Sexual dimorphism is a common phenomenon in many insect taxa and is considered one of the most interesting sources of phenotypic variation (Fairbairn and Preziosi, 1976). Sexual dimorphism in wing morphology may be an adaptive response to flight and behavioral activities, as in dipterans and parasitoids (McLachlan, 1986; Gidaszewski et al., 2009; Benítez et al., 2013). In D. magna the wing size and shape differ significantly between the sexes, with the centroid size of female wings remarkably larger than the male’s, indicating that a female-biased sexual size dimorphism exists, in accordance with approximately 80% of investigated insect species (Honěk, 1993; Teder and Tammaru, 2005). This kind of sexual size dimorphism is primarily ascribed to the strong fecundity advantage of larger females (Allen et al., 2011) and the sensitivity to environmental conditions of females (Teder and Tammaru, 2005). In addition, small size of males may be related with protandry (Jarošík and Honek, 2007), because the faster-developed males can increase the frequency and success of mating or increase the opportunity to access preferred territories (Allen et al., 2011). Significant difference in wing shape is also present between the sexes of D. magna and allometry is an important component of sexual shape dimorphism in the wings. The difference is considered to be associated with flight behavior (Gilchrist, 1990; Gidaszewski et al., 2009; Allen et al., 2011). In general, male insects usually bear shorter and narrower wings because of the fast-beating frequency for courtship and mating, whereas female insects have evolved longer and broader wings to allow them much more easily to find oviposition sites with heavier metsomas carrying eggs (Gilchrist, 1990; Honěk, 1993; Blanckenhorn, 2000; Gidaszewski et al., 2009).
Speciation is an evolutionary process by which new species arise and is considered one of the main ways by which organisms adapt to exploit the diversity of environments available to them (White, 1978; Singh, 2012). Rapid parapatric speciation on the time scale of a few hundred to a few thousand generations is plausible without the need of complete geographic isolation, even when neighboring populations exchange several individuals each generation (Gavrilets et al., 2000). In the present study, wing morphology of D. baiyunshana differs significantly from that of D. magna, supporting the previous research that the former is an evolutionarily independent entity (Zhong and Hua, 2013). In the geographic distribution aspect, D. baiyunshana is located in the hinterland of the Funiu Mountains continuously overlapping with D. magna from eastern Qinling Mountains in a small region.
The variation of wing morphology reflects the evolutionary history with a potential influence of environmental factors, mainly climatic changes (Velzen et al., 2013; Perrard et al., 2014) and geological events (McCulloch et al., 2009). In the present study, significant wing size and shape variations were found only in the females of three D. magna populations from the Qinling Mountains (HDT, JLJ, and TB) and one from the Daba Mountains (NGS). The Qinling Mountains, the biogeographical boundary between the Oriental and Palearctic Regions in central China, also the boundary of the north warm temperate and the north subtropical zones, has been modified greatly in topography under the influence of the East Asian monsoon climate due to the rapid uplift of the Qinghai-Tibetan Plateau during the late Miocene (An et al., 2001; Zhang et al., 2006; Dong et al., 2011; Jorge et al., 2011). The Daba Mountains arose in the Indosinian-Yanshanian orogenies of mid-late Jurassic period, and fixed in the Himalayan orogenic belt during the Miocene-Pleistocene (Wang et al., 2004). Along with the uplift of the Qin-Ba Mountains, the climate of the north Qinling Mountains has gradually changed from subtropics to temperate type (Ying, 1994; Wang and Yan, 2011). The Mecoptera were recorded as early as the Lower Permian and were very prosperous from late Permian to whole Mesozoic era based on fossil records (Byers and Thornhil, 1983; Grimaldi and Engel, 2005; Sun et al., 2007). D. magna is endemic to the Qin-Ba mountain regions and evolved approximately during the late Miocene at 7.5 million years ago (Hu et al., 2015). It has experienced dramatic tectonic uplift during the late Miocene-late Pleistocene in the Qin-Ba Mountains. Due to its weak flight ability, the dispersal of D. magna is severely limited even by a narrow zone of unsuitable habitat, such as the Hanshui River and the series of basins between the Qinling Mountains and Daba Mountains, since the scorpionflies live in the mountain area at high elevations (above 1300 m) and are unable to tolerate the high temperature at the low elevations, so that it is almost impossible for them to pass the Hanshui River under natural conditions. In other words, the Hanshui River is likely a strong geographical barrier to restrict the dispersal of the scorpionflies, thus preventing the gene flow between populations. However, whether reproductive isolation is leading allopatric speciation in different geographic populations need further research.