Effect of water availability on the phenotypic expression of herbivore resistance in northern red oak seedlings (Quercus rubra L.)

Abstract

The phenotypic expression of quantitative characters is a function of the individual's genotype and the environment in which it is measured. In a previous reciprocal transplant study, we found that patterns of genetic differences in resistance to herbivores among adjacent subpopulations of northern red oak (Quercus rubra L.), were consistent with a local adaptation hypothesis. The goal of this study was to determine if variation in water availability may have been a mechanism responsible for these previously observed patterns. In 1989 a common garden study was initiated using acorns from maternal trees occupying either a north- or south-facing slope microhabitat in an oak-hickory forest in east central Missouri, USA. The seedlings were grown under one of two water treatments, irrigated or natural. In 1992, we utilized this experiment to examine the quantitative character of the percentage of leaf area damaged by herbivores, which is a measure of the phenotypically expressed level of resistance. Specifically, we made three predictions: (1) because northern red oak seem to grow best in mesic environments, seedlings receiving more water should show greater resistance to herbivores; (2) if the subpopulations from north- and south-facing slope microhabitats are genetically differentiated with respect to the quantitative character of resistance to herbivores, then there will be a significant effect of maternal slope microhabitat on the percentage of leaf area damaged; and (3) if the pattern of resistance to herbivores found among subpopulations reflects local adaptation to moisture levels in their own microhabitat, then we would expect to find a significant maternal slope microhabitat by water treatment interaction, with north-facing slope seedlings incurring less damage in the wetter (irrigated) treatment and south-facing slope seedlings incurring less damage in the drier (natural) treatment. Our data supported the first two predictions: seedlings in the irrigated treatment showed a significantly lower percentage of leaf area damage than those in the natural treatment, and the percentage of leaf area damaged was significantly lower on seedlings from maternal plants occupying the north-facing slope microhabitat. However, we found no significant interaction between maternal slope microhabitat and water treatment. These findings demonstrate that northern red oak supbopulations respond phenotypically to water availability, but this factor does not appear to be the underlying mechanism behind the previously observed local adaptation expressed as resistance to herbivores.

Costs of defense: correlated responses to divergent selection for foliar glucosinolate content in Brassica rapa

“…Further, naturalized populations of B. rapa exhibit significant additive genetic variation for foliar glucosinolate content Mitchell-Olds 1996, 1998;Siemens et al 2002), suggesting that the lack of additive genetic variation in foliar glucosinolate content in this species is not a factor that constrains the evolution of this trait. It is also important to note that the finding of significant additive genetic variation in defensive traits is not uncommon (Berenbaum et al 1986;Marquis 1990Marquis , 1992Simms and Rausher 1989;Sork et al 1993;Schemske 1993, 1994;Han and Lincoln 1994;Stowe et al 1994;Sagers and Coley 1995;Siemens et al 2002;Alves et al 2007;Andrew et al 2007; but see Núñez-Farfán and Dirzo 1994).…”

“…Typically, studies that have investigated plant defense against insect herbivores demonstrate significant genetic variation in defense (Berenbaum et al 1986;Simms and Rausher 1989;Marquis 1990Marquis , 1992Sork et al 1993;Schemske 1993, 1994;Han and Lincoln 1994;Stowe et al 1994;Sagers and Coley 1995;Siemens et al 2002;Alves et al 2007;Andrew et al 2007; but see Núñez-Farfán and Dirzo 1994). As such, the evolutionary response of defense to herbivore-imposed selection does not appear to be limited by a lack of genetic variation in defense.…”

Insect injury and mortality of seedlings of field penny-cress (Thlaspi arvense L.).

“…Earlier studies had indi-cated that drought stress often makes plants more sensitive to insect damage. Its effects may increase herbivory because of an increasing concentration of foliar nutrients and soluble carbohydrates (STOWE et al 1994). Herbivory may be also influenced by other host plants nearby, e.g.…”

Insect damage to and mortality of seedlings of Chenopodium album L. and Fallopia convolvulus (L.) Á.Löve

“…The intensity of insect damage was found to be correlated with rainfall. Earlier studies had indicated that drought stress often makes plants more palatable to herbivores and more sensitive to insect damage (Stowe et al 1994). The effect of drought stress on the sensitivity of plants to insect damage has been cited by many authors (e.g.…”