F Rosa Rubicondior: Creationism in Crisis - Damselflies Evolved Their Colours At Least 5 Million Years Before 'Creation Week'

Saturday 18 November 2023

Creationism in Crisis - Damselflies Evolved Their Colours At Least 5 Million Years Before 'Creation Week'

Common bluetail damselflies, Ischnura elegans

Credit: Quartl, CC BY-SA 3.0, via Wikimedia Commons
Scientists have solved the damselfly colour mystery | Lund University

So much history, especially the evolutionary history of life on Earth, occurred before the mythical Creation Week, when creationists believe a magic man who existed when nothing existed made the universe out of that nothing, that it’s difficult to keep up with it all.

Here, for example, is a scientific account of how damselflies evolved their colours at least 5 million years before Creation Week, by an evolutionary process guaranteed to have creationists going into abject denialism and lying to one another about it in their echo chambers, if not throwing a tantrum, stamping their feet and shouting abuse at the facts to make them go away, or at the scientists who discovered the facts.

The bluetail damselfly, like many other damsel flies is sexually dimorphic with males being brightly coloured and the females more drab, usually brown. Females of the common bluetail occur in three color forms, one of which mimics the male, and the mystery was how, why and when did this evolve? Note here how a creationist would simply declare they were designed that way by a god whose purpose in doing so is unknowable, whilst science looks for the how and why, and so discovers a much more satisfying answer than the creationist one which makes them satisfied with not knowing.

By comparing the genome of the common bluetail, Ischnura elegans with that of a close tropical relative, Ischnura senegalensis, the scientists were able to show that the colour differences are due to mutations in a specific genetic region on chromosome 13 that arose at least 5 million years ago, so the question resolves down to why was it retained? In other words, what were the environmental selectors that spread the mutations in the population then conserved them for 5 million years?

The research was conducted by scientists at Lund University, Sweden, under biologist Professor Erik Svensson with colleagues at Stockholm University, Sweden, Institut Pasteur, Université Paris Cité, Paris, France, the University of Rennes, France and Tohoku and Chiba Universities, Japan. Their findings are published, open access, in Nature Ecology & Evolution and its significance is explained in a Lund University press release:
For over 20 years, a research team at Lund University in Sweden has studied the common bluetail damselfly. Females occur in three different colour forms - one with a male-like appearance, something that protects them from mating harassment. In a new study, an international research team found that this genetic colour variation that is shared between several species arose through changes in a specific genomic region at least five million years ago.

The question of how and why genetic variation arises and is maintained over long periods of time is of key importance to evolutionary biology, population genetics and conservation biology. In all populations of limited size, genetic variation is lost over time. It is therefore important to understand both the mechanisms that give rise to new genetic variation, and the mechanisms that act to maintain variation. This has significance both for conservating species and for the future evolutionary potential of populations to adapt to rapidly changing environments.

In the new study published in Nature Ecology and Evolution, a research team mapped the extensive and striking colour variation among the females of the bluetail damselfly (Ischnura elegans).

In this damselfly species, there are three genetically determined colour forms in the females, one of which makes them look like males. These male-like females have an advantage because they avoid excessive mating harassment from the males. Our study clarifies when, how and why this variation arose, and shows that this variation has been maintained over long evolutionary time periods through so-called balanced natural selection.

Professor Erik I. Svensson, co-author
Department of Biology
Lund University, Lund, Sweden
By sequencing the DNA of the three colour forms of the bluetail damselfly and comparing it to the two colour forms in its closely related tropical relative Ischnura senegalensis, the researchers were able to demonstrate that this genetic colour variation in females arose at least five million years ago; through several different mutations in a specific genetic region on the damselfly’s thirteenth chromosome.

The great colour variation in insects fascinates the general public, and raises questions about the function of colour signals and its evolutionary consequences for partner choice and conflicts between the sexes.

Professor Erik I. Svensson.
Having located the gene behind the female colour variation, the researchers can now go further and identify different genotypes in the males, and in the aquatic larval stage of these insects. The males lack visible colour forms, but the researchers plan to investigate whether the colour gene affects other characteristics of the larvae and males, including survival and behaviors.

We now have a good knowledge base for investigating the colour variation over longer evolutionary time scales among other species of this damselfly genus, which occurs in Europe, Africa, Asia, Australia, North and South America. These new genetic results help us understand both the evolutionary processes that take place within a species, and what happens over longer evolutionary macroevolutionary time scales of tens of millions of years and across several different species

Professor Erik I. Svensson.
More technical detail is given in the team's paper in Nature Ecology and Evolution:

Sex-limited morphs can provide profound insights into the evolution and genomic architecture of complex phenotypes. Inter-sexual mimicry is one particular type of sex-limited polymorphism in which a novel morph resembles the opposite sex. While inter-sexual mimics are known in both sexes and a diverse range of animals, their evolutionary origin is poorly understood. Here, we investigated the genomic basis of female-limited morphs and male mimicry in the common bluetail damselfly. Differential gene expression between morphs has been documented in damselflies, but no causal locus has been previously identified. We found that male mimicry originated in an ancestrally sexually dimorphic lineage in association with multiple structural changes, probably driven by transposable element activity. These changes resulted in ~900 kb of novel genomic content that is partly shared by male mimics in a close relative, indicating that male mimicry is a trans-species polymorphism. More recently, a third morph originated following the translocation of part of the male-mimicry sequence into a genomic position ~3.5 mb apart. We provide evidence of balancing selection maintaining male mimicry, in line with previous field population studies. Our results underscore how structural variants affecting a handful of potentially regulatory genes and morph-specific genes can give rise to novel and complex phenotypic polymorphisms.


Sexual dimorphism is one of the most fascinating forms of intra-specific phenotypic variation in animals. Sexes often differ in size and colour, as well as the presence of elaborated ornaments and weaponry. Theoretical and empirical studies over many decades have developed a detailed framework of sexual selection and sexual conflict, explaining why these differences arise and how they become encoded in sex differentiation systems1,2,3. However, a growing number of examples of inter-sexual mimicry4,5,6,7 suggest that sexual dimorphism can be evolutionarily fragile and quite dynamic. Inter-sexual mimicry has evolved in several lineages, when individuals of one sex gain a fitness advantage, usually frequency- or density-dependent, due to their resemblance to the opposite sex. For example, males who mimic females, as seen in the ruff (Calidris pugnax) and the Melanzona guppy (Poecilia parae), forgo courtship and ‘sneak’ copulations from dominant males4,5, while females who mimic males, in damselflies and hummingbirds, avoid excessive male-mating harassment6,8. Inter-sexual mimicry thus requires the evolution of a novel sex-mimicking morph in a sexually dimorphic ancestor. The occurrence of inter-sexual mimicry may be an intermediate step in the evolution of sexual monomorphism, it may be an ephemeral state or it may be maintained as a stable polymorphism. In any case, sexual mimics harbour genetic changes that attenuate or prevent the development of sex-specific phenotypes, and can therefore provide insights into the essential building blocks of sexual dimorphism9
Fig. 1: The evolution of female-limited colour polymorphisms in Ischnura damselflies.
a, A previous phylogenetic study and ancestral state reconstruction28 proposed that the genus Ischnura had a sexually dimorphic ancestor, with O-like females (red circle). The O morph is markedly different from males, having a bronze-brown thorax and faint stripes, instead of the black thoracic stripes on a bright blue background of males. b, Male mimicry (A females, blue circle) has evolved more than once, for instance, in an ancestor of the (expanded) clade that includes the common bluetail (I. elegans, outlined with solid line) and the tropical bluetail (I. senegalensis, outlined with dashed line). c, I. elegans is a trimorphic species, due to the recent evolution of a third female morph, I (yellow circle). In I. elegans, morph inheritance follows a dominance hierarchy, where the most dominant allele produces the A morph and two copies of the most recessive allele are required for the development of O females. In contrast, the O allele is dominant in I. senegalensis106 Terminal nodes in the phylogeny represent different species. Grey triangles represent other clades of Ischnura, which are collapsed for clarity. Damselfly images adapted from ref. 25 under a Creative Commons licence CC BY 4.0.

Fig. 4: SVs differentiate morph haplotypes in the common bluetail damselfly (I. elegans).
a, Alignment between morph-specific genomes assembled from long-read nanopore samples with genotypes Ao, Io and oo. Grey lines represent alignments of at least 5 kb and >70% identity. The black line connects regions of genomic content shared by the three morphs within the morph locus. The red to blue gradient represents a ~20 kb region that carries an inversion signature in A and I females relative to the O haplotype (Extended Data Fig. 2). The blue to yellow gradient represents a ~150 kb alignment between the start of the unlocalized scaffold 2 of chromosome 13 in A and a region ~3.5 mb apart in the I haplotype. Coordinates at the bottom are based on the DToL reference assembly. b, Schematic illustration of the hypothetical sequence of events responsible for the evolution of novel female morphs. First, a sequence originally present in O was duplicated and inverted in tandem, potentially causing the initial divergence of the A allele. Second, part of this inversion was subsequently duplicated in A, in association with a putative TE, leading to multiple inversion signatures in the A haplotype relative to an O reference (Extended Data Fig. 3). Finally, part of the A duplications were translocated into a position ~3.5 mb downstream into an O background, giving rise to the I allele. Currently, A females are also characterized by another region of unique content and unknown origin (question mark). A females show elevated sequence divergence in the internal region of the morph locus that is shared by all haplotypes (dark grey bars; see also black line in a). Coordinates on the O haplotype are based on the (DToL) reference assembly. Grey numbers in IV give the approximate size of genomic sequences in A and I that are absent in O. Damselfly images adapted from ref. 25 under a Creative Commons licence CC BY 4.0.

Fig. 5: A shared genomic basis of A females in I. elegans and I. senegalensis.
a, I. senegalensis is a female-dimorphic species, where one female morph (O-like) is distinctly different from males and resembles O females in I. elegans, and the other female morph (A) is a male mimic. Photo credit: Mike Hooper. b, Standardized read depth of pool-seq samples (n = 30 females of each morph per pool) of I. senegalensis, against the A-morph assembly of I. elegans, calculated in 500 bp windows. The x-axis shows the first 1.5 mb of the unlocalized scaffold 2 of chromosome 13. c, Alignments between morph-specific genomes from a homozygous O-like female of I. senegalensis (top), an Ao female of I. elegans (middle) and a homozygous A female of I. senegalensis (bottom). Lines connecting the assemblies represent alignments of at least 500 bp and >70% identity. The black line connects genomic content in the morph locus, which is shared by the three morphs of I. elegans. In I. elegans, this region is rich in SNPs differentiating A females from the other two morphs (see Fig. 2b). The blue-turquoise gradient connects sequences uniquely present in the A morphs of I. elegans and I. senegalensis.

The things that creationists will need to ignore here are:
  1. The mutations happened at least 5 million years before they believe the Universe was made out of nothing.
  2. The mutation included new genetic information arising by duplication and inversion.
  3. The scientists explain the observable evidence in terms of an evolutionary process involving natural selection, with no hint that the Theory of Evolution by natural selection is being discarded as unable to explain the observable facts.
  4. There is no need for magic or supernatural entities in the explanation.
  5. Just another casual refutation of creationism, as with almost all biological research.

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