fitness, and heritability of putative defensive/counter defensive traits. From this, two
major ecological patterns have been extensively documented. (1) Secondary metabolites of plants have an adaptive role, mainly related to defense against herbivores (but
see [30]), and (2) plants and herbivores impose selection to each other.
6.1
Toxins and Digestibility Reducers
Across natural populations, many studies have tested the defensive quality of chemical
traits, estimating the strength to which it can ward off herbivores’ attack (e.g., by
reducing leaf damage or herbivores’ survival) and/or increase plant fitness. A good
example of a chemical trait holding back herbivores is plant’s latex. The sticky white
latex produced by milkweeds (Asclepias spp.: Apocynaceae) is delivered via specialized canals (laticifers) to most plant parts and can be copiously exuded upon tissue
damage [6], suffusing small herbivores (Fig. 4). By addressing the effect of notched
versus undamaged leaves of milkweeds on first-instar monarch butterfly larvae
(Danaus plexippus: Lepidoptera), Zalucki et al. [189] documented a negative impact
of sticky latex on larvae survival. Mortality due to miring in the latex was 27% on the
notched leaves compared with 2% on the intact leaves. Besides of the physical
impediment to herbivores, latex also have a toxic effect on consumers. Latex produced
by milkweeds contents cardenolides, which are bitter tasting steroids that act by
disrupting the sodium and potassium flux in cells, and have toxic effect on most
animals [115]. Latex is an interesting multifaceted defensive trait that can impact
herbivores both mechanically and physiologically. However, most chemical traits
that function as defensive mechanisms do not mechanically prevent herbivores to
freely feed on plants but dissuade them through a toxic or deterrent effect (see the Plant
Apparency Hypothesis, [59, 141]). Toxins or qualitative defenses are small molecules,
peptides or proteins that by interacting with biological macromolecules causing disease
or death when consumed or absorbed by animal tissues [44]. Toxins are predicted to
occur in plants that do not have a foreseeable distribution (i.e., unapparent plants, such
as short-lived plants of early successional stages, sensu [59]), affecting only
Fig. 4 Plant’s latex exuded
while the larvae feeds. Sticky
latex impede larvae from
freely feed and can cause
death by miring or poisoning.
(Original illustration by the
author)
66
E. Kariñho-Betancourt
major ecological patterns have been extensively documented. (1) Secondary metabolites of plants have an adaptive role, mainly related to defense against herbivores (but
see [30]), and (2) plants and herbivores impose selection to each other.
6.1
Toxins and Digestibility Reducers
Across natural populations, many studies have tested the defensive quality of chemical
traits, estimating the strength to which it can ward off herbivores’ attack (e.g., by
reducing leaf damage or herbivores’ survival) and/or increase plant fitness. A good
example of a chemical trait holding back herbivores is plant’s latex. The sticky white
latex produced by milkweeds (Asclepias spp.: Apocynaceae) is delivered via specialized canals (laticifers) to most plant parts and can be copiously exuded upon tissue
damage [6], suffusing small herbivores (Fig. 4). By addressing the effect of notched
versus undamaged leaves of milkweeds on first-instar monarch butterfly larvae
(Danaus plexippus: Lepidoptera), Zalucki et al. [189] documented a negative impact
of sticky latex on larvae survival. Mortality due to miring in the latex was 27% on the
notched leaves compared with 2% on the intact leaves. Besides of the physical
impediment to herbivores, latex also have a toxic effect on consumers. Latex produced
by milkweeds contents cardenolides, which are bitter tasting steroids that act by
disrupting the sodium and potassium flux in cells, and have toxic effect on most
animals [115]. Latex is an interesting multifaceted defensive trait that can impact
herbivores both mechanically and physiologically. However, most chemical traits
that function as defensive mechanisms do not mechanically prevent herbivores to
freely feed on plants but dissuade them through a toxic or deterrent effect (see the Plant
Apparency Hypothesis, [59, 141]). Toxins or qualitative defenses are small molecules,
peptides or proteins that by interacting with biological macromolecules causing disease
or death when consumed or absorbed by animal tissues [44]. Toxins are predicted to
occur in plants that do not have a foreseeable distribution (i.e., unapparent plants, such
as short-lived plants of early successional stages, sensu [59]), affecting only
Fig. 4 Plant’s latex exuded
while the larvae feeds. Sticky
latex impede larvae from
freely feed and can cause
death by miring or poisoning.
(Original illustration by the
author)
66
E. Kariñho-Betancourt