Variation in Body Size and Sexual Size Dimorphism of Ground Beetle Pterostichus montanus Motsch. (Coleoptera, Carabidae) in Altitude Gradient

We sampled beetles at plots on different altitudes of the Barguzin ridge (54 degrees 30 ' N 109 degrees 50 ' E) in 1988-2014: the coast (500 m a.s.l.), low mountains (720 m a.s.l.), middle mountains (1004 m a.s.l.), and high mountains (1667 m a.s.l.). The selected specimens of Pterostichus montanus have been measured for six morphometric traits: the length and the width of elytra, pronotum, and head. Sample size is 968 specimens. The results have been processed in Past3 and R Software. Altitude and sex affect the beetle body size significantly: the smallest beetles dwell at the coast. At other altitudes, the beetle body size does not differ. Sexual size dimorphism (SSD) is female-biased. The highest values of SSD are in the width of elytra and head. The mean value of SSD upon all six traits was the highest at low mountains. RMA II models result in positive regression coefficients in the beetles at all studied altitudes. The body-size variation is the same in females and males. Intercepts are negative in most cases under study, and regression coefficients values are greater than one. This suggests that males were more sensitive to the environmental impact.

Automated summary

This study sampled beetles at different altitudes and found that altitude and sex significantly affect the beetle body size, with female-biased sexual size dimorphism. Regressions showed positive coefficients, indicating that males were more sensitive to environmental impact.