Growth temperature and reaction norms of morphometrical traits in a tropical drosophilid: Zaprionus indianus

Ten isofemale lines of Zaprionus indianus were analysed to study the reacti on norms of five morphometrical traits (wing and thorax length, body weight , sternopleural bristle and ovariole number) in relation to growth temperat ure. All these traits exhibited nonlinear concave reaction norms and were c haracterized by the coordinates of their maximum: MV (maximum value), and T MV (temperature of maximum value). Wing/thorax ratio, which is related to f light capacity, was also calculated and exhibited a monotonically decreasin g reaction norm. Intraclass correlations were on average quite low, with no significant differences between traits, temperature or sex; a highly signi ficant trait-temperature interaction was, however, observed. Sex dimorphism was very low in Zaprionus. contrasting with data previously obtained in ot her species. MVs among lines were positively correlated for the three size- related traits, whereas sternopleural bristle and ovariole number were gene tically independent. TMVs were different between the traits, but higher tha n in D. melanogaster and other cold-adapted species, in agreement with the hypothesis that the norm shape evolves according to species thermal adaptat ion. MVs and TMVs were never correlated, indicating that mean values and pl asticity are genetically independent. Some positive correlations were obser ved among TMVs of different traits, suggesting that the same genetic system might regulate plasticity of different traits.