Calosoma (Castrida) granatense Géhin, 1885
Calosoma granatense Géhin, 1885: 59 (type: N.vlle Grenade; Muséum National d'Histoire Naturelle, Paris)
Calosoma galapagoum Howard, 1889: 191 (misnomer pro galapageium, Hope)
Calosoma howardi Linell, 1899: 251 (type: Duncan island; National Museum of Natural History, Washington)
Calosoma (Callistriga) galapageium Breuning, 1927: 200
Caminara (Camedula) galapageia Lapouge, 1932: 419
Castrida (Microcalosoma) galapageium Jeannel, 1940: 98
Calosoma darwinia Van Dyke, 1953:10 (type: Abemarle island, near Villamil 1300ft; California Academy of Sciences, San Francisco)
Calosoma (Castrida) galapageium Gidaspow, 1963: 289
Castrida granatense Basilewsky, 1968: 189
Castrida granatense darwinia Basilewsky, 1968: 190
Castrida granatense floreana Basilewsky, 1968: 190 (holotype: Floreana island, Black Beach; Institut royal de Sciences naturelles de Belgique, Bruxelles)
Length 14-23 mm. C. granatense is the most common species in the Galapagos Archipelago. As all the endemic species of the Archipelago it has the elytral margin even, without trace of serration. The color of its upper body is metallic bluish green. In an high percentage of specimens, the basal seta of the pronotum is lacking. The metaepisternum is quite smooth with some scattered large punctures.
Jeannel (1940) has considered C. granatense in the subgenus Microcalosoma, previously created by Breuning (1927: 123) for C. linelli, another species of the same Archipelago, but the subgenus has been considered superfluous by Gidaspow (1953), followed in this by Basilewsky (1968) and all the later authors.
C. granatense exists in almost all the islands of the Archipelago, (Archipiélago de Colón): Baltra (South Seymour); Darwin (Culpepper); Española (Hood); Fernandina (Narborough); Floreana (Charles), including Gardner; Genovesa (Tower); Isabela (Abemarle); Marchena (Blindoe); Pinta (Abingdon); Pinzón (Duncan); Santa Cruz (Indefatigable ), including Eden; Santa Fe (Barrington); San Cristobal (Chatham); Santiago (San Salvador, James), including Rabida; Seymour ; Wolf (Wenman).
C. granatense is widespread at low altitude but it is also present, although more rare, at altitudes up to 500m, on Fernandina and on the vulcanoes of Isabela. These altitude populations may present some cases of polymorphism and they may include some individuals with reduced wings. However, in the heights of the oldest islands, namely San Cristobal, Santiago and Santa Cruz, we find other populations, pertaining to three distinct species (C. linelli, C. galapageium and C. leleoporum ), which surely have ancestors in common with C. granatense but that are altogether brachypterous and variously adapted as ground dwellers.
In this regard it should be noted that, because of their capability to react to the selection pressure, the Calosoma of Galápagos Archipelago were the subject of several studies on population genetic structure and differentiation (Desender et Al, 1989, Desender et Al, 1991, Desender et Al, 1998, Dhuyvetter et Al, 2002, Hendrickx et Al, 2015).
It follows from these studies that the populations of the different islands have a relatively high genetic differentiation and therefore long-distance dispersal would seem rather rare. Conversely gene flow within populations of the same island tends to remain high. Therefore phenomena of speciation have been only possible in the most ancient islands, although the genetic isolation is not always perfect and were observed phenomena of introgression.
In the the more recently formed islands, this constant genetic flow has not allowed the morphological differentiation. However Basilewsky (1968) considered two of these populations as valid subspecies: darwinia Van Dyke 1953, localized in the south east of Isabela island, at medium altitude, and floreana Basilewsky 1968, described from Floreana Island, where it is the only occupant. These taxonomic distintions appear unsustainable both from the genetic point of view as well as from the morphological one. However it must be noted that in the south east of Isabela island, on the slopes of Volcano Cerro Azul, the population of the intermediate humid zones (darwinia) is characterized by a higher percentage of individuals with partial reduction of the wings, probably linked to a lower selection pressure (Desender et Al, 1991 cited by Erwin 2007: 95).
Examined specimens and literature’s data
(N.vlle Grenade, wrong locality label): (holotype of C. granatense , MNHN)
Ecuador, Galápagos Archipelago. Española (Hood), San Cristobal (Chatam): March bay (Basilewsky, 1968: 194); Santa Fé (Barrington) (Basilewsky, 1968: 196); Santa Cruz: Academy bay (EM, SB), Puerto Ayore (AC, EM, SB), Reserva de los Galapagos, 200m (Moret, 1986: 92), Horneman Farm, Comway bay (Basilewsky, 1968: 196); Floreana: Las Cuevas bay (sub C. granatense floreana; AVT), Black Beach (sub. C. granatense floreana, NMB); Baltra (SouthSeymour); Pinzón (Duncan): Summit and upper Caldera area (Basilewsky, 1968: 196); Santiago (James), Isabela (Abemarle): Banks bay, Tagos Cove, Cerro Alcedo (Basilewsky, 1968: 197), Near Villamil 1300ft. (sub. C. granatense darwinia, Basilewsky, 1968: 198), Isabela (sub C. granatense darwinia, AVT, NMP), Isabela alt. 1300ft (sub. C. granatense darwinia, NMB), Santo Tomás, Sierra Negra 180-490m (Moret, 1986: 92), Cerro Azul, volcano Darwin, Volcano Wolf (Peck, 2006: 106); Pinta; Genovesa (Tower): Darwin bay; Darwin (Culpepper) (Basilewsky, 1968: 197); Wolf (Wenman); Rábida; Eden; Gardner; Seymour; (Peck, 2006: 106).
Notes: C. granatense is winged, though in some populations you can find more or less commonly specimens with partially reduced wings. It is diurnal and nocturnal, easily attracted to light at night, and preferably it inhabits arid areas of dry vegetation at lower elevations, including tilled fields.
Adults were encountered in activity mostly during the warmer and more humid season in the months from December to May (Basilewsky, 1968), except some populations of zones at medium altitude on Santa Cruz and Isabela island the adults of which were found active in September, with cloudy weather and drizzle (Moret, 1986: 92). However, considering the different habitats where C. granatense fits, likely it can be found active during most of the year (Peck, 2006: 106).
The larva was described by Busato, Desender & Giachino (2001).
Amérique mer., N.vlle Grenade (Typus)
(coll. Muséum National d'Histoire Naturelle, Paris)
Ecuador, Galapagos is., Santa Cruz
Ecuador, Galapagos is., Santa Cruz, VII.65, Angermayer lg
Ecuador, Galapagos is., Isabela, 19.VI.1985,Onore lg.
(sub Castrida granatense darwinia Van Dyke)
(coll Vigna Taglianti)
Ecuador, Galapagos is., Floreana, Las Cuevas Bay,
29.VI.2001, R. Argano lg.
(sub Castrida granatense floreana Basilewsky)
(coll Vigna Taglianti)