Morphometric patterns among diving beetles (Coleoptera: Noteridae, Hygrobiidae, and Dytiscidae) I. Ribera and A.N. Nilsson 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. RCsumC : On trouvera ici les rCsultats d'une Ctude de la forme et de la taille en relation avec les stratkgies natatoires chez les HydradCphages, Noteridae (2 espkces), Hygrobiidae (1 espkce) et, plus particulikrement, chez les Dytiscidae (74 espkces). Les donnkes ont CtC analysCes au moyen de corrklations bidimensionnelles, de diagrammes de dispersion et de deux mkthodes statistiques multidimensionnelles (analyse factorielle et analyse des groupements). Les principaux groupes morphomCtriques form& sont : (i) les espkces de taille moyenne ou grande, larges et fusiformes, dont la largeur maximale se trouve la partie arrikre du corps et la hauteur maximale, a la partie avant, aux tibias courts et tarses longs; ces espkces sont considCrCes comme adaptkes a la nage rapide en eau libre; (ii) les espkces de taille petite ou moyenne a corps sphkrique et a femurs longs; ces espkces sont considCrCes comme adaptkes aux eaux stagnantes; (iii) les espkces de petite taille a silhouette irrkgulikre, au corps Ctroit et long, aux pattes minces; ces espkces sont considCrCes comme de mauvais nageurs en eau courante; (iv) les espkces de taille petite ou moyenne, fusiformes, a corps relativement haut, A pattes courtes et larges; ces espkces sont considCrCes comme adaptCes a la reptation dans la vCgCtation dense ou les dktritus. En dCpit des relations Cvidentes entre la morphomktrie et la classification, la plupart des caractkres se sont avCrCs homoplastiques un grand nombre de fois chez les familles CtudiCes, ce qui appuie l'hypothkse selon laquelle la morphomktrie a valeur d'adaptation chez ces espkces. [Traduit par la Rkdaction] Introduction invasions of the aquatic medium (Lawrence and Newton 1982; Evans 1982, 1985; Nichols 1985; Beutel and Roughley Noteridae, Hygrobiidae, and Dytiscidae are three families of 1988), that have resulted in the Haliplidae, Gyrinidae, and predacious hydradephagan diving beetles that capture their the group formed by the Noteridae, Amphizoidae, Hygro- prey while actively swimming. agree that the biidae, and Dytiscidae. All these authors agree on the mono- aquatic Ade~haga are polyphyletic, with three Dhyly of each of the three families studied here. In these . - - Received April 4, 1995. Accepted August 10, 1995. families the adults have comparable shapes over a wide size range. In the fauna of the Pyrenees, the size range is from I. Ribera1 and A.N. Nilsson. Department of Biology, less than 2 mm in Bidessus minutissirnus (Germar) to more University of Umei, S-901 87 Umei, Sweden (e-mail: than 30 mm in Dytiscus marginalis L. annilsson@biovax.umdc.umu .se). The body shape has always been interpreted as an adap- ' Present address: Environmental Sciences Department, The fation to swimming. Although gravity is not an imponant Scottish Agricultural College, Auchincruive, Ayr factor for small aquatic organisms, shape and size are deter- KA6 5HW, U.K. (e-mail: i. ribera@au.sac.ac.uk). minant characteristics that conform to the drag forces and the Can. J. Zool. 73: 2343-2360 (1995). Printed in Canada 1 Imprime au Canada