A cyanide-producing Austroperla cyrene sits at the top of this picture, with a mimicking Zelandoperla fenestrata in the center and non-mimicking Zelandoperla fenestrata at the bottom.
Credit: University of Otago
I've written before about Batesian mimicry as an example of environment-driven evolution and how it depends on an evolutionary arms race - which makes no sense as the work of a single creator god, as creationists believe is responsible for the 'design' of all living organisms.
Batesian mimicryHowever, Batesian mimicry is not always the advantage it would appear at first sight to be. For example, across the range of the mimic species, the 'model' species population may vary and in some places be absent. In that case, there is no benefit in mimicry, and it may even make the mimic species more conspicuous (after all, in the 'model' species, being conspicuous was part of the strategy) whereas cryptic camouflage would have been a better evolutionary strategy.
Batesian mimicry is a fascinating concept in evolutionary biology named after the English naturalist Henry Walter Bates. It refers to a form of mimicry in which a harmless species closely resembles the appearance of a toxic or dangerous species to deceive predators. This phenomenon is commonly observed in the animal kingdom, particularly among insects, although it can also occur in other groups of organisms.
The key components of Batesian mimicry are:The mimicry is successful when predators mistake the harmless mimic for the dangerous model, and as a result, they avoid attacking it, providing a selective advantage to the mimic population.
- Model Species: The toxic or harmful species that possesses some form of defense mechanism, such as toxicity, stinging, or bad taste. Predators learn to associate the distinct appearance of this model species with the negative consequences of attacking or consuming it.
- Mimic Species: The harmless species that evolves to resemble the model species in appearance. Mimic species benefit from this resemblance by gaining protection from predators who have learned to avoid the model species due to its defenses.
One of the classic examples of Batesian mimicry is the relationship between the Monarch butterfly (Danaus plexippus) and the Viceroy butterfly (Limenitis Archippus) in North America. The Monarch butterfly is toxic to predators because it accumulates toxins from the milkweed plant it feeds on during its larval stage. The Viceroy, on the other hand, is harmless, but it has evolved to resemble the Monarch's bright orange and black pattern. As a result of this mimicry, predators associate the Viceroy's appearance with the Monarch's toxicity and tend to avoid attacking it.
[In fact, this has been disputed as an example of Batesian mimicry because the Viceroy butterfly is at least as distasteful as the Monarch butterfly and is thus an example of Müllerian mimicry – see reference 2 below]
Batesian mimicry plays a crucial role in natural selection and the evolution of species. It demonstrates how adaptations to the environment can shape the survival and reproductive success of organisms. Harmless species that resemble toxic species are more likely to survive and reproduce because they face less predation pressure. Over time, the mimicry becomes more refined as natural selection favors individuals with the most accurate resemblance to the model species.
References:
- Bates HW. (1862). Contributions to an insect fauna of the Amazon Valley. Lepidoptera: Heliconidae. Transactions of the Linnean Society of London, 23(3), 495-566.
- Ritland, D. B., & Brower, L. P. (1991). The viceroy butterfly is not a batesian mimic. Nature, 350(6317), 497-498.
- Ruxton, G. D., Sherratt, T. N., & Speed, M. P. (2004). Avoiding attack: the evolutionary ecology of crypsis, warning signals, and mimicry. Oxford University Press.
ChatGPT3 "Tell me all about Batesian Mimicry and its role in evolution, with references." [Response to user request]
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In other parts of its range, the mimic species may be more abundant than the 'model' species, producing evolutionary pressure on predators to ignore the mimicry.
Now researchers from Otago University, Dunedin, New Zealand, have shown how the dynamics of these competing evolutionary pressures has resulted in genetic and phenotypic variation across the range of a species of stonefly, Zelandoperla fenestrata, which is a mimic of the toxic Austroperla cyrene.
The news release from Otago University explains:
When cheating pays – survival strategy of insect uncoveredThe researchers' findings are published, open access, in the journal Molecular Ecology:
Researchers have revealed the unique ‘cheating’ strategy a New Zealand insect has developed to avoid being eaten – mimicking a highly toxic species.
In nature, poisonous species typically advertise their toxicity, often by producing high contrast colours such as black, white and yellow, like wasps and bees.
Along similar lines, New Zealand’s cyanide-producing stonefly, Austroperla cyrene, produces strong ‘warning’ colours of black, white and yellow, to highlight its threat to potential predators.
In a new study published in Molecular Ecology, University of Otago Department of Zoology researchers reveal that an unrelated, non-toxic species ‘cheats’ by mimicking the appearance of this insect.
Lead author Dr Brodie Foster says by closely resembling a poisonous species, the Zelandoperla fenestrata stonefly hopes to avoid falling victim to predators.
In the wild, birds will struggle to notice the difference between the poisonous and non-poisonous species, and so will likely avoid both. To the untrained eye, the poisonous species and its mimics are almost impossible to distinguish.
Dr Brodie J. Foster, lead author Department of Zoology
University of Otago, Dunedin, New Zealand
The researchers used genomic approaches to reveal a key genetic mutation in a colouration gene which distinguishes cheats and non-cheats.
This genetic variation allows the cheating species to use different strategies in different regions.
However, co-author Dr Graham McCulloch says the strategy, known as Batesian mimicry, doesn’t always succeed.
Co-author Professor Jon Waters adds cheating can be a dangerous game.Our findings indicate that a ‘cheating’ strategy doesn’t pay in regions where the poisonous species is rare.
Dr Graham A. McCulloch, co-author
Department of Zoology University of Otago, Dunedin, New Zealand
If the cheats start to outnumber the poisonous species, then predators will wake up to this very quickly – it’s a bit of a balancing act.
Professor Jonathan M. Waters, co-author
Department of Zoology University of Otago, Dunedin, New Zealand
AbstractCreationists who have managed to get this far, might like to note that, far from abandoning the Theory of Evolution, in favour of a creationist magical superstition, the researchers in New Zealand were in no doubts that the current situation with both mimicking and non-mimicking forms of Zelandoperla fenestrata is due to dynamic balance between competing environmental selectors, in classical Darwinian evolution.
The evolution of Batesian mimicry – whereby harmless species avoid predation through their resemblance to harmful species – has long intrigued biologists. In rare cases, Batesian mimicry is linked to intraspecific colour variation, in which only some individuals within a population resemble a noxious ‘model’. Here, we assess intraspecific colour variation within a widespread New Zealand stonefly, wherein highly melanized individuals of Zelandoperla closely resemble a chemically defended aposematic stonefly, Austroperla cyrene. We assess convergence in the colour pattern of these two species, compare their relative palatability to predators, and use genome-wide association mapping to assess the genetic basis of this resemblance. Our analysis reveals that melanized Zelandoperla overlap significantly with Austroperla in colour space but are significantly more palatable to predators, implying that they are indeed Batesian mimics. Analysis of 194,773 genome-wide SNPs reveals an outlier locus (ebony) strongly differentiating melanic versus non-melanic Zelandoperla. Genotyping of 338 specimens from a single Zelandoperla population indicates that ebony explains nearly 70% of the observed variance in melanism. As ebony has a well-documented role in insect melanin biosynthesis, our findings indicate this locus has a conserved function across deeply divergent hexapod lineages. Distributional records suggest a link between the occurrence of melanic Zelandoperla and the forested ecosystems where the model Austroperla is abundant, suggesting the potential for adaptive shifts in this system underpinned by environmental change.
Foster, B. J., McCulloch, G. A., Foster, Y., Kroos, G. C., King, T. M., & Waters, J. M. (2023).
ebony underpins Batesian mimicry in melanic stoneflies.
Molecular Ecology, 00, 1–13. https://doi.org/10.1111/mec.17085
Copyright: © 2023 The authors.
Published by John Wiley & Sons, Inc. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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