More on plant species (and animal species)

D. Christopher Rogers
Sat, 25 Nov 2006 10:52:07 PST
Really, in zoology, the only thing that hybridizability (for want of a
better term) demonstrates is that two species are in the same genus. It is a
good quantitative definition for zoology, but obviously would never work in

A very important thing for any taxonomist to keep in mind is that different
groups have different defining limits and characters. There is no universal
rule or character for defining all taxonomic units whether at species, genus
or even kingdom level, not even genes!!! Ernst Mayr put it best:

"An unresolved difficulty is posed by the drastically different needs of
different taxonomic groups . . . Dissention and controversy will inevitably
result if specialists in one group of organisms are oblivious to the needs
of specialists in other groups."

This is a reflection on the multifarious solutions to ecological and
reproductive problems produced by organisms. Biological systems are so
amazingly diverse that it is very unlikely that any "grand unifying theory
of biology" could ever be produced.

Just my two cents.

D. Christopher Rogers
Invertebrate Ecologist/Taxonomist

EcoAnalysts, Inc.
(530) 406-1178
166 Buckeye Street
Woodland CA 95695 USA

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-----Original Message-----
From: []On
Behalf Of Joe Shaw
Sent: Wednesday, November 22, 2006 3:16 PM
Subject: [pbs] More on plant species (and animal species)

Hi Gang,


I was thinking more about plant species, and why/how they sometimes
interbreed, etc.  I checked with friends in ecology departments and did some
reading.  It turns out that plants just have looser sterility barriers than
do animals.  But, animal species are not so exempt from inter-fertility as

Fortunately for hybridizers and gardeners everywhere, plants do have some
elasticity in their sterility barriers.  Oaks, cacti, and liliaceous plants
come to mind when I think of species  that can interbreed, but which
typically don't in the wild.

2.  What is a species? (or, I don't know what a species is)

Before I get to the animal discussion I want to point out that surely, some
confusion over inter-specific is because we (we humans) can only do the best
we can, and we're not always able to discern a species from a subspecies or
a variety.  Charles Darwin remarked on this over 150 years ago and his
suggestion was to be careful.

Darwin said, "From these remarks it will be seen that I look at the term
species as one arbitrarily given, for the sake of convenience, to a set of
individuals closely resembling each other, and that it does not essentially
differ from the term variety."

In a letter to a colleague Darwin also wrote, "It is really laughable to see
what different ideas are prominent in various naturalists' minds when they
speak of species; in some, resemblance is everything and descent of little
weight - in some, resemblance seems to go for nothing, and Creation the
reigning idea - In some, descent is the key, - in some, sterility an
unfailing test, with others it is not worth a farthing. It all comes, I
believe, from trying to define the indefinable."

So, the point is that (especially it seems with plants) you are in very good
company if it seems hard to known what is a species and what is just a
variant within a species.  (LINKS 3 and 4)

2.  Mammal species that interbreed

I like John Hawks' Weblog on all things related to evolution, genetics, and
paleoanthropolgy.  His discourses are well thought out, and he uses the
current literature to guide, illuminate, and flesh out his arguments.

One interesting point he makes is that many mammalian species are known that
can interbreed freely if they have no other options, e.g., if they are
isolated from their normal mates.  He points out that members of the
wolf/dog/coyote/jackal clade can and do interbreed and produce viable and
fertile offspring, especially in areas where the various animals are thrust
into contact with each other.  The point is that these species don't
normally interbreed, and they are easily distinguished from each other, but
they can and do interbreed upon occasion. Factors that keep them from
interbreeding include lack of overlapping ranges and behavioral details.

For instance, the four recognized jackal species are found in Asia and
Africa where they seldom overlap with the distribution of wolves and they
seldom have a chance to hybridize (in nature).  Similarly, frequency and
season of estrus can prevent some animals from interbreeding unless they are
forced together in zoos, etc.  Additionally, various species that might be
able to interbreed treat each other as "different;" and they are more likely
to attack or flee than to mate.

In any event, Dr. Hawks reports, "Wolves and coyotes (and dogs) mate fairly
extensively wherever they are sympatric. Bison had a time in history when
they received lots of genes from cattle."  (LINK 2)

LINK 1:  John Hawks
LINK 2:  On Introgression
LINK 3:  Charles Darwin, Origin of a Species by Natural Selection (1856,
Chapter 3, p. 56)…
LINK 4:  Darwin letter to Joseph Hooker…



Conroe TX

Leaves are showing on early Narcissus types (Tazetta hybrids).

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