Sonchiacalles muelleri (Stüben, 2000), Stüben & Astrin, 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

Sonchiacalles muelleri (Stüben, 2000) comb. nov.

(formerly: Acalles ) – La Palma (including type locality), El Hierro

The taxa of this new genus belong to the Acalles sonchi -group which has been revised several years ago ( Stüben, 2000a: 46–53).

Description

Size: 3.8–8.6 mm.

Head: Rostrum short, reaching two-thirds of length of pronotum; rostrum of ♂ wider, more robust and with dense and deep punctures going from the base to the apex.

Pronotum: 1.00–1.10¥ as wide as long; widest in the middle, outline almost linearly narrowed towards base and towards the constriction at the front margin regularly – in robust specimens strongly bellied – rounded. Punctures of pronotum very fine; pronotum sparsely covered with very small, dark bristles; without a clearly visible mid-groove or depression. The colouring corresponds with the darker basic cover of the elytra. Disc of pronotum flattened, the outline forming – in lateral view – together with the crown line of the elytra a straight line.

Elytra: Very elongated, often flattened; 1.40–1.76¥ as long as wide; widest in the middle, outline between middle and base mostly parallel (in Sonchiacalles muelleri slightly rounded), flanks with a slight lateral depression near the apex; the apex rounded obtuse angled. Punctured stripes on the disc of elytra fine up to the second interval, becoming more robust and pit-like and deeper towards the flanks where the punctures clearly overlap the intervals. The colouring is very contrasting: the basic cover is dark brown. On the first third there is a falciform fascia and on the slope of elytra a V-shaped, light brown, clearly contrasting fascia ( Fig. 11A ) with aggregations of bristles on the even, slightly elevated intervals. Here the acuminated bristles are at most 2¥ as long as wide. The flanks only sparsely covered with tiny bristles.

Legs: Short, the front femur reaching the front margin of the eyes, the hind femur reaching the last abdominal sternite. Tibia conspicuously annulated dark brown and black.

Venter: First abdominal sternite longer than the second, the second longer than sternite 3 and 4 combined. Metasternum between the midcoxae very slender and at most half as wide as midcoxae in diameter.

Aedeagus: With a simple, inverse v-shaped structure of the internal sac ( Fig. 11B ).

Differential diagnosis: The species of this new genus are easily distinguished from the species of the genus Aeoniacalles , to which they are not particularly related. The metasternum is more slender between the midcoxae, the elytra are conspicuously longer and more flattened, the legs are shorter and the endophallus without a basal ‘sickle’. See also the ‘Key to the genera and subgenera of Macaronesian Cryptorhynchinae’.

Biology and ecology: The species of this new genus live concealed on several endemic taxa of the genera Sonchus and Tolpis (cf. Fig. 11C ) on the western Canary Islands. They can be found at altitudes between 200 and 700 m at the upper limit of the succulent belt in the transition zone to the former thermophilous shrub-forest (‘bosque termófilo’), which is largely deforested today. The stridulatory organ and its mechanism ( Riede & Stüben, 2000) and the complex breeding behaviour of Sonchiacalles muelleri ( Stüben, 2000a, 2008a) have been studied extensively. The similar habitus, breeding behaviour, and larval development within Tolpis latex resulted in the hypothesis of Sonchiacalles being closely related to Madeiracalles pulverosus (Gemminger, 1871) of Madeira ( Stüben, 2002b). However, according to the molecular dendrogram this does not seem to be the case. Instead, M. pulverosus belongs to the discrete Madeiran clade ( Fig. 1A ).

Most of the more than 30 species of Sonchus s.l. of the Canaries are woody perennials and thus there might well be further undiscovered species of Sonchiacalles . Did the evolution of Sonchiacalles (like the radiation of Aeoniacalles ) follow its endemic host plants (cf. Kim et al., 2008) in a parallel cladogenesis (see Stüben, 2000c)? Concerning the cryptic speciation in Liparthrum bark beetles ( Curculionidae : Scolytinae ) Jordal, Kirkendall & Harkestad (2004) showed that these species, which are associated with different Macaronesian Euphorbiaceae , are clearly monophyletic.

Etymology: The name Sonchiacalles refers to the host plant relationship of S. sonchi and S. silosensis .

Distribution: Endemic to the western Canary Islands (apparently not on Madeira).

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.