Geographical and species variation in circadian rhythm parameters in nemobiine crickets

Abstract. . Locomotor activity rhythms were studied in eight species of nemobiine crickets with different habitat preferences. They showed similar patterns with a major peak of activity around dusk and a minor one around dawn. These patterns did not change within the natural range of daylengm (12–16 h). The acrophase time of the rhythm varied between -3.2 and +3.5 h as measured from dusk, and the free-running period (T) varied between 22.8 and 24.5 h. In the Dianemobius fascipes species complex these circadian parameters varied among nine local strains (8^oS to 43^oN) but did not show any latitudinal trend. In a temperate strain of this species complex (Dianemobius nigrofasciatus from Teshikaga, 43^oN), two lines which differed from each other in mean T by 1.4h were selected, and a high heritability of T, 0.78 + 0.20 (mean±SE) was obtained. On the other hand, in a subtropical strain (Dianemobius fascipes from Ishigaki Island, 24^oN), low heritabilities, 0.35 ± 0.15 for acrophase and 0.17 ± 0.21 for T, were obtained from the full-sib correlations. The variation in i seemed to be random and not related to fitness.