Geographic color variation of Phelotrupes auratus (Coleoptera, Geotrupidae) in the Kinki region, central Japan: A quantitative spectrophotometric analysis

Abstract

We investigated geographic color variation of the beetle Phelotrupes auratus in the Kinki region of central Japan using a spectrophotometer. The reflectance spectrum of the dorsal surface of the elytron was measured for beetles collected from 23 sites. We focused on lmax(a), the wavelength at the peak (a peak) between 400 and 700 nm (human visual sensitivity range), for analyses of color variation. In populations distributed on the Kii Peninsula, in the southern part of the Kinki region, average lmax(a) values were lower (480-497 nm) than in populations distributed in the area west of Lake Biwa, the western part of the Kinki region (618-633 nm). For populations distributed in the areas south and southeast of Lake Biwa, a geographic cline of lmax(a) was observed approximately along an east-west transect, with average lmax values varying continuously from 624 to 557 nm. The easternmost populations along this cline had almost the same lmax(a) values as the populations distributed west of Lake Biwa. The coefficient of variation for lmax(a) tended to be larger in populations with intermediate averages than those with lower or higher average values.

Population genetic structure underlying the geographic variation in beetle structural colour with multiple transition zones

“…Based on the frequency distribution pattern of λmax(α) between 450 nm and 680 nm with three modes corresponding to red, green and indigo colour by human eyes as observed by Akamine et al. (2008) and ourselves, we defined the colour form of each population as “red” if the median of λmax(α) of the population was 600 nm or more, “green” if it was 525–600 nm and “indigo” if it was ≤525 nm.…”

“…Although the adaptive significance of the coloration is still unclear, Müllerian mimicry has been suggested, because a sympatric congener showed parallel colour variation with P. auratus (Watanabe et al., 2002). In the Kinki District, Honshu, Japan, all of these colour forms occur parapatrically in separate areas (Akamine et al., 2008; Mizuno, 1964; Watanabe et al., 2002), which implies the presence of an underlying population genetic structure associated with the distribution of the colour form. The geographic partitioning of the colour forms may stem from geographic or genetic isolation mechanisms or local adaptation in different populations.…”

The physical mechanism of cuticular color in Phelotrupes auratus (Coleoptera, Geotrupidae)

“…Specimens were not distinguished on the basis of sex because it has been shown that sexual dimorphism is not evident in cuticular color in the populations from Nara, Mt Otowa and Otsu (Akamine et al . 2008a).…”

“…2008b). In the Kinki region of central Japan, three distinct color forms of P. auratus occur parapatrically: (i) the indigo form is distributed on the Kii Peninsula (Wakayama and Nara Prefectures and southern Mie Prefecture); (ii) the green form in the area south of Lake Biwa (southern parts of Kyoto and Shiga Prefectures and northern Mie Prefecture); and (iii) the red form in the areas where the indigo and green forms are not found (Hoga 1986; Yamamoto 2002; Akamine et al . 2008a).…”

“…The beetle exhibits a remarkable geographic variation in monochromatic cuticular color (Mizuno 1964;Akamine et al 2008b). In the Kinki region of central Japan, three distinct color forms of P. auratus occur parapatrically: (i) the indigo form is distributed on the Kii Peninsula (Wakayama and Nara Prefectures and southern Mie Prefecture); (ii) the green form in the area south of Lake Biwa (southern parts of Kyoto and Shiga Prefectures and northern Mie Prefecture); and (iii) the red form in the areas where the indigo and green forms are not found (Hoga 1986;Yamamoto 2002;Akamine et al 2008a). Watanabe et al (2002) showed that the three color forms can easily be discriminated by the wavelength of the highest peak in a reflectance spectrum (lmax(a)).…”