Hi David,
If you use hybridization as a strict indicator to rule out two species, then
there should be only one or a few Anas, one or a few Aythya, one ore a few
Larus... I could endlessly continue this list of genera containing accepted
species that hybridize naturally. ...and what about the famous "Swoose" (Mute
Swan X Greylag Goose)? Is Greylag Goose a subspecies of Mute Swan or vice versa?
BTW I'd like to correct a little error: I never said that hybridization ONLY
occurs between "two species nowadays". I said that hybridization ALSO occurs
between "two species nowadays"
Cheers,
Nikolas
----------------
Nikolas Haass
Sydney, NSW
________________________________
From: David James <>
To: Mike Honeyman <>; ""
<>; ""
<>
Sent: Friday, November 25, 2011 6:31 PM
Subject: Definition of a species
Species definitions are indeed a can of worms that have been discussed on B-A
many times, so I do not want to go there.
However, either I don't understand or don't agree with Nikolas and Mike about
hybridisation. A hybrid is simply the offspring of two different forms. The
parents can be individuals from two different genera, species, subspecies
(races), varieties, breeds or cultivars (but not morphs). It is not within the
domain (or interest) of taxonomy to redefine "hybridisation" as something that
only occurs between "two species nowadays".
Of course hybridisation can and is used to indicate species boundaries in ALL
species concepts. It is a line of evidence. When two forms are sympatric and it
is known that they don't hybridise everyone agrees that they are two species
(like the 2 white-tailed black-cockatoos). When they merge into each
other through hybridisation over a broad front then
everyone agrees they are one species (like green and yellow figbirds). In
between there is lots of grey and disagreement, but there is grey and
disagreement in everything to do with taxonomy. Taxonomists can still use
hybridisation as a line of evidence regardless of the species concept they
follow, even if few do. There are at least two big problems with using
hybridisation: 1) to understand it you need data from lots of individuals
across a wide area; and 2) it is not applicable to allopatric species. Neither
is justification to dismiss it as irrelevant to the process of speciation.
A frequent trend in taxonomy these days is to compare the percentage
differences in the Cytochrome B gene. Isn't this just looking for an indication
of whether two forms continue to share genes through the process of
hybridisation, or how long ago they stopped?
Lastly, nearly all existing
checklists are predicated on lines of evidence originally formed around
concepts of speciation based on levels of interbreeding (or the extrapolation
of similar patterns when direct evididence is lacking). Regardless of
contemporary opinions, hybridisation still defines the bird species painted in
the field guides.
David James,
Sydney
==============================
________________________________
From: Mike Honeyman <>
To: ;
Sent: Thursday, 24
November 2011 10:03 PM
Subject: Definition of a species
I hear the sound of a can of worms being opened!
Simon there are many definitions of species, to suit specific 'species
concepts'. There are different species concepts that are preferred for
different phyla.
For birds the two most prevalent species concept are the Biological Species
Concept (BSC) after Mayr, and the Phylogenetic Species Concept (PSC) after
Cracraft.
BSC species = "groups of interbreeding populations reproductively isolated from
other such groups"
PSC species = "the smallest diagnosable cluster of organisms within which there
is a parental pattern of ancestry and descent"
Historically the BSC could use the ability to hybridise or not as an indicator
of species, but I think it's a while since anyone thought that was a reliable
indicator, as Nikolas has pointed out.
Re the owls. It is possible that the morphological
differences are a red herring - there could be an environmental 'switch' (e.g.
the climate / habitats that prevail in Tassie and NZ) that cause a particular
morphology that exists widely within the gene pool of the population to
prevail. This could be tested by moving Qld birds to Tassie and see what they
look like after a couple of generations (I've not looked at any of the papers
by the way, just flying a theoretical kite!)
Cheers
mjh
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