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

Abstract

Theory posits that reproduction carries a cost in terms either of future fecundity, growth or survival. Different life history strategies may evolve in response to different external sources of mortality. In ectothermic organisms, such as insects and reptiles, reproductive characteristics may also vary due to effects of differences in body temperature on activity and physiological performance. In this study, female pygmy grasshoppers [Tetrix subulata (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, plasticity of reproductive characteristics in response to temperature and variation among colour morphs in reproductive strategies. The results revealed that average clutch size decreased progressively from the first to third clutch, and that females producing relatively large clutches displayed a greater reduction (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 reproduction also negatively influenced the time to next clutch:the decrease in mean clutch size with clutch number was associated with a reduction in inter-clutch interval, and clutch interval increased with clutch size across individuals within colour morphs. Females maintained in a warm environment were more likely to oviposit, laid their first clutch earlier, produced more clutches and had shorter intervals between sequential clutchesthan females in a cold environment, suggesting that differences in body temperature may contribute to variation in reproductive performance within and among natural populations. A comparison among colour morphs maintained under identical conditions suggested that females belonging to certain morphs produce relatively large clutches at the expense of fewer clutches per unit time. However, experimental data revealed no difference in relative fat content between dark and pale individuals maintained either in sun-exposed outdoor enclosures (where they were unable to increase their body temperature by basking) or in shaded enclosures. This suggest that the divergence in life history strategies among colour morphs may reflect a response to morph-specific differences in adult survival imposed by visually searching predators, rather than being due to the effects of differences in body temperature.

Geographic variation of reproductive tactics in lubber grasshoppers

“…It seems probable that this stored mass would then be directed toward reproduction during subsequent clutches. These results are different from those for pygmy grasshoppers, which show a trade-off of clutch size with clutch rate, but not storage (Forsman 2001). This may reflect interspecific differences in allocation to current reproduction (i.e., clutch size) versus future reproduction (i.e., somatic storage).…”

“…In addition, there have been several studies on reproductive trade-offs (Dearn 1977;Kaitala 1991;Frankino and Juliano 1999;Seigel and Ford 2001), but few of these have examined timing of reproduction. Most recently, Forsman (2001) investigated trade-offs among morphs (i.e., not latitudinally distinct populations) of pygmy grasshoppers, and he found a trade-off of clutch timing and clutch size, but no evidence that stored fat was also involved in the trade-off. To our knowledge, geographic variation in a trade-off between age at reproduction and somatic storage has been shown only for pied flycatchers (Hemborg et al 1998), and never for insects.…”

“…For species inhabiting a range of climates, early onset of reproduction could increase fitness for individuals in areas subject to seasonal constraints, such as onset of an unfavorable climate (Rowe and Ludwig 1991). Early reproduction has costs, such as reduced investment in offspring, reduced somatic storage, or reduced longevity (De Souza Santos and Begon 1987;Rowe and Scudder 1990;Kaitala 1991;Leroi et al 1994;Djawdan et al 1996;Frankino and Juliano 1999;Forsman 2001). Although advantages of early reproduction may outweigh these costs when seasonal constraints are severe, such costs could diminish fitness in environments in which constraints are minimal (Rowe et al 1994;Glazier 1998Glazier , 2000Johansson and Rowe 1999).…”

“…We tested the hypothesis that there is interpopulation variation for the trade-off among age at first reproduction, somatic storage, and investment in the first clutch (see Djawdan et al 1996;Hemborg et al 1998;Glazier 2000;Forsman 2001). We also examined how reproductive output was packaged, to investigate the trade-off between egg size and egg number.…”

Longevity and fecundity of Dichroplus maculipennis (Orthoptera, Acrididae) at non-outbreaking and outbreaking situations

“…Although in our experiments females of both groups began to oviposit after the fourth week of adulthood, the fecundity curves show that at high density the higher values of fecundity were at week 6 while at low density they were at weeks 11-13. Reproduction is assumed to carry a cost, in terms of future survival, growth or fecundity (De Souza Santos & Begon 1987;Forsman 2001). Insects can accelerate the reproduction or maturation if they inhabit seasonal environments with relatively short growing seasons.…”