Echiumacalles, 2010

Stüben, Peter E. & Astrin, Jonas J., 2010, Molecular phylogeny in endemic weevils: revision of the genera of Macaronesian Cryptorhynchinae (Coleoptera: Curculionidae), Zoological Journal of the Linnean Society 160 (1), pp. 40-87 : 66-68

ECHIUMACALLES STÜBEN & ASTRIN GEN. NOV.

( FIG. 12A–E )

Type species by monotypy: Acalles anagaensis Stüben, 2000

Behne, 2000; Stüben, 2000a; Sprick & Stüben, 2000; Stüben et al., 2003; Germann, 2004; Stüben & Germann, 2005; Germann & Stüben, 2006.

The species of the genus Echiumacalles Echiumacalles anagaensis (Stüben, 2000) comb. nov. (formerly: Acalles , Dendroacalles ) – Tenerife: Anaga Mts (including type locality), La Gomera

An extensive description of the only species of this genus, Echiumacalles anagaensis (Stüben, 2000) (formerly: Acalles , Dendroacalles ), is presented in Stüben (2000a: 80–82).

Description

Size: 4.8–5.9 mm.

Head: Rostrum of the ♂ short, dark brown, with deep and close punctures, half as long as – or slightly longer than – the pronotum; the rubiginous rostrum of the ♀ three-quarters as long as pronotum, more slender and more distantly dotted; the second antennomere one-quarter shorter than the first, the third antennomere slightly longer than wide and the following antennomeres globular.

Pronotum: 1.06–1.16¥ as long as wide, widest at the end of the basal second fifth, at the sides towards the base narrowing rectilinear, towards the foremargin more rounded with a lateral depression; without a hollow on the disk of pronotum; at the front margin and on the disk of pronotum with same accumulations of dark, two to three times as long as wide, upright bristles; at the sides of the pronotum with a small white fascia.

Elytra: Elongated, ‘canoe-like’; 1.51–1.55¥ as long as wide, widest at the end of the basal quarter, in the middle weakly rounded laterally, towards the apex nearly narrowing rectilinear. A peculiar characteristic is the deep black (nearly isosceles) triangular fascia on the elytral slope ( Fig. 12A ).

Legs: Short; the front femur reaching the foremargin of pronotum; the hind femur reaching the penultimate sternite; femur annulated with one, tibia with two dark rings.

Venter: The second abdominal sternite maximum as long as both following sternites combined; with most fine, bright bristles long and slender. Metasternum between the mesocoxae very slender and at most half as wide as mesocoxae in diameter.

Aedeagus: Endophallus only with a double ‘mushroom-shaped’ structure ( Fig. 12B ).

Differential diagnosis: The genus can be easily distinguished from the other taxa of the Canarian archipelago by the flattened, conspicuously elongated habitus, the monophagous host plant relation ( Echium strictum ) and especially by the deep black, equal-sided triangular mark on the elytral slope. Although all species of Dendroacalles and also some species of Silvacalles also present a double structure of the internal sac of aedeagus, there is no further species with a ‘mushroom-shaped’ structure of the endophallus ( Fig. 12B ). See also the ‘Key to the genera and subgenera of Macaronesian Cryptorhynchinae’.

Discussion: Placing the single species of this new genus into any of the existing higher taxa of the Macaronesian Islands always seemed problematic. Only preliminarily was it joined with the succulicole species of the genus Dendroacalles : the Acalles euphorbiacus- group ( Stüben, 2000a: 82), which now represents the subgenus Euphorbioacalles Stüben (2005) . Once again the only reason for this taxonomic decision lay in the double structure of the internal sac ( Fig. 12B ). Meanwhile, it has been proven (Germann, 2004; Stüben & Germann, 2005) that Echiumacalles anagaensis is the only cryptorhynchine species of the entire western Palaearctic region living monophagously on a species of Boraginaceae ( Echium strictum L.) ( Fig. 12C ). It has an elongated, flattened habitus ( Fig. 12A ) and is therefore distinct from the more ‘compact’ species of Euphorbioacalles ( Fig. 4A ) that develop on representatives of the spruce family ( Euphorbiaceae ). The mitochondrial reconstruction clearly rejects the hypothesis of Echiumacalles anagaensis belonging to the genus Dendroacalles . However, the tree also shows a conspicuously high (and fully supported) proximity of Echiumacalles anagaensis to Ficusacalles senilis ( Fig. 1A ). Nevertheless, morphological and ecological reasons forbid the joining of these two genera. The species of Ficusacalles live in other habitats and on different host plants on the Canary and Selvagens Islands (see below) and have a more robust and ‘compact’ habitus while also featuring a distinct endophallic shape (cf. Fig. 13A–E ). This led to our decision to establish the new monotypic genus Echiumacalles .

Etymology and biology: The name Echiumacalles refers to the host plant of Echiumacalles anagaensis (type locality: Anaga Mts, Tenerife), Echium strictum . Recently, Echiumacalles anagaensis was also found on Echium strictum on the island of La Gomera ( Germann & Stüben, 2006). Germann (2004) extensively describes the discovery of the host plant and its distribution on Tenerife. The verification of a member of the borage family ( Boraginaceae ) as host plant of a cryptorhynchine species was quite a surprise after a long period of studying – without success – numerous Canarian and Madeiran plants of this family, especially as these plants use phytochemicals like pyrrolizidine alkaloids (usually strongly toxic to insects) as a defence strategy against herbivores. The genus Echium is represented on the Canary Islands by 23 species out of which 22 are endemic. This suggests that it might be worthwhile to look for further new species of Echiumacalles on all Macaronesian Islands, especially investigating plants of the borage family.

Distribution: Only known from the Anaga Mountains on Tenerife and from La Gomera.

Figures

Figure 1. A, Bayesian 50% majority rule consensus for the two analysed mitochondrial genes. Numbers indicate nodal posterior probabilities. The scale shows the expected nucleotide substitutions per site. Abbreviations in parentheses denote subgenus (see text). Genus names in bold indicate new nomenclature. Circles mark colonization events (in black: invasive species). For many Macaronesian species, the respective host plants are depicted. The second page of the tree shows the taxa corresponding to the ‘Atlantic clade’. B, chronogram based on relaxed phylogenetic analysis of the two mitochondrial genes, using the uncorrelated lognormal model of substitution rate variation. Numbers next to the nodes indicate mean divergence times (in Myr), with 95% confidence intervals of divergence times depicted as bars at the corresponding nodes. N.B. Although the underlying topology is that delivered by MrBayes, BEAST does not allow polytomies, which it resolves arbitrarily.

Figures 2–22. Morphological, biological, and ecological comparison of the genera and subgenera of Macaronesian Cryptorhynchinae along with the respective sections of the tree; (TS) = type species. Figures 4E and 5E show a section of the tree that results when 16S sequences for Aeoniacalles aeonisimilis* and Dendroacalles euphorbiacus* are excluded.