Evolutionary Patterns of Host Plant Use by Delphacid Planthoppers
Total Page：16
File Type：pdf, Size：1020Kb
population dynamics. Plant de specificity are considered with 1 crop varieties resistant to del- plant architecture on the abun n Chapter 3 (Denno). Species Evolutionary Patterns of Host Plant ' geographic and plant patch Use by Delphacid Planthoppers and density and plant diversity on l. The causal mechanisms for Their Relatives 1 and persistence are discussed its such as dispersal ability and ization and persistence. Stephen W. Wilson, Charles Mitter, Robert F. Denno and Michael R. Wilson Introduction Planthoppers (Homoptera: Fulgoroidea) are found on every continent ex cept Antarctica and in all major biomes, including tropical rainforests, deserts, grasslands, and the arctic tundra (O'Brien and Wilson 1985). The more than 9000 described species are divided into 19 families (O'Brien and Wilson 1985; Wheeler and Wilson 1987). All species of Fulgoroidea are phytophagous, sucking fluids from leaves, stems, roots, or fungal hyphae. There are species which feed on woody plants (both angiosperms and gymnosperms), herbs, ferns, and even fungi (O'Brien and Wilson 1985). The largest and most studied family of planthoppers is the Delphacidae which includes more than 2000 species in approximately 300 genera and 6 subfamilies (Asche 1985, 1990). Most continental delphacids are associated with monocots, particularly grasses and sedges (Wilson and O'Brien 1987; Denno and Roderick 1990 ), whereas some species, especially those on oceanic archipelagos, have radiated on dicots as well (Giffard 1922; Zim merman 1948). Their predilection for monocots, phloem-feeding habit, oviposition behavior and ability to transmit pathogens have contributed to the severe pest status of several delphacid species on rice, corn, sugarcane, and several cereal crops (Wilson and O'Brien 1987). Delphacids are intimately associated with their host plants and use them for feeding, mating, oviposition, and protection during winter and from their natural enemies (Claridge l 985a; Denno and Roderick 1990 ). As 7 ~- -- ----·-· ~--·--- -- 8 S. W. Wilson, C. Mitter, R. F. Denno & M. R. Wilson Evolutionalr might be expected for delphacids from this close association, host plant result of such "parallel phylo1 nutrition, and allelochemistry have figured prominently in studies of host phytophage species across h< plant selection (Sogawa 1982; Woodhead and Padgham 1988), performance logenetic divergence sequenc (Mitsuhashi 1979; Denno et al. 1986; Metcalfe 1970), population dynamics ond, lineages which evolve w including dispersal (McNeill and Prestidge 1982; Denno and Roderick strongly influence each other 1990), and community structure (McNeill and Prestidge 1982; Waloff sense, might take several for: 1980). Moreover, other aspects of the host plant, such as persistence and envisioned an "arms race" be growth form, play an important role in shaping the life history strategies of tation, with each innovation J planthoppers (Denno and Roderick 1990, Denno et al. 1991 ). Thus, eluci A major expectation, if a gi dating the causes of current patterns of host plant use in the Delphacidae is significantly while in associat central to understanding many aspects of their biology. Toward that end, we the host taxa should corresi examine planthopper/host plant relationships from a phylogenetic and ev respective herbivores. If insec olutionary perspective. species were attacked by just mediate ancestors, there shou Synopsis of Issu.es phylogenies, except where 01 not (Mitter and Brooks 1983 A recurring question concerning the evolution of host plant use by insects cur between some vertically has been the degree to which it is genetically "constrained" (Mitter and (Munson et al. 1991), but se Farrell 1991 ). If the genetic variation required for recognition and use of dispersive adults have the opi: novel hosts were readily available, host preference might be locally opti substantial cladogram cor:resp mized by natural selection with respect to intrinsic plant traits such as sect and plant lineages is also phenology or chemistry and to ecological variables such as plant and nat to) host plant species other t ural enemy abundance. If this were the case, there should be little phylo vided that these hosts are re genetic pattern to host plant associations, which would be best understood Raven's (1964) model, fore: as adaptation to local environments. The genetic variation for host use traits that evolve temporary itfunur commonly observed in phytophage populations (Futuyma and Peterson zation most likely to come fi 1985), and the rapid accumulation of herbivore species on some intro antecedent defense. Even if 1 duced plants (Strong et al. 1984 ), suggest that host use evolution might be dom, cladistically basal (and relatively unconstrained by genetic barriers. occur on correspondingly pr If, in contrast, adoption of a novel host required simultaneous change in tions were rapidly obscured a number of genetically independent traits, genotypes capable of such a host choice. shift might rarely occur. Such genetic "constraint" could slow or channel Although concordance of p the evolution of host associations and impede local optimization of host it could also result from he preference (Mitter and Farrell 1991 ). Most species might be expected to subsequent to plant diversifi, feed on hosts similar or identical to those of their near relatives elsewhere, chemistry or other traits) co1 with local host use only fully interpretable in a phylogenetic context (Far phylogenetic relatedness. To i rell and Mitter, in press). diversification, independent , The association of many insect genera or higher-ranking taxa with par patterns, or "molecular clockl ticular taxa of host plants (Ehrlich and Raven 1964) is consistent with the their associated insect lineag1 existence of strong genetic limits on host use. If major host shifting were not necessarily imply coevol rare, the association of particular herbivore and plant lineages might persist simply responded independei over geological time and through their subsequent diversification. One ance. However, the existence nno & M. R Wilson Evolutionalry Patterns of Host Plant Use 9 iis close association, host plant result of such "parallel phylogenesis" is that the present-day distribution of I prominently in studies of host phytophage species across host taxa might reflect simply the age or phy td Padgham 1988 ), performance logenetic divergence sequence of the associated taxa (Zwolfer 1978). Sec life 1970 ), population dynamics ond, lineages which evolve while associated could have the opportunity to ~e 1982; Denno and Roderick strongly influence each other's evolution. Such "coevolution," in the broad Ill and Prestidge 1982; Waloff sense, might take several forms. For example, Ehrlich and Raven ( 1964) t plant, such as persistence and envisioned an "arms race" between plant defense and insect counteradap >ing the life history strategies of tation, with each innovation permitting an episode of radiation. Denno et al. 1991). Thus, eluci A major expectation, if a given insect and plant lineage have diversified t plant use in the Delphacidae is significantly while in association, is that phylogenetic relationships among eir biology. Toward that end, we the host taxa should correspond in some fashion to those among their ips from a phylogenetic and ev- respective herbivores. If insect species were so host specific that each plant species were attacked by just the descendants of the herbivores of its im mediate ancestors, there should be an exact match between insect and plant phylogenies, except where one lineage has speciated while its partner has not (Mitter and Brooks 1983). Such strict "parallel phylogenesis" may oc tion of host plant use by insects cur between some vertically transmitted endosymbionts and their hosts .cally "constrained" (Mitter and (Munson et al. 1991), but seems unlikely for planthoppers, in which the 1ired for recognition and use of dispersive adults have the opportunity to select alternative hosts. However, reference might be locally opti substantial cladogram correspondence between synchronously evolving in to intrinsic plant traits such as sect and plant lineages is also expected if insects colonize (transfer or shift variables such as plant and nat to) host plant species other than the ones on which they developed, pro ~se, there should be little phylo vided that these hosts are related (Farrell and Mitter 1990). Ehrlich and which would be best understood Raven's ( 1964) model, for example, implies periodic radiation by plants :netic variation for host use traits that evolve temporary immunity from herbivores, with subsequent coloni tlations (Futuyma and Peterson zation most likely to come from herbivores on related plants bearing the :rbivore species on some intro antecedent defense. Even if newly available hosts were colonized at ran that host use evolution might be dom, cladistically basal (and hence older) herbivore taxa should tend to rs. occur on correspondingly primitive plant taxa, unless early host associa required simultaneous change in tions were rapidly obscured through extinction or phyletic evolution of ts, genotypes capable of such a host choice. 1nstraint" could slow or channel Although concordance of phylogenies suggests diversification in concert, 1pede local optimization of host it could also result from herbivore colonization and speciation entirely ,st species might be expected to subsequent to plant diversification if the plant similarities (in secondary of their near relatives