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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
 
What is a species ?

So what exactly is a species ? Well basically it is a creature that can only interbreed with another biologically identical creature. To prevent interbreeding, each species has uniquely shaped genitalia - the male "key" only fitting the correct female "lock".

Museums are full of species that are so rare that they may be known only from one or two specimens. Often the male and female of a particular butterfly are totally different in appearance, and may not initially be recognised as belonging to the same taxon. By examining the "lock and key" genitalia, taxonomists have often discovered that 2 insects previously classified under entirely different genera are actually the same species !

Closely related species are often so similar that it is not possible from visual examination to determine whether they represent varieties or subspecies of one butterfly, or whether they are biologically different ( but visually identical ) species. Conversely, sometimes a single species will produce several varieties or morphs which are very different visually, but biologically identical.

A good example of the latter is the Mocker Swallowtail Papilio dardanus - the male is cream in colour, and possesses tails on the hindwings, but the female has an entirely different wing shape, does not possess tails, and produces several forms, each differing in colour and pattern, but all mimicking various toxic species from the Danaine genera Danaus and Amauris, and the Acraeine genus Bematistes.

Cladistics

In order to unravel such mysteries, taxonomists rely heavily on cladistics ( a system of taxonomy based on the quantitative analysis of comparative data, which is used to construct cladograms illustrating the assumed phylogenetic relations and evolutionary history of groups of organisms ). Note the use of the word "assumed".

In simple terms, if two sample specimens were analysed, and found to share only a very low number of common characteristics, this would imply that they should be placed in separate families. At the other extreme, if the number of shared characteristics was extremely high, it would imply that the taxa were very closely related members of the same genus. For both sample insects to be recognised as belonging to the same species, ALL characteristics ( of the same sex ) would of course be identical.

Proponents of species fixism here point out that while establishing common characteristics might indicate the 2 or more samples are "related", that does not necessarily prove that they evolved from a common ancestor - it could simply be the case that a "creator" used common design characteristics.

The primary method favoured by entomologists involves microscopic examination and measurement of the constituent parts of the genitalia of both sexes. Dozens, or even hundreds of these characteristics need to be analysed and quantified to enable the relationships between species to be established.

Genitalia analysis is the primary tool used in determining relationships and "evolutionary trees", but only tells part of the story. Other methods of determination include study of wing-scale structure, leg structure, egg, caterpillar and chrysalis morphology, larval host-plant usage, behavioural analysis and DNA sequencing.

Hybrids

Despite Nature's mechanisms for the prevention of interbreeding, hybridisation between species does occasionally occur, but hybrids are by definition infertile, so they cannot pass on their characteristics to another generation.

 

... and what is a subspecies ?

Climatic extremes ( e.g. ice ages or periods of localised or global warming ) can cause habitats such as rainforests and temperate grasslands to shrink, forcing populations of formerly widespread butterflies to contract and become isolated from each other for thousands of years. These isolated colonies develop into "subspecies" which exhibit minor visual and biological differences compared with the ancestral populations.

It is generally assumed that, given sufficient time, they would evolve into new species. However, DNA analysis of various subspecies of Ornithoptera on remote islands in Melanesia have shown that they contain less genetic material than their brethren on mainland Papua, quite the opposite of what we would expect if evolution was at work.

The term "sub-species" might therefore be regarded as an unscientific term, but one that is in very widespread usage, describing visually separable "races" that have been geographically isolated from each other. In isolation, genetic entropy has resulted in visual differences between the "sub-species" and the ancestral species, but biologically they are the same species, and no evolution has taken place.

Climatic changes and their effect on the expansion and contraction of ( e.g. ) rainforest refugiae can result in previously isolated "sub-species" becoming re-united, so it is quite possible for more than one "sub-species" to occur at any particular location, despite them having "evolved" in isolation.

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Text and butterfly photographs protected by Copyright © Adrian Hoskins 2007-2008, and must not be reproduced or published in part or in whole elsewhere in any form without written permission from Adrian Hoskins. Breach of copyright will be pursued by litigation.
 
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