Summary 1.Offspring from older parents often have shorter adult lifespans than offspring of younger mothers. We examine the effects of offspring genotype, maternal age and paternal age on offspring survival, development and adult lifespan in the seed beetle, Callosobruchus maculatus . 2. Females took about a quarter of a day longer to develop from an egg to an adult and lived ≈ 7 days longer than males. Mortality patterns were best described by a logistic mortality model, and all three model parameters differed significantly between the sexes; females had a higher baseline mortality rate than males but the mortality rate increased more slowly in females than in males. Females also showed a delay, relative to males, in the age at which mortality became age-dependent. 3. The proportion of eggs that hatched and larval survivorship both declined with increasing maternal age, while egg-to-adult development time increased substantially. Contrary to the pattern observed in many other organisms, offspring of older mothers lived longer than offspring of younger mothers, even after controlling for heterogeneity among families. There was no evidence that paternal age affected any offspring traits. 4. The effect of maternal age on offspring lifespan was greater for male offspring than for female offspring (consistent with the general observation that the genetic and environmental factors affecting lifespan differ between the two sexes) and varied among sire families (indicating that offspring genotype mediated the non-genetic effect of maternal age on lifespan).

Most studies of phenotypic plasticity investigate the effects of an individual environmental factor on organism phenotypes. However, organisms exist in an ecologically complex world where multiple environmental factors can interact to affect growth, development and life histories. Here, using a multifactorial experimental design, we examine the separate and interactive effects of two environmental factors, rearing host species (Vigna radiata, Vigna angularis and Vigna unguiculata) and temperature (20, 25, 30 and 35 degrees C), on growth and life history traits in two populations [Burkina Faso (BF) and South India (SI)] of the seed beetle, Callosobruchus maculatus. The two study populations of beetles responded differently to both rearing host and temperature. We also found a significant interaction between rearing host and temperature for body size, growth rate and female lifetime fecundity but not larval development time or larval survivorship. The interaction was most apparent for growth rate; the variance in growth rate among hosts increased with increasing temperature. However, the details of host differences differed between our two study populations; the degree to which V. unguiculata was a better host than V. angularis or V. radiata increased at higher temperatures for BF beetles, whereas the degree to which V. unguiculata was the worst host increased at higher temperatures for SI beetles. We also found that the heritabilities of body mass, growth rate and fecundity were similar among rearing hosts and temperatures, and that the cross-temperature genetic correlation was not affected by rearing host, suggesting that genetic architecture is generally stable across rearing conditions. The most important finding of our study is that multiple environmental factors can interact to affect organism growth, but the degree of interaction, and thus the degree of complexity of phenotypic plasticity, varies among traits and between populations.

We examine the inbreeding load for adult life span and mortality rates of two seed beetle species, Callosobruchus maculatus and Stator limbatus. Inbreeding load differs substantially between males and females in both study populations of C. maculatus-life span of inbred females was 9-13% shorter than the life span of outbred females, whereas the life span of inbred males did not differ from the life span of outbred males. The effect of inbreeding on female life span was largely due to an increase in the slope of the mortality curve. In contrast, inbreeding had only a small effect on the life span of S. limbatus-life spans of inbred beetles were $5% shorter than those of outbred beetles, and there was no difference in inbreeding load between the sexes. The inbreeding load for mean life span was $0.4-0.6 lethal equivalents per haploid gamete for female C. maculatus and $0.2-0.3 for both males and females of S. limbatus, all within the range of estimates commonly obtained for Drosophila. However, contrary to the predictions of mutation-accumulation models, inbreeding load for loci affecting mortality rates did not increase with age in either species, despite an effect of inbreeding on the initial rate of increase in mortality. This was because mortality rates decelerated with age and converged to a mortality plateau for both outbred and inbred beetles.T HE evolution of life span, mortality rates, and patterns of senescence is of substantial interest because there is tremendous variation in these traits at all taxonomic levels (Promislow 1991) and because of the medical implications of understanding the genetics underlying mortality rates. Studies on mice, Drosophila, and Caenorhabditis elegans have identified numerous genes that influence life span and/or rates of senescence (Harshman 2002). Recent studies of life span in Drosophila melanogaster indicate that inheritance of life span can be quite complex, with both dominance and epistasis having significant effects on variation in life span (Harshman 2002;Leips and Mackay 2002;Mackay 2002;Spencer et al. 2003;Spencer and Promislow 2005). These studies also show that the genetic architecture (number of genes and degree of allelic and genic interactions) underlying life span differs between the sexes and depends on the environmental conditions in which individuals are reared.One of the major genetic mechanisms proposed to underlie senescence is the accumulation in populations of late-acting deleterious alleles due to the declining force of selection with increasing age (mutation-accumulation theory) (Hughes and Reynolds 2005). Research has now identified many genes and chromosomal regions (QTL) that affect life span in model organisms but we have few data on the frequency of deleterious alleles affecting life span (De Luca et al. 2003;Carbone et al. 2006). We have less data on the sources of variation in deleterious alleles and the age specificity of expression of those alleles and thus their effects on age-specific mortality rates.Inbreeding studies are a com...

Con£icts between the sexes over control of reproduction are thought to lead to a cost of sexual selection through the evolution of male traits that manipulate female reproductive physiology and behaviour, and female traits that resist this manipulation. Although studies have begun to document negative ¢tness e¡ects of sexual con£ict, studies showing the expected association between sexual con£ict and the speci¢c behavioural mechanisms of sexual selection are lacking. Here we experimentally manipulated the opportunity for sexual con£ict in the cockroach Nauphoeta cinerea and showed that, for this species, odour cues in the social environment in£uence the behavioural strategies and ¢tness of males and females during sexual selection. Females provided with the opportunity for discriminating between males but not necessarily mating with preferred males produced fewer male o¡spring than females mated at random. The number of female o¡spring produced was not a¡ected, nor was the viability of the o¡spring. Experimental modi¢cation of the composition of the males' pheromone showed that the fecundity e¡ects were caused by exposure to the pheromone component that makes males attractive to females but also makes males less likely to be dominant. Female mate choice therefore carries a demographic cost but functions to avoid male manipulation and aggression. Male^male competition appears to function to circumvent mate choice rather than directly manipulating females, as the mate choice can be cryptic. The dynamic struggle between the sexes for control of mating opportunities and outcomes in N. cinerea therefore reveals a unique role for sexual con£ict in the evolution of the behavioural components of sexual selection.

The planting of transgenic crops expressing Bacillus thuringiensis endotoxins is widespread throughout the world; the prolific increase in their application exposes nontarget organisms to toxins designed to control pests. To date, studies have focused upon the effects of Bt endotoxins on specific herbivores and detritivores, without consideration of their persistence within arthropod food webs. Here, we report the first quantitative field evaluation of levels of Bt endotoxin within nontarget herbivores and the uptake by higher order arthropods. Antibody-based assays indicated significant quantities of detectable Cry1Ab endotoxin within nontarget herbivores which feed on transgenic corn (including the corn flea beetle, Chaetocnema pulicaria, Japanese beetle, Popillia japonica and southern corn rootworm, Diabrotica undecimpunctata howardi). Furthermore, arthropod predators (Coccinellidae, Araneae, and Nabidae) collected from these agroecosystems also contained significant quantities of Cry1Ab endotoxin indicating its movement into higher trophic levels. This uptake by predators is likely to have occurred by direct feeding on plant material (in predators which are facultatively phytophagous) or the consumption of arthropod prey which contained these proteins. These data indicate that long-term exposure to insecticidal toxins occurs in the field. These levels of exposure should therefore be considered during future risk assessments of transgenic crops to nontarget herbivores and arthropod predators.