Early ontogenetic patterns in chemical defense in Plantago (Plantaginaceae): genetic variation and trade‐offs

Abstract

Predictions based on the plant age and growth-differentiation balance hypotheses of defense were tested in two congeneric species, Plantago lanceolata and P. major, by quantifying iridoid glycosides, defensive chemicals, in seeds and leaves during the first 6 wk of growth. Concentrations decreased from the seed to 2-wk-old seedling stage in P. lanceolata, but increased during this period in P. major. In both species, levels were similar for 2- and 4-wk-old plants, then significantly increased from 4 to 6 wk. Genetic variation in the ontogeny of iridoid glycoside production was significant in both species at the maternal family level and at the population level. To examine whether allocation costs could explain the low production of iridoid glycosides in seedlings, relationships between growth and defense (iridoid glycosides) were characterized. Growth and defense had a positive or null relationship in all age groups, indicating that there was no trade-off in these plants at any age. This study provides some support for the growth-differentiation balance hypothesis, but offers no support for the plant age hypothesis. Measuring how herbivory affects plant fitness at different ontogenetic stages may shed light on these patterns in Plantago and on the evolution of the ontogeny of defense.

Soil nitrogen availability and herbivore attack influence the chemical defenses of an invasive plant (Linaria dalmatica; Plantaginaceae)

“…genetic variation due to varying selective pressures), that may be important drivers of variation in L. dalmatica allelochemistry. Other studies investigating plants containing iridoid glycosides have demonstrated that genetic, ontogenetic, biotic, and abiotic environmental variation can all influence these defense compounds Bowers and Stamp 1993;Adler et al 1995;Darrow and Bowers 1999;Marak et al 2002;Fuchs and Bowers 2004;Barton and Bowers 2006;Barton 2007;Wurst et al 2008).…”

Arbuscular mycorrhizal fungal species suppress inducible plant responses and alter defensive strategies following herbivory

“…Unlike the case of fungal endophytes, in which endophytic fungi produce their own compounds, AM fungi manipulate the defensive chemical concentrations already produced by P. lanceolata. Nevertheless, given the ubiquity of AM fungal infection in terrestrial communities, the influence of AM fungi on plant defense will likely also have important cascading effects through terrestrial ecosystems, especially given the lack of a trade-off between growth and constitutive defense in P. lanceolata (Barton 2007) and that induction of iridoid glycosides has been shown to have broad-spectrum effects against other plant antagonists (Biere et al 2004). While previous models demonstrate that mycorrhizal modification of plant defense can have profound effects on the dynamics of such plant-herbivore interactions (Bennett et al 2006), these models have not yet considered the implications of mycorrhizal modification of the induction of plant responses and do not scale up these potential effects through terrestrial food webs.…”

Growth and chemical defense in willow seedlings: trade-offs are transient

“…Young plants are more heavily defended in some species (Bryant and JulkunenTiitto 1995), while older plants are more greatly defended in other species (Fritz et al 2001;Barton 2007;Goodger et al 2007). Surprisingly, relatively few studies have tested for age-specific costs (Barton 2007;Boege et al 2007). In one study, Barton (2007) tested for trade-offs between growth and iridoid glycoside production in two Plantago species, Plantago major and Plantago lanceolata.…”

“…Age-specific costs might also be expected because seedlings, saplings, and mature plants often differ dramatically in defenses (Briggs and Schultz 1990;Fritz et al 2001;van Dam et al 2001;Del Val and Dirzo 2003;Schaffner et al 2003;Albrectsen et al 2004;Fuchs and Bowers 2004;Barton 2007;Boege et al 2007;Goodger et al 2007;Elger et al 2009). Young plants are more heavily defended in some species (Bryant and JulkunenTiitto 1995), while older plants are more greatly defended in other species (Fritz et al 2001;Barton 2007;Goodger et al 2007).…”

“…Surprisingly, relatively few studies have tested for age-specific costs (Barton 2007;Boege et al 2007). In one study, Barton (2007) tested for trade-offs between growth and iridoid glycoside production in two Plantago species, Plantago major and Plantago lanceolata. From week 2 to week 4, the concentration of iridoid glycosides remained low for both species.…”