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

[John Grehan]

Ken,

I'm a bit puzzled as to why the ecological characteristics of Kryptolebias
marmoratus has anything to do with trans-Atlantic hypotheses when K
marmoratus is more closely related S American taxa than those of Africa.
Please clarify your argument.

John Grehan


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
>
>
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