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Mimicry thread: Boyd comments on K. Johnson, Zimmer, Alexander
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----- Original Message -----
From: Brian Boyd (FOA ENG)
To: 'Vladimir Nabokov Forum'
Sent: Tuesday, September 03, 2002 8:35 PM
Subject: RE: mimicry thread
This thread is thickening into a rope, and sometimes twisting itself in knots. Let me untie one knot and throw a few loops.
Kurt Johnson's comments (September 3) should be a warning to us all; none of us, not even he, is an expert in mimicry. I know my own ignorance.
In his second paragraph Kurt responded to Dieter's September 1 posting,
O "To my knowledge there has not been a single instance so far proving that, yes, less perfect mimicry would afford just the same protection."
In picking up on this phrase Kurt may have overlooked what followed:
O "Predation usually does not happen in an atmosphere of leisure where a predator can quietly contemplate and appreciate the degree of perfection in his potential prey. He has to decide quickly whether he wants to risk taking a pick at a lep that is in movement and only partly visible to him. So even a very imperfect mimic might enjoy some protection, benefiting from a moment of doubt as to its palatability. This, however, does not exclude that a more perfect mimic might enjoy more protection."
In his mimicry section in A Guide to Nabokov's Butterflies and Moths 2001, a little masterpiece within a larger one, Dieter shows he is very aware of the advantages and commonness of imperfect mimicry.
Now for some loops around earlier contributions by Dieter Zimmer and Victoria Alexander:
First, Dieter, August 31 posting:
O Contrary to what most believe, however, [Nabokov] never went deep into mimicry as a scientific problem, citing very few actual cases and frankly inventing some to prove his point.
I am not sure of Dieter's evidence here, and suspect his claim relies on absence of evidence, which isn't evidence of absence. We would not have known that Nabokov knew Herodas if it weren't for three lines of ADA, or even that he knew Spenser, if it weren't for one word in the same novel, but if he had died before writing those books we would have been wrong to conclude therefore that he had never read either author.
The fact that Nabokov did not publish much on mimicry does not indicate that he didn't know a good deal about it (although of course there was simply a lot less to know about it in the late 1950s, when he last had regular access to an academic library, than has been discovered since). He had an intense and scholarly curiosity about the subject since he was a boy, and an almost eidetic memory.
As Dieter knows and notes in his Guide, Nabokov did write about mimicry in a 1942 talk, never published and now lost, and in the early 1950s leapt at the chance of writing a major book on mimicry, which he was prepared to spend three years on, and which he would no doubt have taken far longer on had he started (as he took far longer on the Eugene Onegin translation and commentaries than he first envisaged). But he had no occasion to focus on mimicry in his scientific papers, nearly all on Lycaenidae, where mimicry is not an issue (although he half-playfully considers Lycaenid wing-markings in terms of possible cryptic or pseudoaposematic functions in an unused note, Nabokov's Butterflies, 311), and he had little occasion to focus on the subject in his fiction. But he does focus on it in The Gift, in Speak, Memory, and in Ada, the three long works where lepidopterists feature (Fyodor and his father, VN himself, and Ada).
Apart from the well-known passages in The Gift and Speak, Memory that Dieter usefully musters in the Guide, 59-60, we should not forget two other important examples of his paying attention to mimicry OUTSIDE Lepidoptera: both in ADA, the fireflies of I.12 and the orchids of I.16. In the former case, Nabokov bases Van's fireflies on the fact that females of the genus Photuris mimic the signal flashes of the females of Photinus in order to attract and then devour Photinus males (ADA 71-72: "The males of the firefly, a small luminous beetle. . . . each flashed his pale-lemon light every five seconds or so, signaling in his own specific rhythm (quite different from that of an allied species, flying with Photinus ladorensis, according to Ada, at Lugano and Luga) to his grass-domiciled female pulsating in photic response after taking a couple of moments to verify the exact type of light code he used"). In the latter case, the lips of orchids of the genus Ophrys imitate the females of a particular insect species, and the males of the species, attempting to copulate with them, pollinate the flower with pollen from the flowers they have most recently attempted to pseudocopulate with.
Two comments on these cases: first, that they are outside Lepidoptera, one in the order Coleoptera, the other not only outside the subphylum Insecta but in a different Kingdom entirely, Plantae; and second, that Nabokov happens to mention these only because a) one of the narrators is a naturalist and b) sex and imitation are central topics in ADA. Both facts suggest Nabokov has a wide-ranging knowledge of mimicry that he rarely finds occasion to use.
Second, Victoria, September 2 posting:
O The question about mimetic forms concerns how they arise. Do they arise gradually, through natural selection? or do they arise suddenly, by chance?(and then, perhaps, get selected).
Problem 1:
Surely if mimetic forms arose by chance, in particular individuals, this would not explain how a particular mimetic pattern becomes established as a species-wide trait, which after all is the real explicandum. A particular mimetic pattern could not occur by CHANCE again and again in every member of the species. The problem is to explain how the pattern becomes established as a species trait.
O If mimetic forms arise suddenly by chance and are not shaped gradually by natural selection, then we will want to try to understand the mechanics behind the formation of these patterns and understand why they might be probable. The preferred approach to this question these days is through physics. The desire is to try to understand the laws of pattern formation. If computer simulations of reaction diffusion processes can produce "eye-spots" and viceroy-monarch patterns spontaneously (without the help of predators or natural selection) then there is no need to posit additional explanations (e.g. function) for the existence of these patterns.
Problem 2:
Patterns like eyespots and other circular or linear markings can clearly be generated by computer algorithms, but I would have thought that the mathematics of combinatorial explosion would make it unlikely that a particular COMBINATION of patterns would be coincident in otherwise unrelated species of, say, Lepidoptera, without the selective pressure of natural selection.
For this would require not just the existence of eyespots but the simultaneous presence of the same combination of colors (out of how many possible colors that can be discriminated? the human eye can discern millions, and bird color vision is usually superior to the human), and of patterns (out of how many possible patterns?), and of the positions of the pattern within, say, the wing (out of how many possible positions?), and of wing shape (out of how many different wing designs?), and of size (out of what range of wing sizes?). Do computer algorithms operate on five different dimensions at once, and produce patterns coinciding on all five dimensions?
Or to take the plant example Nabokov touches on. Orchids attract pollinators through form, size, color, patterning, texture and scent, six distinct dimensions. Many orchids, most notably those of the genus Ophrys, mimic the females of particular insect species whose males then pseudocopulate with them and in so doing pollinate the flower. It is not in an orchid's normal color range to produce a metallic sheen, yet Ophrys flowers do, thereby increasing the resemblance to the wing sheen of the female insect mimicked. Ophrys speculum, the "mirror-of-Venus blossom" Ada imitates, mimics the female of the wasp Camposcolia ciliata in form, color, size, in different aspects of its texture (the hairs on the labellum mimic the long hairs of the female wasp, the large hairless speculum mimics the smoothness of the wings), and its scent even contains a species-specific substance mimicking the sexual attractant of the female wasp. Do computer algorithms suggest that form, size, color, sheen, pattern, texture, and smell (out of millions of possible smells, to take this one dimension) can simultaneously converge by chance?
Problem 3:
If similarities of the order we find in mimicry could be explained largely by spontaneous pattern-formation, would we not expect there to be similarities, as marked and as frequent as those of accepted mimicry, linking random features of random species, species that are both phylogenetically and geographically unrelated? Does this in fact occur with anything like the same frequency as mimicry between species in the same geographical area and offering similar cues for predators or copulators?
If pattern were a sufficient explanation, would there not for instance be a tendency for orchids to mimic the patterns of insects (or other organisms: tortoises, toadstools) that are never pollinators, or that are never and have never been found in the area where the particular species of orchid grows? Does mimicry occur in such cases? I think not. And if not, the answer is surely because there is no selection pressure for variations to converge that way.
O Although it might be theoretically possible to observe the evolution of mimetic forms by observing predators and butterflies engaged in a feedback relationship for many generations, it is practically impossible. (A number of human cultures might rise and fall during the time necessary to observe these changes.) The only confirmed observations of adaptation that I know of are the studies on bacteria that I have already mentioned (they are sufficiently simple and replication times sufficiently rapid) and moth populations in England that adapted darker camouflage coloring in response to the soot-stained bark in certain industrial regions. (In my talk at St. Petersburg I explain why camouflage is fairly easy for natural selection to find, while a mimetic form is not. This was Nabokov's argument. That talk will be available online soon.) The numerous studies attempting to measure the abilities of predators to interpret shapes are, in my opinion, inconclusive. Some try to argue that predators are careless and might think any pair of spots are eye-like, thereby initiating the unlikely adaptation of owl's eye spots on butterfly wings; other studies try to argue that predators are especially keen and are only fooled by very eye-like spots, thereby fine tuning the mimetic representations of owl's eyes on butterfly wings. Since computer simulations have shown that "eye-spots" occur spontaneously and frequently without any kind of selection pressure, these studies become superfluous to understanding why "eye-spots" exist. Similar arguments can be made for the viceroy-monarch relation and even the dead leaf mimic.
As Kurt Johnson's September 3 posting suggests, there is a large literature detailing observational and experimental evidence for the advantages of particular mimetic, cryptic or aposematic forms.
O My argument agrees more or less with Dieter Zimmer's findings. The only significant differences lies in my lack of interest in the studies of predator/prey behaviors. I generally don't find field studies very reliable since they involve so much subjectivity on the part of the scientists and are also insufficient in terms of time scales. I much prefer the approach of theoretical biologists.
Problem 4:
If predator-prey relations play an insignificant part compared with spontaneous pattern formation, would we not expect to find that there are cases of elaborate visual mimicry where predators cannot see the pattern involved? For instance, in night-flying moths would there not be proportionately as many cases of elaborate mimicry of wing-patterns in the undersides of the wings (the upper sides of the wings of course are often camouflaged to escape detection while the moths rest by day) as there are on the wing patterns of day-flying butterflies, even though in butterflies predators can be duped by the result and in the case of night-flying moths predators like bats pay no attention to visual detail? Is this pattern of mimicry actually found? Or another example: each species of Lepidoptera has its own strikingly distinct genitalic apparatus in male and female, although these are minute and not readily visible. These are more conservative than wing-markings, but still very distinct from species to species (or they would not be the single characteristic taxonomists find most reliable in determining species). If the visual apparatus of predators played no significant part in shaping mimetic patterns, would not there be repeated cases of the elaborate genitalic armature of one species mimicking the armature of another unrelated species, even though the armatures can be seen clearly only under a microscope?
I find it odd that predator-prey relations, which are so crucial everywhere in nature, and shape even our own morphology, psychology and behavior, should be of no interest to a biologist, and that theoretical biology should be seen as independent of naturalistic observation and experiment, when biologists from Darwin to Hamilton have been distinguished theorists AND naturalists and experimenters. Field work and experiment may be painstaking and difficult to do right, but all forms of inquiry have their difficulties, including mathematical and computer modeling, yet all should be welcome insofar as they can throw light on a given problem.
----- Original Message -----
From: Brian Boyd (FOA ENG)
To: 'Vladimir Nabokov Forum'
Sent: Tuesday, September 03, 2002 8:35 PM
Subject: RE: mimicry thread
This thread is thickening into a rope, and sometimes twisting itself in knots. Let me untie one knot and throw a few loops.
Kurt Johnson's comments (September 3) should be a warning to us all; none of us, not even he, is an expert in mimicry. I know my own ignorance.
In his second paragraph Kurt responded to Dieter's September 1 posting,
O "To my knowledge there has not been a single instance so far proving that, yes, less perfect mimicry would afford just the same protection."
In picking up on this phrase Kurt may have overlooked what followed:
O "Predation usually does not happen in an atmosphere of leisure where a predator can quietly contemplate and appreciate the degree of perfection in his potential prey. He has to decide quickly whether he wants to risk taking a pick at a lep that is in movement and only partly visible to him. So even a very imperfect mimic might enjoy some protection, benefiting from a moment of doubt as to its palatability. This, however, does not exclude that a more perfect mimic might enjoy more protection."
In his mimicry section in A Guide to Nabokov's Butterflies and Moths 2001, a little masterpiece within a larger one, Dieter shows he is very aware of the advantages and commonness of imperfect mimicry.
Now for some loops around earlier contributions by Dieter Zimmer and Victoria Alexander:
First, Dieter, August 31 posting:
O Contrary to what most believe, however, [Nabokov] never went deep into mimicry as a scientific problem, citing very few actual cases and frankly inventing some to prove his point.
I am not sure of Dieter's evidence here, and suspect his claim relies on absence of evidence, which isn't evidence of absence. We would not have known that Nabokov knew Herodas if it weren't for three lines of ADA, or even that he knew Spenser, if it weren't for one word in the same novel, but if he had died before writing those books we would have been wrong to conclude therefore that he had never read either author.
The fact that Nabokov did not publish much on mimicry does not indicate that he didn't know a good deal about it (although of course there was simply a lot less to know about it in the late 1950s, when he last had regular access to an academic library, than has been discovered since). He had an intense and scholarly curiosity about the subject since he was a boy, and an almost eidetic memory.
As Dieter knows and notes in his Guide, Nabokov did write about mimicry in a 1942 talk, never published and now lost, and in the early 1950s leapt at the chance of writing a major book on mimicry, which he was prepared to spend three years on, and which he would no doubt have taken far longer on had he started (as he took far longer on the Eugene Onegin translation and commentaries than he first envisaged). But he had no occasion to focus on mimicry in his scientific papers, nearly all on Lycaenidae, where mimicry is not an issue (although he half-playfully considers Lycaenid wing-markings in terms of possible cryptic or pseudoaposematic functions in an unused note, Nabokov's Butterflies, 311), and he had little occasion to focus on the subject in his fiction. But he does focus on it in The Gift, in Speak, Memory, and in Ada, the three long works where lepidopterists feature (Fyodor and his father, VN himself, and Ada).
Apart from the well-known passages in The Gift and Speak, Memory that Dieter usefully musters in the Guide, 59-60, we should not forget two other important examples of his paying attention to mimicry OUTSIDE Lepidoptera: both in ADA, the fireflies of I.12 and the orchids of I.16. In the former case, Nabokov bases Van's fireflies on the fact that females of the genus Photuris mimic the signal flashes of the females of Photinus in order to attract and then devour Photinus males (ADA 71-72: "The males of the firefly, a small luminous beetle. . . . each flashed his pale-lemon light every five seconds or so, signaling in his own specific rhythm (quite different from that of an allied species, flying with Photinus ladorensis, according to Ada, at Lugano and Luga) to his grass-domiciled female pulsating in photic response after taking a couple of moments to verify the exact type of light code he used"). In the latter case, the lips of orchids of the genus Ophrys imitate the females of a particular insect species, and the males of the species, attempting to copulate with them, pollinate the flower with pollen from the flowers they have most recently attempted to pseudocopulate with.
Two comments on these cases: first, that they are outside Lepidoptera, one in the order Coleoptera, the other not only outside the subphylum Insecta but in a different Kingdom entirely, Plantae; and second, that Nabokov happens to mention these only because a) one of the narrators is a naturalist and b) sex and imitation are central topics in ADA. Both facts suggest Nabokov has a wide-ranging knowledge of mimicry that he rarely finds occasion to use.
Second, Victoria, September 2 posting:
O The question about mimetic forms concerns how they arise. Do they arise gradually, through natural selection? or do they arise suddenly, by chance?(and then, perhaps, get selected).
Problem 1:
Surely if mimetic forms arose by chance, in particular individuals, this would not explain how a particular mimetic pattern becomes established as a species-wide trait, which after all is the real explicandum. A particular mimetic pattern could not occur by CHANCE again and again in every member of the species. The problem is to explain how the pattern becomes established as a species trait.
O If mimetic forms arise suddenly by chance and are not shaped gradually by natural selection, then we will want to try to understand the mechanics behind the formation of these patterns and understand why they might be probable. The preferred approach to this question these days is through physics. The desire is to try to understand the laws of pattern formation. If computer simulations of reaction diffusion processes can produce "eye-spots" and viceroy-monarch patterns spontaneously (without the help of predators or natural selection) then there is no need to posit additional explanations (e.g. function) for the existence of these patterns.
Problem 2:
Patterns like eyespots and other circular or linear markings can clearly be generated by computer algorithms, but I would have thought that the mathematics of combinatorial explosion would make it unlikely that a particular COMBINATION of patterns would be coincident in otherwise unrelated species of, say, Lepidoptera, without the selective pressure of natural selection.
For this would require not just the existence of eyespots but the simultaneous presence of the same combination of colors (out of how many possible colors that can be discriminated? the human eye can discern millions, and bird color vision is usually superior to the human), and of patterns (out of how many possible patterns?), and of the positions of the pattern within, say, the wing (out of how many possible positions?), and of wing shape (out of how many different wing designs?), and of size (out of what range of wing sizes?). Do computer algorithms operate on five different dimensions at once, and produce patterns coinciding on all five dimensions?
Or to take the plant example Nabokov touches on. Orchids attract pollinators through form, size, color, patterning, texture and scent, six distinct dimensions. Many orchids, most notably those of the genus Ophrys, mimic the females of particular insect species whose males then pseudocopulate with them and in so doing pollinate the flower. It is not in an orchid's normal color range to produce a metallic sheen, yet Ophrys flowers do, thereby increasing the resemblance to the wing sheen of the female insect mimicked. Ophrys speculum, the "mirror-of-Venus blossom" Ada imitates, mimics the female of the wasp Camposcolia ciliata in form, color, size, in different aspects of its texture (the hairs on the labellum mimic the long hairs of the female wasp, the large hairless speculum mimics the smoothness of the wings), and its scent even contains a species-specific substance mimicking the sexual attractant of the female wasp. Do computer algorithms suggest that form, size, color, sheen, pattern, texture, and smell (out of millions of possible smells, to take this one dimension) can simultaneously converge by chance?
Problem 3:
If similarities of the order we find in mimicry could be explained largely by spontaneous pattern-formation, would we not expect there to be similarities, as marked and as frequent as those of accepted mimicry, linking random features of random species, species that are both phylogenetically and geographically unrelated? Does this in fact occur with anything like the same frequency as mimicry between species in the same geographical area and offering similar cues for predators or copulators?
If pattern were a sufficient explanation, would there not for instance be a tendency for orchids to mimic the patterns of insects (or other organisms: tortoises, toadstools) that are never pollinators, or that are never and have never been found in the area where the particular species of orchid grows? Does mimicry occur in such cases? I think not. And if not, the answer is surely because there is no selection pressure for variations to converge that way.
O Although it might be theoretically possible to observe the evolution of mimetic forms by observing predators and butterflies engaged in a feedback relationship for many generations, it is practically impossible. (A number of human cultures might rise and fall during the time necessary to observe these changes.) The only confirmed observations of adaptation that I know of are the studies on bacteria that I have already mentioned (they are sufficiently simple and replication times sufficiently rapid) and moth populations in England that adapted darker camouflage coloring in response to the soot-stained bark in certain industrial regions. (In my talk at St. Petersburg I explain why camouflage is fairly easy for natural selection to find, while a mimetic form is not. This was Nabokov's argument. That talk will be available online soon.) The numerous studies attempting to measure the abilities of predators to interpret shapes are, in my opinion, inconclusive. Some try to argue that predators are careless and might think any pair of spots are eye-like, thereby initiating the unlikely adaptation of owl's eye spots on butterfly wings; other studies try to argue that predators are especially keen and are only fooled by very eye-like spots, thereby fine tuning the mimetic representations of owl's eyes on butterfly wings. Since computer simulations have shown that "eye-spots" occur spontaneously and frequently without any kind of selection pressure, these studies become superfluous to understanding why "eye-spots" exist. Similar arguments can be made for the viceroy-monarch relation and even the dead leaf mimic.
As Kurt Johnson's September 3 posting suggests, there is a large literature detailing observational and experimental evidence for the advantages of particular mimetic, cryptic or aposematic forms.
O My argument agrees more or less with Dieter Zimmer's findings. The only significant differences lies in my lack of interest in the studies of predator/prey behaviors. I generally don't find field studies very reliable since they involve so much subjectivity on the part of the scientists and are also insufficient in terms of time scales. I much prefer the approach of theoretical biologists.
Problem 4:
If predator-prey relations play an insignificant part compared with spontaneous pattern formation, would we not expect to find that there are cases of elaborate visual mimicry where predators cannot see the pattern involved? For instance, in night-flying moths would there not be proportionately as many cases of elaborate mimicry of wing-patterns in the undersides of the wings (the upper sides of the wings of course are often camouflaged to escape detection while the moths rest by day) as there are on the wing patterns of day-flying butterflies, even though in butterflies predators can be duped by the result and in the case of night-flying moths predators like bats pay no attention to visual detail? Is this pattern of mimicry actually found? Or another example: each species of Lepidoptera has its own strikingly distinct genitalic apparatus in male and female, although these are minute and not readily visible. These are more conservative than wing-markings, but still very distinct from species to species (or they would not be the single characteristic taxonomists find most reliable in determining species). If the visual apparatus of predators played no significant part in shaping mimetic patterns, would not there be repeated cases of the elaborate genitalic armature of one species mimicking the armature of another unrelated species, even though the armatures can be seen clearly only under a microscope?
I find it odd that predator-prey relations, which are so crucial everywhere in nature, and shape even our own morphology, psychology and behavior, should be of no interest to a biologist, and that theoretical biology should be seen as independent of naturalistic observation and experiment, when biologists from Darwin to Hamilton have been distinguished theorists AND naturalists and experimenters. Field work and experiment may be painstaking and difficult to do right, but all forms of inquiry have their difficulties, including mathematical and computer modeling, yet all should be welcome insofar as they can throw light on a given problem.