Host‐associated variation in sexual size dimorphism and fitness effects of adult feeding in a bruchid beetle

Abstract

We studied the effect of larval host (two Convolvulus L. species, Convolvulaceae) on sexual size dimorphism and on the fitness consequences of adult feeding in the bruchid beetle Megacerus eulophus (Erichson) (Coleoptera: Bruchidae). Whereas Convolvulus chilensis Pers. occurs in low density in semiarid habitats, Convolvulus bonariensis Cav. occurs in less stressful environments and exhibits higher population density. Host plants neither differ in seed mass nor in seed nitrogen content, and there were no consistent host‐associated differences in female fitness. Consequently, host quality was considered to be similar. Sexual size dimorphism, expressed as the female:male ratio of body size, was significantly greater in C. chilensis than in C. bonariensis. A greater female size in the C. chilensis population could be selectively advantageous due to higher survival during host‐plant search in stressful environments. Female longevity was affected by food availability (starvation vs. honey‐pollen solution) and by the interaction between food availability and larval host. Fed females lived longer than starved females. This trend was found in both hosts, but it was of greater magnitude in C. chilensis than in C. bonariensis. Fecundity was significantly affected by adult feeding and larval host, and marginally affected by their interaction. Fed females laid more eggs than starved females. However, the increase in fitness of fed females was greater in C. chilensis. Results might be explained by differential selection on plasticity in life‐history traits in contrasting environments. Females in stressful environments should take a greater advantage of the transient availability of resources.

Effects of maternal diet and host quality on oviposition patterns and offspring performance in a seed beetle (Coleoptera: Bruchidae)

“…This demonstrates that a diet with low sugar availability produces similar effects on longevity as the lack of diet. A recent study (Gianoli et al 2007) and current results suggest that in M. eulophus adult feeding determines its longevity.…”

“…Considering that offspring provisioning strategies can be dynamic and that intergenerational effects may also be detectable in offspring traits more generations later (Plaistow et al 2006(Plaistow et al , 2007, adaptive maternal effects for M. eulophus may not be discarded. Despite this apparent "reset" of conditions for offspring future fitness, the maternal effects on egg size plasticity and quality might play a crucial role in the evolutionary ecology of this seed beetle under more stressful environments, such as arid ecosystems (Gianoli et al 2007) where food sources may be scant and host seeds are greatly reduced in size (Gianoli and González-Teuber 2005).…”

“…Due to the fact that the offspring morphological traits measured were highly correlated among them, a multivariate ANCOVA (MANCOVA) was done to evaluate the effects of host quality and maternal diet on them (N=20-25 per treatment). Considering that sexual dimorphisms have been reported for other bruchidae species, and also for M. eulophus (Gianoli et al 2007), the MANCOVA was done separately for females and males. Because offspring longevity was not correlated with other offspring traits (P>0.05), it was not included in the MANCOVA analysis.…”

“…Such environmental maternal effects have been detected for oviposition patterns in seed beetles. Fed females show an increase in both egg size and fecundity in comparison with starved females (Fox and Dingle 1994;Gianoli et al 2007); females mated with well-fed males lay larger eggs than those mated with poorly fed males (Takakura 2004), and multiple mating increases female longevity but only in starved females (Fox 1993). Few studies have manipulated as a whole different maternal diets and their effects on oviposition patterns to different host qualities.…”

Relationship Among Phenolic Contents, Seed Predation, and Physical Seed Traits in Mimosa bimucronata Plants

“…Among the most important seed predators are the bruchid beetles (Janzen 1971;Southgate 1979). Given that all bruchid larvae feed exclusively in seeds (Southgate 1979), their adult body size, potential fecundity, and longevity are determined by resources obtained during larval development, even though these aspects also depend on whether they continue to feed as adults (Timms 1998;Gianoli et al 2007). Thus, seed quality-mainly the amount of nutrients and concentrations of chemical defensesstrongly influences bruchid behavior, infestation, survival, life-history traits, and fitness (e.g., Fox et al 1994;Thiery et al 1994;Fox and Mousseau 1996;van Huis and de Rooy 1998;Or and Ward 2004).…”