PREFERENCE HIERARCHIES AND THE ORIGIN OF GEOGRAPHIC SPECIALIZATION IN HOST USE IN SWALLOWTAIL BUTTERFLIES

Four allopatric populations of the widely distributed western anise swallowtail butterfly, Papilio zelicaon, use different plant genera as hosts, but simultaneous choice experiments showed that these populations have diverged only slightly in oviposition preference. Of the four populations—two from southeastern Washington State, one from coastal southwestern Washington State, and one from central California—three use hosts that are not available to any of the others. Although variation for the degree of preference for particular plant species occurred within and among populations, all four populations ranked hosts in the same overall order. Monophagy on a local, low-ranking host outside the range of high-ranking hosts did not necessarily lead to the loss of preference for those high-ranking hosts, thereby indicating that the high-ranking hosts would still be accepted, and in some cases even preferred, if a population encountered them again. Hence, the overall preference hierarchy among P. zelicaon populations appears to be evolutionarily conservative. Analyses of differences among families within the California population indicated that increased preference for some hosts is inversely correlated, whereas preference for other hosts may be uncorrelated. Positive correlations may also occur but were not observed among the plant species tested. Overall, the results indicate local monophagy on different plant species in P. zelicaon has not involved major reorganizations in the preference hierarchy of ovipositing females, even in populations that may have fed on a low-ranking host for many generations. Instead, small increases in preference for local hosts have occurred within an evolutionarily conservative preference hierarchy.     

Host plant choice in the comma butterfly-larval choosiness may ameliorate effects of indiscriminate oviposition

In most phytophagous insects, the larval diet strongly affects future fitness and in species that do not feed on plant parts as adults, larval diet is the main source of nitrogen. In many of these insect-host plant systems, the immature larvae are considered to be fully dependent on the choice of the mothers, who, in turn, possess a highly developed host recognition system. This circumstance allows for a potential mother-offspring conflict, resulting in the female maximizing her fecundity at the expense of larval performance on suboptimal hosts. In two experiments, we aimed to investigate this relationship in the polyphagous comma butterfly, Polygonia c-album, by comparing the relative acceptance of low- and medium-ranked hosts between females and neonate larvae both within individuals between life stages, and between mothers and their offspring. The study shows a variation between females in oviposition acceptance of low-ranked hosts, and that the degree of acceptance in the mothers correlates with the probability of acceptance of the same host in the larvae. We also found a negative relationship between stages within individuals as there was a higher acceptance of lower ranked hosts in females who had abandoned said host as a larva. Notably, however, neonate larvae of the comma butterfly did not unconditionally accept to feed from the least favorable host species even when it was the only food source. Our results suggest the possibility that the disadvantages associated with a generalist oviposition strategy can be decreased by larval participation in host plant choice.     

水生观赏植物的调查和研究

水生绿化观赏植物是美化园林水景的重要植物材料,作者通过几年的调查研究和引种栽培,提出了28种(其中荷花含18个品种,睡莲含20个品种)水生绿化观赏植物,同时介绍了20种(其中荷花含6个品种)观赏价值较高的水生绿化观赏植物。     

Divergence in the ovipositional behavior of the Papilio glaucus group

This study contrasts the ovipositional profiles of four members of the Papilio glaucus group, P. glaucus , P. multicaudatus , P. canadensis , and P. rutulus. We used seven choice oviposition bioassays containing leaves from hosts in seven plant families utilized by members of the P. glaucus group. Specifically, we contrast the overall ovipositional profiles of these species and their acceptance of a host in a novel plant family ( Populus tremuloides : Salicaceae) and a host in a putatively ancestral host plant family ( Liriodendron tulipifera : Magnoliaceae). Significant differences were observed between the ovipositional profiles of P. glaucus and P. multicaudatus relative to each other and to P. canadensis and P. rutulus. In contrast, no significant differences were observed between the ovipositional profiles of P. canadensis and P. rutulus , which were also the only species that accepted P. tremuloides. Unlike the acceptance of P. tremuloides , the acceptance of L. tulipifera was present throughout the group despite the inability of the larvae of most species in the group to utilize this host. These results support the prediction of the "hierarchical threshold model" that ancestral host plants are likely to be retained in the ovipositional hierarchy while novel hosts should only be accepted by derived populations.     

HOST PLANT UTILIZATION,HOST RANGE OSCILLATIONS AND DIVERSIFICATION IN NYMPHALID BUTTERFLIES: A PHYLOGENETIC INVESTIGATION

It has been suggested that phenotypic plasticity is a major factor in the diversification of life, and that variation in host range in phytophagous insects is a good model for investigating this claim. We explore the use of angiosperm plants as hosts for nymphalid butterflies, and in particular the evidence for past oscillations in host range and how they are linked to host shifts and to diversification. At the level of orders of plants, a relatively simple pattern of host use and host shifts emerges, despite the 100 million years of history of the family Nymphalidae. We review the evidence that these host shifts and the accompanying diversifications were associated with transient polyphagous stages, as suggested by the “oscillation hypothesis.” In addition, we investigate all currently polyphagous nymphalid species and demonstrate that the state of polyphagy is rare, has a weak phylogenetic signal, and a very apical distribution in the phylogeny; we argue that these are signs of its transient nature. We contrast our results with data from the bark beetles Dendroctonus, in which a more specialized host use is instead the apical state. We conclude that plasticity in host use is likely to have contributed to diversification in nymphalid butterflies.     

A DIGESTIVE LIPASE OF Pieris brassicae L. (LEPIDOPTERA: PIERIDAE): PURIFICATION, CHARACTERIZATION, AND HOST PLANTS EFFECTS

The properties of a digestive lipase from the larval midgut of Pieris brassicae were studied by performing biochemical purification, characterization, effect of host plants, and extracted inhibitors. The purification process revealed a lipase with a purification fold of 42, recovery of 18.12%, molecular weight mass of 72.3 kDa, optimal pH at 11, and optimal temperature at 30°C, as well as stability at the optimal temperature for 12 h. The purified enzyme was inhibited by the ions Na(+) , Mn(+) , Fe(2+) , and Cu(2+) and the inhibitors SDS, EDTA, TTHA, and mercaptoethanol. Ca(2+) and Mg(2+) increased activity of the purified lipase, but urea, PMSF, EGTA, and DTC had no effect on enzymatic activity. Feeding of larvae on three host plants, Trepaeolus majus, Brassica olearcea var. alba, and B. olearcea var. rubra revealed the highest lipase activity on T. majus, but the two varieties of B. olearcea significantly decreased lipase activity. Extraction of a crude inhibitor from two varieties of B. olearcea demonstrated that the crude inhibitor inhibited the purified lipase up to 75%. The inhibitor changed the kinetic parameters of the enzyme by elevating the K(m) , as in competitive inhibition. The data suggest a possible role for plant lipase inhibitors in host plant resistance.     

A review of the pre-oviposition behaviour of small cabbage white butterfly, Pieris rapae(lepidoptera: Pieridae)

This paper reviews the literature concerning the ovipositional behaviour of Pieris rapae (small cabbage white butterfly) and where appropriate considers results from studies involving other butterflies. The paper considers searching behaviour, stimuli utilised in host plant finding and identification and concludes with a general section on the role of learning and prior experience in ovipositional behaviour.     

Implications of a temperature increase for host plant range: predictions for a butterfly

Although changes in phenology and species associations are relatively well‐documented responses to global warming, the potential interactions between these phenomena are less well understood. In this study, we investigate the interactions between temperature, phenology (in terms of seasonal timing of larval growth) and host plant use in the polyphagous butterfly Polygonia c‐album. We found that the hierarchy of larval performance on three natural host plants was not modified by a temperature increase as such. However, larval performance on each host plant and temperature treatment was affected by rearing season. Even though larvae performed better at the higher temperature regardless of the time of the rearing, relative differences between host plants changed with the season. For larvae reared late in the season, performance was always better on the herbaceous plant than on the woody plants. In this species, it is likely that a prolonged warming will lead to a shift from univoltinism to bivoltinism. The demonstrated interaction between host plant suitability and season means that such a shift is likely to lead to a shift in selective regime, favoring specialization on the herbaceous host. Based on our result, we suggest that host range evolution in response to temperature increase would in this species be highly contingent on whether the population undergoes a predicted shift from one to two generations. We discuss the effect of global warming on species associations and the outcome of asynchrony in rates of phenological change.     

A TRADE-OFF FOR HOST PLANT UTILIZATION IN THE BLACK BEAN APHID,APHIS FABAE

Many studies on insect herbivores have sought to find trade-offs between utilization of alternate host plants, both to understand the prevalence of specialization and to appreciate the likelihood of sympatric speciation due to disruptive selection. To date, few studies have found trade-offs. Seventy-seven clones of the black bean aphid, Aphis fabae, were collected from field sites in East Anglia, U.K., over an area of about 10,000 km². These clones exhibit a trade-off in fitness between two alternative hosts, broad bean and nasturtium. This pattern is maintained in the F2 generation. The predominance of broad bean in the area, the fact that clones were only sampled from one of these two hosts, and the absence of “master-of-all-trades” genotypes after recombination all point to the importance of antagonistic pleiotropy rather than linkage disequilibrium in maintaining this trade-off. It is concluded that this population presents strong evidence for a fundamental trade-off for host utilization.     

厦门园林草坪和地被植物初探

本文介绍园林草坪和地被植物的基本概念和作用,从生态学的角度探讨草坪和地被植物的类型及用途,并报道了厦门地区可以利用的野生和栽培的草坪和地被植物资源。     

Structure of the phytophagous insect fauna of Onopordum thistles in the northern Mediterranean basin

Thistles of the genus Onopordum (Asteraceae: Cardueae) have become serious weed problems in parts of Australia and North America following introduction from their native Eurasian ranges, and are the target of a biological control programme in Australia. This paper analyses the results of three separate surveys of insects feeding and breeding on thistles of the genus Onopordum in the Mediterranean region. Of the 129 species found feeding, 74 species also bred on these thistles. Endophages comprised 54% of the breeding insects, with species that fed in the capitula and within the rosette crown/root area predominating. The Coleoptera and Hemiptera were the dominant endophage and ectophage taxa, respectively. Differences in the Onopordum fauna were noted between host species and between geographic regions, but this was largely due to the generalist component of the fauna. Onopordum specialists showed little variability across regions or between different species within the host genus. On comparing the fauna of Onopordum with that of other thistle genera, it was suggested that plant-herbivore interactions between Onopordum and its fauna are less highly evolved, in that there is less host specialization and a lesser degree of niche partitioning. This appears to be related to the low rate of speciation and habitat specialization within the host genus itself. The potential of certain genus-specific insects as biological control agents for Onopordum spp. is discussed. It is argued that the absence of a high degree of niche specialization could favour successful biological control, as the agent would be capable of inflicting damage over a wider range of resource gradients.     

PARALLEL RACE FORMATION AND THE EVOLUTION OF MIMICRY IN HELICONIUS BUTTERFLIES: A PHYLOGENETIC HYPOTHESIS FROM MITOCHONDRIAL DNA SEQUENCES

Mimicry has been a fundamental focus of research since the birth of evolutionary biology yet rarely has been studied from a phylogenetic perspective beyond the simple recognition that mimics are not similar due to common descent. The difficulty of finding characters to discern relationships among closely related and convergent taxa has challenged systematists for more than a century. The phenotypic diversity of wing pattens among mimetic Heliconius adds an additional twist to the problem, because single species contain more than a dozen radically different-looking geographical races even though the mimetic advantage is theoretically highest when all individuals within and between species appear the same. Mitochondrial DNA (mtDNA) offers an independent way to address these issues. In this study, Cytochrome Oxidase I and II sequences from multiple, parallel races of Heliconius erato and Heliconius melpomene are examined, to estimate intraspecific phylogeny and gauge sequence divergence and ages of clades among races within each species. Although phenotypes of sympatric races exhibit remarkable concordance between the two species, the mitochondrial cladograms show that the species have not shared a common evolutionary history. H. erato exhibits a basal split between trans- and cis-Andean groups of races, whereas H. melpomene originates in the Guiana Shield. Diverse races in either species appear to have evolved within the last 200,000 yr, and convergent phenotypes have evolved independently within as well as between species. These results contradict prior theories of the evolution of mimicry based on analysis of wing-pattern genetics.     

ALTERNATION OF GENERATIONS IN LAND PLANTS: NEW PHYLOGENETIC AND PALAEOBOTANICAL EVIDENCE

Current ideas on the evolution of alternation of generations in land plants are reviewed in the context of important recent advances in plant systematics and the discovery of remarkable new palaeobotanical evidence on early embryophyte life cycles. An overview of relationships in major groups of green plants is presented together with a brief review of the early fossil record as a prelude to discussing hypotheses of life cycle evolution. Recent discoveries of life cycles in the early fossil record are described and assessed. The newly discovered gametophyte and sporophyte associations are based on exceptionally well-preserved material from the Rhynie Chert, Scotland (Middle Devonian: 380–408 Myr) and compression fossils from other Devonian localities. These data document diplobiontic life cycles in plants at the ‘protracheophyte’ and early tracheophyte level of organization. Furthermore, the early fossils have a more or less isomorphic alternation of generations, a striking departure from life cycles in extant embryophytes. This unexpected similarity between gametophyte and sporophyte calls for a cautious approach in identifying ploidy level in early groups. Viewed in a systematic context, the neontological and palaeontological data contribute towards the formulation of a coherent hypothesis of life cycle evolution in major, early embryophyte groups. Evidence from extant groups strongly supports a single direct origin of the diplobiontic life cycles of land plants from haploid, haplobiontic life cycles in ancestral ‘charophycean algae’. The interest of the new palaeobotanical data lies in its relevance to life cycle evolution at the restricted level of vascular plants rather than at the more general level of embryophytes (vascular plants plus ‘bryophytes’). The occurrence of morphologically complex, axial gametophytes in early vascular plants is consistent with the moss sister-group proposed in some cladistic analyses. Similarities of moss gametophytes to fossils in the vascular plant stem-group are discussed, and it is argued that the late appearance of mosses in the macrofossil record may be due to the problem of recognizing stem-group taxa. The new palaeobotanical evidence conflicts with previous hypotheses based on extant groups that interpret morphological simplicity as the plesiomorphic condition in the gametophytes of vascular plants. These new data indicate that a significant elaboration of both gametophyte and sporophyte occurred early in the tracheophyte lineage, and that the gametophytes of extant ‘pteridophytes’ are highly reduced compared to those of some of the earliest ‘protracheophytes’. Vestiges of this early morphological complexity may remain in the gametophytes of some extant groups such as Lycopodiaceae.     

Malaria parasites (Apicomplexa,Haematozoea) and their relationships with their hosts: is there an evolutionary cost for the specialization?

Parasite–host specialization is frequently considered to be a derived state such that it represents an 'evolutionary dead end' that strongly limits further evolution. In this study, it was tested whether this theory is applicable to the relationship of malaria parasites and their vertebrate hosts. For this, we revisited Perkins and Schall (2002) analysis of the phylogenetic relationships of the malaria parasites (belonging to the genera Plasmodium , Haemoproteus and Hepatocystis ) based on the mitochondrial Cytochrome b gene sequence, and inferred, using a maximum likelihood (ML) approach, the putative ancestral vertebrate hosts. As the topology in this study presents several unresolved branches and is slightly different from that of Perkins and Schall, a Shimodaira and Hasegawa (SH; 1999) test has been performed in order to properly consider several alternative topologies. The results of this study suggest that the common ancestor of all these malaria parasites was a reptile (more specific of the order Squamata), and that the host switches from Squamata to Aves and vice versa were quite frequent along the evolution of these parasites. On the contrary, a strong evidence that the host shift from Squamata to Mammalia had occurred only once during the evolution of these organisms was found. This evidence (added to the current knowledge about the association of the malaria parasites with their vertebrate hosts) allows us to suggest, at least considering the species included in this study, that the adaptation in mammals had required a high level of specialization. Hence, the acquisition of this host class had culminated in an evolutionary dead end for the mammalian malaria parasites.     

HOST–PARASITE GENETIC INTERACTIONS AND VIRULENCE-TRANSMISSION RELATIONSHIPS IN NATURAL POPULATIONS OF MONARCH BUTTERFLIES

Evolutionary models predict that parasite virulence (parasite-induced host mortality) can evolve as a consequence of natural selection operating on between-host parasite transmission. Two major assumptions are that virulence and transmission are genetically related and that the relative virulence and transmission of parasite genotypes remain similar across host genotypes. We conducted a cross-infection experiment using monarch butterflies and their protozoan parasites from two populations in eastern and western North America. We tested each of 10 host family lines against each of 18 parasite genotypes and measured virulence (host life span) and parasite transmission potential (spore load). Consistent with virulence evolution theory, we found a positive relationship between virulence and transmission across parasite genotypes. However, the absolute values of virulence and transmission differed among host family lines, as did the rank order of parasite clones along the virulence-transmission relationship. Population-level analyses showed that parasites from western North America caused higher infection levels and virulence, but there was no evidence of local adaptation of parasites on sympatric hosts. Collectively, our results suggest that host genotypes can affect the strength and direction of selection on virulence in natural populations, and that predicting virulence evolution may require building genotype-specific interactions into simpler trade-off models.     

Host use evolution in Chrysochus milkweed beetles: evidence from behaviour, population genetics and phylogeny

In two sister species of leaf beetles with overlapping host associations, Chrysochus auratus and C. cobaltinus, we established diet breadth and food preference of local populations for evaluation together with genetic differentiation between populations. While C. auratus turned out to be monophagous on the same plant wherever we collected the beetles, the studied populations of C. cobaltinus fed on three different plant species in the field. Plant preference and ranking of the potential host plants significantly differed between these populations. The amount of genetic differentiation between populations was measured by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay of a 1300 bp mitochondrial DNA (mtDNA) sequence. In addition, the dominant genotypes of all populations were sequenced. No genetic differentiation between the populations of C. auratus could be detected in the RFLP assay and sequence divergence was low (= 0.3%). In C. cobaltinus, on the other hand, genetic differentiation between populations was high, revealing a lack of gene flow over a much smaller scale and a maximum of 1.3% sequence divergence. C. cobaltinus thereby has the prerequisites for host race formation on different plants from the original host spectrum. Our sequence-based phylogeny estimate allows us to reconstruct historical diet evolution in Chrysochus. Starting from an original association with Asclepiadaceae, the common ancestor of C. auratus and C. cobaltinus included Apocynaceae in its diet. The strict specialization on Apocynum and the loss of acceptance of Asclepiadaceae observed in C. auratus could have resulted from a process similar to that displayed by C. cobaltinus populations.     

Vertical stratification of ithomiine butterfly (Nymphalidae: Ithomiinae) mimicry complexes: the relationship between adult flight height and larval host-plant height

Data are presented which confirm previous findings that sympatric mimicry complexes dominated by unpalatable Neotropical ithomiine butterflies (Nymphalidae: Ithomiinae) are vertically stratified by height of flight. Flight height of ithomiine species is positively correlated with the height of their larval host-plants. Thus members of a mimicry complex utilize host-plants of similar heights. Non-mimetic British woodland butterflies also show a positive relationship between flight height and host-plant height, which suggests that the relationship is independent of mimicry. I propose that female butterflies fly at heights which maximize the probability of encountering their larval host-plants, and that males fly at similar heights to females in order to maximize the probability of encountering potential mates. Female butterflies probably encounter plants of similar heights to their larval hosts more frequently than they encounter plants of other heights. I suggest that butterfly species may therefore be more likely to make host shifts to plant species of a similar height to their current host-plants. Finally, I discuss how the relationship between flight height and height of larval host-plants, coupled with microhabitat-dependent selection on colour pattern, could lead to the evolution in sympatry of vertically stratified mimicry complexes.     

PHYLOGENETIC ANALYSIS OF BREEDING SITE USE AND α-AMANITIN TOLERANCE WITHIN THE DROSOPHILA QUINARIA SPECIES GROUP

The Drosophila quinaria group is unusual within the genus in that it comprises both mycophagous and nonmycophagous species. DNA sequence data from three regions of the mitochondrial genome were used to infer relationships among four mycophagous species and three that breed on decaying water plants. Phylogenetic analysis of these species show that breeding in mushrooms and tolerance of high levels of α-amanitin were the ancestral states within the group. Thus, breeding in decaying water plants and intolerance of α-amanitin are derived conditions. We also found that the D. quinaria species group does not comprise separate mycophagous and nonmycophagous clades, but rather that (1) the shift from mushrooms to decaying plants occurred on at least two occasions; or (2) mycophagy reevolved within a lineage that had previously shifted to breeding on plants. The correlation between mycophagy and α-amanitin tolerance is perfect across the species we have examined, indicating that there is no detectable time lag between an ecological shift to a new breeding site and correlated changes in biochemical adaptation. The genetic distance between the mycophagous D. recens and the nonmycophagous D. quinaria indicates that these species split only about 1 M.Y.B.P. In terms of α-amanitin tolerance, D. recens and D. quinaria are typical of other ecologically similar species within the group. Thus, evolutionary changes in α-amanitin tolerance can evidently occur on the order of about 1 million yr. Our data also indicate that, in comparison to other groups of Drosophila, the quinaria species group may be undergoing an adaptive radiation.