Age and size at maturity: A quantitative review of diet‐induced reaction norms in insects

Abstract

Optimality models predict that diet-induced bivariate reaction norms for age and size at maturity can have diverse shapes, with the slope varying from negative to positive. To evaluate these predictions, we perform a quantitative review of relevant data, using a literature-derived database of body sizes and development times for over 200 insect species. We show that bivariate reaction norms with a negative slope prevail in nearly all taxonomic and ecological categories of insects as well as in some other ectotherm taxa with comparable life histories (arachnids and amphibians). In insects, positive slopes are largely limited to species, which feed on discrete resource items, parasitoids in particular. By contrast, with virtually no meaningful exceptions, herbivorous and predatory insects display reaction norms with a negative slope. This is consistent with the idea that predictable resource depletion, a scenario selecting for positively sloped reaction norms, is not frequent for these insects. Another source of such selection-a positive correlation between resource levels and juvenile mortality rates-should similarly be rare among insects. Positive slopes can also be predicted by models which integrate life-history evolution and population dynamics. As bottom-up regulation is not common in most insect groups, such models may not be most appropriate for insects. K E Y W O R D S :Amphibians, catch-up growth, compensatory growth, meta-analysis, phenotypic plasticity, spiders.

Life-history plasticity in female threespine stickleback

“…This may be especially important when breeding opportunities are limited, as in semelparous fish (Crespi and Teo, 2002), in monocarpic plants (Burd et al, 2006) and in short-lived organisms such as threespine stickleback and guppies (Reznick et al, 1990). Plasticity for size/age at reproduction has been extensively modeled (Berrigan and Koella, 1994;Marty et al, 2011), comprehensively reviewed recently in insects (Teder et al, 2014) and has been demonstrated in a wide array of fish species (Morita and Fukuwaka, 2006;Hutchings and Jones, 2008). Early-life reproduction is likely to be particularly important in short-lived species living in strongly seasonal environments that constrain breeding to a short period of the year (Adolph and Porter, 1996;Merila et al, 2000).…”

“…In long-lived iteroparous organisms, this maturation plasticity may permit the organism to skip reproductive events entirely (Rideout et al, 2005;Skjaeraasen et al, 2012). Some of the established determinants of the expression of plasticity for maturity in fishes include early-life growth rate (Bertechy and Fox, 1999;Copp and Fox, 2007), size (Teder et al, 2014) and energetic status (for example, lipid content; Thorpe, 2007).…”

Sources of variance in immunological traits: evidence of congruent latitudinal trends across species

“…In insects, adult size is typically a strong predictor of individual fitness: especially in females, reproductive output is often proportional to adult or pupal mass (Tammaru et al, 1996(Tammaru et al, , 2002Honeǩ, 1993). Typically, low larval growth rates induced by suboptimal food quality translate into low adult mass and long development periods (Teder et al, 2014). Consequently, high larval growth rates, short development periods and high pupal mass can all be used as correlates of individual fitness.…”

Metamorphosis is induced by food absence rather than a critical weight in the solitary bee, Osmia lignaria

“…The feeding ecology of insects falls along a continuum: species that consume potentially limitless food resources and species that have a discrete quantity of a resources (71). Many hymenopterans, including solitary bees such as O. lignaria, fit into the discrete-resource category, because larvae feed exclusively on a discrete quantity of food (67).…”

“…Many hymenopterans, including solitary bees such as O. lignaria, fit into the discrete-resource category, because larvae feed exclusively on a discrete quantity of food (67). Other insects that fall into the discrete-resource category include parasitic, seed-eating, and dung-feeding insects (71). Insects with discrete resources are likely to have different metamorphic responses than M. sexta and D. melanogaster, because once larvae consume their provisions, there is no possibility of obtaining more.…”