[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

One Old, One New: Phylogeny and Speciation

Helbig, A.J.; Knox, A.G.; Parkin, D.T.; Sangster, G.; and Collinson, M.
2002. Guidelines for assigning species rank. _Ibis_ 144: 518-525.


"Developments in several fields of study (including bio-acoustics and the
analysis of DNA) together with reappraisals of the nature of species have
impacted significantly on avian taxonomy.  The BOU's Taxonomic
Subcommittee has developed guidelines for the application of species
limits to sympatric, parapatric, allopatric and hybridizing taxa.  These
are published here to assist researchers understand the rationale behind
the committee's taxonomic recommendations relating to the British List."

Quoted from the Introduction:

"No species concept so far proposed is completely objective or can be used
without the application of judgement in borderline cases.  This is an
inevitable consequence of the artificial partitioning of the continuous
processes of evolution and speciation into discrete steps.  It would be a
mistake to believe that the adoption of any particular species concept
will eliminate subjectivity in reaching decisions.  Adopting a different
species concept merely moves the boundaries, and changes the individual
taxonomic decisions that are controversial."

More interesting excerpts on terms with -patry in them, just to further
the discussion:

"Since reproductive incompatibility is the fundamental requirement that
keeps gene pools from merging, it is useful, in practical terms, to devise
guidelines for assignment of species rank with respect to the four
distributional situations discussed above:

*  sympatry, where gene flow is prevented by intrinsic isolating
mechanisms (rather than geographical isolation),

* parapatry and hybrid zones, where gene flow may be restricted to various
extents by intrinsic isolating mechanisms and/or an ecotone, but not by
geographic isolation,

* allopatry, where the lack of gene flow may be due solely to geographical


Philopatry does not refer to a speciation event or even to evolution, but
rather is a manner of ecology where an animal returns to the location of
its birth. Ernst Mayr defined philopatry as the drive or tendency of an
individual to return to, or stay in, its home area, birthplace, or another
adopted locality, In his 1963 book _Animal Species and Evolution_.


Springer, M.S.; Teeling, E.C.; Madsen, O.; Stanhope, M.J.; de Jong, W.W.
2001. Integrated fossil and molecular data reconstruct bat echolocation.
_Proceedings of the National Academy of Sciences, USA_ 98 (11): 6241-6246.


"Molecular and morphological data have important roles in illuminating
evolutionary history. DNA data often yield well resolved phylogenies for
living taxa, but are generally unattainable for fossils. A distinct
advantage of morphology is that some types of morphological data may be
collected for extinct and extant taxa. Fossils provide a unique window on
evolutionary history and may preserve combinations of primitive and
derived characters that are not found in extant taxa. Given their unique
character complexes, fossils are critical in documenting sequences of
character transformation over geologic time and may elucidate otherwise
ambiguous patterns of evolution that are not revealed by molecular data
alone. Here, we employ a methodological approach that allows for the
integration of molecular and paleontological data in deciphering one of
the most innovative features in the evolutionary history of
mammalslaryngeal echolocation in bats. Molecular data alone, including an
expanded data set that includes new sequences for the A2AB gene, suggest
that microbats are paraphyletic but do not resolve whether laryngeal
echolocation evolved independently in different microbat lineages or
evolved in the common ancestor of bats and was subsequently lost in
megabats. When scaffolds from molecular phylogenies are incorporated into
parsimony analyses of morphological characters, including morphological
characters for the Eocene taxa Icaronycteris, Archaeonycteris,
Hassianycteris, and Palaeochiropteryx, the resulting trees suggest that
laryngeal echolocation evolved in the common ancestor of fossil and extant
bats and was subsequently lost in megabats. Molecular dating suggests that
crown-group bats last shared a common ancestor 52 to 54 million years

  The phylogeny is a molecular one that used the work of Simmons and
Geisler (1998: _Bulletin of the American Museum of Natural History_ 235:
182pp.) to utilize morphological data of fossil taxa, and added them in an
echolocatory context to that data in the molecular study. The following
tree was produced, rooted in some euarchontans: 

  |  `--Dermoptera
           |  `--+--Palaeochiropteryx
           |     `--+--Emballonuridae
           |        `--+--Vespertillionoidea
           |           `--+--+--Thyropteridae
           |              |  `--Myzopodidae
           |              `--+--Phyllostomidae
           |                 `--+--Morpoopoidea
           |                    `--Molossoidea

  The Laurasiatheria idea of chiropteran relationship was discussed but
not tested, and from the abstract, it is noted that at 54 mya of molecular
timing, bat echolocation had just developed. The author's state:
"Similarly, molecular dates that were calculated by Nikaido et al. (17)
suggest that flight and echolocation evolved during a 25 million year
window extending from 83 million years to 58 million years."

  The citation is:

  Nikaido M.; Harada M.; Cao Y.; Hasegawa M.; and Okada N. 2000.
Monophyletic origin of the order Chiroptera and its phylogenetic position
among mammalia, as inferred from the complete sequence of the
mitochondrial DNA of a Japanese megabat, the Ryukyu flying fox (*Pteropus
dasymallus*). _Journal of Molecular Evolution_ 51: 318-328.


"Complete sequences of mitochondrial DNA (mtDNA) are useful for the
reconstruction of phylogenetic trees of mammals and, in particular, for
inferring higher-order relationships in mammals. In this study, we
determined the complete sequence (16,705 bp) of the mtDNA of a Japanese
megabat, the Ryukyu flying fox (Pteropus dasymallus). We analyzed this
sequence phylogenetically by comparing it with the complete sequence of
mtDNAs of 35 mammals in an effort to reevaluate the enigmatic relationship
between Megachiroptera and Microchiroptera and the relationships between
them and other mammals. Maximum-likelihood analysis of 12 concatenated
mitochondrial proteins from 36 mammals strongly suggested the monophyly of
the order Chiroptera and its close relationship to Fereuungulata
(Carnivora + Perissodactyla + Cetartiodactyla). We estimated that megabats
and microbats diverged approximately 58 MyrBP and discussed the origin and
early evolution of Chiroptera based on our findings."

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.