Rosa Rubicondior: Creationism Refuted - Butterfly Speciation

Heliconius elevatus, a hybrid between Heliconius melpomene and Heliconius pardalinus

New butterfly species created 200,000 years ago by two species interbreeding - News and events, University of York

About 200,000 years ago, in the Amazon rainforest of South America, something happened that creationists claim cannot happen. Not only did it happen long before the world existed according to creationist mythology, but a new species arose without the intervention of a supernatural entity, and without the magical creation of a new species without ancestors.

As reported in the journal Nature, a new species of butterfly, Heliconius elevatus, arose through hybridisation involving the ancestors of two related Heliconius species, Heliconius melpomene and Heliconius pardalinus. Today, all three species coexist in the Amazon rainforest.

But that is not the only problem for creationists who continually demand evidence of a “speciation event”, as though speciation were a single moment involving a single individual, rather than the population-level process explained by the Theory of Evolution. This example shows that speciation can be rapid in evolutionary terms, yet still go completely unnoticed. A single hybrid, even if found, would not be regarded as a new species, but as the product of a chance mating between two related species. It is only if hybridisation produces a population that remains distinct over generations, with its own ecological niche, mating preferences and genetic identity, that taxonomists are justified in recognising it as a new species.

In plants, hybrid speciation often involves polyploidy — a doubling of chromosome number — which can prevent hybrids from breeding with either parent species while allowing them to breed with one another. But Heliconius elevatus is a much rarer example of homoploid hybrid speciation, in which a new species arises without a change in chromosome number. The picture is complicated by the fact that, over time, there has been continuing gene flow from one of the parent lineages, H. pardalinus, which has homogenised about 99% of the genome. However, the remaining small islands of DNA introgressed from H. melpomene control traits that help maintain H. elevatus as a distinct species: colour pattern, wing shape, host plant preference, sex pheromones, mate choice and flight behaviour. It is this distinctive combination of traits that enables the new species to coexist with both parent species rather than being absorbed back into either of them.

Hybrid Speciation^ How Evolution Makes New Species Without Magic. Creationists often talk as though a new species should appear in a single dramatic moment, with one animal giving birth to something wholly different. That is not what evolutionary biology predicts. Speciation is normally a population process, in which a lineage gradually becomes genetically, behaviourally or ecologically isolated from related populations.

Hybrid speciation is one way this can happen. Although many hybrids are sterile or less successful than either parent species, hybridisation is not always an evolutionary dead end. Sometimes a hybrid population inherits a useful mixture of traits from both parent lineages. If those traits allow the hybrids to survive, reproduce and mate mainly with one another, the hybrid population can become an independently evolving species.

That is what appears to have happened with Heliconius elevatus. Genomic evidence shows that it arose through hybridisation involving lineages related to H. pardalinus and H. melpomene, and has persisted as an independent species for at least 180,000 years, despite continuing gene flow with H. pardalinus. Most of its genome now resembles H. pardalinus, but small islands of DNA inherited from H. melpomene contain genes affecting colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Those traits help keep H. elevatus distinct.

This is especially interesting because it is an example of homoploid hybrid speciation — speciation by hybridisation without a change in chromosome number. Hybrid speciation through polyploidy is well known in plants, where chromosome doubling can instantly create reproductive barriers. In H. elevatus, however, the barrier was not produced by extra chromosomes, but by a combination of ecological and behavioural traits assembled through introgression.

In other words, evolution did not need magic, foresight or the sudden creation of a new “kind”. It needed only variation, hybridisation, natural selection and time. The result was not a butterfly without ancestors, but a new branch produced by the same natural processes that creationists keep insisting do not happen.

The discovery, the result of a decade-long study by an international team led by researchers including Professor Kanchon Dasmahapatra of the University of York’s Department of Biology, is explained in a University of York news item.

New butterfly species created 200,000 years ago by two species interbreeding
Researchers have shown that an Amazonian butterfly is a hybrid species, formed by two other species breeding together almost 200,000 years ago.
The discovery, by an international team led by scientists at the University of York and Harvard University, demonstrates how the formation of new species can be more complex than previously imagined.

Species are often thought of as the tips, or leaves in a ‘tree of life’. In this model, new species are produced by the tips splitting to form new species over thousands to millions of years.

Scientists now understand, however, that the branches in the tree of life are tangled, with genes being transferred from one species to another by occasional interbreeding. This can theoretically result in the formation of a new species; a process known as hybrid speciation.

Decade-long study

However, proving hybrid speciation is possible in animals is a difficult task, as scientists need to demonstrate that breeding between two species actually triggered the formation of an entirely new species that is genetically distinct from both parents.

The team of scientists, which includes researchers from a number of South American countries, have now found an example of a hybrid species among the brightly coloured Heliconius butterflies of the Amazon.

In a decade-long study, the researchers accumulated genetic and ecological evidence demonstrating that almost 200,000 years ago, the ancestor of today’s Heliconius melpomene and Heliconius pardalinus contributed parts of their genomes to produce a distinct third species, Heliconius elevatus, and that all three species now co-exist in the Amazon rainforest.

Genetic basis

Hybrid speciation may not be that uncommon, but convincing examples of animal hybrid species are really difficult to come by. In the few examples that exist, either the supposed hybrid species have only existed for a few generations and may be short-lived entities, or the hybrid species does not live alongside its parental species, making it difficult to know whether it is actually a new species.

Professor Kanchon K. Dasmahapatra, senior author
Department of Biology
University of York
York, UK.

Lead author Dr Neil Rosser, postdoctoral researcher at the University of York and now at Harvard University, spent several years in the Amazon crossing the species involved to uncover the genetic basis of multiple traits that are important for maintaining a species’ distinctiveness. These traits included colour pattern, wing shape, host plant preference, sex pheromones, mate choice and flight.

Unique combination

Remarkably, we found that in Heliconius elevatus, the parts of the genome controlling these important traits are often derived from Heliconius melpomene. This finding is key to demonstrating that hybridisation drove the evolution of Heliconius elevatus, because it endowed the species with a unique combination of traits that prevent it from interbreeding with either of its parents.

Dr Neil Rosser, co-first author.
Department of Organismic and Evolutionary Biology
Harvard University
Cambridge, MA, USA.

With species' distributions changing rapidly due to human actions and climate change, opportunities for hybridisation or mixing between species are likely to increase, which has important implications. This increased mixing will likely cause more genes to move among species, in some cases leading to species being swamped by other species’ genes, and in other cases possibly to the formation of new hybrid species in the future.

Professor Kanchon K. Dasmahapatra.

Publication:
Rosser, N., Seixas, F., Queste, L.M. et al.
Hybrid speciation driven by multilocus introgression of ecological traits. Nature 628, 811–817 (2024). https://doi.org/10.1038/s41586-024-07263-w

Abstract
Hybridization allows adaptations to be shared among lineages and may trigger the evolution of new species^1,2. However, convincing examples of homoploid hybrid speciation remain rare because it is challenging to demonstrate that hybridization was crucial in generating reproductive isolation³. Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies. We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years. This is despite pervasive and ongoing gene flow with one parent, Heliconius pardalinus, which homogenizes 99% of their genomes. The remaining 1% introgressed from the other parent, Heliconius melpomene, and is scattered widely across the H. elevatus genome in islands of divergence from H. pardalinus. These islands contain multiple traits that are under disruptive selection, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Collectively, these traits place H. elevatus on its own adaptive peak and permit coexistence with both parents. Our results show that speciation was driven by introgression of ecological traits, and that speciation with gene flow is possible with a multilocus genetic architecture.

Fig. 1: Summary of key findings, geographical distributions of species and evidence that H. elevatus has a hybrid genome.

a, Evolutionary relationships and main introgression events described in this study. We test the hypothesis that introgression of major pre-mating and post-mating ecological isolating traits from H. melpomene led to the establishment of H. elevatus as a new stable hybrid species. Mya, million years ago. b, Geographical distributions of major clades. Locations at which both H. elevatus and H. pardalinus were sampled are numbered. c, Distance-based network using genome-wide independent SNPs. This concatenated tree shows the existence of two distinct clusters, Amazonian versus non-Amazonian, in both H. elevatus and H. pardalinus. d, Topology weighting analysis (TWISST) showing the percentage of the 11,509 non-overlapping genomic windows of 1,000 SNPs in which the majority of subtrees (that is, topology weighting ≥ 0.5) clusters H. elevatus (ele) with either H. pardalinus (par) (93.2%; top) or H. melpomene (mel) (0.52%; bottom). Note that although H. elevatus groups with H. pardalinus in 93.2% of windows, only 1.61% of those trees yield the two species as reciprocally monophyletic. By contrast, all three species are monophyletic in 81% of the windows for which H. elevatus groups with H. melpomene. Subscripts indicate geographical distributions for H. elevatus and H. pardalinus (Ama, Amazon; And, Andes; Gui, Guianas) and subspecies for H. melpomene (Agl, aglaope; Ams, amaryllis). e, A multispecies coalescent model with introgression supports a hybrid origin of H. elevatus, with the introgression time coinciding closely with the origin of the species (the 95% HPD intervals are given within parenthesis). Images of butterfly wings are copyright of the authors and Michel Cast.

Rosser, N., Seixas, F., Queste, L.M. et al.
Hybrid speciation driven by multilocus introgression of ecological traits. Nature 628, 811–817 (2024). https://doi.org/10.1038/s41586-024-07263-w

Copyright: © 2024 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

So, once again, we have a scientific discovery that only makes sense in the light of the Theory of Evolution. The researchers were not looking for a magical moment of creation, nor for a butterfly appearing without ancestors. They were looking at genomes, gene flow, inherited traits, ecological separation, mate choice and reproductive isolation — exactly the things evolutionary theory predicts should matter when populations diverge and new species arise.

And that is why the creationist caricature of evolution is so useless. It asks for “one kind turning into another” while ignoring the real, observable processes by which populations change over time. In this case, hybridisation did not blur species boundaries into nothingness, nor did it produce a sterile evolutionary dead end. Instead, it helped assemble a stable, distinct lineage with its own combination of traits, allowing Heliconius elevatus to coexist with the related species from which it inherited its genome.

None of this required a supernatural intervention, a designer adjusting wing patterns, or a sudden act of special creation. It required only the natural mechanisms already known to evolutionary biology: inheritance, variation, hybridisation, recombination, selection, mate preference and ecological adaptation. The Theory of Evolution did not merely survive this discovery; it provided the framework that made the discovery intelligible in the first place.

Creationism, by contrast, explains nothing here. It predicted none of the genomic pattern, none of the small islands of introgressed DNA, none of the traits maintaining reproductive isolation, and none of the evidence that a new species arose naturally and persisted for almost 200,000 years. As so often, creationists are left not with an explanation, but with denial, special pleading and the hope that their followers will not look too closely at the evidence.

In the real world, however, the evidence is clear: new species do arise, they arise from pre-existing species, and their origins can be reconstructed from the genetic and ecological traces they leave behind. That is not a problem for evolution; it is evolution doing exactly what the Theory of Evolution says it does.

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