User:Grady.303/sandbox

Research topic: Evolution in color mimicry for Heliconius Butterflies

Bibliography

Mallet, James. “Speciation, Raciation, and Color Pattern Evolution in Heliconius Butterflies: Evidence from Hybrid Zones.” Hybrid Zones and the Evolutionary Process. Edited by Richard Gerald Harrison. Oxford University Press. 1993

Mallet, James, and LAWRENCE E. GILBERT. "Why are there so many mimicry rings? Correlations between habitat, behaviour and mimicry in Heliconius butterflies." Biological Journal of the Linnean Society 55.2 (1995): 159-180.

A V Brower. “Rapid morphological radiation and convergence among races of the butterfly Heliconius erato inferred from patterns of mitochondrial DNA evolution.” PNAS 1994 91 (14) 6491-6495.

John R. G. Turner, Michael S. Johnson and Walter F. Eanes. “Contrasted Modes of Evolution in the Same Genome: Allozymes and Adaptive Change in Heliconius.” Proceedings of the National Academy of Sciences of the United States of America, Vol. 76, No. 4 (Apr., 1979), pp. 1924-1928 Published by: National Academy of Sciences Article Stable URL: http://www.jstor.org.proxy.lib.ohio-state.edu/stable/69627

Joel Smith and Marcus R. Kronforst. “Do Heliconius Butterflies species exchange mimicry alleles?” Bio. Lett. 2013 9, 20130503, published 17 July 2013.

Heliconius Genome Consortium. "Butterfly genome reveals promiscuous exchange of mimicry adaptations among species". Nature. 487 (7405): 94-8. 2012.

––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

Wikipedia Assignment two: Edited and commented on: https://en.wikipedia.org/wiki/Heliconius Sentence added: And in a DNA sequencing comparison involving species H. m. aglope, H. timareta, and H. m. amaryllis, it was found that gene sequences around mimicry loci were more recently diverged in comparison with the rest of the genome, providing evidence for speciation by hybridization over speciation by ancestral polymorphism.

Using citation: Joel Smith and Marcus R. Kronforst. “Do Heliconius Butterflies species exchange mimicry alleles?” Bio. Lett. 2013 9, 20130503, published 17 July 2013.

Suggestions for talk page: This article has good information, but I think there are several places to go more in depth. One area is how DNA sequencing supports hybridization in comparison with other speciation hypothesis (such as selection in combination with ancestral polymorphism). I’m adding one sentence that touches on this, but I think it is something to look into. Also, why is hybridization even happening in the first place? How do specifically Heliconius species interact and choose mates? One last thing that could contribute to this article is to talk about how there are different mimicry rings in the same area. This is important, because if the only force creating Mullerian mimicry was predation education cost, it seems likely all the butterflies in one area would look the same. Grady.303 (talk) 18:27, 1 October 2014 (UTC)

--

FINAL DRAFT STARTS HERE

Evolution of Heliconius Butterflies

In the evolutionary world, a prime organism being researched and studied is the Heliconius butterfly. Its massive diversity in wing color and pattern is well known, and raises the question of how and why such an evolutionary phenomenon would occur. There have been many instances of both divergence and convergence, and researchers have been striving to understand such rapid speciation changes. Overall, this organism has shown examples of all sorts of different evolutionary concepts, including selection effects, introgression, assortative mating, and more. This gives researchers an opportunity to study and learn more about speciation mechanisms, especially with Heliconius’ adaptive radiation. There is still much not understood, and the butterflies’ evolution is certainly not simple, but its study has extended knowledge on butterflies, and evolution as a whole.

A common theme in describing the evolution of Heliconius butterflies is its defense mechanism of Müllerian mimicry. This form of mimicry embodies multiple unpalatable organisms sharing visual characteristics to spread the cost of educating predators (The Heliconius Genome Consortium, 2012). If butterflies evolve to look similar, and predators learn to avoid these certain butterflies, they will have a higher fitness, that is, a higher survival rate and ability to pass on their genes. One problem with this idea is that if Müllerian mimicry were the only force driving the butterflies’ evolution, it would be predicted the butterflies would all eventually converge on the same color and pattern; instead Heliconius butterflies are greatly diverse, and even form multiple ‘mimicry rings’ within the same geographical area (Mallet 1984). Multiple mimicry rings means a certain region has several groups of species mimicking each other, despite Mullerian mimicry theorizing every butterflying looking the same would allow the highest predator education. Mallet, in 1984, suggested mimicry rings formed due to different habitats and hunters within an area. This is a very plausible, but likely only part of the explanation of his specific observations. Overall, a predator-prey interaction is a major mode of selection for certain traits, but as researchers have continued to study them, they have grasped the complexity and number of factors influencing the butterflies’ morphologies. There are many influencing Heliconius’ evolution, and the development of new technology and studies has increased this knowledge.

A common and impacting behavior of Heliconius butterflies is the creation of hybrids. While hybrids in nature are known for having lower fitness, in certain organisms it is a major method of evolution. Melo, Nadeau, and the Heliconius Genome Consortium talk about certain species being hybrids, and all pinpoint to H. heurippa as a specific example. Nadeua claims H. heurippa likely was created from the mix of H. melpomene and an H. timerata (Nadeau et al., 2012) while the Heliconius Genome Consortium and Melo refer to a melpomene/cydno hybridization (The Heliconius Genome Consortium, 2012; Melo et al., 2008). Although following gene flow and ancestry can be a tedious process to follow, the existence of functioning hybrids has very high support. The significance of these hybrids, if they mix primarily with themselves (are reproductively isolated from their parental species), is the possibility of rapid speciation (Melo, 2008). This could contribute to the explanation of the massive and various types of butterflies that have occurred. The limitation to hybridization, however, is hybrids also have a high chance of displaying traits that make them susceptible to predators (Brower, 1994). Therefore, there is a balance to a hybrid’s survival rate, but if the right genes are passed, a new species can be created. As Melo said, the hybrids that were the most “abundant” and had the most “successful” colors/patterns reflected the possession of alleles with higher fitness, and therefore these beneficial traits would be driven to fixation in its particular environment. (Melo et al., 2008.

The process of gene flow from one species to another via hybrids is called introgression. This means the hybrids have a high enough fitness to survive and are competent enough to reproduce. Introgression is also a big determinate in the evolutionary process of Heliconius butterflies, and has been a heavily researched topic. With Müllerian mimicry being the main defense mechanism, color and pattern are caused to be major adaptive traits. Therefore, selection factors push introgression to revolve around these genes (Nadeau et al., 2012). While another explanation for the inheritance of these alleles is through polymorphic ancestors, Smith studied their genome and found more recent “splitting of the alleles with low sequence divergence.” Smith goes on to explain this observation is correlated with introgression, while ancestral polymorphism would show the opposite (Smith and Kronforst, 2013). This hybridization and backcross to the parental species would create faster genome change, which also supports Melo’s talk of rapid speciation. Another team that has found evidence of introgression is The Heliconius Genome Consortium, who says it is a reasonable explanation for the rise of mimetic butterflies. Their data pertaining to the comparison of H. melpomene and H. timerata genomes showed that most of the introgression they found centered on the two chromosomes they knew contained mimicry alleles (The Heliconius Genome Consortium, 2012). This means the most successful gene flow consists of color and wing patterns. A third article to back up the effects of introgression is Supple, whose results showed SNP’s being polymorphic mostly around hybrid zones of a genome, and claimed this supported the mechanism of introgression over ancestral variation for genetic material exchange (Supple et al, 2013). Although introgression cannot explain all of Heliconius’ convergence and divergence, these results from various groups show its significance, especially in the case of mimicry alleles.

Another important aspect in the evolution of Heliconius butterflies is assortative mating and mate recognition. Introgression and hybridization would be ineffective for speciation if the butterflies did not have some sort of mating preference. Melo did a study on the hybrid H. heurippa to see its mating habits in regards to preference between other hybrids and its parental species, and it showed some interesting results. H. heurippa chose to reproduce among backcross species (hybrids between itself and parental species), while the parental species were highly unlikely to reproduce with the backcrosses (Melo et al., 2008). This is significant, because hybrids’ mating behavior would relatively quickly isolate itself from its parental species, and eventually form a species itself, as defined by lack of gene flow. The results also show the importance of mate recognition. Color patterns allow mate recognition, which would be the major cause of hybrids developing differing reproductive behaviors (Nadeau et al., 2012). Melo et al (2008), however, pondered about how such behaviors could appear in the H. heurippa hybrids. His team hypothesized that along with a mixed inheritance of color and pattern, the hybrids also obtained a mixed preference for mates from their parental species genes. Therefore, the H. heurippa had a genetic attraction for other hybrids, leading to its reproductive isolation and speciation. Mate recognition is an important influence on successful speciation and gene flow, but it has also experienced selection effects from predation.

In its environment, Heliconius butterflies’ fitness depends on a balance of color/pattern to allow both successful matings, and the most efficient warning sign for predators. Predators act as a selective force against the butterflies causing the color/patterns that maximizes Müllerian mimicry effect to be selected for. Many butterflies would converge on a similar color. However, the species wing characteristics would have to be subtly various enough that different species could recognize its own kind and produce viable offspring. (Llaurens et al., 2014). While hybrids have shown to have success and evolutionary potential, that doesn’t disregard their high chance of predation. In Llaurens’ research, the team used techniques to determine the butterflies’ and birds’ visual capabilities, along with some of the color qualities of the butterflies. They found that color was more vivid on the dorsal side of the butterflies rather than on the ventral. Also, for the comparison of sexes, females appeared to have differing brightness in specific spots. As for the birds, their research showed they had lower discriminatory abilities than the butterflies. All these results revealed how butterflies have evolved in response to predatory selection. The butterflies are similar enough to keep Müllerian mimicry in effect, yet different enough that they can discern among other co-mimics. These selection factors are driving forces in the butterflies’ evolution. (Llaurens et al., 2014). One last thing to highlight about the study of the evolution of Heliconius butterflies is its complexity and how its understanding has been, and still is, a continuing process. Despite the gains as technology has progressed, there are a lot of grey areas and hypothesis altered. One example of this was seen in the above paragraph, describing the discrepancies of H. heurripa’s origin, that is, which cross between species caused its creation. Another example is Mallet, in 1994, saying “Hybrids between sympatric species have never been found in nature” (Mallet, 1994). However, in more recent research, hybrids and introgression have been a key factor in speciation. Also, despite the emphasis on introgression significance, it does not explain all of the mimicry seen in the butterflies. Instead independent evolution of similar colors is very much so a valid explanation. Supple has found evidence for this in a genome study, saying two co-mimics, H. erato and H. melpomene, had no shared single nucleotide polymorphisms (SNPs), which would be indicative of introgression, and therefore Supple hypothesized the same regulatory genes for color/pattern had comparably changed in response to the same selective forces (Supple et al., 2013). Bottom line is, there is still much to learn about how Heliconius’ have evolved into their current state today.

Heliconius butterflies are an excellent study for the various components of evolution. They experience various selection, and are known for rapid speciation into a multitude of types. Predation and fitness demand they continuously evolve, and the unique defense of Müllerian mimicry will oftentimes cause them to converge on similar colors/patterns. This convergence also can be a reflection of gene flow and hybrid affects, which is not always a successful tactic for organisms to use. They are also shaped by assortative mating and sexual selection, but in balance with predation forces. The complexities of these insects keep researchers searching and striving for answers. Their efforts have allowed an expanding knowledge on evolutionary forces, and an increased understanding of the natural world.

Literature Cited Brower, Andrew. February 1994. Rapid morphological radiation and convergence among races of the butterfly Heliconius erato inferred from patterns of mitochondrial DNA evolution. Proc. Natl. Acad. Sci. USA. Vol. 91, pp. 6491-6495.

Llaurens,V., Joron, M., and Théry, M. 2014. Cryptic difference in colour among Mulerian 	mimics: how can capacities of predators and prey shape the evolution of wing colours? Journal of Evolutionary Biology. 27 (2014) 531-540.

Mallet, J., Gilbert, L. 1994. Why are there so many mimicry rings? Correlations between habitats, behaviour, and mimicry in Heliconius butterlies. 1994. Biological Journal of the 	Linnean Society (1995), 55: 159-180.

Melo, M., Salazar, C., Jiggins, C., and Linares, M. 2008. Assortative mating preferences among hybrids offer a route to hybrid speciation. Evolution 63.6 (2009: 1660-1665).

Nadeau, N., Martin, S., Kozak, K., Salazar, C., Dasmahapatra, K., Davey, J., Baxter, S., Blaxter, M., Mallet, J., Jiggins C. 2012. Genome-wide patterns of divergence and gene flow across a butterfly radiation. Molecular Ecology (2013) 22, 814-826.

Smith, J., and Kronforst, M. 2013. Do Heliconius butterfly species exchange mimicry alleles? Biol letter 9: 20130503.

Supple, M., Hines, H., Dasmahapatra, K., Lewis J., Nielsen D., Lavoie, C., Ray, D., Salavar, C., Mcmillan, O., Counterman, B. 2103. Genomic architecture of adaptive color pattern divergence and convergence in Heliconius butterflies. Genome research (2013): gr-150615.

The Heliconius Genome Consortium. 2012. Butterfly genome reveals promiscuous exchange of mimicry adaptations among species. Nature (2012) vol. 487.

Additions to the Heliconius Wikipedia Page https://en.wikipedia.org/wiki/Heliconius

A research team used techniques to determine some the color qualities of a set of butterflies. They found that color was more vivid on the dorsal side of the butterflies rather than on the ventral. Also, for the comparison of sexes, females appeared to have differing brightness in specific spots. (Llaurens,V., Joron, M., and Théry, M. 2014. Cryptic difference in colour among Mulerian mimics: how can capacities of predators and prey shape the evolution of wing colours? Journal of Evolutionary Biology. 27 (2014) 531-540. )

Melo did a study on the hybrid H. heurippa to see its mating habits in regards to preference between other hybrids and its parental species. The results showed H. heurippa chose to reproduce via backcrossing, while the parental species were highly unlikely to reproduce with the backcrosses. This is significant, because hybrids’ mating behavior would relatively quickly isolate itself from its parental species, and eventually form a species itself, as defined by lack of gene flow. His team also hypothesized that along with a mixed inheritance of color and pattern, the hybrids also obtained a mixed preference for mates from their parental species genes. Therefore, the H. heurippa had a genetic attraction for other hybrids, leading to its reproductive isolation and speciation. (Melo, M., Salazar, C., Jiggins, C., and Linares, M. 2008. Assortative mating preferences among hybrids offer a route to hybrid speciation. Evolution 63.6 (2009: 1660-1665). )

Hybridization is correlated with introgression. Results from Supple and his team have revealed showed SNP’s being polymorphic mostly around hybrid zones of a genome, and they claimed this supported the mechanism of introgression over ancestral variation for genetic material exchange. Selection factors can drive introgression to revolve around genes correlated with wing pattern and color. Research has shown introgression centering on two known chromosomes that contain mimicry alleles. (Supple, M., Hines, H., Dasmahapatra, K., Lewis J., Nielsen D., Lavoie, C., Ray, D., Salavar, C., Mcmillan, O., Counterman, B. 2103. Genomic architecture of adaptive color pattern divergence and convergence in Heliconius butterflies. Genome research (2013): gr-150615.) (Nadeau, N., Martin, S., Kozak, K., Salazar, C., Dasmahapatra, K., Davey, J., Baxter, S., Blaxter, M., Mallet, J., Jiggins C. 2012. Genome-wide patterns of divergence and gene flow across a butterfly radiation. Molecular Ecology (2013) 22, 814-826.) (The Heliconius Genome Consortium. 2012. Butterfly genome reveals promiscuous exchange of mimicry adaptations among species. Nature (2012) vol. 487. )

Also, Supple had found evidence of two co-mimics H. erato and H. melpomene having no shared single nucleotide polymorphisms (SNPs), which would be indicative of introgression, and hypothesized the same regulatory genes for color/pattern had comparably changed in response to the same selective forces

One puzzling thought with Mullerian mimicry/convergence is it would be predicted the butterflies would all eventually converge on the same color and pattern for the highest predator education. Instead Heliconius butterflies are greatly diverse, and even form multiple ‘mimicry rings’ within the same geographical area. Additional evolutionary forces are likely at work. Mallet, J., Gilbert, L. 1994. Why are there so many mimicry rings? Correlations between habitats, behaviour, and mimicry in Heliconius butterlies. 1994. Biological Journal of the Linnean Society (1995), 55: 159-180. Wikipedia Page