[Taxacom] Taxacom Digest, Vol 185, Issue 14

[John Grehan]

'Jump in', in the sense of getting directly involved in the discussion,
just wanted to mention that particular item.

On Wed, Sep 22, 2021 at 10:26 PM John Grehan <calabar.john at gmail.com> wrote:

> Rich - I'm not going to jump in on this conversation since it is directed
> to Heads, but I would point out that I have seen one instance where the
> proponents of a 'freak' event did indeed use that term. Cheers, John
>
> On Wed, Sep 22, 2021 at 10:19 PM Richard Pyle via Taxacom <
> taxacom at mailman.nhm.ku.edu> wrote:
>
>> Thanks!  This is great feedback, and exactly the sort I was hoping for.
>>
>>
>>
>> > Your 'Scenario 3 was:' A population rapidly expands the size of its
>> geographic footprint over time.
>>
>> > The conditions that facilitated that geographic expansion are
>> short-lived, resulting in a limitation
>>
>> > or elimination of gene flow...'. [bold added] . You commented: 'I
>> *think* Scenario 3 is an example
>>
>> > of chance = jump = long distance dispersal', but this is not 'chance
>> dispersal' as used by most authors.
>>
>> > In chance dispersal, dispersal doesn't stop because the conditions
>> change - it's random, and not
>>
>> > related to any other factor, physical or biological. A single,
>> one-in-ten million years freak event
>>
>> > that no-one could have predicted. It is thought, by its proponents, to
>> be mediated not by normal
>>
>> > means of dispersal but by 'non-standard means'.'.
>>
>>
>>
>> Perfect!  I chose my words carefully in articulating Scenario 3 with the
>> hope of focusing on exactly the issue you raised.  So let’s compare these
>> two things:
>>
>> 1.      The conditions that facilitated that geographic expansion are
>> short-lived, resulting in a limitation or elimination of gene flow.
>> 2.      The circumstances that facilitated that geographic expansion are
>> exceedingly rare (e.g., only occurred once in 10 million years), resulting
>> in a limitation or elimination of gene flow.
>>
>>
>>
>> I would argue that #2 above represents the same as what you report that
>> most authors mean when they refer to “chance dispersal”.  I know that I
>> didn’t use words like “random”, “chance”, and “freak” in my expression of
>> the concept, but it’s debatable whether “random” even exists in the
>> universe (“haphazard” might be a better term), “chance” suffers some of the
>> same pitfalls as “random”, and “freak” is a bit hyperbolic.  But in both
>> your wording and mine, the situation is essentially the same:
>>
>> *       A patch of Earth was never occupied by any individuals of a given
>> population prior to time X
>> *       After time X, at least one individual* of said population
>> occupied that patch of Earth
>>
>> *If we’re talking about sexually reproducing organisms, and we’re talking
>> about subsequent allopatric differentiation through evolutionary processes,
>> then presumably at least two such organisms shared the same patch of novel
>> Earth for a period that overlapped both of their lifespans.
>>
>>
>>
>> But the key thing is that we have different patches of Earth, and
>> eventually we have organisms derived from the same source population
>> occurring on those different patches, and genetic connectivity between them
>> is not maintained (for whatever reason).
>>
>>
>>
>> I can’t speak for “most authors”, but my area of interest & expertise
>> concerns the majority of Earth’s surface (and likely the majority of
>> organisms that have ever lived; and hence the majority of biogeographic
>> history on Earth) – that is, the Oceans.  Specifically, my area of
>> interest/expertise involves coral-reef organisms, most of which have
>> planktonic larvae -- which very likely facilitate the majority of
>> historical genetic transfer over large distances via movements of said
>> larvae.  In that paradigm, what you describe as “random”, “chance”, “freak”
>> events that lead to individuals traversing some distance to places not
>> previously occupied by members of the same source population might not just
>> be possible; but perhaps even represents the norm.
>>
>>
>>
>> > At a single biogeographic break zone, the breaks in all pairs of sister
>> groups,
>>
>> > with one on one side and one on the other, are thought to have
>> different ages.
>>
>>
>>
>> Well… one could argue that all living things on Earth share exactly the
>> same “age” (at least if we assume a single origin for all life on Earth)…
>> but I get what you mean here (i.e., the “birth” of one group happened when
>> members of its population first trod on novel ground/sea, never to share
>> genes with their elder siblings in the source population).
>>
>>
>>
>> > When the conditions changed and the seas regressed, huge numbers
>>
>> > of widespread coastal groups were stranded inland and differentiated.
>>
>> > This is not chance dispersal, but a series of events that has affected
>>
>> > the whole community globally.
>>
>>
>>
>> Yeah, but I see this more as one end of a spectrum of evolutionary
>> (hi)stories, the opposite end of which would be a one-in-ten-million-year
>> set of conditions that allowed a group of planktonic larvae from, say, the
>> western Pacific to settle off the shores of, say, the Hawaiian Islands –
>> ultimately yielding two genetically isolated populations (after which
>> sufficient allopatric differentiation yielded what we hairless-ape
>> taxonomists deem to represent as distinct species).
>>
>>
>>
>> And this is my point – emphasizing the extreme ends of the spectrum might
>> present a false dichotomy in modes and “circumstances” that allow an
>> expanded subset of a source population to fail to share genes with its
>> brethren for long periods of subsequent time.
>>
>>
>>
>> > We are not saying that unique, one-in-ten million year events that are
>>
>> > unrelated to any particular factor (conditions) don't happen in
>> individual groups
>>
>>
>>
>> I can’t imagine any examples of an “event” that was “unrelated to any
>> particular factor (conditions)”.  I think what you might mean here is that
>> the set of factors/conditions affected only a small set of organisms, as
>> opposed to many different kinds of organisms at the same time? I mean… laws
>> of physics are at play with pretty-much any organism’s movements across
>> space.  But maybe I’m interpreting factors/conditions too generally here?
>>
>>
>>
>> > We are saying that these types of unique events in single individuals
>> of a single species
>>
>> > in a community do not explain the main biogeographic/evolutionary
>> patterns that
>>
>> > are observed. These are all repeated in large numbers of clades, e.g.
>> the 'enigmatic'
>>
>> > Hawaii - SE Polynesia connection seen in so many marine and land groups
>>
>>
>>
>> OK, I think I’m getting a better sense of what you’re talking about
>> here.  But it still seems like a bit of semantics.  I’ll propose two more
>> hypothetical scenarios to focus on the distinction:
>>
>> 1.      A one-in-10-million-year anomalous set of circumstances (precise
>> combination of wind, current, temperature, storm pattern, whatever)
>> facilitates the transfer of planktonic larvae of multiple different species
>> from one part of the Pacific to another, leading to allopatric
>> differentiation between source populations and founder populations.
>> 2.      A one-in-10-million-year anomalous set of circumstances (precise
>> combination of wind, current, temperature, storm pattern, spawning
>> behavior, genetic mutation, whatever) facilitates the transfer of
>> planktonic larvae of a single species from one part of the Pacific to
>> another, leading to allopatric differentiation between source populations
>> and founder populations.
>>
>> [differences highlighted in bold].
>>
>>
>>
>> Would you consider #1 vicariance and #2 chance dispersal, or both
>> vicariance, or both chance dispersal, or have I failed to provide enough
>> information to distinguish these modes?
>>
>>
>>
>> Sorry to belabor this, but I’m genuinely not trying to be combative
>> (‘though maybe just a bit snarky in some places – not to be insulting, but
>> to keep the tone of the conversation light).  I’ve watched these
>> discussions for many years on Taxacom, and while I generally follow them
>> with at least some level of understanding, I’ve always been a little bit
>> fuzzy on where to draw the line between vicariant vs. dispersal modes of
>> population expansion and subsequent allopatry.
>>
>>
>>
>> Aloha,
>>
>> Rich
>>
>>
>>
>> Richard L. Pyle, PhD
>> Senior Curator of Ichthyology | Director of XCoRE
>>
>> Bernice Pauahi Bishop Museum
>>
>> 1525 Bernice Street, Honolulu, HI 96817-2704
>>
>> Office: (808) 848-4115;  Fax: (808) 847-8252
>>
>> eMail: deepreef at bishopmuseum.org
>>
>>  <http://hbs.bishopmuseum.org/staff/pylerichard.html> BishopMuseum.org
>>
>> Our Mission: Bishop Museum inspires our community and visitors through
>> the exploration and celebration of the extraordinary history, culture, and
>> environment of Hawaiʻi and the Pacific.
>>
>>
>>
>> From: Michael Heads <m.j.heads at gmail.com>
>> Sent: Wednesday, September 22, 2021 3:15 PM
>> To: Richard Pyle <deepreef at bishopmuseum.org>
>> Cc: Brendon E. Boudinot <boudinotb at gmail.com>; Taxacom <
>> taxacom at mailman.nhm.ku.edu>
>> Subject: Re: [Taxacom] Taxacom Digest, Vol 185, Issue 14
>>
>>
>>
>> Rich,
>>
>> It's always good to have your input. I agree with all your points except
>> one.
>>
>>
>>
>> Your 'Scenario 3 was:' A population rapidly expands the size of its
>> geographic footprint over time.  The conditions that facilitated that
>> geographic expansion are short-lived, resulting in a limitation or
>> elimination of gene flow...'. [bold added] . You commented: 'I *think*
>> Scenario 3 is an example of chance = jump = long distance dispersal', but
>> this is not 'chance dispersal' as used by most authors. In chance
>> dispersal, dispersal doesn't stop because the conditions change - it's
>> random, and not related to any other factor, physical or biological. A
>> single, one-in-ten million years freak event that no-one could have
>> predicted. It is thought, by its proponents, to be mediated not by normal
>> means of dispersal but by 'non-standard means'.'.
>>
>>
>>
>> At a single biogeographic break zone, the breaks in all pairs of sister
>> groups, with one on one side and one on the other, are thought to have
>> different ages. The ages vs taxa graph for a single break zone always shows
>> a smooth curve, and the break in each pair is attributed to a different,
>> idiosyncratici event (chance dispersal) unrelated to conditions. If you
>> accepted the dates, this would be excellent evidence that allopatry is
>> never the result of vicariance, a community-wide process caused by changing
>> conditions.
>>
>>
>>
>> One example of your scenario 3 would be the great expansion of many
>> coastal taxa with the epicontinental marine transgressions of the
>> Cretaceous, seen in all the continents.  When the conditions changed and
>> the seas regressed, huge numbers of widespread coastal groups were stranded
>> inland and differentiated. This is not chance dispersal, but a series of
>> events that has affected the whole community globally.
>>
>>
>>
>> We are not saying that unique, one-in-ten million year events that are
>> unrelated to any particular factor (conditions) don't happen in individual
>> groups, We are saying that these types of unique events in single
>> individuals of a single species in a community do not explain the main
>> biogeographic/evolutionary patterns that are observed. These are all
>> repeated in large numbers of clades, e.g. the 'enigmatic' Hawaii - SE
>> Polynesia connection seen in so many marine and land groups.
>>
>>
>>
>> On Thu, Sep 23, 2021 at 10:46 AM Richard Pyle <deepreef at bishopmuseum.org
>> <mailto:deepreef at bishopmuseum.org> > wrote:
>>
>> I already know I'm going to regret sending this message.  But wisdom is
>> hard-won, and I've evidently not won it yet, so here goes:
>>
>> Michael heads wrote:
>> > [...] nearly always
>> > by in situ allopatric differentiation (vicariance) (not chance = jump =
>> long
>> > distance dispersal)
>>
>> With the *sincere* hope of not stirring up (yet another) dispersal vs.
>> vicariance debate (ha... fat chance...), I want to parse the statement
>> above and ask for a bit of clarification, and a sincere question.
>>
>> First, we have the statement, "nearly always by in situ allopatric
>> differentiation".  I'm on board with that much, for sure (I certainly
>> believe "sympatric differentiation" *can* happen, and it might even happen
>> in a situation that isn't really just something I might label as
>> "micro-allopatry").  So that's not my request for clarification or my
>> question.
>>
>> My request for clarification is this:
>>
>> When you structure the sentence, "in situ allopatric differentiation
>> (vicariance) (not chance = jump = long distance dispersal)", are you saying:
>> 1) "Allopatric differentiation is associated with vicariance; and not
>> associated with chance=jump=long distance dispersal"; or
>> 2) "Allopatric differentiation is associated with both vicariance and
>> chance=jump=long distance dispersal, but when I say "nearly always" I am
>> referring to vicariance as the basis of allopatric differentiation"
>> 3) Something else altogether?
>>
>> Regardless of the answer, I want to get my head around the seemingly
>> dichotomous and mutually exclusive notions of "vicariance" vs.
>> "chance=jump=long distance dispersal".
>>
>> My premises are:
>> 1) "Taxa" exist as sets of many individuals that exist across space and
>> time somewhere/when on planet Earth.
>> 2) For simplicity, I will refer to such sets of individuals as
>> "populations".
>> 3) Populations of many/most organisms do not encompass the entire planet,
>> and are generally bounded in some way (e.g., terrestrial vs. aquatic; one
>> continent or another; only on one island; etc.).
>> 4) Population boundaries may fluctuate over time; sometimes occupying a
>> smaller footprint on Earth, and at other times occupying a larger footprint.
>> 5) Allopatric differentiation occurs among subsets of populations over
>> time, presumably as the result of various evolutionary processes, and
>> probably involving uneven or discontinuous rates of gene flow among
>> individuals between the different subsets.
>>
>> If I haven't slipped up on the phrasing of the above premises, I'd like
>> to frame my question.
>>
>> Scenario 1: A population slowly expands the size of its geographic
>> footprint over time.  Something happens that limits or eliminates gene flow
>> between one part of the population and another part of the population.
>> Over time, the separated parts of the population accumulate differences
>> allopatrically.
>>
>> Scenario 2: A population rapidly expands the size of its geographic
>> footprint over time.  Something happens that limits or eliminates gene flow
>> between one part of the population and another part of the population.
>> Over time, the separated parts of the population accumulate differences
>> allopatrically.
>>
>> Scenario 3: A population rapidly expands the size of its geographic
>> footprint over time.  The conditions that facilitated that geographic
>> expansion are short-lived, resulting in a limitation or elimination of gene
>> flow between one part of the population and another part of the
>> population.  Over time, the separated parts of the population accumulate
>> differences allopatrically.
>>
>> I *think* Scenario 1 is an example of vicariance.  And I *think* Scenario
>> 3 is an example of chance = jump = long distance dispersal.  So my question
>> is:  Are these really dichotomous and mutually exclusive alternatives?  Or
>> are they more like end-points on a spectrum, with many "flavors" of
>> intermediate scenarios (e.g., Scenario 2) in-between?
>>
>> In other words, how much of the debate between alternate modes of
>> establishing circumstances for allopatric differentiation (i.e., vicariance
>> vs. dispersal) ultimately boils down to semantics, rather than evolutionary
>> biology?
>>
>> ...climbing back under a rock for shelter...
>>
>> Aloha,
>> Rich
>>
>> Richard L. Pyle, PhD
>> Senior Curator of Ichthyology | Director of XCoRE
>> Bernice Pauahi Bishop Museum
>> 1525 Bernice Street, Honolulu, HI 96817-2704
>> Office: (808) 848-4115;  Fax: (808) 847-8252
>> eMail: deepreef at bishopmuseum.org <mailto:deepreef at bishopmuseum.org>
>> BishopMuseum.org
>> Our Mission: Bishop Museum inspires our community and visitors through
>> the exploration and celebration of the extraordinary history, culture, and
>> environment of Hawaiʻi and the Pacific.
>>
>> > -----Original Message-----
>> > From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu <mailto:
>> taxacom-bounces at mailman.nhm.ku.edu> > On Behalf Of
>> > Michael Heads via Taxacom
>> > Sent: Wednesday, September 22, 2021 11:47 AM
>> > To: Brendon E. Boudinot <boudinotb at gmail.com <mailto:
>> boudinotb at gmail.com> >
>> > Cc: Taxacom <taxacom at mailman.nhm.ku.edu <mailto:
>> taxacom at mailman.nhm.ku.edu> >
>> > Subject: Re: [Taxacom] Taxacom Digest, Vol 185, Issue 14
>> >
>> > Good questions.
>> >
>> > 1. The original distribution of a clade is established by evolution -
>> nearly always
>> > by in situ allopatric differentiation (vicariance) (not chance = jump =
>> long
>> > distance dispersal). The spatial pattern of differentiation is repeated
>> in a large
>> > number of taxa in the region and so has a general (tectonic or
>> climatic) cause.
>> > This original area of a clade may be very large, e.g. if a worldwide
>> form
>> > differentiates into northern and southern hemisphere forms. The original
>> > distribution may be modified by subsequent range expansion as part of a
>> > community-wide 'geodispersal' (not by chance dispersal, a mode of
>> speciation)
>> > caused by geological/climatic change, or by range contraction.
>> >
>> > 2. As far as I know, areas of endemism for ants are always repeated in
>> other
>> > groups, consistent with the processes in 1. One example is  the group of
>> > Leptomyrmex species in Australia with a phylogenetic/biogeographic node
>> at
>> > the McPherson-Macleay Overlap (see my Australasia book, Fig. 4.16).
>> >
>> >
>> >
>> > On Wed, Sep 22, 2021 at 5:54 PM Brendon E. Boudinot
>> > <boudinotb at gmail.com <mailto:boudinotb at gmail.com> >
>> > wrote:
>> >
>> > > Dear John and Michael,
>> > >
>> > > Would you explain in ≤ 300 words for each point (vis à vis an
>> abstract):
>> > > 1. How extant (and extinct) species came to be distributed as they
>> are.
>> > > 2. How ant biogeography can be explained by point 1 above.
>> > >
>> > > This would be the best way of proceeding in our conversation.
>> > >
>> > > All the best,
>> > > Brendon
>> > >
>> >
>> >
>> > --
>> > 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 <
>> http://www.cambridge.org/9781107041028>
>> >
>> >
>> > *Molecular panbiogeography of the tropics. *University of California
>> Press,
>> > Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968 <
>> http://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 <
>> http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&>
>> &dq=panbiogeography&
>> > source=gbs_navlinks_s>
>> > _______________________________________________
>> > Taxacom Mailing List
>> >
>> > Send Taxacom mailing list submissions to: taxacom at mailman.nhm.ku.edu
>> <mailto:taxacom at mailman.nhm.ku.edu>  For
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>> Taxacom email archive back to 1992 can be
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>> >
>> > Nurturing nuance while assailing ambiguity for about 34 years,
>> 1987-2021.
>>
>>
>>
>>
>>
>>
>> --
>>
>> 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 <
>> http://www.cambridge.org/9781107041028>
>>
>>
>>
>> Molecular panbiogeography of the tropics. University of California Press,
>> Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968 <
>> http://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>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
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>>
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>> You can reach the person managing the list at:
>> taxacom-owner at mailman.nhm.ku.edu
>> The Taxacom email archive back to 1992 can be searched at:
>> http://taxacom.markmail.org
>>
>> Nurturing nuance while assailing ambiguity for about 34 years, 1987-2021.
>>
>