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 plants. 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. Christopher D. Christopher Rogers Invertebrate Ecologist/Taxonomist ((,///////////=====< EcoAnalysts, Inc. (530) 406-1178 166 Buckeye Street Woodland CA 95695 USA ? Invertebrate Taxonomy ? Invertebrate Ecological Studies ? Bioassessment and Study Design ? Endangered Invertebrate Species ? Zooplankton ? Periphyton/ Phytoplankton Moscow, ID ? Bozeman, MT ? Woodland, CA ? Neosho, MO ? Selinsgrove, PA http://www.ecoanalysts.com/ -----Original Message----- From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org]On Behalf Of Joe Shaw Sent: Wednesday, November 22, 2006 3:16 PM To: pbs@lists.ibiblio.org Subject: [pbs] More on plant species (and animal species) Hi Gang, 1. 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 imagined. 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 http://johnhawks.net/weblog/ LINK 2: On Introgression http://tinyurl.com/ydewrh/ LINK 3: Charles Darwin, Origin of a Species by Natural Selection (1856, Chapter 3, p. 56) http://literaturepage.com/read/… LINK 4: Darwin letter to Joseph Hooker http://the_imperfect_planet.tripod.com/sorensenpor… Cordially, Joe Conroe TX Leaves are showing on early Narcissus types (Tazetta hybrids). _______________________________________________ pbs mailing list pbs@lists.ibiblio.org http://www.pacificbulbsociety.org/list.php