Adelaeus anachoretus Ratcliffe, 2014

Ratcliffe, Brett C., 2014, A New Genus and Species of Dynastinae (Coleoptera: Scarabaeidae) from the Galápagos Islands, Ecuador, other New Species of Cyclocephalini, Pentodontini, and Phileurini from South America, and a Revised Key to the Genera of New World Pentodontini, The Coleopterists Bulletin 68 (4), pp. 663-680 : 663-680

Adelaeus anachoretus Ratcliffe , new species ( Figs. 17–20 )

Type Material. Holotype male with labels:

“Rt. wing. [with tiny wing mounted on label]//

Chatham I. / Galapagos. / VII-1906 // Coll. by F. X. Williams // Neoryctes / galapagoensis/ (G. R. Water.)” and with my red holotype label. Type deposited at the U.S. National Museum (Washington, DC) .

Holotype. Male. Length 15.6 mm; width 8.9 mm. Color reddish brown. Head: Frons coarsely rugopunctate except for narrow, nearly smooth area mesad of each eye. Frontoclypeal suture weakly impressed, extending to each lateral margin. Clypeus subtriangular, apex narrowly subtruncate, surface transversely rugose; base either side of middle and just in front of frontoclypeal suture with small low, transverse tubercle. Mandibles large, exposed, arcuate up to apex where small, subapical “tooth” with longitudinal ridge beneath. Interocular width equals 4.8 transverse eye diameters. Antenna 9-segmented, club subequal in length to antennomeres 2–6. Pronotum: Surface convex, lacking fovea or tubercles, punctures moderate in size and density, becoming slightly denser on apical third. Base with marginal bead except in front of scutellum where obsolete. Elytra: Surface with moderately large, moderately dense, shallow, glabrous punctures, some in indistinct rows. Apices bluntly rounded, appearing foreshortened, elytra together wider than long. Hind wings short, nearly vestigial, 4.0 mm in length. Pygidium: Surface rugulose in basal fifth and angles. Disc shiny, with a few small, glabrous punctures, becoming impunctate on apical third. In lateral view, surface weakly convex (nearly flat). Legs: Protibia tridentate. Metatibia at apex slightly expanded, subtruncate, with 15 short spinules. Venter: Prosternal process long, subrectangular, thick, slightly recurving, apex truncate. Parameres: Broadly rounded in basal half, distal half long, slender, and with pointed apices ( Figs. 18–19 ).

Etymology. The specific epithet is derived from the Greek anachoretes, meaning a hermit or recluse. It is used here as a masculine noun in apposition to re-emphasize, along with the generic name, the reclusiveness of this rare species.

Distribution. Adelaeus anachoretus is known only from San Cristóbal Island in the Galápagos Archipelago, Ecuador. San Cristóbal was the first island in the archipelago visited by Charles Darwin in 1835 while on the Beagle expedition.

Locality Record. ECUADOR (1): GALÁPAGOS (1): San Cristóbal Island ( Fig. 20 ).

Temporal Distribution. July (1).

Diagnosis. The characters listed in the generic diagnosis, greatly reduced flight wings, the unique form of the parameres, and the occurrence in the Galápagos Islands will serve to distinguish this species. The only other New World dynastine with this form of parameres is Tomarus rostratus Dupuis.

Natural History. The holotype of A. anachoretus lacks detailed collecting information. It may have been collected during the 1905–1906 California Academy of Sciences expedition to the Galápagos Islands and then possibly exchanged or gifted to the USNM. The July 1906 material collected by F. X. Williams is mentioned in Van Dyke’ s (1953) overview of the Coleoptera of the Galápagos Islands, but San Cristóbal Island is not mentioned as among the localities for the 18 dynastine specimens collected by Williams. Since no other specimens have been found in the intervening 108 years, it could be surmised that A. anachoretus is an extremely rare endemic that has not been observed in previous collecting efforts due to a secretive life style, or that it is now extinct due possibly to the introduction of predatory invasive vertebrates. Cook et al. (1995) observed that the then-known four Neoryctes species in the Galápagos Islands were all rare, due possibly to the inaccessibility of the high elevation habitat, short period of adult nocturnal activity that coincided with rain, or predation by introduced rats, pigs, and ants.

The volcanic islands of the Galápagos Archipelago are approximately 800–1,000 km west of mainland Ecuador. All of the islands are volcanic in origin and semiarid with the lowlands having a short wet season, while the highlands catch fog and rain clouds and are moister ( Van Dyke 1953). Tye et al. (2002) observed that isolation of the islands has led to a high degree of endemism for vertebrates, and Peck (2005) suggested that limitations for establishment of colonizing beetles is more related to the strongly seasonal, semiarid climate of the large, lowland areas of the islands and the prevalence of large areas of young and unweathered lava substrates that are not conducive to beetles. Peck (2005) recorded the beetle fauna of the Galápagos Islands at 56 families, 297 genera, and 486 species with 266 endemic species, 110 indigenous species, and 110 introduced species. Previously, Neoryctes was the only endemic genus of scarabs in the Galápagos Islands. Peck (2005) concluded that generic endemism and species diversification is strongly correlated with secondary loss of flight wings after colonization, and that most colonization has not been followed by much speciation. Both A. anachoretus and N. linelli inhabit San Cristóbal ( Fig. 20 ), and both have reduced hind wings.

Figures

Figs. 17–19. Adelaeus anachoretus, holotype. 17) Habitus; 18) Parameres, caudal view; 19) Parameres, lateral view.

Fig. 20. El Junco area on Isla San Cristóbal, Galápagos Islands, possible habitat for Adelaeus anachoretus. Photograph courtesy of K. Thalia Grant (Isla Santa Cruz, Galapágos Islands).