Clutch size versus clutch interval: life history strategies in the colour-polymorphic pygmy grasshopper Tetrix subulata

Theory posits that reproduction carries a cost in terms either of future fe cundity, growth or survival. Different life history strategies may evolve i n response to different external sources of mortality. In ectothermic organ isms, such as insects and reptiles, reproductive characteristics may also v ary due to effects of differences in body temperature on activity and physi ological performance. In this study, female pygmy grasshoppers [Tetrix subu lata (L.) Orthoptera: Tetrigidae] belonging to four different colour morphs were maintained under two different temperatures, and data on reproductive life history traits were used to test for costs of reproduction, plasticit y of reproductive characteristics in response to temperature and variation among colour morphs in reproductive strategies. The results revealed that a verage clutch size decreased progressively from the first to third clutch, and that females producing relatively large clutches displayed a greater re duction (in both absolute and relative terms) in the number of eggs to the following clutch, as expected from the hypothesis that present reproduction negatively affects future fecundity. Great expenditure on present reproduc tion also negatively influenced the time to next clutch:the decrease in mea n clutch size with clutch number was associated with a reduction in inter-c lutch interval, and clutch interval increased with clutch size across indiv iduals within colour morphs. Females maintained in a warm environment were more likely to oviposit, laid their first clutch earlier, produced more clu tches and had shorter intervals between sequential clutches than females in a cold environment, suggesting that differences in body temperature may co ntribute to variation in reproductive performance within and among natural populations. A comparison among colour morphs maintained under identical co nditions suggested that females belonging to certain morphs produce relativ ely large clutches at the expense of fewer clutches per unit time. However, experimental data revealed no difference in relative fat content between d ark and pale individuals maintained either in sun-exposed outdoor enclosure s (where they were unable to increase their body temperature by basking) or in shaded enclosures. This suggest that the divergence in life history str ategies among colour morphs may reflect a response to morph-specific differ ences in adult survival imposed by visually searching predators, rather tha n being due to the effects of differences in body temperature.