[Taxacom] trans-Atlantic "rafting" fish (great candidate)

[Michael Heads]

Hi Ken,

Kryptolebias being sister to all the other rivulids doesn't mean that it is
'primitive'. Its sister-group is equally primitive.

If the New World group (Rivulidae) was derived from its African sister
group, rivulids would be nested in the African group, not sister to them.

Michael


On Tue, Apr 8, 2014 at 2:37 AM, Ken Kinman <kinman at hotmail.com> wrote:

> Hi All,               I've been reading various research papers on the
> Aplocheiloid killifishes, and in a recently published paper by Costa, 2013
> [Vertebrate Zoology, 63(2): 139-154], I was very surprised to see his
> results showing that genus Kryptolebias was sister group to ALL of the
> other genera of the New World family Rivulidae.
>
>           Is it merely coincidence that the primitive American genus
> Kryptolebias just happens to be a great candidate for a fish that could
> disperse on a raft of vegetation from Africa to South America?  (1) It's
> not only very tolerant of salt water, but more importantly (2) it can
> survive out of water for weeks at a time (66 days in one case).  (3) And
> guess where Kryptolebias marmoratus spends much of its time while out of
> the water----in logs and cavities of trees (which would be the main
> structural components of a large transoceanic raft).
>          Those are the three things I thought of offhand which pointed to
> possible trans-Atlantic dispersal.  But then I began wondering about yet
> another strange thing about Kryptolebias fish.  They often exhibit various
> types of hermaphroditism, and even its most extreme form
> (self-fertilization, which is apparently absent in vertebrates except for
> Kryptolebias).  So just a few of these fish (or even a single individual)
> could have established a population on another continent.  And the
> proximity of northern South America to the end-Cretaceous bolide impact off
> southern Mexico (and the resulting mass extinction) would have meant lots
> of empty niches that needed to be refilled in the early Tertiary.
>          I'm not saying that this is definitely how the first Rivulid got
> to the New World, but it is certainly worth serious consideration.  As for
> possible dispersal among the clades and subclades back in the Old World
> (Families Aplocheilidae and Nothobranchidae) versus the proposed vicariance
> explanations, I am definitely still on the fence and hoping to find more
> evidence either way.   It could be a case where vicariance best explains
> the Old World pattern, but then followed by Cenozoic dispersal to the New
> World.  But if there were no Aplocheiloids in existence when Madagascar
> (and India) split off of Africa, dispersal would trump vicariance there as
> well.
>        Anyway, I can certainly understand why there has been a backlash in
> recent years among so-called "dispersalists" who believe that others have
> sometimes been too quick to assume vicariance where the evidence is frankly
> equivocal and some of them seem too quick to dismiss (or to just ignore)
> possible dispersal just because it appears unlikely.  If a
> proto-Kryptolebias genus in Africa did disperse to South America by rafting
> sometime in the early Tertiary, hopefully a closely related genus might
> still exist in western Africa.  But we won't know if we don't look for
> evidence (molecular or morphological) for that relationship in particular.
>  Sometimes more intensive sampling (especially molecular) in a particular
> area of interest can reveal important information that limited sampling
> have simply missed.  A sister group relationship between Kryptolebias and
> some West African aplocheiloids might be found, even if it is in molecular
> trees which aren't the shortest (and thus overlooked).
>                                  -------------------Ken Kinman
>
>
> _______________________________________________
> Taxacom Mailing List
> Taxacom at mailman.nhm.ku.edu
> http://mailman.nhm.ku.edu/mailman/listinfo/taxacom
> The Taxacom Archive back to 1992 may be searched at:
> http://taxacom.markmail.org
>
> Celebrating 27 years of Taxacom in 2014.
>



-- 
Dunedin, New Zealand.

My recent books:

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

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