Evolutionary Ecology of Egg Size and Number in a Seed Beetle: Genetic Trade-Off Differs Between Environments

Abstract

Abstract. In many organisms, large offspring have improved fitness over small offspring, and thus their size is under strong selection. However, due to a trade-off between offspring size and number, females producing larger offspring necessarily must produce fewer unless the total amount of reproductive effort is unlimited. Because differential gene expression among environments may affect genetic covariances among traits, it is important to consider environmental effects on the genetic relationships among traits. We compared the genetic relationships among egg size, lifetime fecundity, and female adult body mass (a trait linked to reproductive effort) in the seed beetle, Stator limbatus, between two environments (host-plant species Acacia greggii and Cercidium floridum). Genetic correlations among these traits were estimated through half-sib analysis, followed with artificial selection on egg size to observe the correlated responses of lifetime fecundity and female body mass. We found that the magnitude of the genetic trade-off between egg size and lifetime fecundity differed between environments-a strong trade-off was estimated when females laid eggs on C. floridum seeds, yet this trade-off was weak when females laid eggs on A. greggii seeds. Also differing between environments was the genetic correlation between egg size and female body mass-these traits were positively genetically correlated for egg size on A. greggii seeds, yet uncorrelated on C. floridum seeds. On A. greggii seeds, the evolution of egg size and traits linked to reproductive effort (such as female body mass) are not independent from each other as commonly assumed in life-history theory. Offspring size at birth, hatching, or germination is often under strong selection; large offspring frequently mature earlier, have improved ability to avoid or withstand predation or competition, or survive better in stressful environments compared to small offspring (e.g., low quality host plants; Fox et al. 1997, reviewed in Roff 1992Carrière and Roff 1995;Azevedo et al. 1997;and Fox and Czesak 2000), although small offspring may have fitness advantages in some cases (e.g., hatch earlier; Fox 1997). Selection also generally favors high female fecundity, and it is generally assumed that the simultaneous evolution of large offspring and high fecundity is constrained by a trade-off between these two traits (e.g., Smith and Fretwell 1974;Parker and Begon 1986;McGinley et al. 1987;Winkler and Wallin 1987). Many studies have demonstrated a phenotypic correlation between offspring size and number (e.g., Sinervo and Licht 1991;Vaughton and Ramsey 1998), but few studies have examined their underlying genetic relationship (but see Lynch 1984Lynch , 1985Snyder 1991;Ebert 1993;Schwarzkopf et al. 1999).A trade-off between offspring size and number may be obscured if total reproductive effort varies substantially among females, either through variation in the amount of resource stores or variation in acquisition of resources from the environment (van Noordwijk and de J...

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

“…Further studies are needed to understand in detail maternal plasticity on offspring provisioning strategies in M. eulophus. Egg size variation is often correlated with offspring performance (Roff 1992;Fox et al 1997), but this relationship may change with the environment (Parker and Begon 1986;Czesak and Fox 2003) and with the total number of eggs laid (Bernardo 1996). In the present case, divergence in the pattern of egg size plasticity according to the maternal diet was accompanied with similar progeny performance in the low-quality host.…”

Warmer temperatures attenuate the classic offspring number and reproductive investment trade-off in the common lizard, Zootoca vivipara

“…Patterns of selection acting on life-history traits are known to vary between habitats [5,6]. For example, the balance between number and size of offspring may depend on the ecological context: females should invest more in fewer offspring if juvenile survivorship is poor, but may enhance their litter size (LS) in high-quality environments [7].…”

“…As a consequence, interactions between traits may circumstantially magnify, diminish or disappear along environmental gradients. The influence of environmental conditions on the intensity of trade-offs has been considered in theoretical works [3,8] or tested experimentally [5], but studies of natural populations are still scarce [9].…”

A limit on the extent to which increased egg size can compensate for a poor postnatal environment revealed experimentally in the burying beetle, Nicrophorus vespilloides

“…A positive association between egg size and offspring fitness is often assumed to exist (Smith and Fretwell 1974), and there is general support for this assumption in vertebrates and invertebrates, with many studies finding that smaller eggs have lower hatching success and produce lower fitness hatchlings than larger eggs (Roff 1992; Czesak and Fox 2003). In some species, however, the relationship between egg size and offspring fitness depends on the quality of the environment experienced by offspring, with a stronger relationship between egg size and offspring fitness occurring in low‐quality environments than in high‐quality environments (Fox 2000; Czesak and Fox 2003; Bashey 2006). Consistent differences between populations in environmental quality can lead to evolutionary divergence in egg size, with selection favoring larger eggs or newborns in poor quality environments and smaller eggs or newborns in high‐quality environments (Hutchings 1991; Rollinson and Hutchings 2013).…”