Introduction
The highly speciose genus Timarcha Latreille, 1829 comprises more than three hundred described taxa, almost all from the Palaearctic (Gómez-Zurita 2008, Kippenberg 2010, Warchalowski 2010), and is relatively well-known from chromosomal standpoints because 42 taxa have been surveyed to date and their range of diploid numbers goes from 2n = 18 to 2n = 44 (Gómez-Zurita et al. 2004, Petitpierre 2011).
Herein, we report the chromosome numbers, male sex-chromosome systems, and main features of their karyotypes of T. (Metallotimarcha) metallica (Laicharting, 1781), T. (Timarcha) carmelenae Petitpierre, 2013 and T. (Timarcha) parvicollis ssp. seidlitzi Kraatz, 1879 to enlarge the cytogenetic analysis of the genus and discuss the most relevant trends of its chromosomal evolution.
Discussion
The diploid number of 2n = 38 chromosomes shown in Timarcha (Metallotimarcha) metallica should correct a previous miscounting report of 2n = 20 chromosomes (Petitpierre 1982). The high chromosome number found in this species is not displayed by any other Timarcha from the Palaearctic (subgenus Timarcha s.str.), whose range of numbers goes from 2n = 18 to 2n = 30 (Gómez-Zurita et al. 2004, Petitpierre 2011). However, high chromosome numbers are characteristic of the two species of the subgenus Americanotimarcha Jolivet, 1948, e.i., T. intricata Halderman, 1854 with 2n = 44 (Petitpierre and Jolivet 1976) and T. cerdo Stal, 1860 with 2n = 38 (Jolivet and Petitpierre 1992). These high chromosome numbers are in agreement with the similar morphological traits, the male genitalia and the molecular phylogenetic resemblances between the subgenera Metallotimarcha Motschulsky, 1860 and Americanotimarcha (Jolivet 1948, Iablokoff-Khnzorian 1966, Gómez-Zurita et al. 2000, Gómez-Zurita et al. 2004, Jolivet et al. 2013). Although the species of both subgenera show some plesiomorphic features, such an incomplete fusion of elytra, weak sexual dimorphism, aedeagus with a long tegmen cap, and a basal position in the molecular phylogenetic tree, their high chromosome numbers can not be considered as an ancestral character. First, because 2n = 20(Xyp) is assumed to be the plesiomorphic and most frequent karyotype condition for Coleoptera of the suborder Polyphaga (Smith and Virkki 1978, Angus et al. 2007). Besides, this is the most common karyotype in the genus Timarcha where more than a half of the 42 surveyed taxa show 2n = 20(Xyp) (Petitpierre 2011). And third, the karyotypes of both T. metallica and T. intricata share a quite high number of acrocentric autosome pairs, seven and fourteen respectively, which is an indication of their derived origin by multiple centric fissions or chromosomal dissociations from meta- or submetacentric chromosomes. Therefore, we assume that a hypothetic karyotype of 2n = 20(Xyp) chromosomes, mostly composed of metacentrics or submetacentrics, would have been the plesiomorphous state for the genus, from which all the taxa of the three present subgenera, Americanotimarcha, Metallotimarcha and Timarcha s.str. may have radiated.
The karyotype of T. (T.) carmelenae with 2n = 20(Xyp), with two larger autosomal bivalents and the remaining gradually decreasing, is similar to those of T. (T.) intermedia Herrich-Schäffer, 1838, and T. (T.) lugens Rosenhauer, 1856 (Petitpierre 1970, 1976). These three species share close morphological resemblances and a feeding on Brassicaceae plants, Hormathophylla spinosa (L.) Küpfer, 1974 for both T. (T.) carmelenae and T. (T.) lugens (González-Megías and Gómez 2001, Petitpierre and Daccordi 2013) and Carrichtera annua (L.) DeCandolle, 1821 for T. (T.) intermedia (Petitpierre 1971, Jolivet and Petitpierre 1973), in contrast with the prevalent trophism on plants of Rubiaceae and/or Plantaginaceae reported for almost all the other taxa of the subgenus Timarcha s.str. (Jolivet and Petitpierre 1973).
T. (T.) parvicollis ssp. seidlitzi shows a karyotype of 11 + Xyp male meioformula, thus 2n = 24(Xyp) chromosomes, which separates it strikingly from the related Andalusian species with 2n = 20(Xyp) such as T. (T.) insparsa Rosenhauer, 1856, T. (T.) marginicollis Rosenhauer, 1856, T. (T.) intermedia, T. (T.) lugens Rosenhauer, 1856 and T. (T.) carmelenae, sharing a bifid mesosternum and elytra covered with spare and fine puncturation.
Another species of Timarcha with 2n = 24 chromosomes, T. (T.) pratensis (Duftschmid, 1825) (Petitpierre 1976), from Central and Eastern Europe, and Northern Italy, belongs to a very different group without any close interrelationship with T. (T.) parvicollis (Bechyné 1948, Warchalowski 2003).