dispersal after the geographic separation of New
Caledonia.

Many endemic groups in New Zealand and New
Caledonia have worldwide, diverse sisters (Heads, 2014).
The best-known of these groups in New Caledonia is
the plant Amborella, endemic there and sister to all
other angiosperms (Simmons, 2017). Likewise, the New
Caledonian endemic orchid Pachyplectron is sister to the
rest of the subtribe Goodyerinae, an almost cosmopolitan
group (A´ lvarez-Molina & Cameron, 2009). In Myrtaceae,
Myrtastrum of New Caledonia is sister to all other Myrteae,
a cosmopolitan group (Vasconcelos et al., 2017); the authors
dated the divergence at 65 Ma and attributed it to
vicariance.

The repetition of the Amborella pattern requires an
explanation other than chance dispersal to New Caledonia
or chance extinction elsewhere. The repetition is consistent
with a single, early vicariance event in each global clade at
a break in or around pre-New Caledonia, and persistence
of the local vicariants in the region. The presence of the
pattern at the basal node in angiosperms, and then again,
within groups such as Myrtaceae and Orchidaceae, implies
at least two breaks between New Caledonia and the rest
of the world, consistent with phases of pre-drift rifting in
Gondwana.

Amborella is the sister group of all other angiosperms. It
is much less diverse than its sister, and so it is termed the
‘basal’ angiosperm, but the term ‘basal’ is confusing and the
relationship often misinterpreted. The term means only that
Amborella is the less diverse of two sister groups – it does not
mean that Amborella is older than the other angiosperms, that
it has a more primitive morphology, that it is the ancestor of
the other angiosperms, or that New Caledonia is the centre
of origin of angiosperms. There is no reason to assume that
any of these are true.

A phylogenetic break can occur anywhere in a group’s
range. If the break develops through the middle of the group’s
distribution, this will result in two descendants with ranges of
similar sizes. For example, a global group can divide into one
descendant in the northern hemisphere and one in the south.
Alternatively, a phylogenetic break can occur such that one
descendant has a very large range and one a very small range.
For example, a break in a global ancestor that developed
between NewCaledonia and rest of the world, would result in
a small (apparently ‘relict’) clade in New Caledonia, and one
everywhere else.

Nattier et al. (2017, p. 6) wrote that Amborella is ‘a
remarkable relict whose phylogenetic position places it alone
on a long branch apparently sister to all flowering plants,
but whose biogeographic significance remains paradoxically
difficult to interpret’. (Italics added). Yet the origin of Amborella
can be explained simply if a global ancestor split into
a New Caledonia clade and its sister found in the
rest of the world. This was followed by invasion of
New Caledonia by the sister group. The persistence of
Amborella in New Caledonia through the Paleogene flooding
can be explained most simply by the same process of
metapopulation dynamics that has allowed survival in other
groups.

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On Tue, Dec 11, 2018 at 9:37 AM Kenneth Kinman <kinman at hotmail.com> wrote:

> Dear All,
>         I was reading an interesting 2015 article on fruiting in Amborella
> of New Caledonia.  It offers hypotheses about how fruits (or seeds) of this
> ancient angiosperm's ancestors probably arrived in New Caledonia by avian
> dispersal, but have now lost such dispersibility during evolution on the
> island.  Here are two quotes from the paper followed by a weblink to the
> paper:
>
>  "Another hypothesis to explain the particular fruiting cycle of A.
> trichopoda might refer to one of the “insular syndromes” described by Sir
> Sherwin Carlquist: the loss of dispersibility in island plants (Chapter 11
> in Carlquist 1974<
> https://link.springer.com/article/10.1007/s10265-015-0744-5#CR001>). The
> flora of oceanic islands must have arrived by long-distance dispersal, yet,
> during evolution on the island, some groups may have naturally lost
> dispersibility."
>
> "The original dispersing bird species might no longer be present in New
> Caledonia as many extinctions/extirpations of bird species have been shown
> to have occurred in the last 4,000 years subsequently to the arrival of
> Melanesian settlers (Balouet and Olson 1989<
> https://link.springer.com/article/10.1007/s10265-015-0744-5#CR5>; Pascal
> et al. 2006<
> https://link.springer.com/article/10.1007/s10265-015-0744-5#CR35>). The
> hypothesis of a pre-human extinction of the avian disperser(s) of A.
> trichopoda, while not proven, also remains open."
>
> Here's a weblink to the article:
>
> https://link.springer.com/article/10.1007/s10265-015-0744-5
>
>
> ------------------------------Ken Kinman
>
>
> ________________________________
> From: Michael Heads <m.j.heads at gmail.com>
> Sent: Monday, December 10, 2018 6:33 PM
> To: Ken Kinman
> Cc: Taxacom
> Subject: Re: [Taxacom] New Caledonia as a classic lesson in dispersal
>
> Hi Ken,
>
> The problem with the Nattier paper is that the approach they used, long
> distance dispersal theory, didn't work; it did not
> explain critical groups such as the New Caledonian endemic Amborella,
> sister to all other angiosperms. Dispersal theorists
> concluded that the group remains ‘puzzlingly enigmatic’ (Grandcolas et
> al., 2008, p. 3312) and ‘paradoxically difficult to
> interpret’ (Nattier et al., 2017, p. 6).
>
> Michael
>
> On Tue, Dec 11, 2018 at 3:09 AM Kenneth Kinman <kinman at hotmail.com<mailto:
> kinman at hotmail.com>> wrote:
> Dear All,
>          The paper by Nattier et al. (2017) is definitely worth reading.
> Here is a weblink to that article:
>
> https://www.nature.com/articles/s41598-017-02964-x
>
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