Box 3 (continued)
The proposed hypothetical figure shows two bouts of the escape and radiate
process, producing starburst of speciation in the plant-host and the herbivore/
parasite. Each oval encircles only the initial starburst of speciation in the host
lineage resulting from new defenses or the initial starburst of speciation in the
parasite lineage resulting from new counter-defenses (Modified from Thompson [167]).
5.2
Host Shift and Speciation
Speciation events of plants and herbivores taxa are not only related to the conserved
use of host-plants by phytophagous insects but also to host shifts. In a relative recent
compilation of phylogenies of insect herbivores, Winkler and Mitter [187] found that
close to 10% of speciation events involve host shifts to a nonrelated plant family.
Although the role of host-plant shifts in insect diversification may seems limited,
hosts shift has been widely documented in several plant lineages (e.g., [90, 91]) and
has important implications for the evolution of host range. Host shifts may occur if
the developmental aspects required to colonize/exploit a novel niche (host plant) and
the ancestral, overlap at some point. Thus, if the range for overlapping increases,
more plasticity for using new host is expected. Changes in feeding habits (e.g.,
polyphagy) should increase shifts by colonization of new hosts. Consequently, the
evolution of host plant range appears to be closely linked to the diversification of
host use through colonization [89]. Changes in host use by phytophagous insects
across plant phylogeny also revealed a key link between diversification of plants and
herbivores lineages and plant secondary chemistry. Empirical evidence suggests that
host shifts are often constrained by similarity in the chemical profile of host species.
For instance, phylogenetic analysis showed that historical patterns of host shift of
Blepharida (Coleoptera) into Bursera (Burseraceae) correspond to chemical similarity based on terpenoids of host-plants [16]. The importance of secondary metabolites
to drive host use patterns has been also demonstrated at molecular level. Cruciferous
plants (Brassicaceae) usually hosts butterflies from the Pierinae family [48], and are
known by the production of glucosinolates. Wheat et al. [183] showed that the
occurrence of NSP (nitrile-specifying protein) glucosinolate detoxification gene on
butterflies matched the occurrence of glucosinolate in their host-plants. The detoxification mechanism likely evolved shortly after the diversification of Brassicales,
allowing the colonization of new glucosinolate-base host. The host shift has led to
adaptive radiation in the Brassicales-feeding butterflies. Key innovation breakthrough of Brassicaceas and butterflies has been recently revisited. Based on gene
family analysis, Edger et al. [47] confirmed the molecular fitting between secondary
compounds of plants and counter defenses of insects by means of gene and genome
duplications. The study documented a repeated escalation of key innovations and
burst of diversification on each side of the plant-insect interaction (Fig. 3). These
examples show how genetic mechanisms can be linked to macroevolutionary
58
E. Kariñho-Betancourt
The proposed hypothetical figure shows two bouts of the escape and radiate
process, producing starburst of speciation in the plant-host and the herbivore/
parasite. Each oval encircles only the initial starburst of speciation in the host
lineage resulting from new defenses or the initial starburst of speciation in the
parasite lineage resulting from new counter-defenses (Modified from Thompson [167]).
5.2
Host Shift and Speciation
Speciation events of plants and herbivores taxa are not only related to the conserved
use of host-plants by phytophagous insects but also to host shifts. In a relative recent
compilation of phylogenies of insect herbivores, Winkler and Mitter [187] found that
close to 10% of speciation events involve host shifts to a nonrelated plant family.
Although the role of host-plant shifts in insect diversification may seems limited,
hosts shift has been widely documented in several plant lineages (e.g., [90, 91]) and
has important implications for the evolution of host range. Host shifts may occur if
the developmental aspects required to colonize/exploit a novel niche (host plant) and
the ancestral, overlap at some point. Thus, if the range for overlapping increases,
more plasticity for using new host is expected. Changes in feeding habits (e.g.,
polyphagy) should increase shifts by colonization of new hosts. Consequently, the
evolution of host plant range appears to be closely linked to the diversification of
host use through colonization [89]. Changes in host use by phytophagous insects
across plant phylogeny also revealed a key link between diversification of plants and
herbivores lineages and plant secondary chemistry. Empirical evidence suggests that
host shifts are often constrained by similarity in the chemical profile of host species.
For instance, phylogenetic analysis showed that historical patterns of host shift of
Blepharida (Coleoptera) into Bursera (Burseraceae) correspond to chemical similarity based on terpenoids of host-plants [16]. The importance of secondary metabolites
to drive host use patterns has been also demonstrated at molecular level. Cruciferous
plants (Brassicaceae) usually hosts butterflies from the Pierinae family [48], and are
known by the production of glucosinolates. Wheat et al. [183] showed that the
occurrence of NSP (nitrile-specifying protein) glucosinolate detoxification gene on
butterflies matched the occurrence of glucosinolate in their host-plants. The detoxification mechanism likely evolved shortly after the diversification of Brassicales,
allowing the colonization of new glucosinolate-base host. The host shift has led to
adaptive radiation in the Brassicales-feeding butterflies. Key innovation breakthrough of Brassicaceas and butterflies has been recently revisited. Based on gene
family analysis, Edger et al. [47] confirmed the molecular fitting between secondary
compounds of plants and counter defenses of insects by means of gene and genome
duplications. The study documented a repeated escalation of key innovations and
burst of diversification on each side of the plant-insect interaction (Fig. 3). These
examples show how genetic mechanisms can be linked to macroevolutionary
58
E. Kariñho-Betancourt