Might Epigenetics Hold The Secret To Super-Fast Adaptation?

Adult male house sparrow (Passer domesticus).
(Credit: Simon Griffith.)
Epigenetic mechanisms.
Epigenetic mechanisms are affected by several factors and processes including development in utero and in childhood, environmental chemicals, drugs and pharmaceuticals, ageing, and diet. DNA methylation occurs when methyl groups — an epigenetic factor found in some dietary sources — tag DNA, thereby activating or repressing genes. Histones are proteins around which DNA can coil for compaction and gene regulation. Histone modification occurs when the binding of epigenetic factors to histone “tails” alters the extent to which DNA is wrapped around histones thereby altering the availability of genes in the DNA to activation. These alterations in gene expression or function can affect and influence a variety of traits. (Credit:
National Institutes of Health / Public domain.)

Might epigenetics be invasive species’s secret superpower?

Fly into any city in the world, and there they are. You don’t have to be a birder to notice house sparrows, Passer domesticus. These small birds are clad in subdued tans and greys with rich rufous-brown plumage on their wings and backs, and the males also have a black “bib” whose size signals his age and social rank.

Yes, house sparrows can even be found in Moscow, Russia. In winter.
House sparrows (Passer domesticus) perching on a wall in the snow in Moscow, Russia.
(Credit:
Andrey / Creative Commons Attribution 2.0 Generic license.)

Molecular techniques confirm three separate sparrow introductions into Australia

A research collaboration at Macquarie University replicated and expanded upon the original 2013 study of the Kenyan house sparrow introduction (ref) to see whether the Australian sparrows showed the same molecular patterns. To begin, the research team identified 15 sites throughout eastern Australia that can be linked to the three historically independent introduction events for house sparrows (Figure 1):

Figure 1. Map of the Eastern half of Australia labelled with the 15 study sites and their corresponding epigenetic diversity (epi-h) values. Sites derived from the same introduction event are grouped within an oval; 1, the South Australia introduction; 2, the Victoria/New South Wales introduction; 3, the Queensland introduction. The house sparrows’ estimated range edge is also plotted.
(doi:
10.1098/rsos.172185)
Figure 2. (a) The scatter plot for the CoA of the 16 sample localities with the three clusters that were identified. (b) The scatter plot from the DAPC which used the three population labels with the individual genotypes (n = 623 individuals). © The membership probabilities for the DAPC in (b). The sample labels 1–16 correspond to the sampling localities: Tolga, Townsville, Charleville, Pittsworth, Armidale (removed from epigenetic analyses due to low sample sizes), Dubbo, Cobar, Wentworth, Burrumbuttock, Melbourne, Geelong, Bridport, Mt Gambier, Broken Hill, Adelaide and Coober Pedy, respectively.
(doi:
10.1098/rsos.172185)
Figure 3. Mantel’s test comparing genetic and epigenetic pairwise estimates of ΦST, across all sample sites; there is no relationship (R2 = 0.124, n = 15, p = 0.159).
(doi:
10.1098/rsos.172185)

The “epigenetics mystery” deepens

“[T]he house sparrow really provides excellent opportunities to study fundamental questions like this, because there are so many introductions across the world,” said senior author, evolutionary ecologist Simon Griffith, a professor at Macquarie University, in email. “They are fairly well-documented and occurred at approximately the same time. As a result, these introductions provide excellent pseudo-experiments and provide a really fantastic way of addressing questions about micro-evolutionary processes, and adaptation to things like climate change.”

Adult male house sparrow (Passer domesticus). (Credit: Adamo / CC BY 2.0 de.)

Source:

E. L. Sheldon, A. Schrey, S. C. Andrew, A. Ragsdale and S. C. Griffith (2018). Epigenetic and genetic variation among three separate introductions of the house sparrow (Passer domesticus) into Australia, Royal Society Open Science, 5(4):172185 | doi:10.1098/rsos.172185

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