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Metabolic respiration by groups of resting Myrmica ruginodis and M. scabrinodis worker ants from five sites representing a range of latitudes, have been compared by measuring rates of CO2 production—standardised by fat-free weight—at 5 and 25 °C. M. ruginodis which lives in cooler habitats than M. scabrinodis consistently produced more CO2 .A t 5°C ants of both species from southern latitudes were metabolically more active than those from more northerly latitudes, whereas at 25°C the situation was reversed. Estimates of Q10 were positively correlated with latitude indicating that the respiratory metabolism of northern populations increases relatively more in response to rising temperatures than southern populations. Values of Q10 at different latitudes were the same for both species. The results are discussed in terms of seasonal fluctuations of temperature at different latitudes. © 1999 Published by Elsevier Science Ltd. All rights reserved.

Regression lines of development rate on temperature appeared significantly different between long (22 h) and short (12 h) day conditions and intersected each other at 23.8°С. Thus, the rate of growth and development was higher at temperatures below the intersection point under short-day but above the intersection point it was higher under long day. Ecological relevance of this effect seems as follows: in autumn, as nights become longer and average daily temperature decreases, larvae have to speed up their development because it is only imago that overwinters. Conversely, midsummer offers long days and usually higher temperature, so again it is advantageous to develop as fast as possible in order to have at least one more generation per year. These results are compared with other studies showing interactions between photoperiod and temperature, and some possible general patterns are outlined. The lower thermal threshold for larval development depended on photoperiodic conditions; therefore rate isomorphy must be violated in this species. Development at higher temperatures generally resulted in smaller adults, as is usual with ectotherms according to the "temperature-size rule", but body weight depended significantly on temperature only under short day. Our estimates of the lower temperature thresholds for growth and development in both cases did conform to the generalization made previously by Walters and Hassall (2006) in spite of another formula used by us. We briefly discuss this phenomenon and argue that relative position of these thresholds can be explained mathematically and per se may lack any biological sense.