Monday 27 November 2023

Anchonidium selvanum: A new species of Weevil from northern Portugal.

The Weevil genus Anchonidium currently contains three valid species, all of which are found in Western Europe. Several from Africa and the Caucasus region which were previously assigned to the genus are now considered to be erroneous, and some of these have been reassigned to other genera.

In a paper published in the journal Alpine Entomology on 24 October 2023, Christoph Germann of the Naturhistorisches Museum Basel and the Naturhistorisches Museum Bern, and Carlo Braunert of the Musée National d’Histoire Naturelle de Luxembourg, describe a new species of Anchonidium from northern Portugal. 

The new species is named Anchonidium selvanum, where 'selvanum' refers to the ancient native Oak-forests of Portugal, which are referred to in Portuguese as 'la selva', which is the environment in which the Weevils were found. These Weevils are 2.1-3.3 mm in length, excluding the rostrum (snout) and auburn in colour. Their dorsal surface is covered with large punctures arranged in lines which run lengthwise along the body, the ventral surface has similar punctures, but more randomly arranged.

Anchonidium selvanum. (1) Male. (2) Female. (3) Male underside. Germann & Braunert (2023).

The distribution of all four species of Anchonidium follow mountain chains and river valleys in Portugal. Anchonidium braunerti is found in the Serra de Monchique south of the Rio Tajo, at altitudes of about 890 m above sealevel, on the upper parts of mountains where heather and mosses dominate, but where Oak forests were found on the lower slopes in the past but are now gone. Anchonidium spathiferum is found in the Serra da Estrela at altitudes of about 1290 m above sealevel, again in an environment dominated by heather and mosses, above slopes that were once covered by Oak woodland. Both of these species are considered rare. Only Anchonidium unguiculare is more widely distributed being found in Oak forests from Morocco to southern England. Anchonidium selvanum is still relatively common within its environment, the ancient Oak woodlands of the Serra do Marão and Serra do Alvão, at altidudes of between 750 m and 1180 m above sealevel.

Records from Anchonidium sensu stricto in Western Europe. Anchonidium unguiculare (blue dots), Anchonidium braunerti (green dot), Anchonidium spathiferum (red dot) and Anchonidium selvanum (yellow dots). Germann & Braunert (2023).

The Oak woodlands in which Anchonidium selvanum is found are a relic of ancient woodlands which once covered much of the mountains of Portugal, and which today are threatened by over-extraction of timber, and replacement of the Oaks by plantations of straighter, faster growing species valued by the timber industry, such as Eucalyptus and Mimosa trees from Australia or the Aleppo Pine. Pinus halepensis. Monocultural stands of these trees create a very different environment to ancient Oak wooklands, which is not a usable habitat for species which evolved in those woodlands. Worse still, all of these trees are addapted to survive periodic forest fires, which clear rival trees (and the wildlife dependant on those trees) from the environments where they are found. Their introduction has led to an increased fire frequency in mountainous areas of Portugal, presenting an additional threat to its indigenous wildlife. For this reason, Germann and Braunert conclude that Anchonidium selvanum should be regarded as a threatened species, but also that it can serve as a useful indicator species for the health of the woodlands in which it is found.

(Top) Habitat at type locality of Anchonidium selvanum at Bobal, 880 m above sealevel, Serra do Alvão. A small remaining part of the ancient Oak forest with Mosses, Lichens and a deep leaf litter layer at ground where the new species lives in remarkable densities. (Bottom) Remains and replantation of Oak forest in the Serra do Marão close to Ansiães. A good example for small remains of the ancient forests where only few individuals of Anchonidium selvanum were found. Carlo Braunert in Germann  Braunert (2023).

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