Interstructural correlations in evolution of darkling beetles of the tribe Helopini (Coleoptera: Tenebrionidae)

Abstract

Various morphological structures of Helopini [sensu Nabozhenko, 2002a], their functions and evolution are considered. Some adaptations to arid environmental conditions and the main evolutionary trends in the tribe are discussed. The adaptations to digging are characteristic of Xanthomus which inhabits sandy coasts of Mediterranean. Many of Xanthomus have a digging type of fore tibiae (tibiae weakly flat, frequently with denticles and erected hairs on hide external margin.). The most part of other Helopini hide in wide hollows of ground, so some structures are adapted for movement in these hollows (epypleura, thoracic part, pronotum, body form). The genera Hedyphanes, Catomus, Physohelops have hedyphanous type of thoracic part moving in lateral and dorsoventral directions. Other groups of the tribe have nalassous type of thoracic part moving only in dorsoventral direction. Epypleura can be hedyphanous or nalassous also. Three evolutionary lines are traced in the tribe: helopious line (the subtribe Helopina), cylindronotous line (the subtribe Cylindronotina, the genera Cylindronotus, Odocnemis, Armenohelops, Reitterohelops, Stenomax) and “nalassous” line (the subtribe Cylindronotina, the genera Nalassus, Zophohelops, Turcmenohelops, Ectromopsis, Pseudoprobaticus, Stygohelops). Correlative connections between various structures of these three morphological types show precise enough bounds of the subtribes and groups of genera. Nalassous type of larvae, gastral spicula and female sexual ducts are characteristic for groups with nalassous type of male genitalia. Corresponding tendencies are observed in helopious and cylindronotous lines. Structural type of female sexual ducts frequently correlates with male aedeagus type. However an intricate structure of combined spermatheca in some nalassous groups confirms supposition about independent transformation of spermatheca in various groups of the tribe Helopini. This correlation can be used carefully in reasonings about phylogenetic relations and evolutionary advanced Helopini group. Complicate questions of the tribe classification are considered on the basic of outlined data. The analysis of morphological structures confirms parallel evolution of two basic Helopini branches (the subtribes Helopina and Cylindronotina) in adaptation to arid environmental conditions.

Keywords

• Tenebrionidae
• Helopini
• morphology
• adaptations
• evolutional trends
• classification