[Taxacom] Yoder, dispersal, and Madagascar's biota

[Ken Kinman]

Michael and John,
      Well, the funny thing is that I was inclined to give you the benefit of the doubt on cichlids (as was Yoder and Nowak), but I am now actually less inclined to do so.   I would like to emphasize the last two sentences of Yoder and Nowak's abstract:   "For those studies that include divergence time analysis, we find an overwhelming indication of Cenozoic origins for most Malagasy clades. We conclude that most of the present-day biota of Madagascar is comprised of the descendents of Cenozoic dispersers, predominantly with African origins."   I think that their use of the word "overwhelming" is important to note, and I found no reason to think that they were exaggerating in doing so.  As for the cichlids in particular, in the text they admit that among the vertebrates, "the cichlid fishes of Madagascar represent the most challenging puzzle for differentiating vicariance from dispersal."   And then they are careful to give the arguments either way.  I thought it was a very thoughtful and balanced review, and how Michael dismisses the included studies as ONLY showing the importance of calibration method has me scratching my head in disbelief.  I think that it is a narrow and unfair assessment of the Yoder and Nowak review and of the studies they were reviewing.                                                                            It's too bad Michael (in 2012) obviously didn't have the more recently published and thorough study on the subject of cichlid biogeography, which concluded that it was dispersal, not vicariance, which produced the present distribution of those fishes:   Title: Molecular and fossil evidence place the origin of cichlid fishes long after Gondwanan rifting.    by Matt Friedman, Benjamin P. Keck, et al., 2013.    They state:  "It is important to note that our relaxed-molecular-clock analysis shares no palaeontological data in common with either our analysis of the distribution of cichlid-bearing fossil horizons or our database of outgroup-based age constraints. We interpret the convergence of these three semi-independent approaches, which all deliver age estimates for cichlids that are within error of one another, as a consequence of genuine evolutionary signal that strongly contradicts the time scales for cichlids demanded by hypotheses of Gondwanan vicariance."
        And even if one doesn't agree with Friedman et al.'s conclusions, the cichlids are just one of many taxa reviewed by Yoder and Nowak, not only among vertebrates, but plants and invertebrates as well.  Many appear to have dispersed late enough that it stretches credibility to suggest that fossil calibration is a problem with so many of them dispersing (as opposed to a very early vicariance).  Especially the rodent and carnivore dispersal between 20 and 25 million years ago (see Ali and Huber, 2010;  Nature 463, 653-656; Mammalian biodiversity on Madagascar controlled by ocean currents).  The Ali and Huber paper solved the "problem" of ocean currents presumably going the wrong way for dispersal to occur, showing that the currents went the other way in the early-to-mid Tertiary.    
                                          -------------------Ken Kinman                           Date: Sat, 22 Mar 2014 10:46:58 +1300
Subject: Re: [Taxacom] Madagascar's biota overwhelmingly from Cenozoic dispersers
From: m.j.heads at gmail.com
To: kinman at hotmail.com; taxacom at mailman.nhm.ku.edu

Hi Ken, Here is what I wrote (2012) about Yoder and Nowak's paper:    Yoder and Nowak (2006) gave a thorough
review of the molecular clock literature on Malagasy taxa. In every study of
plants the fossil-calibrated clocks dated the Madagascar clades as younger than
80 Ma and so they were all attributed to post-Gondwana dispersal, none to
vicariance. With a single exception, studies of animal taxa showed the same
result. All molecular dating studies of Malagasy invertebrates, reptiles and
mammals have concluded in favor of dispersal, as the inferred
(fossil-calibrated) divergence times were post-Mesozoic. The only sequenced
group in Yoder and Nowak’s review (2006) whose presence on Madagascar has been
attributed to vicariance is the fish family Cichlidae. Molecular dating studies
of this group avoided the use of fossil calibrations completely (Sparks, 2004,
Sparks and Smith, 2004; see Chapter 2). Instead, the vicariant distribution of
the two main molecular clades: Madagascar-Africa-South America, and
Madagascar-India-Sri Lanka, was correlated with tectonics – the opening of the
Mozambique Channel – and this was used as a calibration. (The same method is used
here for primates). So although Yoder and Nowak (2006: 416) concluded that the
importance of dispersal ‘cannot be denied’, really the only thing the cited
studies show is the importance of the calibration method.  
Michael Heads


On Sat, Mar 22, 2014 at 7:49 AM, Ken Kinman <kinman at hotmail.com> wrote:

Has Vicariance or Dispersal Been the Predominant Biogeographic Force in Madagascar? Only Time Will TellAnnual Review of Ecology, Evolution, and SystematicsVol. 37: 405-431 DOI: 10.1146/annurev.ecolsys.37.091305.110239by Anne D. Yoder and Michael D. Nowak


Abstract.   Madagascar is one of the world's hottest biodiversity hot spots due to its diverse, endemic, and highly threatened biota. This biota shows a distinct signature of evolution in isolation, both in the high levels of diversity within lineages and in the imbalance of lineages that are represented. For example, chameleon diversity is the highest of any place on Earth, yet there are no salamanders. These biotic enigmas have inspired centuries of speculation relating to the mechanisms by which Madagascar's biota came to reside there. The two most probable causal factors are Gondwanan vicariance and/or Cenozoic dispersal. By reviewing a comprehensive sample of phylogenetic studies of Malagasy biota, we find that the predominant pattern is one of sister group relationships to African taxa. For those studies that include divergence time analysis, we find an overwhelming indication of Cenozoic origins for most Malagasy clades. We conclude that most of the present-day biota of Madagascar is comprised of the descendents of Cenozoic dispersers, predominantly with African origins.








______________________________________________