У меня такое чувство. что словесные аргументы уже высказаны, от повторения не будет большого смысла. Мне кажется. ваша гипотеза может быть проверена - по косвенным свидетельствам. 1) существуют реконструкции массовых пород в лесах разных эпох. Можно представить себе реконструкцию запахов. Хвойные пахнут падалью7 в самом деле? Это можно установить. Никакого другого метода, чем метод актуализма - заключения от того. что известно. к тому. что не известно. у нас нет. И минимизация необоснованных догадок. Может в п.1 получить запах лесов до появления покрытосеменных. 2) можно восстановить энтомофауну к моменту появления покрытосеменных. то есть это уже сделано. я имею в виду - просто найти работы и прочитать, какие отряды, в каком обилии. И по современным представителям 9а насекомые с точностью до отряда сейчас примерно те же) - понять. так кто же там был и как себя вел и опылял или ел. Например, этот п.2 позволит проверить высказанную Вами добавочную гипотезу - что растения могли бы привлекать еще и тех, кто на падаль, раз уж все равно. какой запах выбрать. Там можно проверить и понять. осмыслено ли такое поведение. 3) совсем по ващшей части - тут я ничего сделать не могу. Разобрать химию производства всех этих ароматических эфиров в цветах - и посмотреть. из чего они получаются, на что увязаны, сравнить со стадиями эволюции растительности и попытаться понять, насколько древние это запахи. например. посмотрев разнообразие запахов на разнообразие растений, примитивных и продвинутых. грубо говоря - как пахнет магнолия, как - осока. Думаю, по результатам таких проверок доказано ничего не будет - но зато будут отсеяны некоторые гипотезы.
I talked to a molecular biologist friend over lunch and he suggested an explanation that makes a lot of sense to me. Let me try it on you. All flowers cannot be carrion flowers. Why?
Because carrion is scarce in nature and finding carrion by an insect requires extreme sensitivity to carrion smells. If all flowers start to smell like carrion, carrion insects will not be able to find carrion and so become extinct. Without such pollinators, there is no point in smelling like carrion. So the majority of flowers cannot smell like carrion. It is simple ecology.
This addresses one of your points. Doubling on carrion insects benefits a plant only if few other flowering plants pursue the same strategy, so an insect mistakes a flower for carrion. Having the specific smell signal, by contrast, makes it possible for a flower to co-exist with a lot of other flowers. It is the adaptation selected by long-term advantage for angiosperms as a class rather than any individual plant. The cheaters cannot occupy a large niche. The straight players can, and so they prevail.
This sounds right to me. This does not quite explain chosing the fruty smell as a signal to pollinators, but at least it answers the original question: why the carrion flowers are so infrequent. It also explains why my idea about excrement origin of fruity smell is likely to be incorrect. It could have worked only when angisperms were beginning to colonize the planet. The advantage is too short lived. The smell signal cannot be generic.
Если честно, мне это объяснение совершенно не нравится. Но я понимаю, что оно модное. На мой взгляд - это довольно пустое умствование, которое может быть и верным. и неверным - на самом деле может быть и так, и эдак. Примерная причина такой моей реакции: дело заключается во взаимодействии множества факторов; объяснение пытается сделать ситуацию простой, не обращая внимания на массу специфических эффектов, которые есть и которые могли бы быть. То есть это объяснение, на мой взгляд, обладает исключительно риторической убедительностью - тем, кто любит аргументы такого сорта, оно кажется пригодным. но - как понятно - риторика не лучший способ убедить естественника. Для меня аргументами будут те, что я пытался назвать - указание на группы, которые тогда ели пыльцу голосеменных и покрытосеменных (предположим. жуки и скорпионницы). наличие среди них форм. которые питаются падалью. Выяснение, что за падаль, как находят - по современных формам. Реконструкция следствий и проверка на имеющемся материале цветков. Вот из чего-то такого вырастет эволюционный сценарий, который будет мне казаться убедительным - пока не появится другой сценарий, опирающийся на иные факты.
OK, another friend pointed me to a paper http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2010.01451.x/full on comparative analysis of floral scents in angio- and gymno- sperms and insects. It a lot like a crossover between mine and your ideas. The fruity smell (monoterpenes) has already been produced by gymnosperms while benzenoids are produced by insect and non-insect arthropods; insect herbivores & their gymnosperm hosts share a lot of scent molecules with both groups of plants. It sounds like I reinvented bicycle: the question has been asked before and the dilemma has been also recognized before. There are a lot of overlap between floral and insects scents, so it seems that either plants mimicked insect smells to attract pollinators or the herbivorous insects used the scent molecules from plants to their own ends and were recruted by plants through this dependence. I was right (there were preexisting sources of flowery/fruity smells) but you were also right (the origin of the scents is through the gymnosperms and the herbivores living on them). The dung idea IS excessive because I was wrong: the gymnosperms do produce a fraction of the floral scents produced by the angiosperms. The correct answer might be the fusion of the two lines of thought. Here is the conclusion:
Two evolutionary scenarios may account for the patterns of associations between floral and insects aromatics, namely coevolution and one-sided evolution. Coevolution between pollinators and flowers makes the assumption that (1) ‘floral’ compounds have primarily evolved in pollinators, and (2) scent production in plants and pollinators evolved at approximately the same time. However, none of the compounds was produced exclusively by pollinator groups. Additionally, the insects’ use of ‘floral’ aromatics precedes the evolution of flowers, because aromatics are widespread in both early (e.g. Hemiptera) and late (e.g. Lepidoptera) diverging insect orders. Some floral aromatics are even used in non-insect arthropods.
As an alternative, one-sided evolution predicts that one partner has evolved similarities to a pre-existing pattern in the other partner. One-sided evolution can principally occur in insects and plants, however a scenario where insects evolve onto patterns of plants seems unlikely as it assumes, similar to coevolution, that ‘floral’ VOCs have evolved primarily in pollinator insects, which is not supported by my dataset. In the reverse scenario, floral signals evolved to match pre-existing sensory signals of their pollinators during the relatively recent radiation of angiosperms. This ‘pre-existing bias’ hypothesis thus assumes that (1) floral scent is associated with insect volatiles in both pollinator and non-pollinator groups, since their commonness should not be influenced by an association with flowers, and (2) insect volatiles should be evolutionarily older than floral scent. In support of the pre-existing bias hypothesis, floral aromatics were correlated with aromatics from pollinators and herbivores and marginally correlated with insects with no association to plants. Additionally, ‘floral’ aromatics appear to have originated in arthropods well before the angiosperm radiation.
Pre-existing bias may be an important selective force for the evolution of mutualisms. Invoking pre-existing bias as the driver of floral scent evolution suggests that plants exploited sensory or neuronal preferences of their pollinators outside the context of sexual selection by mimicking volatiles with established receptors and perceptual preferences. In a mutualistic relationship, the operators (in this case, the pollinators) are selected to respond to a mimetic signal, even if it is not identical to the model. Therefore, this scenario does not predict an exact one-to-one match between insect and floral volatile chemistry. Instead, it suggests a loose overlap with floral scents that contain both insect-like and plant-specific components. This pattern is prevalent in floral bouquets.
Let's leave it here. I thinik I've learned my lesson for now. I do think I understand the problem better. That we have floral scents is the result of convergence of the two interdependent biochemistries that were mimicking and exploiting each other from the time immemorial. It started long before the angisperms evolved or their pollinators evolved. That we would enjoy the smell of flowers had been decided when the first arthropods started to graze on the first land plants, which started this collision course.
спасибо, очень интересные данные. Я когда-то давно читал нечто специальное по коэволюции антофилии и энтомофилии, но давно уже не видел современных работ. Интересно посмотреть, до чего добрались. Очень признателен.
Мне кажется, Вы не учитываете упескаете тот момент, что подавляющее число видов покрытосеменных вообще не пахнут, ибо в опылителях не нуждаются. Ни злакам, ни осокам они не нужны. Да и многие цветковые растения утратили нужду в опылителях.
Еще дополнительно отмечу, что многие нектароносы пахнут привлекательно только для насекомых (тех что опыляют и ароматные цветки), но не для нашего носа. Например анигозантос - рекордсмен по выделению нектара, пахнет довольно неприятно. Так что здесь наши настройки не всегда совпадают с настройками насекомых...
да, конечно, ветроопыляемых огромное море. Причем злаки и осоки - как я понимаю, это и есть та фоновая "трава", которой покрываются степи и остепненные учстки, то есть те ла,ншафты, где вервые травы появились в значимом количестве.
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I talked to a molecular biologist friend over lunch and he suggested an explanation that makes a lot of sense to me. Let me try it on you. All flowers cannot be carrion flowers. Why?
Because carrion is scarce in nature and finding carrion by an insect requires extreme sensitivity to carrion smells. If all flowers start to smell like carrion, carrion insects will not be able to find carrion and so become extinct. Without such pollinators, there is no point in smelling like carrion. So the majority of flowers cannot smell like carrion. It is simple ecology.
This addresses one of your points. Doubling on carrion insects benefits a plant only if few other flowering plants pursue the same strategy, so an insect mistakes a flower for carrion. Having the specific smell signal, by contrast, makes it possible for a flower to co-exist with a lot of other flowers. It is the adaptation selected by long-term advantage for angiosperms as a class rather than any individual plant. The cheaters cannot occupy a large niche. The straight players can, and so they prevail.
This sounds right to me. This does not quite explain chosing the fruty smell as a signal to pollinators, but at least it answers the original question: why the carrion flowers are so infrequent. It also explains why my idea about excrement origin of fruity smell is likely to be incorrect. It could have worked only when angisperms were beginning to colonize the planet. The advantage is too short lived. The smell signal cannot be generic.
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http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2010.01451.x/full
on comparative analysis of floral scents in angio- and gymno- sperms and insects. It a lot like a crossover between mine and your ideas. The fruity smell (monoterpenes) has already been produced by gymnosperms while benzenoids are produced by insect and non-insect arthropods; insect herbivores & their gymnosperm hosts share a lot of scent molecules with both groups of plants. It sounds like I reinvented bicycle: the question has been asked before and the dilemma has been also recognized before. There are a lot of overlap between floral and insects scents, so it seems that either plants mimicked insect smells to attract pollinators or the herbivorous insects used the scent molecules from plants to their own ends and were recruted by plants through this dependence. I was right (there were preexisting sources of flowery/fruity smells) but you were also right (the origin of the scents is through the gymnosperms and the herbivores living on them). The dung idea IS excessive because I was wrong: the gymnosperms do produce a fraction of the floral scents produced by the angiosperms. The correct answer might be the fusion of the two lines of thought. Here is the conclusion:
Two evolutionary scenarios may account for the patterns of associations between floral and insects aromatics, namely coevolution and one-sided evolution. Coevolution between pollinators and flowers makes the assumption that (1) ‘floral’ compounds have primarily evolved in pollinators, and (2) scent production in plants and pollinators evolved at approximately the same time. However, none of the compounds was produced exclusively by pollinator groups. Additionally, the insects’ use of ‘floral’ aromatics precedes the evolution of flowers, because aromatics are widespread in both early (e.g. Hemiptera) and late (e.g. Lepidoptera) diverging insect orders. Some floral aromatics are even used in non-insect arthropods.
As an alternative, one-sided evolution predicts that one partner has evolved similarities to a pre-existing pattern in the other partner. One-sided evolution can principally occur in insects and plants, however a scenario where insects evolve onto patterns of plants seems unlikely as it assumes, similar to coevolution, that ‘floral’ VOCs have evolved primarily in pollinator insects, which is not supported by my dataset. In the reverse scenario, floral signals evolved to match pre-existing sensory signals of their pollinators during the relatively recent radiation of angiosperms. This ‘pre-existing bias’ hypothesis thus assumes that (1) floral scent is associated with insect volatiles in both pollinator and non-pollinator groups, since their commonness should not be influenced by an association with flowers, and (2) insect volatiles should be evolutionarily older than floral scent. In support of the pre-existing bias hypothesis, floral aromatics were correlated with aromatics from pollinators and herbivores and marginally correlated with insects with no association to plants. Additionally, ‘floral’ aromatics appear to have originated in arthropods well before the angiosperm radiation.
Pre-existing bias may be an important selective force for the evolution of mutualisms. Invoking pre-existing bias as the driver of floral scent evolution suggests that plants exploited sensory or neuronal preferences of their pollinators outside the context of sexual selection by mimicking volatiles with established receptors and perceptual preferences. In a mutualistic relationship, the operators (in this case, the pollinators) are selected to respond to a mimetic signal, even if it is not identical to the model. Therefore, this scenario does not predict an exact one-to-one match between insect and floral volatile chemistry. Instead, it suggests a loose overlap with floral scents that contain both insect-like and plant-specific components. This pattern is prevalent in floral bouquets.
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Let's leave it here. I thinik I've learned my lesson for now. I do think I understand the problem better. That we have floral scents is the result of convergence of the two interdependent biochemistries that were mimicking and exploiting each other from the time immemorial. It started long before the angisperms evolved or their pollinators evolved. That we would enjoy the smell of flowers had been decided when the first arthropods started to graze on the first land plants, which started this collision course.
Thank you for this lesson.
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Еще дополнительно отмечу, что многие нектароносы пахнут привлекательно только для насекомых (тех что опыляют и ароматные цветки), но не для нашего носа. Например анигозантос - рекордсмен по выделению нектара, пахнет довольно неприятно. Так что здесь наши настройки не всегда совпадают с настройками насекомых...
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