Understanding the physiological and behavioral mechanisms underlying host-plant specialization in holometabolous species, which undergo complete development with a pupal stage, presents a particular challenge in that the process of host-plant selection is generally carried out by the adult stage, whereas host-plant utilization is more the province of the larval stage (Thompson 1988a, 1988b). Thus, within a species, critical chemical, physical, or visual cues for host-plant identification may differ over the course of the life cycle. An organizing principle for the study of host-range evolution is the preference-performance hypothesis (Jaenike 1978). According to this hypothesis, ovipositing females should maximize their fitness...

Natural selection should favor female phytophagous insects that have a preference for ovipositing on resources where their offspring will have the highest fitness (Dethier 1959a, 1959b; Singer 1972; Jaenike 1978). This assertion has been termed the naïve adaptationist hypothesis (Courtney and Kibota 1990). This hypothesis has been tested by measuring oviposition preference and offspring performance in a wide range of interactions, and contrary to initial expectations a wide range of preference-performance relationships have been found (Thompson 1988; Courtney and Kibota 1990; Mayhew 1998, 2001). General hypotheses explaining broad patterns in preference-performance relationships have been largely lacking, with the exception of...

The evolutionary ecology of polyphagy by phytophagous insects has been overshadowed by an intense focus on the evolutionary ecology of their host specificity. This bias reflects the preponderance of host specificity in phytophagous insects (reviewed by Weis and Berenbaum 1989 and Novotny and Basset 2005) and its fascinating consequences for community structure and evolutionary diversification. Truly, the study of host-specific herbivores has provided many key insights and motivated the conceptual side of the study of plant-insect interactions (e.g., Brues 1924; Dethier 1954; Fraenkel 1959; Ehrlich and Raven 1964; Feeny 1976; Rhodes and Cates 1976) as well as the broader issues...

Phenotypic plasticity is the ability of an organism, a single genotype, to exhibit different phenotypes in different environments (Fig. 4.1A). Such plasticity is nearly ubiquitous in nature and occurs in various animal and plant phenotypes, including behavior, physiology, and morphology. Phenotypic plasticity may be observed as both adaptive and nonadaptive responses to the biotic or abiotic environment, though we focus on adaptive responses in interacting species.

Phenotypic plasticity plays an important role in the interactions between plants and herbivorous insects (Tables 4.1 and 4.2). In particular, plants and herbivores have traits that are expressed in response to their interactions with...

Basic and applied research programs can both benefit by approaching concerns regarding resistance to herbivores from a perspective centering on natural selection and genetic architecture of resistance. In natural systems, quantification of selection, determination of genetic correlations with other traits, and evaluation of genetic architecture (i.e., estimation of additive and nonadditive genetic effects) can enhance our ability to predict the evolutionary trajectory of plant resistance. Evaluation of genetic architecture has become increasingly emphasized because hybridization is widespread in plant species. Moreover, genetic architecture studies involving interpopulational or interspecific hybrids can give insight into the processes of population differentiation, speciation, and...

Hybridization has been recognized by some as a potent evolutionary force that rapidly can generate new (novel) gene combinations for adaptive evolution and speciation (Arnold 1997; Burke and Arnold 2001; Schluter 2001; McKinnon et al. 2004). However, others have historically viewed it as a minor evolutionary force (barring allopolyploids in plants) or simply as a local or transient type of evolutionary noise or dead end (Rhymer and Simberloff 1996; Schemske 2000; Barton 2001). While definitive proof is generally lacking, especially for animals, diploid hybrid recombinant speciation may represent a mechanism of evolution of new species (Dowling and Secor 1997), especially...

Speciation in animals is promoted by the evolution of behavioral differences that reduce attraction, mating, and fertilization between individuals in diverging populations (Mayr 1963; West-Eberhard 1983; Eberhard 1985, 1994, 1996; Coyne and Orr 2004). Behavioral traits involved in communication between the sexes often provide the most immediate contributions to reproductive isolation (Blair 1955; Claridge 1990; Ryan and Rand 1993; Bridle and Ritchie 2001; Gerhardt and Huber 2002; Kirkpatrick and Ravigné 2002). Consequently, identifying the evolutionary forces that lead to changes in sexual communication is necessary to understand the evolution of behavioral isolation and its contribution to divergence and speciation.

The...

Biodiversity is an inherent outcome of evolution. Despite substantial progress toward discerning the nature of the evolutionary processes shaping and maintaining biodiversity, critical questions still remain. For example, what traits promote rapid speciation and how do they originate? Are certain groups of organisms more diverse than others and, if so, why?

Phytophagous insects are the most prevalent form of animal life on Earth. Weis and Berenbaum (1989) estimate roughly 361,000 species of plant-feeding insects, compared to their roughly 308,000 species of green plant hosts. Most phytophagous insects are relative specialists, feeding, mating, and ovipositing on a limited subset of possible...

For much of the twentieth century, the study of speciation had two major emphases. One was evaluating the geographic circumstances under which speciation occurred, and specifically whether geographic isolation (allopatry) was required (Mayr 1942, 1947; Bush 1969; Futuyma and Mayer 1980; Coyne and Orr 2004). The other was deciphering the genetic architecture of speciation, that is, the roles played by chromosomal translocations, and the kinds, numbers, linkage and epistatic relationships, and phenotypic effects of the genes involved in reproductive isolation (Noor et al. 2001; Orr 2001; Rieseberg 2001; Ortiz-Barrientos et al. 2002). Only recently have the contributions of natural selection...

Host-specific herbivorous insects have inspired speculation about sympatric speciation at least since the 1860s, when Walsh (1864) described the now famous host races of the apple maggot (Berlocher and Feder 2002). Even Ernst Mayr, who lamented that “sympatric speciation is like the Lernaean Hydra which grew two new heads whenever one of its old heads was cut off,” admitted that “host races [of phytophagous insects] are a challenging biological phenomenon, and constitute the only known case indicating the possible occurrence of incipient sympatric speciation” (Mayr 1963, p. 460). He immediately added, though, that “even in this case a process of...

Insects and flowering plants are among the most diverse macroorganisms on earth, and their mutual interactions provide little doubt that each group is in part responsible for the other’s diversity (Hairston et al. 1960; Ehrlich and Raven 1964; Strong et al. 1984; Novotny et al. 2006). However, exactly how diversification of flowering plants has affected the diversity of insects, and vice versa, is not well understood for the vast majority of plant and insect groups. Fossil evidence suggests that flowering plants were not associated with the initial modern diversification of insects that began 245 million years ago (Labandeira and Sepkoski...

Interactions between plants, their herbivores, and their pollinators are thought to have led to the diversification of both plants and insects. Historically, studies of plant-herbivore and plant-pollinator interactions have occurred independently. Research at both micro-and macroevolutionary levels has focused on the evolution of plant resistance in the context of herbivory, and on floral traits in the context of pollination. For example, researchers have long recognized the role of plant secondary chemicals in herbivore feeding preferences (e.g., Dethier 1941). Fraenkel (1959) proposed that the “reason for existence” of plant secondary chemicals was to attract and deter herbivores rather than as products...

A fundamental question in evolutionary biology is how adaptive radiation proceeds on continents, where most of it occurs. The question is most pressing when insects are considered, especially in phytophagous taxa, which represent over 25% of terrestrial biodiversity. Each taxon has, no doubt, followed a unique trajectory through time, but unifying themes should reveal some general patterns and processes, even if the answers recognize that with different starting points, different end points will result (cf. MacArthur 1972). Given the great diversity of insect herbivores, we should expect both divergent and convergent modes of adaptive radiation, which therefore require a pluralistic...

Biologists have long sought an answer to the question, “What determines species diversity?” Indeed, this question is one of only 25 key questions featured in the 125th anniversary issue ofSciencethat were intended to expose critical gaps in scientific knowledge (Pennisi 2005). ANaturearticle by Emerson and Kolm (2005a; but see also Cadena et al. 2005; Emerson and Kolm 2005b) suggests that species diversity itself might help to promote speciation. Put another way, these authors argue that species cause species.

Emerson and Kolm (2005a) used species lists of the plants and arthropods from the Canary and Hawaiian islands...

From a humble beginning in the early Cretaceous, angiosperm plants have quickly conquered the earth so that they now make up one of the most ubiquitous and species-rich groups (Crane et al. 1995; Wikström et al. 2001; Stuessy 2004; Friis et al. 2005). Likewise, the pioneer insects that once colonized this novel resource have multiplied to such an extent that they have become an ecologically dominating group in all terrestrial ecosystems (Mitter et al. 1988; Farrell 1998). Together, the seed plants and the insects that feed on them make up a good half of all described species, and their diversification...

We are faced with three seemingly conflicting observations regarding the diversification of plant-feeding insects. Insects can evolve at astoundingly rapid rates when confronted with new selection pressures, as shown in hundreds of studies in recent decades. Nevertheless, most insect lineages remain highly conservative in the range of species with which they interact. Occasionally, though, insects make great phylogenetic jumps, even jumping between eudicotyledonous and monocotyledonous plant taxa. It is the juxtaposition of these three observations that has historically created the conceptual tension between fields of study that focus on current selection, such as evolutionary ecology and population genetics, and fields...

Cophylogeny provides a framework for the study of historical ecology and community evolution. Plant-insect cophylogeny has been investigated across a range of ecological conditions including herbivory (Farrell and Mitter 1990; Percy et al. 2004), mutualism (Chenuil and McKey 1996; Kawakita et al. 2004), and seed parasitism (Weiblen and Bush 2002; Jackson 2004). Few examples of cophylogeny across three trophic levels are known (Currie et al. 2003), and none have been studies of plants, herbivores, and their parasitoids. This chapter compares patterns of diversification in figs (FicussubgenusSycomorus) and three fig-associated insect lineages: pollinating fig wasps (Hymenoptera: Agaonidae: Agaoninae:Ceratosolen),...

The dramatic expansion of research on insect-plant interactions prompted by Ehrlich and Raven’s (1964) essay on coevolution focused at first mainly on the proximate mechanisms of those interactions, especially the role of plant secondary chemistry, and their ecological consequences. Subsequently, in parallel with the resurgence of phylogenetics beginning in the 1970s and 1980s, there arose increasing interest in the long-term evolutionary process envisioned by Ehrlich and Raven (e.g., Benson et al. 1975; Zwölfer 1978; Berenbaum 1983; Mitter and Brooks 1983; Miller 1987). Since the early 1990s, spurred in part by the increasing accessibility of molecular systematics, there has been a...

“If Darwin were alive today the insect world would delight and astound him with its impressive verification of his theories of survival of the fittest. Under the stress of intensive chemical spraying the weaker members of the insect populations are being weeded out” (Carson 1962). When Rachel Carson wrote that insightful passage inSilent Spring, evolution of insecticide resistance had been documented in about 100 species of pests. In the ensuing 30 years, the number jumped to more than 500 species (Georghiou and Lagunes-Tejeda 1991). This remarkable ability of insects to adapt quickly to toxins used to control them threatens...

The increasing movement of organisms to new regions by humans is enabling species to breach natural dispersal barriers that normally constrain their geographic distribution. Oddly enough, despite being introduced to areas that may be very different from their home region, some exotics become spectacularly more successful in evolutionarily novel environments than in areas in which they evolved. How some exotics come to dominate these new habitats, despite being often inconspicuous members of their native community, is one of ecology’s central mysteries. Unraveling this mystery involves understanding how introduced organisms faced with novel abiotic or biotic conditions make accommodations to their...

A life-history strategy encompasses an integrated suite of traits associated with reproduction (e.g., fecundity, age to first reproduction, offspring size, and voltinism) and the placement of offspring on suitable resources in space (e.g., dispersal) and time (e.g., diapause) (Southwood et al. 1974; Denno et al. 1996; Roff 2002). Notably, there is tremendous variation, both within and among species, in particular lifehistory traits (Denno et al. 1991, 1996; Roff 1992, 2002; Schmidt et al. 2005), and the challenge is to explain how such trait diversity arises and what factors influence the evolution of particular traits (Roff 1992, 2002).

Despite the clear...

What are the causes of bouts of rapid evolution and selective sweeps in the field, and what proportion of such changes in managed or “pristine” landscapes are nowadays anthropogenic? Evolutionary events may occur independently of environmental change, as when a mutation or hybridization confers increased fitness in existing environments or when an immigrant arrives in a population suffering from inbreeding depression. Alternatively, evolution may comprise responses to environmental changes—changes that may be natural but are more and more often anthropogenic. Anthropogenic triggers of evolution may be obvious, as in the introduction of exotic species that both evolve adaptation to...

It goes without saying that one cannot consider the conservation of plants without thinking about their relationship with the creatures that eat them—and herbivorous insects have long been among the worst enemies of the global flora (Becerra 1997, 2003, 2005). And as anyone who has worked extensively with butterflies or other herbivorous insects can tell you, the distribution, abundance, and phenology of food plants are absolutely key to understanding the dynamics and conservation of their populations. It is no accident that the entire field of coevolution sprung from a study of the reciprocal evolutionary interaction of butterfly caterpillars and...