A question about evolution

Seeing as you are starting within one species to begin with why do you think interbreeding would necessarily produce new species?That is not what the theory of evolution says. It is only when the two sub-species mix and then fail to interbreed that speciation has occurred.Enjoy.

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The storm is a straw man in the question as posed. Break it down into three parts (1) Before migration, population is 100% aa, (2) After migration and before storm, population is 90% aa and 10% bb, (3) After migration AND after storm, population is 90% aa and 10% bb.The migration did change the frequency of alleles -- IN the specific population in question. However both populations existed before: thus in a larger context evolution did NOT occur. The population can only be said to change if there were no continued communication between populations in the specific area and other surrounding ones.The storm did not change the frequency of alleles in the specific population in question.If there had been a change then natural selection in favor of one allele over the other would have occurred - and then it would qualify as well. In the larger context it isn't. Only when movement is generally prevented or restricted can it influence specific populations. This is where population dynamics come into play - when populations choose not to intermix due to a number of factors.I agree with Crash that the "original population" must be a species definition population for the question to make any sense, in which case no evolution occurred, there was just a movement within the total population of where the aa and bb alleles occurred, not a change in proportions.If we are talking about a variety population then the answer is still no, because there was no change within the aa variety population or the bb variety population, other than loss in numbers due to the storm - there was no interbreeding within the context of the question.I'd be interested in what your professor says to these criticisms.Enjoy.

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Speciation has been observed, so obviously changes can occur on the species level.Whether they are rare or not is immaterial as long as they exist, as natural selection will filter the results.Natural selection is the driving element of change, mutation just provides the resources for natural selection to act on.

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Sure. But when something comes in from "out of the frame", as it were, that should not confuse us into thinking that evolution is happening just because somebody walked into the room. If they're not part of the same reproductive community, then by definition, it's two different species.I don't mean to imply that it's always cut-and-dry whether or not two individuals are in the same reproductive community. How this is tested, practically, is a large area of debate among biologists. Because that could be what's going on here. This could be two seperate species.You're not an ant, yes. You'll never be in the ant species. The reason for this is not because you lack the "ant essence", it's because you'll never be part of a reproductive community of ants.You don't, obviously, join the community just because you're near an anthill. You don't join any other communities just by physical proximity either. You have to be part of the reproductive community. That is to say, mating with members of that community. Until you're mating in it, your claim to be part of it is tenuous. We might give you a bogey on it in a practical situation. As a human being we might assume you're going to be mating with humans sometime in the future.It's not stipulated that these are the same species. It's not stipulated that they aren't but I find that a tenuous basis to go off assuming a massive introduction of new alleles into a population. They're called "airplanes." There's nowhere in the world you can go where you aren't part of that reproductive community. I don't see that there are any evolutionarily-relevant populations that don't include you in an age of easy intercontinental travel. And I think that would be pedantic and dumb. If I lost points on such a question because I wasn't willing to be pedantic, I'd certainly argue it with the prof. (During office hours.) Welcome to biology, I guess. Things are fuzzy. Species boundaries cannot be rigidly drawn. In a real sense, there may not even be species or reproductive communities. In a sense, there is just the individual and the environment, and they interact.I think it can be argued either way and I think you've done a great job advancing your position. I think there's basically no wrong answer to this question because it's framed so poorly. I'd like to know what the person who wrote it thought the right answer was.

I'm reading a book, an old book - "The Forest and The Sea" by Marston Bates (Random House 1960) - and in it he describes his early research into malaria and mosquito's (although the book is more generally about ecology in layman terms). He does this to exemplify the problems with the concept of species (starting on page 133 near the bottom):

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One case that I worked on for several years involved a group of anopheline mosquitos of southern Europe. The chief vector of malaria in that region was thought to be a mosquito called Anopheles maculipennis. Wherever there was malaria, this mosquito was found. But in some places where the mosquito was extremely abundant, there was no malaria, which led to intensive study of this phenomenon of "anophelism without malaria."

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It was early thought that there might be two "biological races" of the mosquito: one, for some reason, capable of transmitting malaria, and the other not, and a search was started for means by which these "races" might be recognized. It was presently discovered that, even though the mosquitos looked the same everywhere, different "varieties" could be destinguished by microscopic examination of the pattern of spots on the eggs. By breeding mosquitos of known egg type in the laboratory, it was possible to make comparative studies of different aspects of their behavior.
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It turned out that the mosquito "species," Anopheles maculipennis, realy consisted of seven independent populations which differed from each other in many fundamental respects - but which happened to look alike as adult mosquitoes. The different populations had different biting habits - only those kinds that liked to bite man could transmit malaria.
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These mosquitoes differed from each other in all sorts of ways. The larvae had different habitats: two of the populations were found mostly near the coast, where the larvae lived in brackish water. Another was found only in the vicinitiy of inland marshes, or breeding in thick reeds of lake margins. Another preferred to breed in small ponds and stagnant ditches.

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But most strikingly, each had characteristic mating habits. ... In nature, sexually excited male mosquitoes gather in dancing swarms, to which females are attracted. ... In short, each of these mosquito populations had a different kind of sexual behavior, which would keep them from cross-mating in nature. ... Each of these kinds of mosquitoes was a reproductively isolated population, a species. ... The adults all looked alike to an entomologist, but the mosquitoes could tell each other apart easily enough - and this, from the biological point of view, was the important thing.

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Thus there were seven populations with distinct alleles - aa, bb, cc, dd, ee, ff and gg - and their overlapping in areas did not constitute evolution by changing the proportions of alleles in the "original" population.They had already speciated.Enjoy.Edited by RAZD, : typo

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General reply:
1) It is reasonably to assume that they are the same species (they can interbreed).2) It is reasonable to assume that a and b are different alleles of the same gene (If you were wondering).*As this is a hypothetical question there is no reason to argue over these points (they are arbitrary).*As stated in the OP this is a question in ecology, and when studying ecology you cannot take into account the whole population of the species - you must restrict yourself to researching a certain population (meaning "population" is also arbitrary).
Population (as my professor defines it): All of the creatures that can potentially interbreed and give fertile offspring, but...
1) Not all of the individuals breed in practice ( this also describes me).
2) They must be together for awhile (geographic isolation --> different populations).
BTW: How would you define a population that "breeds" asexually.Reply to RAZD: The definition of population resolves this - so by this definition evolution did occur. Forget the storm - It was just an obvious diversion for those students who didn't do their homework. I always do my homework . I have a lecture Sunday, I'll ask him.(BTW: thank you for your responses Crash, RAZD, NJ, Jar, CS, Phalanx, Modulous)

I have two problems with this: (1) is that, as presented the bb population just got there and had not had time to interbreed -- therefore "for awhile" does not readily apply, they weren't there long enough, and (2) the bb population could just as easily be a migratory variation to a non-migratory aa population -- they could pass through every year on their migratory route, but still never interbreed because they aren't there during breeding season, whether they could "potentially interbreed and give fertile offspring" or not.There are behavior barriers to mating that prevent interbreeding even if it is possible. The best example of this is the "ring species" the asian greenish warbler:Greenish warblers

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Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow. By studying geographic variation in the ring of populations, we can study how speciation has occurred. This unusual situation has been termed a 'circular overlap' or 'ring species'.

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Each variation breeds with the neighboring one except at the northern overlap in Siberia where the viridanus and plumbeitarsus varieties ignore each other.

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It is relatively easy to hear the song differences in the field, and playback experiments have shown that the birds distinguish between types of songs. A male greenish warbler will aggressively respond to songs that it recognizes as belonging to its own species, intending to chase an intruding male out of its territory, but it usually will not respond to song from a distantly related population. Females probably also use the song differences to distinguish among potential mates.

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Different behavior affecting breeding.The alleles in the area of overlap between viridanus and plumbeitarsus are in different proportions than in the rest of the habitat for each subspecies , but they are not interbreeding so it doesn't matter. Agreed. BUT if one variety had survived more than the other then it would have been natural selection changing the frequency of alleles in the combined population (if we agree that they now make one population, otherwise it is just survival preference for one population over another). A very good question.What makes a sexually breeding population 'special' is the population dynamics of gene flow between individuals within a species. This can act to hold a species in stasis where it is adequately adapted to its habitat to survive, as sexual pressure can tend to direct the population as a whole towards an average.In asexual populations the gene flow is only in one direction, and as each individual organism picks up mutations those will only be passed to their offspring. It very well could be that what we see as single cell "species" are the remains when interconnecting variations have been removed by natural selection.Genetics can measure the DNA and see how closely related populations are, behavioral and ecological studies can show how they have same reactions to chemicals and habitat, but this may only be an artifact of removal of intermediates to other single cell species.Certainly such populations are isolated from other similar ones -- in many cases (but not all).I did a google and found:(1) http://members.aol.com/darwinpage/mayrspecies.htm

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There are a number of suggestions of how species taxa in asexual organisms can be delimited and defined, but this is outside the present discussion. However, I find that any endeavor to propose a species definition that is equally applicable to both sexually reproducing and asexual populations misses the basic characteristics of the biological species definition (the protection of harmonious gene pools).

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He also talks about other definitions of species that are more historical, but which would have been in effect when asexual species were first type cast.(2) Observed Instances of Speciation

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4.2 Cases Where the Biological Species Concept Does Not Apply

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There is no unambiguous criterion for determining that a speciation event has occurred in those cases where the BSC does not apply. This is especially true for obligately asexual organisms. Usually phenetic (e.g. phenotypic and genetic) differences between populations are used to justify a claim of speciation. A few caveats are germane to this. It is not obvious how much change is necessary to claim that a population has speciated. In my humble opinion, the difference between the "new species" and its "ancestor" should be at least as great as the differences among recognized species in the group (i.e. genus, family) involved. The investigator should show that the change is persistent. Finally, many organisms have life cycles/life histories that involve alternative morphologies and/or an ability to adjust their phenotypes in response to short term changes in ecological conditions. The investigator should be sure to rule these things out before claiming that a phenetic change constitutes a speciation event.

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That seems fairly reasonable. This would be the same kind of difference that is used in paleontology to seperate fossils into different species over time when there is no way to see if {organism 1 million years ago} can breed with {organism 5 million years ago}.(3) http://www.msu.edu/course/plb/418/speciesconcepts.htm

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Diagnosability Species Concept

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The smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals.

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Genealogical Species Concept

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Species are defined by basal exclusivity; individuals of a species are more closely related to one another than to any individuals outside the group.

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Reasons there is little agreement on species concepts

• Variation is complex
• Breeding systems are variable
• Levels of gene flow is variable
• Speciation is ongoing so all stage are present in the environment
• Relative to the number of species in the environment we know too little to generalize

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This is the only one they list for asexual (they also list BSC - biological species concept - and some others)(4) Birky Lab Home

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Theory and some experimental evidence suggests that the loss of sexual reproduction should reduce the effectiveness natural selection. Asexual lineages should accumulate detrimental mutations, leading to extinction. They should also have difficulty retaining and fixing advantageous mutations, which would make it difficult to adapt to new environments and speciate. In fact the definition of species in asexual organisms is controversial, since the "biological" species definition cannot be applied. We are studying the long-term consequences of the loss of asexual reproduction, and the preliminary results are exciting! The bdelloid rotifers are a widespread group of freshwater invertebrates which have been reproducing asexually for at least 40 million years and undergone substantial differentiation into species differing in morphology, habitat, and behavior.

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we used basic population genetic theory to show that asexual organisms, like sexual organisms, should fall into clusters representing independently evolving lineages. We devised a new species concept, the Evolutionary Genetic Species Concept, for asexuals which describes clusters that are comparable to biological species in sexual organisms. We also devised a species criterion, the 4-time rule, that can be used to identify such asexual species from DNA sequences of small samples.

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Asexual organisms are also not constrained by the population gene sharing of sexual species so they can have more variation within a population and the only thing holding that in check is survival of those individuals.From these it looks like asexual species are populations of organisms with similar characteristics that have become isolated by natural selection and time.This is more of an "amoeba" in time description that what remains after selection over time is a species...That's the best I've got at this time.Enjoy.

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I agree. I don’t think that the ”walking into the room’ situation (I hope we’re both on the same page with that) constitutes actual evolution but it seems to me that according to the bare bones definition of evolution, that the ”walking into the room’ situation might count as evolution, by definition. I guess my point is that the boiled down definition of evolution is too simple because it can include situations where non-evolution can be included. Sort of the same way that the boiled down definition of species gets into problems. Wouldn’t that be different populations? Aren’t there species that have different populations that are different reproductive communities but are still the same species? understood WRT the question in the OP, the two populations of birds are assumed to be the same species though. You mean like your claim that I’m part of the Australian airport population just because I could fly over there and mate if I wanted to. But its easy for you to consider these populations of birds as evolutionarily-irrelevent. What’s the distinction? The ease of interaction? The one bird population flew to and joined the other. busted . but there is a point.It exemplifies the problems with the definition of ”species’ ”population’ and ”evolution’ and how confusion and misunderstanding are easily evoked. I’m honestly trying to better understand how I should, um, understand the meanings of these words. It seems that the stripped down definitions that I currently accept have some problems. Sure, me too. And the argument you’ve presented in this thread would certainly have convinced me to reimburse you those points if I was the prof.The question, itself, has its own problems. I already took biology. One of the issues I have, I guess, is that sometimes things are presented as ”rigidly drawn’ and well defined, but when we apply some of the definitions to real life scenarios, the fuzziness is brought out. I don’t think biology classes admit enough that they don’t have all the answers and that some things are still pretty fuzzy. Awe, thanks for the compliment. Yes, it was and I hope kalimero posts the prof response and explanation of the question.Thanks for the discussion so far, I feel like I getting a better understanding

Well, I agree with you. But I'm sure you know what the problem is. The universe is continuous; our words are discreet. For instance we might say "hot" and "cold" are temperatures, but actual temperatures can be anywhere in between hot and cold. So we get more precise - we say "degrees Celsius." But you can have a temperature between 91 and 92 degrees. So we say we can have decimal degrees. But between any two points on the thermometer, you can have an intermediate temperature.We apply discreet labels, like "species" or "evolution", to phenomena in the universe that vary continuously and in infinite directions. It's no surprise at all that we should find phenomena that meet dictionary definitions of our words, but that we intuit aren't actually examples of what we were trying to describe in the first place. Well... it depends on what you mean by "reproductive community."Sorry. That wasn't made explicit in the OP, but it has been since, so I'll consider it stipulated that all these birds are conspecifics. I agree. Part of the problem is that the creation/evolution debate is always kind of in the background, biology instructors know that a fair number of their students are sitting there looking for an opening that looks like a failing of biology or any kind of hand-waving, and so they portray a certainty or a rigidity that isn't really supported by the facts. Another part of the problem is that no expert wants to look like there's something major he doesn't know. How much respect could biology unjustly lose because it looks like we all have our heads up our asses and we don't even know what a species is?I mean, everybody thinks they know what a species is, if you ask them, they'll even give examples. "Squirrels." "Dogs". etc. To the layperson, "species" simply means "all the organisms of the same type." But the dirty little secret (and the reason creationism is wrong) is that organisms aren't typed. They don't come with serial numbers that tell you what species they're an individual of. It's not stamped on their fur or under a leaf. It's not even encoded in their genetics.We just have to guess what species they are, based on what other organisms they're similar to. "Similar" could mean many things - similar in shape, color, or other physical characters, or similar in terms of their genetics. Similar in form gets tricky when you realize that individuals vary in form. Males are different than females, but in the same species. (Of course, what's a "male"? What's a "female"? Sometimes that means different things for different organisms.)There's an exception to every rule, and exceptions to the exceptions. Things in the natural world mostly make sense, but there's no framework you can develop where an organism hasn't evolved that doesn't fit neatly inside it.But it wouldn't be any fun, otherwise!Edited by crashfrog, : No reason given.Edited by crashfrog, : No reason given.

I had a class on Tuesday were I though I would ask the tutor about thisquestion, but... when I got to class I realized that I couldn't think ofany specific question to ask, on Sunday I will ask the prof. (Dr.), soif you could give me ideas as to how to approach this... I'll post onSunday (promise).

any word from the prof?

I still don't have a question to ask him.
I have a class on Sunday again, maybe you can suggest a specific question?

Oh, I thought there was some question in this thread that you were gonna ask him. I didn't see it at quick glance.Maybe you could print out the thread and let him read it. There were a couple arguments made as to why this does NOT count as evolution that might interest him. Or at least print out just the arguments against his 'yes' answer to the quetion.

This tread is too long. I need a specific question to ask.

See Message 37Do the temporarily temporally coincident groups with aa and bb genes really constitute a "population" if

• the bb population just got there and had not had time to breed with the aa population -- "for awhile" does not readily apply if they weren't there long enough to breed,
• the bb population is a migratory variation to a non-migratory aa population -- they pass through every year on their migratory route, but never interbreed because they aren't there during breeding season,
• there have behavior barriers to mating that prevent interbreeding even if it is possible.

The best example of this last situation is the "ring species" the asian greenish warbler: the two end species do not interbreed even thought they share a habitat and breed with other varieties that complete a ring of breeding.
Greenish warblers

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