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| Aberrations, Sexual Dimorphism, Forms and Variation |
What is an aberration?
An aberration is a variation in the wing pattern of a butterfly species which is different in some way to the normal pattern. This can occur as a genetic or environmentally produced/induced variation of the usual form of the
species. Aberrations are generally very rare. Some aberrant forms although rare recur on a fairly regular basis, as a result, many have been specifically named.
Example of recurring aberrants include the Comma form reichstettensis (see photo right photographed at Fermyn Wood (Northamptonshire) in 2006) shown with a 'normal' specimen for comparison..
How do aberrations occur?
Butterfly aberrations occur for a variety of reasons, generally, extreme temperature changes especially while the butterfly is developing during the pupal (chrysalis) stage may cause aberrations to occur. Very cold conditions can produce very dark forms of some
species while heat shock (sudden temperature changes or extreme temperature) may cause dramatic changes in wing pattern.
Personal experience in the field has shown that aberrant forms often occur on individual butterflies which appear to have deformed wings. These deformities may be caused as a result of the pupa becoming damaged as the butterfly developed inside.
The two photographs below are of the same male Adonis Blue photographed on Rodborough Common in 2008. The wings appear undamaged until the other side could be seen.
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| Aberrations |
| Comma |
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| Aberrant form reichstettensis above left, compared with the normal form above right.
Find out more about the Comma |
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| Adonis Blue |
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| Aberrant form krodeli above left, compared with the normal form above right.
Find out more about the Adonis Blue |
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What's Sexual Dimorphism?
Males and females of the same species may differ dramatically in wing coloration from each other. Such species are said to be sexually dimorphic. In many species, sexual dimorphism is not present or extremely subtle while in others, it may only be an obvious but consistent difference in wing coloration and pattern between the sexes of the same species.
The Common Blue is a species which displays a classic example of sexual dimorphism, where the male is completely blue while the female is brown sometimes with hints of blue towards the base of the wings nearest the body.
The Orange-tip probably has the most obvious differences between the sexes. The males, have orange-tips to their wings. The orange colouration is completely absent in the females (see photos right).
Males of the species may only vary in wing pattern in the area known as the androconica or sex brand. Pheromones are released from these patches in order to attract a female. |
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Androconica
Males of the species may only vary in wing pattern in the area known as the androconica or sex brand. These patches consist of specialised wing scales from which sexual pheromones are released in order to attract a female.
In many species, the sex brand of the male is not visible although other wing variations may allow the individual to be sexed easily. However, in some species such as the Gatekeeper (see photos right), the male sex brands on the upper forewings are clearly visible. |
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| Sexual Dimorphism |
| Orange-tip |
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| A male above left, compared with the female above right.
Find out more about the Orange-tip |
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| Androconica or Sex Brand |
| Gatekeeper |
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| A male above left, compared with the female above right.
Note dark sex brand on forewing of the male.
Find out more about the Gatekeeper |
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What are forms and variations?
These are more common occurrences within a species and in general are a reasonably consistent variation which are often limited in their distribution. Variations may occur due to local geography, climate and population interaction.
Small local populations (colonies) which do not or cannot breed with other colonies due to obstruction (by mountain ranges or human development such as roads, towns and cities) may result in interbreeding within the colony. In Britain, many species are at risk due to habitat fragmentation and isolation of colonies due to road building, housing and industrial developments. On their own, these developments rarely pose any major threat except for extremely rare species or regional variations of species which are present in very localised colonies... however, the combination of multiple developments over time can cause regional extinctions or the complete extinction of a distinctive regional species variation.
A good example of general butterfly variation is the Small Copper Lycaena phlaeas which also has a common variation known as Lycaena phlaeas form caeruleopunctata.
The Brown Argus, Northern Brown Argus and the intermediate 'Durham Argus' (also known as the Castle Eden Dene Argus) are forms of the same species which have evolved to be slightly difference in appearance and have slightly different lifecycles due to regional isolation. However, all three forms can breed successfully as they are the same species. The Durham Argus is known as a 'Cline'.
A cline is a term used in the study of population genetics, and is described as 'a gradual change of a character or feature in a species over a geographical area, often as a result of environmental heterogeneity'.
What are variations?
Variation may also occur over a butterflies individual life span. Young, freshly emerged butterflies tend to have a rich coloration and undamaged wings while old specimens may have damaged wings and coloration which has faded. This is generally due to the loss of surface scales on the wings. |
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| Age Variation |
| Dark Green Fritillary |
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| A fresh Dark Green Fritillary above left contrasts sharply with an aging individual on the right.
Find out more about the Dark Green Fritillary. |
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| Wear and Tear |
| Comma and Silver-washed Fritillary |
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| On the left, a rather tatty Comma showing the effects of both age and missing wing parts, probably the result of a bird strike... this individual making a lucky escape while on the right, a male Silver-washed Fritillary showing the effects of age.
Find out more about the Comma and the Silver-washed Fritillary |
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