Allometric growth in two species of Ectobius (Dictyoptera: Blattidae)

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Abstract

Allometric growth of the postembryonic stages of Ectobius lapponicus (Linn.) and E. panzeri Stephens is described and analysed. Alternative methods of computing the allometric growth equation are discussed and applied, with the necessary significance tests, to a large number of skeletal structures in all developmental stages of each sex. The validity of Dyar's Law and its modifications are assessed quantitatively.

Summary:

The growth in linear dimensions of 74 exosketetal structures has been studied quantitatively in all instars of both sexes of Ectobius lapponicus and E. panzeri.

Almost all the investigated structures show some statistically significant degree of allometric growth, but relatively few of them grow by simple allometry. Some possible reasons for this are indicated.

Well-defined growth gradients exist in the appendages and along the main axis of the body. Allometric growth contours, showing sexual and specific differences, express the temporal and spatial variations in the allometric growth ratio.

The limitations of Dyar's Law and Przibram's Rule are discussed and it is shown that conformity with Dyar's Law is not improved by allowing for differences in the duration of the instars.

It is emphasized that allometric growth studies should involve the choice of a suitable reference dimension and the selection of an appropriate statistical model to which the growth data are fitted. The estimation of the allometry parameters a and b, as well as the appropriate significance tests, depend on the model chosen, though the two models compared in this study do not yield appreciably different estimates.

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