Die Antennen‐Putzeinrichtung der Adephaga (Coleoptera), parallele evolutive Vervollkommnung einer komplexen Struktur

SUMMARY The antenna cleaner of the Adephaga (Coleoptera), parallel evolutionary perfection of a complex structure Independent evolutionary perfection of a complex character ist to be expected in a splitting phylogenetic line, if selective advantages for improving this character persist in the various lines after splitting. Independent perfection leading to very similar results is termed “parallel perfection”. It can either be based on a narrow channelling, due to limitations of the evolutionary substrate (i. e. morphological structures and patterns of behaviour, inherited from the common ancestor), or on very specific functional advantages. The evolution of the antenna cleaner on the protibia of adephagous beetles is analysed under this aspect. The phylogenetic relationships within the Geadephaga are discussed. After defining the terms “anisochaetous” and “isochaetous” somewhat differently from previous usage, the two phylogenetic lines Anisochaeta (Carabidae in a broad sense) and Isochaeta (Metriidae, Ozae-nidae, Paussidae) may be considered sister groups. The Cicindelidae might have split off from the line of the Anisochaeta very early. The Rhysodidae are interpreted as an aberrant offshoot from the primitive adephagous stock. An attempt is made to reconstruct the antenna cleaner of the common ancestor of Anisochaeta and Isochaeta from the sum of plesiomorphous characters. This primitive cleaner might have corresponded in many respects to the array of setae found on an undifferentiated protibia (see comparison with mesotibia). The cleaner of the Cicindelidae, in spite of many plesiomorphous characters cannot be regarded as a model for the common ancestral form, because it already shows some differentiation towards the condition found in the Anisochaeta. The antenna cleaners of highly evolved Anisochaeta and Isochaeta, which correspond surprisingly well in many details, can be traced back to a common basis, but most of their conformities must have evolved independently. The following parallelisms were established: the ventral side of the tibia is shifted to the functional inner side and forms an oblique groove (cleaning channel); the antenna cleaning comb, originally placed transversely, becomes lengthwise oriented and is shifted in proximal direction; several setae are modified so as to form together a pressure clamp; the cleaning channel is completed by a spine-like extension projecting from the tibia; the terminal setal ring forms an additional comb. The gradual perfection of the antenna cleaner can be studied in the more primitive species in both the groups Anisochaeta and Isochaeta. Apparently, the two lines entered different pathways of perfection to begin with, and the cleaners became similar again by convergence later on. This indicates a very slight channelling effect of the common evolutionary substrate. The numerous conformities in the higher evolved genera must result from “parallel selection” (channelling for functional reasons). By observing grooming behaviour in primitive and highly evolved genera, the following advantages connected with the more complex structures could be established: the engagement of the antenna into the cleaning channel is facilitated; the mechanical strain on the antenna during grooming is reduced; the cleaning of antennae and eyes becomes more effective. That the antenna cleaner itself can better be kept clean by a comb of the Mesotibia was proved quantitatively.