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

[Ken Kinman]

John,      I don't understand why you are puzzled.  Kryptolebias phylogenetically splits off right between the African family Nothobranchidae (on one side) and the clade containing all of Rivulidae except for Kryptolebias (on the other side), so it is closely related to both families (sharing immediate plesiomorphies with Nothobrachids as well as synapomorphies with Rivulids).  
         And splitting off at the base of Rivulidae, it would be our primary model for a proto-Kryptolebias fish which rafted from Africa to South America.  And that model shows characteristics which would easily enabled it raft over a large expanse of ocean.  What puzzles me is why Costa didn't realize the importance of the basal position of Kryptolebias  (or chose not to discuss it in his paper).                   ---------------Ken       

Date: Tue, 8 Apr 2014 04:04:01 +1200
Subject: Re: [Taxacom] trans-Atlantic "rafting" fish (great candidate)
From: calabar.john at gmail.com
To: kinman at hotmail.com
CC: taxacom at mailman.nhm.ku.edu

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





_______________________________________________

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.