The adaptation of death-feigning (thanatosis), a subject that has been overlooked in evolutionary biology, was inferred in a model prey-and-predator system. We studied phenotypic variation among individuals, fitness differences, and the inheritance of death-feigning behaviour in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Two-way artificial selections for the duration of death-feigning, over 10 generations, showed a clear direct response in the trait and a correlated response in the frequency of death-feigning, thus indicating variation and inheritance of death-feigning behaviour. A comparison of the two selected strains with divergent frequencies of death-feigning showed a significant difference in the fitness for survival when a model predator, a female Adanson jumper spider, Hasarius adansoni Audouin (Araneomophae: Salticidae), was presented to the beetles. The frequency of predation was lower among beetles from strains selected for long-duration than among those for short-duration death-feigning. The results indicate the possibility of the evolution of death-feigning under natural selection.

Costs of reproduction include costs of producing eggs and of mating itself. In the present study, we made an experimental investigation of costs of reproduction in the Mediterranean fruit fly (medfly, Ceratitis capitata). We demonstrated that virgins live longer than non-virgin females. However, in strong contrast to most findings within the Diptera, non-virginity had no detectable effect on egg production. Therefore the increased longevity of the virgin females cannot be attributed to an increase in egg production in non-virgin females, and instead indicates a cost of mating. A comparison of the life spans of normal females and those sterilized by low doses of X-irradiation, revealed an additional cost of egg production. There were no significant differences in remating levels between females that did and did not lay eggs, showing that the cost of producing eggs is independent of mating frequency. Medfly females therefore suffer a decrease in survival as a result of egg production and of mating, and these costs are independent of one another. To put our results into context, we reviewed the existing literature on the effects of mating on longevity, egg production and sexual receptivity for 64 species of Diptera, and examined the pattern of mating effects that emerged.

Sexually antagonistic selection generates intralocus sexual conflict, an evolutionary tug-of-war between males and females over optimal trait values [1-4]. Although the potential for this conflict is universal, the evolutionary importance of intralocus conflict is controversial because conflicts are typically thought to be resolvable through the evolution of sex-specific trait development [1-8]. However, whether sex-specific trait expression always resolves intralocus conflict has not been established. We assessed this with beetle populations subjected to bidirectional selection on an exaggerated sexually selected trait, the mandible. Mandibles are only ever developed in males for use in male-male combat, and larger mandibles increase male fitness (fighting [9, 10] and mating success, as we show here). We find that females from populations selected for larger male mandibles have lower fitness, whereas females in small-mandible populations have highest fitness, even though females never develop exaggerated mandibles. This is because mandible development changes genetically correlated characters, resulting in a negative intersexual fitness correlation across these populations, which is the unmistakable signature of intralocus sexual conflict [1]. Our results show that sex-limited trait development need not resolve intralocus sexual conflict, because traits are rarely, if ever, genetically independent of other characters [11]. Hence, intralocus conflict resolution is not as easy as currently thought.

The melon fly, Bactrocera cucurbitae, is a destructive insect of cucurbit and other fruits. It invaded the Southwestern Islands of Japan from 1919 to 1974. The sterile insect technique (SIT) was successfully applied from 1972 to 1993 to eradicate the melon fly. Technical research into SIT functions, such as suppression of density, mass-rearing, sterilization, shipment, release, evaluation of efficacy, and quality control of mass-reared insects, was conducted for this eradication project. Fundamental research into the dispersion, mating and oviposition behavior, population dynamics and estimation of density, eradication models, spatial distribution, genetics, and evolution of the melon fly was also undertaken and supported the success of the eradication project.

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Weapons used in male fighting can be costly to males and are often reported to trade off with other characters such as wings or spermatogenic investment. This study investigated whether increased investment into weapons can generate evolutionary changes in mating strategy for armed males. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male -male competition. We subjected these weapons to 12 generations of bidirectional selection and found trade-offs between weapons and two other male characters: wing and testis size. In addition, probably as a consequence of the observed changes in investment, dispersal ability and ejaculatory volume differ significantly between the lines. This indicates that the exaggeration of a weapon can be associated with dispersal and ejaculatory strategies. Thus, altered investment into weapons can lead to correlated changes in life-history traits.

A prey animal may have the alternative of flying away or feigning death when it encounters predators. These alternatives have a genetic base as anti-predator strategies in the adzuki bean beetle, Callosobruchus chinensis . A negative genetic correlation between death-feigning intensity and flying ability was found in C. chinensis , i.e. lower flying ability is genetically connected to escaping by dropping from a perch and then feigning death, whereas higher flying ability does not correspond to death-feigning behaviour. Two bidirectional artificial selections for death-feigning duration and flying ability were conducted independently in C. chinensis . The strains selected for shorter (longer) duration of death-feigning had higher (lower) flying ability, while the strains selected for lower (higher) flying ability showed longer (shorter) duration of death-feigning. When the two traits were compared in 21 populations of C. chinensis derived from different geographical regions, a significant negative correlation was found between death-feigning intensity and flying ability. Based on these results, the choice between alternative escaping behaviours in animals is discussed from two points of view: phenotypic plasticity, an individual with two tactics; and pleiotropic genetic correlation, different individuals with opposite strategies.