Quantitative genetic analysis of subspecific differences in body shape in the snail-feeding carabid beetle Damaster blaptoides

Abstract

A dimorphic pattern of macrocephalic (wide, short) and stenocephalic (narrow, long) body shapes is observed in snail-feeding carabid beetles globally. The former exhibits high performance in crushing snail shells with powerful jaws, whereas the latter specializes in eating snails' soft body directly by inserting the head into the shell. In the snail-feeding species Damaster blaptoides, the subspecies D. b. capito has a wide, short forebody, and D. b. fortunei has a narrow, long forebody. They exhibit distinct morphologies despite their geographic and phylogenetic proximity. To examine the genetic basis of the morphological differences between these two subspecies, we conducted quantitative genetic analyses by crossing these subspecies and producing F 1 and backcross hybrids. The hybrids had body shapes intermediate between the parental subspecies. The variation between wide, short and narrow, long forebodies was based on negative genetic correlations between width and length of the head and thorax. Between one and eight genetic factors were involved in the morphological differences between subspecies. We suggest that the morphological integration of forebody parts in a small number of loci has facilitated the marked morphological diversification between subspecies of D. blaptoides.

A maladaptive intermediate form: a strong trade‐off revealed by hybrids between two forms of a snail‐feeding beetle

“…Because the details of our crossing design and feeding procedure were described in our previous report (Konuma et al 2013), we include only an overview here. Because the details of our crossing design and feeding procedure were described in our previous report (Konuma et al 2013), we include only an overview here.…”

“…We used Damaster blaptoides capito (stout-shaped), D. b. fortunei (slender-shaped), and their F 1 and two backcross hybrids in feeding experiments (see Appendix B for details about these beetles). Because the details of our crossing design and feeding procedure were described in our previous report (Konuma et al 2013), we include only an overview here. First, we produced laboratory-reared individuals of D. b. capito (hereafter, P 1 ) and D. b. fortunei (P 2 ) under constant light and temperature conditions (n ¼ 198 and 76, respectively).…”

“…However, we can cross stout and slender subspecies to produce F 1 and backcross hybrids that have intermediately shaped bodies (Konuma et al 2013). Can intermediate beetles perform both crushing and inserting behaviors, or neither of them?…”

“…This trade-off may cause diversification in snail-feeding carabid beetles (Sturani 1962, Ishikawa 1978, Sota and Ishikawa 2004, Konuma et al 2011 (Appendix A). However, we can cross stout and slender subspecies to produce F 1 and backcross hybrids that have intermediately shaped bodies (Konuma et al 2013). In the present study, we examined the snail-feeding performances of intermediate beetles by comparing the performances of parental individuals and hybrids.…”

Utility of geometric morphometrics for inferring feeding habit from mouthpart morphology in insects: tests with larval Carabidae (Insecta: Coleoptera)

“…insulicola and Ca. blaptoides: successful laboratory rearing to adult in various studies (Sota, 2000;Sota, Kusumoto & Kubota, 2000;Konuma, Chiba & Sota, 2013); the other seven species: successful laboratory rearing to adult on a focal diet (mealworms, snails or earthworms), and rejection of/death on the other two diets (K. Sasakawa, unpubl. data).…”