Thursday, 26 May 2016

A is for aberration ...

Duke of Burgundy (Hamearis lucina)

West Sussex, May 2016

When it comes to natural selection, we should consider two classes of aberration [a characteristic that deviates from the ‘normal’ type] - those that are passed from generation to generation in the species’ genetic make-up, and those, which are not e.g. those that are determined by the environment. Such variation may be caused by changes or mutations in the genetic composition as the individual develops, or to changes in the physical makeup of the individual as a result of environmental conditions. Aberrations caused by environmental factors e.g. extremes of temperature, are probably not influenced by natural selection since they are not part of the gene pool and are therefore not likely to be inherited; this includes certain examples of colouring and markings. Aberrations may also be the result of a reproduction ‘error’ that is neither genetic, nor associated with the environment, such as gynandromorphs and hybrids.

Those aberrations that are carried in the gene pool [and from generation to generation], and that are visible in terms of colour and markings, clearly do not provide the population with any advantage otherwise they would be widespread. This is where the term ‘aberration’ really doesn't stand up to scrutiny. An individual is considered an aberration if it deviates from the norm. But if it becomes widespread, it is the norm and therefore no longer an aberration. A case in point is ab. caeruleopunctata (Rühl, 1893) in the Small Copper (Lycaena phlaeas) that has a row of blue spots above the copper marginal band on the hindwing. It could be argued that individuals without the blue spots are actually the ‘aberration’ in some populations where this feature occurs frequently. However, answering the question of why this occurs, these aberrations should simply be seen, in my opinion, as a reflection of the rich gene pool available that potentially allows populations to respond to changes in their environment.

2016 has been a good season for aberrant Duke of Burgundy in Sussex. In descending order the above images show a ‘normal’ female, a female referable to ab. albomaculata (Blachier, 1909), and a rather exciting find of a female currently referable to ab. gracilens (Derenne, 1927) + ab. albomaculata (Blachier, 1909). However, with regards to the third individual, albomaculata is only a hindwing aberration whereas this specimen has the same condition on the forewings as well. In addition, the spots in the lunules to the forewings are streaks instead of spots. The underside was also of a paler appearance than ‘normal’. It is therefore quite possible, as none of the existing combinations of names really cover it, that a new name may be required for this form.

My thanks to Peter Eeles, Alec Harmer and Rupert Barrington for their assistance.

More at:

Ford, E.B. (1945). Butterflies. London: Collins (New Naturalist), pp. 219-247.
Harmer, A.S. (2000). Variation in British Butterflies. Lymington, Hampshire: Paphia Publishing Ltd., pp. 53-96.

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