[Taxacom] Overdoing vicariance again? (tree shrews)

[John Grehan]

Ken,

If you provide some empirical evidence for centers of origin in the cases
you mention then I will not say that they are imaginary. As for 'chance
dispersal' you keep presenting cases of chance dispersal to explain
allopatry (i.e. dispersal that is not tectonically mediated) so I am not
sure what else to call it. Dispersal (translation in space + form-making)
forever repeats anyway :)

Cheers, John

On Thu, Jun 28, 2018 at 2:23 PM, Kenneth Kinman <kinman at hotmail.com> wrote:

> Dear all,
>
>       Chatterjee, 2006, has a very nice map (Figure 3) for gibbon
> evolution and dispersal, and it shows gibbons also having a proposed center
> of origin in Yunnan Province (and then dispersal both to the south and to
> the west).  The only major difference for tree shrews is that Anathana went
> further west.
>
>        Anyway, John's constant use of the phrase "chance dispersal" ad
> nauseum is like listening to a broken record.  The same with "imaginary
> centers of origin".  Everything he doesn't like is imagined or just
> chance.   Perhaps he should criticize Heads for an imagined "widespread
> proto-Scandentia".   Therefore, I won't be wasting any more time responding
> to his posts.
>
>               ------------Ken
>
> P.S.   For anyone interested, Chatterjee's Figure 3 can be found in his
> 2006 article on gibbons here:  https://link.springer.com/article/10.1007/
> s10764-006-9044-1
>
>
> ------------------------------
> *From:* John Grehan <calabar.john at gmail.com>
> *Sent:* Thursday, June 28, 2018 9:49 AM
> *To:* Kenneth Kinman
> *Cc:* taxacom
> *Subject:* Re: [Taxacom] Overdoing vicariance again? (tree shrews)
>
>
> Thanks Ken for outlining your perspective on tree shew biogeography as it
> illustrates quite well the traditional dispersalist paradigm as first
> proposed by Darwin and dominating biogeography ever since (and especially
> in its molecular clock version). As noted below, Ken asserts belief in a
> limited center of origin for widespread allopatry, the center of origin
> being determined by one or other criteria that are imagined to represent
> the imagined center of origin. So this is a nice illustration of the
> different perspectives in biogeography.
>
> “I believe dispersal was the dominant factor …….And I especially see no
> compelling evidence of a "widespread proto-Scandentia" splitting up as a
> "simple vicariance".
>
> This observation is fine as a personal opinion. Heads has presented the
> spatial evidence for a vicariance understanding of the distribution (which
> is also consistent with patterns of allopatry of other groups in the
> region) and it is for every reader to determine for themselves.
>
> “A more limited center of origin followed by dispersals seems more
> probable (and also more interesting).”
>
> When it comes to asserting probability then it would be desirable to know
> the basis for that. Whether vicariance or chance dispersal is considered
> more ‘interesting’ has no bearing on what actually happened.
>
> “ It looks like tree shrews most likely had their center of origin in or
> near the area of Myanmar or Yunnan Province (China).  The oldest known
> fossil tree shrew (Ptilocercus kylin of the Early Oligocene) was recently
> discovered in Yunnan (note: whether or not the older Eodendrogale fossil is
> a tree shrew is controversial).”
>
> What Ken is introducting here is one of the several contradictory criteria
> that have been invented to identify the imaginary center of origin. The
> location of the oldest fossil has historically been invoked as being or
> approximating the center of origin. Trouble here is that the location of
> the oldest fossil only denotes the location of the oldest fossil. The rest
> is invention
>
> “The dispersal of Ptilocercus southward towards Borneo could very well
> have begun early in the Cenozoic since it split off so early.”
>
> The dispersal is invented based on location of the oldest fossil imagined
> to represent the imagined center of origin.
>  “Dendrogale and Tupaia would have expanded southward much later.
> Anathana instead dispersed westward into India.”
>
> All imagined stories based on a misunderstanding of what the location of
> the oldest fossil actually informs.
>
> “So I don't see any need to invoke "simple vicariance" (much less a
> widespread proto-Scandentia) in a case where there was a combination of
> both vicariance and dispersal (perhaps a lot more of the latter than the
> former).”
>
> Heads illustrated the fact that the patterns of allopatry and sympatry
> were consistent with original allopatry followed by some subsequent range
> overlap. Naturally if one wishes to invoke a center of origin followed by
> chance dispersals to get the current distributions that is certainly an
> alternative, but not one based on any empirical evidence as Ken’s argument
> has showed – in my opinion.
>
> John Grehan
>
>
> On Thu, Jun 28, 2018 at 7:48 AM, Kenneth Kinman <kinman at hotmail.com>
> wrote:
>
> Dear All,
>
>        Heads (2012) says "Tupaia has expanded its range to overlap that of
> the two basal genera, and the two basal genera
> themselves show minor overlap, but apart from this, the biogeography of
> the Scandentia genera reflects their original evolution by simple
> vicariance."  And he makes reference to a "widespread proto-Scandentia".
>
>       Although I would agree with Heads that there was some vicariance
> involved in the evolution of tree shrews, I believe dispersal was the
> dominant factor (dispersal over land or temporary land bridges, but no
> evidence of any transoceanic dispersal in this case).  And I especially see
> no compelling evidence of a "widespread proto-Scandentia" splitting up as a
> "simple vicariance".  A more limited center of origin followed by
> dispersals seems more probable (and also more interesting).
>
>        It looks like tree shrews most likely had their center of origin in
> or near the area of Myanmar or Yunnan Province (China).  The oldest known
> fossil tree shrew (Ptilocercus kylin of the Early Oligocene) was recently
> discovered in Yunnan (note: whether or not the older Eodendrogale fossil is
> a tree shrew is controversial).  The dispersal of Ptilocercus southward
> towards Borneo could very well have begun early in the Cenozoic since it
> split off so early.  It was presumably well-established across a large area
> before those other genera began to split away from one another.
>  Dendrogale and Tupaia would have expanded southward much later.  Anathana
> instead dispersed westward into India.
>
>       Therefore, the present distribution of the basal genus Ptilocercus
> is probably just a relict of a much broader distribution before genus
> Tupaia later won the competition for much of that broad territory.
> Dendrogale no doubt lost territory to Tupaia as well.   Anathana met no
> such competition once it expanded into southern India (although it was
> perhaps competition that eliminated it from the territory where it
> originated).  Lucky break for Anathana that India had crashed into Asia
> earlier.    Tupaia vs. Ptilocercus (and Dendrogale) have probably managed
> to coexist where they do because Ptilocercus and Dendrogale are more
> arboreal than Tupaia, and Ptilocercus is the only tree shrew that is
> nocturnal.
>
>       So I don't see any need to invoke "simple vicariance" (much less a
> widespread proto-Scandentia) in a case where there was a combination of
> both vicariance and dispersal (perhaps a lot more of the latter than the
> former).  As with primates, I think that male aggression could have played
> a role in Tupaia's expansion at the expense of Ptilocercus and Dendrogale.
> But in the case of tree shrews, it was the younger genus Tupaia that
> largely prevailed, probably because it dispersed over land (not a chance
> dispersal over water).  And also the fact that Tupaia species are mostly
> larger and heavier (and have longer, sharper claws) would tend to make them
> physically dominant.  I would predict that carefully designed studies would
> provide evidence of this,  But unfortunately, the research that has been
> done regarding Tupaia aggression has been on conspecific males.  Research
> on Tupaia males vs. Ptilocercus or Dendrogale males would be more helpful
> and interesting.
>
>                         ---------------Ken
>
> P.S.   Anyway, I found Roberts et al. (2011) to be much more informative,
> so here is a weblink to that paper  ( http://linkolson.org/research/
> publications/My%20pubs/Roberts%20et%20al.%202011.pdf ).
>
> And here is a weblink to the paper describing the earliest known fossil
> tree shrew:  https://www.nature.com/articles/srep18627
>
> ________________________________
> From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of John
> Grehan <calabar.john at gmail.com>
> Sent: Tuesday, June 26, 2018 3:24 PM
> To: taxacom
> Subject: [Taxacom] tree shrew vicariance and tectonics
>
> Below and excerpt (allowing for typos) from Heads (2012) for those curious
> about the relationship between vicariance and tectonics. A nice
> illustrative example for the Scandentia (tree shrews) showing patterns of
> vicariance and dispersal (sympatry) in tree shew distribution and phylogeny
> show tectonic concordance and evidence of primary allopatry as the result
> of vicariance. Sorry not to be able to reproduce the map here.
>
> "The Southeast Asian order Scandentia (Fig. 5-17) is closely related to
> primates (Fig. 5-1). In the main clade of Scandentia (Olsonet al., 20005),
> Anathana (Indian Plate) is allopatric with its sister group Tupaia
> (Eurasian plates) + Urogale (Philippine mobile belt). These breaks
> correlated with the India/Eurasia plate boundary and the Eurasia
> plate/Philippine mobile belt boundary. Olsen et al. (2005: 666) wrote that
> the circumstances leading to the disjunction between Anathana and the other
> genera across the Bay of Bengal “remain a mystery fo which our results
> offer no clear explanation.” The same break occurs in lorisid primates
> (Fig. 5-18) and could be the result of vicariance. As Olson et al. (2005:
> 668) noted, the absence of Scandentia from such proximatee islands as the
> Andamans “suggests severe limitations to overwater dispersal [and]
> vicariance can almost certainly be assumed to have played a prominent role
> in the past diversification and resulting distribution of tree shrews.” The
> same conclusion is reached here for primates.
>
> The two basal clades in the Scandentia, Ptilocercus and Dendrogale, have
> different overall distributions but meet and overlap in Borneo. The main
> clades in the widespread Tupaia also have their main breaks in Borneo:
>
> Tupaia group 1: Borneo species basal to others which range to Nepal.
> Tupaia group 2: Borneo species basal to others which range to Thailand>
> Tupaia group 3: (T. gracilis): Borneo.
>
> Although these phylogenetic breaks all involve Borneo, this does not
> necessarily imply a center of origin there. (Likewise, the oldest fossils
> of Scandentia are found in Thailand, but this does not necessarily mean the
> area was a center of origin). Borneo is a geological composite, and several
> clades may have been juxtaposed there with terrane accretion of
> differentiated during accretion. Thus Borneo – or rather the terranes that
> became Borneo – could represent sites of differentiation in an already
> widespread proto-Scandentia. The distribution of Ptilocercus is centered on
> the Riau (Riouw) Islands region (off Singapore), while that of Dendrogale
> is based further north around the central South China Sea, and the two are
> almost completely allopatric. (The South China Sea basins opened with the
> Late Cretaceous and Cenozoic rifting of continental crust). The allopatry
> of the two genera suggests early zones of differentiation around the two
> regions before the opening of the South China Sea and before the plate
> boundary breaks in Anathana/Tupaia/Urogale. Within Borneo, Ptilocerus and
> Dendrogale are restricted to the north and northwest of the island (north
> of the Lupar line, cf. Heads, 2003, and west of the Mangkalihat terrane).
> Within this region they remain largely allopatric. Tupaia has complex
> diversity in different parts of Borneo, including the south and east, and
> so perhaps this was its original sector in “Borneo”. When the terranes of
> Borneo were juxtaposed, so were the genera. Tupaia has expanded its range
> to overlap that of the two basal genera, and the two basal genera
> themselves show minor overlap, but apart from this, the biogeography of the
> Scandentia genera reflects their original evolution by simple vicariance.
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