Macrodactylini

Fuhrmann, Juares, 2019, Taxonomy of Neotropical genera Compsodactylus and Dasyus and notes on claw movement in Macrodactylini (Coleoptera: Scarabaeidae: Melolonthinae), Zootaxa 4679 (1), pp. 139-163 : 155-160

Macrodactylini tarsal claw flexion

The tarsal claw flexion of Macrodactylini shows two main patterns. The claw flexion process is intermediated by muscular retraction of unguitractor, a small sclerite contiguous to empodium and connected to claws by membrane ( Snodgrass 1935).

Claws in rest position (empodium protracted) are positioned subparallel to each other and have their longitudinal axis parallel to longitudinal axis of tarsus, when claws and empodium are retracted two main patterns are observed: type I, a claw stays with its longitudinal axis strongly divergent or almost oppositely directed regarding other claw, and stays subtransversally oriented regarding longitudinal axis of tarsus, the inner deflection of claws remains in resting position or is deflected less than 45 degrees ( Fig. 41 A–C); type II, the longitudinal axis of each claw stays subparallel to each other (as in resting position), the inner deflection of claws is deflected almost 180 degrees regarding resting position ( Fig. 44 detail).

It appears that type I flexion is mainly related to the spreading process of claws, probably to enlarge the contact area between claws and contact surface. Flexion type II appears related to the grasping process.

The above-mentioned claw deflection types are useful as generic diagnoses for macrodactylines (as supplement data to the key provided by Fuhrmann & Vaz-de-Mello 2017):

Type I is found in all legs of: Ampliodactylus Smith, 2008 , Alvarinus Blanchard, 1850 , Byrasba Harold, 1869 , Canestera Saylor, 1938 , Ceratolontha Arrow, 1948 , Chariodactylus Moser, 1919 , Clavipalpus Laporte, 1832 , Compsodactylus , Dicrania LePeletier & Audinet-Serville, 1828 , Euryaspis Blanchard, 1851 , Extenuoptyophis Smith & Mondaca, 2015 , Hamatoplectris Frey, 1967 , Hieritis Burmeister, 1855 , Isonychus Mannerheim, 1829 , Insimuloissacaris Smith & Mondaca, 2015 , Issacaris Fairmaire, 1889 , Junkia Dalla Torre, 1913 , Macrodactylus Dejean, 1821 , Manodactylus Moser, 1919 , Modialis Fairmaire & Germain, 1860 , Neuquenodactylus Smith & Mondaca, 2015 , Paulosawaya Martínez & d’Andretta, 1956 , Phytholaema Blanchard, 1851 , some species of Plectris LePeletier de Saint–Fargeau & Audinet–Serville, 1828 , Pristerophora Harold, 1869 , Pseudodicrania Gutiérrez, 1950 , Pseudoserica Guérin-Méneville, 1838 , Pusiodactylus Smith, 2008 , Ptyophis Redtenbacher, 1868 , Rhinaspis Perty, 1833 , and Schizochelus Blanchard, 1850 . All these genera have a short empodium, inner area of tarsomere V without carina or tubercle and with claw sulci short or indistinct.

Type II is found in all legs of: Ancistrosoma , Ceraspis , Chariodema , Faula , Mallotarsus Blanchard, 1850 , Manopus Laporte, 1840 , Pectinosoma Arrow, 1913 , and Pseudopectinosoma Katovich, 2011 . All these genera have a long empodium, inner area of tarsomere V with a proximal raised carina or tubercle and with claw sulci long.

Calodactylus and Dasyus have type I in prothoracic legs (with empodium and sulci short) and type II in medial and metathoracic legs (with empodium and sulci long).

Anomonyx Saylor, 1940 , Barybas , Oedichira Burmeister, 1855 , Philochloenia Dejean, 1833 , and some species of Plectris have same claw deflection pattern of Calodactylus and Dasyus but all empodia are short.

The monotypic Astaenoplia Martínez, 1957 (including A. miserabilis Martínez, 1957 ) is not studied, but it is originally described with protarsal and mesotarsal claws bifid and with short empodium, and metatarsal claws simple and empodium absent ( Martínez 1957). The claw deflection type needs to be checked for this taxon. The metatarsus without empodium is not found in other Macrodactylini but is found in Hopliini .

The Asian Diphycerini ( Dichelomorpha Burmeister, 1855 , Dicheloschema Moser, 1924 , Diphycerus Deyrolle & Fairmaire, 1878 , and Xenoceraspis Arrow, 1920 ) and the New World Dichelonychini ( Coenonycha Horn, 1876 , Dichelonyx Harris, 1827 , and Gymnopyge Linell, 1896 ) are other Melolonthinae tribes that have tarsal deflection type II in all legs and empodium and claw sulci long, similar to Ancistrosoma , Ceraspis , and other above mentioned genera.

A similar grasping claw movement is also observed in Rutelinae and Hopliini (Melolonthinae) , two large scarab lineages that are widely known by their claw movement (e. g., Arrow 1917; Lacroix 1997). These tarsal characteristics were used to group Hopliini within Rutelinae (e. g., Baraud 1985), but phylogenetic hypotheses show two distinct evolutionary events in both taxa ( Ahrens et al. 2011). Despite the importance of grasping claws in systematics of scarab groups, within Melolonthinae these characteristics are diagnostic for some tribes (as Diphycerini, Dichelonychini , and Hopliini ), and within Macrodactylini they are used to differentiate some genera, as above noted. The cladistic implications of the characters discussed are being further studied by the author.

Figures

FIGURES 38–45. Dasyus collaris. 38, prothorax, anterior (right side with cervix and coxa omitted); 39, prothorax, posterior (right without intersegmental membrane and coxa omitted); 40, prothorax, ventral (right side with hypomeron bridge detached); 41, protibia-tarsus of males (with protracted pretarsus), details: a, tarsomere V with retracted pretarsus, b–c, tarsomere V, inner (with protracted/retracted pretarsus, respectively), d, tarsomere I detail; 42, 43, mesotibia-tarsus (female, male); 44, metatibiatarsus of male (with protracted pretarsus) and detail of tarsomere V with retracted pretarsus; 45, apex of metatibia. am1, angulate margin between hypomeron and posterior fold of pronotum; am2, angulate margin between dorsal and ventral areas of posterior fold of pronotum. Scale = 1 mm.