Are flightless Galapaganus weevils older than the Galápagos Islands they inhabit?

Abstract

The 15 species in the weevil genus GalapaganusLanteri 1992 (Entiminae: Curculionidae: Coleoptera) are distributed on coastal Perú and Ecuador and include 10 flightless species endemic to the Galápagos islands. These beetles thus provide a promising system through which to investigate the patterns and processes of evolution on Darwin's archipelago. Sequences of the mtDNA locus encoding cytochrome oxidase subunit I (COI) were obtained from samples of seven species occurring in different ecological zones of the oldest south‐eastern islands: San Cristóbal, Española and Floreana, and the central island Santa Cruz. The single most parsimonious tree obtained shows two well‐supported clades that correspond to the species groups previously defined by morphological characters. Based on a mtDNA clock calibrated for arthropods, the initial speciation separating the oldest species, G. galapagoensis (Linell) on the oldest island, San Cristóbal, from the remaining species in the Galápagos occurred about 7.2 Ma. This estimate exceeds geological ages of the extant emerged islands, although it agrees well with molecular dating of endemic Galápagos iguanas, geckos and lizards. An apparent explanation for the disagreement between geological and molecular time‐frames is that about 7 Ma there were emerged islands which subsequently disappeared under ocean waters. This hypothesis has gained support from the recent findings of 11‐Myr‐old submarine seamounts (sunken islands), south‐east of the present location of the archipelago. Some species within the darwini group may have differentiated on the extant islands, 1–5 Ma.

Cryptic differentiation in the endemic micromoth Galagete darwini (Lepidoptera, Autostichidae) on Galápagos volcanoes

“…A similar trend is observed also in other Galápagos insects, such as the flightless Galapaganus weevils (Sequeira et al 2000). This biogeographic pattern suggests that colonization of the higher elevations, or a possible niche shift into humid highland habitat on the western islands of Fernandina, Isabela and Santiago by an arid lowland ancestor resulted in clearly differentiated populations from those in the lowlands.…”

“…Also, three divergent lineages were found representing at least two cryptic taxa in the giant tortoise population of Santa Cruz (Russello et al 2005). But no evidence of cryptic taxa has been revealed by genetic studies in insects in the archipelago (Finston & Peck 1997;Sequeira et al 2000Sequeira et al , 2008.…”

“…Galapaganus weevils (Sequeira et al 2000), Calosoma carabid beetles, Neoryctes scarab beetles and Gryllus crickets (Peck 2001). Such a scenario is consistent with the Galápagos having been drier than they are currently, with the vegetated areas of the wetter upland forests diminished or even absent (Colinvaux 1972).…”

Natural colonization and adaptation of a mosquito species in Galápagos and its implications for disease threats to endemic wildlife

“…Actual mutation rates would need to be between 200 and 1,000 times higher, respectively, to push the confidence intervals into the period of first discovery (Ϸ1535 A.D.) or colonization (early 20th century) by humans. In contrast, colonization by other endemic insects, some of which arrived soon after the archipelago was formed, was ancient (Ͼ5 million years ago) (21). This relatively recent colonization of A. taeniorhynchus compared with other Galápagos endemic fauna suggests that its arrival into a system with no other mosquito disease vectors may have precipitated alterations of the dynamics for existing endemic vector-borne pathogens or allowed novel diseases to invade, signatures of which might still be discernible today in both hosts and pathogens.…”

Coastal evolution on volcanic oceanic islands: A complex interplay between volcanism, erosion, sedimentation, sea-level change and biogenic production

“…In these archipelagos, the linear array of island edifices serves as "stepping stones" for organisms to expand their geographic range, thus promoting the process of internal colonization (i.e. within the same archipelago) -a process that explains how some species are apparently older than the geological age estimates of the islands they inhabit (Rassmann, 1997;Sequeira et al, 2000). On smaller, more remote archipelagos in which islands are arranged in clusters instead of linear chains and where the history of edifice emergence above sea level is typically non-linear, the process of biological colonization of new edifices is generally more complex and somewhat more erratic.…”