Morphometric patterns among diving beetles (Coleoptera: Noteridae, Hygrobiidae, and Dytiscidae)

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Abstract
A study of shape and size in relation to swimming strategies among Hydradephaga, with an emphasis on Dytiscidae, was performed with nearly 1600 adult specimens belonging to the families Noteridae (2 species), Hygrobiidae (1 species), and Dytiscidae (74 species). The data were studied by means of bivariate correlations, scatter plots, and two multivariate statistical methods (factor and cluster analysis). The main morphometric groups found included (i) large to medium-sized, streamlined, wide species with the maximum width in the rear part of the body and the maximum height in the front part, with short tibiae and long tarsi; they are considered to be adapted to high-speed swimming in open waters; (ii) small to medium-sized species with a spherical body and long femora; they are considered to be adapted to manoeuvring in stagnant waters; (iii) small species with a discontinuous outline, a narrow body, and long, slender legs; they are considered to be poor swimmers in running waters; and (iv) small to medium-sized species having, in general, a streamlined, relatively high body with short, wide legs; they are considered to be adapted to crawling among dense vegetation or detritus. Despite the clear relationships between systematics and morphometry, most characters were found to be homoplastic a number of times within the families studied. This supports the adaptive interpretation of the morphometry of the species.