Acalles echinatus

Schütte, André & Stüben, Peter E., 2015, Molecular systematics and morphological identification of the cryptic species of the genus Acalles Schoenherr, 1825, with descriptions of new species (Coleoptera: Curculionidae: Cryptorhynchin, Zootaxa 3915 (1), pp. 1-51: 11-12

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Acalles echinatus


Acalles echinatus  species complex

Large p-distances at high morphological variability

The Central and Eastern European species Acalles echinatus (Germar, 1824)  is the sister taxon to the Atlantic species Acalles misellus Boheman, 1844  . Both belong in a higher-level clade with Acalles fallax Boheman, 1844  and the type species of the genus Acalles  , Acalles camelus (Fabricius, 1792)  . Acalles camelus  falls—which was morphologically expected—in the center of the Acalles  species.

Also assigned to the Acalles echinatus  species complex—but more distant—are Acalles gadorensis Stüben, 2001  (Southern Spain) and Acalles biokovoensis Stüben, 2008  ( Croatia). Contrary to the assumption of Lachowska et al. 2009 (based on karyotype studies), Acalles fallax Boheman, 1844  does not belong to the Acalles echinatus  complex. By requiring that the genus Acalles  follows phylogenetic systematics, the classification of L. Dieckmann (1982) is correct regarding the Acalles echinatus  group (with variable species such as A. micros  , A. fallax  = A. commutatus  and maybe A. petryszaki  ), but it is difficult to maintain his disposition of an Acalles parvulus  group (with A. dubius  and A. misellus  ).

Also, when comparing the types of Acalles echinatus (Germar, 1824)  and Acalles echinatus  var. squamosus  A. & F. Solari, 1907 syn., in 2003 the second author came to a different evaluation than L. Dieckmann. Dieckmann claimed the aedeagus ("identische Penisform", Dieckmann 1982: 199) of the two species have an identical shape but in fact, the shapes of the aedeagi of specimens from the type locality (Carinthia) and west of Slovenia differ significantly from the ones from France (for example Haute Savoie, Sixt, Nambride, 850 m; Stüben et al. 2003). The aedeagus of those from France is, as aptly depicted in the drawing by A. & F. Solari (1907: 535), much longer and lancet-shaped, while the specimens from the type locality and areas located nearby are shorter, wider and more rounded on the sides. The French specimens might be a separate subspecies of Acalles echinatus  , namely Acalles echinatus squamosus  A. & F. Solari, 1907. Acalles echinatus  seems to be a polymorphic species.

We also disagree with Dieckmann’s observation that the shape of the penis, even with material from different geographical areas, is fairly constant („die Form des Penis ist auch bei Material unterschiedlicher geographischer Herkunft ziemlich konstant“, Dieckmann 1982: 205). This observation is based on an insufficient number of specimens, but we agree with his observation of the high variability in appearance of the exoskeleton. The scales on the pronotum can vary from being rounded and smooth to being pointed and more narrow. The lateral punctures of the elytra can be larger and deeper, but also smaller and less deep. The erect bristles on the elytral intervals can be wider and shorter or significantly longer and narrower. This extraordinary variability in the outer appearance of Acalles echinatus  is supported by 13 DNA sequences, derived from specimens collected between northern Italy and Moscow. Even though there is a high intraspecific variance between these species, there is no clear speciesspecific clade. The CO 1 p-distance range between different A. echinatus  populations is 1.4 % to 9.1 %. The wide distribution area ranges from southern Sweden to Albania and from the French Jura region to the Caucasus. Since this area is far more extensive than the current coverage by molecular data, larger p-distance values have to be assumed by increasing the sampling rate. So far we doubt it might be possible to find sufficient molecular or morphological characters for a species separation by taxonomy or DNA barcoding with CO 1. This also applies to other genes like mitochondrial 16 S or nuclear gene 28 S (Astrin et al. 2012). Extensive cross-breeding might be a promising approach ( Stüben 2005).

Reliable distance values for species delineation (for example based on CO 1 barcoding sequences) are not so easy to set up for the few Cryptorhynchinae  with a very large distribution area. Obviosly it's different when dealing with flying insects (easier to reach the common gene pool for them), or with widely distributed flightless Cryptorhynchinae  .

In this case, one must expect not only 'morphological clines' along ecological parameters (e.g. habitat), but also with very large p-distance values of the CO 1 gene. Like in the previously handled species complex A. parvulus  / A. temperei  , here it is very likely that the genetic exchange between subpopulations has stopped and genetic differences (mutations) are not being homogenized anymore ( Stüben & Astrin 2006). For a comprehensible assessment of species and species complexes, two steps might point us in the right direction: first, specific CO 1 distance values for reliable species delineations for each Curculionidae  subfamily; and second, an algorithm that broadly estimates 'relief and distribution' of the specimen of interest: a 'molecular map'. This would be a worthwhile research area which would take into account the possibility that flightless insects, separated by mountain ranges or huge rivers (making use of geological maps), might have not evolved in the same manner that flying ones did during the evolutionary young history (in Western Palearctic, 27 million years ago, Stüben & Astrin 2010: fig. 1 B).


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