[Taxacom] Meliaceae (vicariance??)

Sat Nov 16 17:18:09 CST 2019

The mahogany family Meliaceae (700 spp.) and its sister Simaroubaceae (100
spp.) form a pantropical clade that also occurs in some warmer temperate
regions. The most striking anomalies in the distribution are two great
areas of absence, one in a large region of the central Pacific (Hawaii,
Cooks to Marquesas) and one in SW Australia. There are no known *ecological*
factors that would exclude the clade from these regions, and introduced
members of the clade are naturalised there. So what is the reason for the
absences? An enquiry into possible *historical* factors soon comes up
against three facts:

1. Meliaceae + Simaroubaceae are absent from the two regions, but the
clade’s sister, the orange family Rutaceae, has notable centres of endemism
and diversity in both.

2. The two regions are also well-known as centres of endemism for many taxa
other than Rutaceae, and centres of endemism are invariably areas of
anomalous absence in other groups.

3. Despite their allopatry in the two regions, Meliaceae + Simaroubaceae
and Rutaceae *do* occur together through tropical America, Africa and Asia
and on thousands of islands (in the West Indies, Indonesia, Melanesia, SW
Pacific).

Because of molecular clock dates, it is now common to ascribe allopatry not
to vicariance but to priority effects – the first colonizers keep out new
entrants by competitive exclusion. For example, as Ken suggests, dispersal,
priority, and competitive exclusion might account for Rutaceae being on
islands where Meliaceae + Simaroubaceae are absent. However, the theory
does not account for the distributions of the two families as a whole,
without bringing in further, ad hoc arguments.

The facts can be accounted for by 1. Initial vicariance between the two
clades; 2. Massive overlap through most of the tropics, with the initial
allopatry preserved in just two regions.

Ken wrote that: ‘There is already lots of published evidence that a
considerable amount of dispersal occurred in this case. Panbiogeographers
just dismiss all of it...'. This is incorrect; no-one is denying dispersal.
For example, in my paper the geographic overlap of Meliaceae +
Simaroubaceae and Rutaceae through most of the tropics is explained by
early range expansion of one or both clades by normal dispersal using
normal means.

On Sat, Nov 16, 2019 at 8:02 AM Kenneth Kinman via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> Hi All,
>            There is already lots of published evidence that a considerable
> amount of dispersal occurred in this case.  Panbiogeographers just dismiss
> all of it with the same old arguments about fossil calibration errors.  If
> they would only widen the taxonomic context (as I did in the
> Lepidoptera-Trichoptera posts on November 4th), perhaps they would realize
> that the evidence presented by dispersalists is good science (not to be
> dismissed with the same old tired arguments).   Go beyond the
> Meliaceae-Simaroubaceae-Rutaceae clade, and you are likely to see how
> evidence from outgroup relatives fits better with dispersal than with
> vicariance.
>        Muellner-Riehl et al. (2016) proposed that Sapidales arose about
> 112 million years ago, and that the two subfamilies of Meliaceae split as
> early as 89.8 million years ago.  This fits in pretty well with the recent
> 2018 (Atkinson, 2018) report of a stem-lineage fossil of Meliaceae dated at
> 79 million years ago, and the stem-lineage could easily go back more than
> 10 million years before that fossil.  But that still does not mean it goes
> back far enough  that vicariance explains the biogeography of Family
> Meliaceae.   Africa and South America separated much earlier (about 140
> million years ago), and they had separated from East Gondwana about 180
> million years ago.   Arguments seem unconvincing blaming an imagined poor
> fossil record that far back.
>        A center of origin in Africa of Family Meliaceae makes more sense
> (about 85-90 million years ago), although an origin in Eurasia is also
> possible.    It would then have expanded north into Europe and from there
> into North America before they separated about 80 million years ago.
> Therefore, with the stem-lineage fossil of Meliaceae (Atkinson, 2018) in
> North America at 79 million years ago, one would expect that they had
> spread from Africa into Europe about 80-85 million years ago.   The
> eastward expansion through southern Asia could have begun about the same
> time (but didn't reach Australia until much much later, so Rutaceae could
> have claimed SW Australia first and competitive exclusion kept Meliaceae
> out).   Competitive exclusion could also explain the absence of Meliaceae
> in Hawaii.
>                                  -----------Ken Kinman
>
> Muellner-Riehl et al. 2016
> https://onlinelibrary.wiley.com/doi/abs/10.12705/655.5
>
> Atkinson, 2018:
>
> http://2018.botanyconference.org/engine/search/index.php?func=detail&aid=327
>
> Koenen et al., 2015
> https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.13490
>
>
>
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-- 
Dunedin, New Zealand.

My books:

*Biogeography and evolution in New Zealand. *Taylor and Francis/CRC, Boca
Raton FL. 2017.
https://www.routledge.com/Biogeography-and-Evolution-in-New-Zealand/Heads/p/book/9781498751872

*Biogeography of Australasia:  A molecular analysis*. Cambridge University
Press, Cambridge. 2014. www.cambridge.org/9781107041028

*Molecular panbiogeography of the tropics. *University of California Press,
Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968

*Panbiogeography: Tracking the history of life*. Oxford University Press,
New York. 1999. (With R. Craw and J. Grehan).
http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC
<http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&source=gbs_navlinks_s>