Truncaudum impexum Schedl, comb. n.
Creators: name: Hulcr, Jiri
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Curculionidae
Truncaudum
Truncaudum impexum

description: Truncaudum impexum (Schedl), comb. n.
Xyleborus impexus Schedl, 1942c
Xyleborus dentatulus Browne, 1981 syn. n. Xyleborus circumspinosus Schedl, 1972b, syn. n. Xyleborus falcarius Schedl 1942c, syn. n.
Xyleborus subdentatulus Browne, 1986 syn. n. Xyleborus vernaculus Schedl, 1975b, syn. n. Xyleborus putputensis Browne, 1986, syn. n.
Specimens examined. T. impexum: New Guinea (holotype, NHMW); New Guinea (2, BHJ); New Guinea (FICB); New Guinea, Madang Prov. (8, Hulcr det., MSUC), Oro Prov. (30, Hulcr det., MSUC), West Sepik (4, Hulcr det., MSUC). X. dentatulus: New Guinea, New Ireland, Kamdaru (holotype, BMNH); Takehara coll. 1975.; New Guinea, Morobe Province, Bulolo (3, Hulcr det., FICB); New Guinea, Madang Prov. (225, Hulcr det., MSUC), West Sepik (3, Hulcr det., MSUC). X. circumspinosus: New Guinea, Morobe Province, Bulolo (1, Schedl det., MSUC); New Guinea, Morobe, Umboi (paratype, NHMW). X. subdentatulus: New Guinea (holotype, BMNH). X. falcarius: New Guinea (holotype, NHMW). X. vernaculus: New Guinea, Manus island, Nuvok (holotype, NHMW). X. putputensis: New Guinea, New Britain (holotype, BMNH).
Comments. T. impexum has a very characteristic abruptly truncated elytra, with the declivity surrounded by conspicuous serrate costa. Serrations on the costa are extraordinarily variable and often different between the lower and the upper margin of the declivity. This variation is not correlated with genetic distance between individuals.. A preliminary analysis of intraspecific DNA sequence variation suggests that T. impexus morphotypes with different declivities belong to a single lineage. 28S rDNA sequence divergence (p-distance) of two very different morphotypes does not exceed 0.1%, while p-distances to T. longior and T. agnatum is 0.008 and 0.005, respectively. Differences between sequences of CO1 mtDNA are larger (randomly chosen variants of T. impexum) between 0.109 and 0.116 (nearly all substitution in 3rd codon sites), but much lower than average between-species difference among Truncaudum spp. (average p-distance = 0.147, never below 0.130) (data from Cognato et al., 2011).
Holotype of X. dentatulus Browne is virtually identical to that of T. impexum, only the serrations on the upper edge of declivity are slightly smaller. The declivity in X. subdentatulus has tubercles larger than in most T. impexum, but not exceedingly large, and in homologous positions. X. falcarius was described based on a single difference, a tooth on first interstria on declivital apex (Schedl, 1942c). X. vernaculus was described as different from X. falcarius (syn. with T. impexum here) by its gradually decreasing size of teeth on upper declivital margin (Schedl, 1975b). The actual difference in teeth size is minor, fully within the variation in T. impexum. Holotype of X. putputensis is a male of Truncaudum impexum.
description: Published as part of Hulcr, Jiri, 2010, New genera of Palaeotropical Xyleborini (Coleoptera: Curculionidae: Scolytinae) based on congruence between morphological and molecular characters, pp. 1-33 in Zootaxa 2717 on page 26, DOI: 10.5281/zenodo.199742