Discussion

Male Ceruchus primarily use their broad, thick mandibles for excavating decaying wood rather than for frequent combat. Species of this genus are adapted to cold and temperate climates; these beetles typically inhabit high-altitude areas at low latitudes and low-altitude areas at high latitudes across the Palaearctic and Nearctic regions.

In China, the core distribution of the genus Ceruchus is concentrated along the eastern margin of the Qinghai-Tibet Plateau and in the Hengduan Mountains (Fig. 6). Species are densely distributed along these complex north–south-oriented mountain systems. This pattern suggests that the Hengduan Mountains may represent a major centre of diversification or refugium for the genus in East Asia. In addition, certain species (e.g., C. minor and C. yangi) extend eastward beyond the Hengduan region, dispersing along mountain systems such as the Qinling and Daba Mountains into mid- to high-elevation habitats in central and southern China. Overall, the broad distribution pattern of Ceruchus closely follows the major topographic transition zones of China, implying that geographic isolation imposed by complex landscapes (e.g., deep gorges and high mountains), together with associated microhabitat variation, likely played a crucial role in the radiation and present-day distribution of the genus.

Figure 6.: Distribution map of the genus Ceruchus in China.

Interspecific differences within Ceruchus are generally slight, and male polymorphism is not strongly developed. Traditionally, mandibular morphology and the density of setae on the mesofemora have been regarded as characters of high diagnostic value. Based on our dissections, male genitalia may exhibit some degree of variation among different geographic populations, whereas female genitalia appear to show only limited interspecific differentiation. Nevertheless, specific aspects of the aedeagus morphology, such as the parameres, median lobe, and the caudal margin of the basal piece in ventral view, when combined with selected external morphological characters, may still provide useful taxonomic evidence.

Unlike many other lucanid groups, in which male allometry produces extreme intraspecific variation (Rowland and Emlen 2009), Ceruchus presents a distinct taxonomic challenge. Specimens of this genus are scarce in the collections available to us, such as C. ganyanae and C. luojishanensis, and some species are known from only a few records, with very limited material available for examination. As noted by Lim et al. (2012), the prevalence of singletons and rare species poses a fundamental challenge to species delimitation because it restricts the assessment of true intra- and interspecific variation. Consequently, many diagnostic characters still require further evaluation based on additional specimens and, where possible, support from molecular data. Future taxonomic revisions will therefore require broader field surveys to obtain additional specimens, together with rigorous population-level morphometric analyses and molecular phylogenetic evidence, in order to establish a stable taxonomic framework for the genus.