The following collage supports an earlier suggestion by Brody (1998), Brody & Pearce (1998) that our "categorization mechanisms" for assigning the label of "species" is misleading. An emerging hypothesis is that behavioral separation occurs (through groups' occupying different niches or through their evolving different fixed action patterns and secondary sexual characteristics); this separation has outcomes that are correlated with our putting them in different categories (species). The visual (auditory, olfactory?) appearance of being a separate species does not indicate the reproductive incompatibility of gametes if mixed with those from the mother stock.
From Brody & Pearce (1998, Evolutionary morals and supernormal stimuli. To be presented at the Human Behavior and Evolution Society, July 1998. Also posted, www.behavior.net/mhn/)
"Supernormal stimulus (SNS) was suggested by Lorenz and Tinbergen in the 1930s as a result of ethological research on stickleback aggression and gull feeding behavior (Hess, 1962). Even though the concept was first applied to ethologist-produced stimuli, the methods revealed the power of specific stimulus characteristics -- larger, brighter, and perhaps livelier - to elicit action patterns and to direct preferences (Miller, 1998). The SNS phenomenon has the potential not only to direct momentary behavior, but also to influence the longterm, cross generational outcomes of such behavior. This possibility is most likely in the domains of sexual selection, orthoselection, and speciation. It is also could be a significant cultural factor to the extent that SNS preferences erode "tit-for-tat" strategies of reciprocal altruism in large human organizations.
"Secondary sexual traits in the male are considered to be evolved as a consequence of female preferences. It could be that peacock or male widowbird tails are the essential cues for the hen - through her own psychological adaptations - both to identify a male of her species, to pick between alternative males, and to regulate the intensity of her attraction and fidelity once she has made a choice. Her sensory mechanisms may operate in a manner similar to those of sticklebacks and gulls ... larger displays more effectively trigger mating responses. A dad with a more colorful tail may produce children with colorful tails, who because of their color, are themselves more likely to mate. A positive feedback loop is established and rapid changes occur, (Miller, 1998) limited mainly by homeostatic costs (Bateson, 1963) or by shifts in predator success. "
From Conversations about Speciation on the Paleopsych List_Serve (emphases added, JB)
5/11/98 11:08:33 PM Eastern Daylight Time
I've scratched my head for some time about mechanisms of speciation. The notion of incremental changes' suddenly one morning producing changes that are incompatible with mating always struck me as a bit magical. I accept the notion of incremental adjustments in behavior and stimulus patterns and a separation of mating "practice" because of sensory/preference changes. However, the gametes may still be mutually compatible if a couple of research assistants mixed them together.
If we are to define "species" on the basis of an inability to produce children when bred with the mother stock, then we need evolutionary changes in genes that will (1) produce the same changes in both males and females and at the same time, (2) produce a large number of boys and girls who can mate with each other without the costs of inbreeding.
I couldn't think of a suitable mechanism until yesterday morning when looking at Maynard Smith's new edition of "Evolutionary Genetics." There it was in the first couple of pages, a reference to a virus, Q-beta, that lives in the gut of E. coli and in test tubes and that makes an enzyme that replicates RNA.
Viruses could tinker with gene structure, in many settings, exerting largely the same effects in males and females at the same time and at the same point on the chromosome, and do so to large numbers at once, and produce a large cluster of organisms that can breed with each other but not with the parent stock.
This mechanism would require some modification of Weismann's model. Maynard Smith (1998), however, already describes several exceptions to it. Viral invasions of DNA seems possible, even of the DNA in our gametes. Likely not to happen too often. Thus, saltation? (not a popular idea, I understand).
Isolation, in and of itself, despite all kinds of progressive changes in physical appearances, should not produce mating incompatibilities (at least not according the criterion of eggs and sperm that won't merge into a zygote). There was a news release about 5 months ago to the effect that camels and llamas [?] produce fertile young even though the two "species" separated 12 mya. And how many generations (5000?) of dogs underlie two breeds that can still make puppies together?
From: Howard Bloom
In a message dated 98-05-11 23:08:33 EDT,
Jbrody@compuserve.com writes: << Viruses could tinker with gene structure, exerting largely the same effects in males and females at the same time and at the same point on the chromosome, and do so to large numbers at once, and produce a cluster of organisms that can breed with each other but not with the parent stock. >>
Could someone please explain to me *how* this happens.
Meanwhile, Jim, many of your questions about intermediate phases on the way to speciation are answered by some of Kelly Kissane's rather amazing postings on spiders. Here's what I've got of Kelly's contributions in my notes:
"Behaviorally, we have hybrids. This happens even in my lowly spiders - populations of the same species can have very different courtship behaviors. In some cases, these differences are so different to cause one member to not recognize the other, even though they are the same species! And as my mentor Dan Papaj mentioned in his book "Insect learning" sometimes these behaviors are learned, not genetically wired. Kelly C. Kissane to IPP 5/2/98
"My own work involves differences in courtship behaviors between populations of the fishing spider Dolomedes triton, which has led to some reproductive isolation....These animals can produce viable, fertile offspring when different populations are "force-mated" - a process that involves putting the female in a sleepy mode so she doesn't kill her suitor - and these offspring often are "hybrids" behaviorally, having characteristics of both parents. This is also seen in two sister species of Schizocosa, work by Gail Stratton found that hybrids were often rejected by both parental species, but the hybrids were responsive to each other." Kelly Kissane to IPP 5/03/98
Date: Tue, 12 May 1998 08:37:12 -0400 (EDT)
From: Kelly Caithlin Kissane
If you are going to include viruses, then you should also include transposons - especially retrotransposons. These little snippets of DNA can excise themselves out of the genome, move to other parts, replicate themselves, etc. I just finished a paper discussing the different mechanisms that evolved to counter the potentially destructive efffects of transposons.
Date: Thu, 14 May 1998 01:03:50 EDT
From: Howard Bloom
Kelly understands the manner in which transposons function far better than I do. However they are in the tool kit which bacteria use in the adaptive reeingineering they perform on their own genomes, per Eshel Ben Jacob and James Shapiro.
Meanwhile, viruses apparently manage their rapid morphing in part because they are based on RNA rather than DNA and do not have the normal cellular mechanisms for checking the accuracy of replication. (per Dr. Pavel Yutsis).
Date: 5/13/98 9:36AM
From: James Brody
The viral role may not be impossible ... I've a lot of respect for those little suckers.
Kelly's note (goodness, we can type all day citing Kelly at each other) mentions transposons and retrotransposons. Guess I gotta look them up
It would be fun to sort out whether spiders or humans are the more sensitive to such meddling (if it exists). Humans obviously but only if we were a rigid structure (all "and" circuits?) and without systems redundancy. However, we have a lot of redundancy (a logical necessity given the fragility of DNA as well as our psychological adaptations) and system flexibility ("or," "nor" wiring?). "Therefore"? we have more flexibility (an asset and a liability) than spiders; that's what they deserve for wearing their ears in their arms.
Date: 5/12/98 12:06A.M.
From: Joseph C. Daniel
A couple of things that people need to remember about the definitions of species is that they are arbitrary and that there are many of them depending on which points you want to emphasize. Most people generally use the biological species concept in that if the animals can't normally breed in the wild they are different species. The important point here is IN THE WILD. Many different but fairly closely related species can breed if eggs and sperm are mixed together in the lab. That does not mean they are the same species.
Lions and tigers can breed quite easily when put together, but they don't in the wild because they occupy different niches. Their behaviors and choice of territories keep them apart, thus they are different species. What about dogs you say? They are after all generally considered the same species, just different breeds because if helped they can all interbreed, right? This is due to tradition and not biological common sense. St. Bernards and dachshunds are no more the same species than chimps and humans. True, the length of time the dog breeds have been separated is very short compared to chimps and humans, but different species they are nonetheless. Actually, this is an excellent example of directed evolution controlled by man for specific purposes.
Evolution does not have to happen over hundreds of thousands or years if driven hard enough. Someone mentioned a difficulty with incremental change in speciation. Forgive me if I am mangling the comment's intent. But perhaps the leopard frog example will illustrate how this can work in speciation. The leopard frog can be found all along the eastern U.S. Throughout the range the frogs can easily interbreed. However, enough change has occurred in the population that the two endpoints, i.e. the northern leopard frog and the southernmost leopard frogs can not interbreed at all and are quite separate species. Yet at no point in the range can there be found a place to demarcate the change. It happens gradually and subtly so that broadly they comprise a single interbreeding population but closer inspection reveals a series of interbreeding subspecies creating different full species. Thus is shown the arbitrariness of the species concept.
The species concept also fails miserably at the moneran and most especially in the prokaryote kingdoms. There is so much DNA swapping at this level that calling something a species is simply a matter of degree of difference and is decided upon by little more than personal preference.
Plants are almost as bad as bacteria in this regard. Plants are notorious in their ease of hybridization. Here again is another full kingdom where the biological species concept breaks down and some other concept takes over. Nature, especially ecology, does not play games of black and white. There (are) only shades of grey. Demarcations between things are only ways of simplifying things to make them easier deal with and we must never forget that they are our simplifications, not nature's.
Date: Tue, 12 May 1998 11:00:35 EDT
Inbreeding has always been such a *dirty* word, but I wonder if the creation of a new species doesn't *rely* on inbreeding. Are recessive genes always undesirable? I am a blue-eyed blonde and haven't been too unhappy about that.
I have limited genetic knowledge, but I understand that the problem with inbreeding is that the frequency of familial diseases and genetic anomalies is proportionally increased with incest. It seems to me that this might be a contributing factor to the demise of a species unless new genetic material is introduced, but what about the "beginning" of a new species? Could it not be like a "bell curve"?
I am thinking of the species which developed in isolation like the kangeroo. There must have been inbreeding in the dawn of its creation, and is it not likely that those incestuous pairs who had the "good" genes produced an abundance of healthy offspring?
Inbreeding does bring out undesirable traits, but won't those eventually disappear because they probably won't reproduce healthy offspring? I understand how they would proliferate in the dome of the bell curve, but it seems to me that these would ultimately be partially responsible for the extinction of the species, or the traits and diseases themselves would disappear.
Date: Tue, 12 May 1998 13:18:14 -0400 (EDT)
From: Kelly Caithlin Kissane
The creator of F-statistic (which measures population structure and inbreeding), Sewell Wright, was the product of a first cousin marriage. He found it amusing that he studied inbreeding, and few scientists were more inbred than him. Inbreeding worked for him - he lived to be 99.9 year old, and was a super genius.
But you are right, inbreeding results in the decrease of heterozygotes, increasing homozygosity. Depending on the allele, this can be a good thing, a bad thing, or even a lethal thing. Some alleles can be lost altogether due to genetic drift and skewed fixation of alleles.
But I would not advocate eugenics based on increasing the frequency of a certain set of alleles. Inbreeding works great on endoparasites, but thankfully, I am not a tapeworm. And as a result, I (and my offspring, and my offspring's offspring, etc.) must be *genetically* able to respond to environmental changes. If all the super geniuses were dumped in Antartica without a paddle or anything else, I'd bet my life savings that quite a few would die before they hit on a solution that would allow them to survive - and it wouldn't be IQ that was the deciding factor in who survived.
From: Martha Sherwood
Date: Tue, 12 May 1998 11:34:47 -0800
Bravo! Let's hear it for plants, and bear in mind that most of the work people are most familiar with in speciation has been done with mammals, a group which has evolved very rapidly in the Cenozoic and where the most interesting genera contain relatively few, well-marked species.
Through the phenomenon of polyploidy, you can even get viable, fertile intergeneric hybrids in flowering plants, a great boon to plant breeders. The nuclei of polyploid hybrids contain a complete set of chromosome from each of the parents.
Keep in mind also that most described biological species concepts are based on discontinuity in morphological characters and geographical isolation, not on experimental evidence as to whether interbreeding can take place either in nature or in the laboratory.
Some years ago I wrote a world taxonomic monograph of Coccomyces, a genus of fungi most of whose members grow as asymptomatic endophytes in living leaves and bark, fruiting later as saprophytes on senescent material. One would expect such a well-adapted parasite to be host specific, and on this basis people had described as different species things which appeared morphologically identical but occurred on, say oaks and ericaceae respectively. I had to decide whether to treat the species as distinct or synonymize them, and I did not have the resources to attempt crosses then, nor would I now have the resources for DNA sequencing.
The genus has ca. 50 species, half of which are clearly host-specific at the generic or family level and tend to be geographically restricted. At the other end of the spectrum there is C. dentatus, which can be found on just about any broad-leaved tough-leaved woody plant in the north temperate zone. I suspect this is all one species in the sense of being able to cross-breed, but that the populations on different hosts are somewhat better adapted to their hosts physiologically and therefore are somewhat reproductively isolated. It's a testable hypothesis, but nobody's going to pay me to study an obscure genus of nonpathogenic fungi at anything other than the morphological level.
Date: Tue, 12 May 1998 18:02:14 -0400 (EDT)
Warren S. Sarle
There was an article in Scientific American earlier this year that you might find interesting, about how bacteria swap genes via viruses and what not.
Date: Wed, 13 May 1998 09:42:12 +1000
On Tue, 12 May 1998 14:10:29 -0400 David Berreby wrote:
|Anyone familiar with Michael T. Ghiselin's Metaphysics and the Origin of
|Species (SUNY Press, 1997) ? It appears to propose that the best way to
|think of a species is as a kind of single individual, rather than a class.
|I say appears since I haven't actually read the book. It is, like a lot of
|others, waiting patiently for me to get to it. Perhaps someone on the list
I am doing my PhD on this very topic, and yes, I have the book. There's a particularly nasty review of it by Michael Ruse in "Evolution" a couple of issues ago.
|One argument that has been made for the ``reality'' of species is that
|they're often classified the same way by different cultures. For example,
|Murray Gell-Mann cites Ernst Mayr's account of finding 127 bird species in
|New Guinea when he was there as a young researcher, while the local tribe
|counted 126, disagreeing with him only about two species of gerygone that
|they called one. (Gell-Mann, The Quark and the Jaguar, Freeman, 1994, pp. 12-
|However all this establishes, if it is universally true, is that species
|break down the same to all people. Not to all the universe.
Ed Wilson reports in one of his books that when he tried the same test, also in PNG, about ants, he got two classes (big ones and little ones) for several scores of species. Autochthonous classification is based around the sorts of discriminations that culture makes for cultural reasons, but when they make them, the classifications tend to be natural.
See Scott Atran's "The cognitive foundations of natural history" c 1990 for the anthropology of local classifications. Atran makes the point that folk taxonomies tend to do very well locally but are not very extensible. This is true of Linneaus.
Hull once wrote, in one of those bon mots that one wishes one had kept a ref to, that no matter how absurd the case, there's an example of it in biology. Species are only *mostly* distinct, like the character in "The Princess Bride" who was only *mostly* dead. Sometimes they are members of "superspecies" - groups of persistently distinct but interfertile species. Sometimes they exchange genetic materielle without interbreeding as such. I have refs at home to claims that around 20% or even more of the typical mammalian genome is retrovirally introduced, although little of it is expressed as anything.
Date: Wed, 13 May 1998 08:03:51 -0600 (CST)
From: Ruth Strain
Hello; this is a response to the speciation conversation that is taking place - from an undergraduate, so my response may be a bit naive, but I've just studied such phenomonen and there are several means by which speciation can occur.
One is the virus infection which has been suggested.
Others include inversions and translocations in the chromosomes which result in rearrangement of genes and thus mutations. If members of species A should become separated geographically, for instance, and such mutations occur in each group independently, over time and many generations the situation could result such that no pairing could occur at meiosis - i.e. these two groups could no longer breed anymore and you would now have two new species, B and C.
The text used in the course I recently completed was An Introduction to Genetic Analysis, Sixth Edition, Contributing authors; A. Griffiths, J. Miller, D. Suzuki, R. Lewontin and W. Gelbart. It's an excellent resource for basic and advanced questions in genetics.
Date: 5/13/98 4:42 PM
From: Jim Brody
The "mutation problem" remains with crossover errors. You've got one offspring, the mutant, who has no one with whom to breed.
Geographic isolation ... certainly a likely factor in sexual selection (both behavioral and physical traits) but I suspect you get different looking and different acting critters that could still produce viable offspring (and fertile ones) if the gametes were put in a tube and mixed.
Implication is that there may be many many fewer species that estimated on the basis of external appearance.
Many of us assume that with sufficient divergence, you eventually get two creatures that CAN'T breed; that idea troubles me as glib and unlikely.
Thanks for the comment about viral mechanisms!
Date: Thu, 14 May 1998 09:39:53 +0100
From: Marie Haskell
Just why and how speciation occurs is extremely interesting. I recently heard of some research from the field of genetics which might be relevant, but which would only serve to show that, perhaps, something other than random mutations leading to populations drifting apart is occurring.
Maternal and paternal imprinting refers to the 'memory' that a gene has of which parent it came from. Thus, genes, or at least expression of the gene, may be switched on or off depending on which parent it came from. Examples have been found in which there is an 'arms race' in which paternal genes for pre-natal growth are being switched on, whereas maternally-derived gametes have these genes switched off in favour of genes favouring post-natal growth. Presumably so the mother isn't endangered by giving birth to large offspring.
The other place that this imprinting occurs (which is more relevant to this discussion!!) is that there is a kind of 'lock and key' system in which maternally derived genes are 'on' and paternally derived genes are 'off', which is being assumed to be a mechanism to prevent two gametes from the same parent fusing at conception. Further growth is apparently halted without the appropriate configuration.
I find this rather amazing, but how would a system like this evolve when both sexes have to have shifted in the appropriate direction at the same time? Strange! Also, although only a handful of imprinted genes have been found, they are all in mammals. <>