Evolution, 57(11), 2003, pp. 2540±2556

RADIATION, DIVERSITY, AND HOST-PLANT INTERACTIONS AMONG ISLAND AND CONTINENTAL LEGUME-FEEDING PSYLLIDS

DIANA M. PERCY1 Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom

Abstract. Island archipelagos and insect-plant associations have both independently provided many useful systems for evolutionary study. The arytainine psyllid (Sternorrhyncha: Hemiptera) radiation on broom (Fabaceae: Genisteae) in the Canary Island archipelago provides a discrete system for examining the speciation of highly host-speci®c phytophagous insects in an island context. Phylogenetic reconstructions based on three datasets (adult and nymph morphological characters, and two mitochondrial DNA regions: part of the small subunit rRNA, and part of cytochrome oxidase I, cytochrome oxidase II and the intervening tRNA leucine) are generally consistent. The combined molecular tree provides a well-supported estimate of psyllid relationships and shows that there have been several colonizations of the Macaronesian islands but that only one has resulted in a signi®cant radiation. Psyllid diversi®cation has apparently been constrained by the presence of suitable host groups within the genistoid legumes, and the diversity, distribution, and abundance of those groups. The phylogeny, by indicating pairs of sister species, allows putative mechanisms of speciation to be assessed. The most common conditions associated with psyllid speciation are geographical allopatry with a host switch to closely related hosts (six examples), or geographical allopatry on the same host (four examples). Where allopatric speciation involves a host switch, these have all been to related hosts. There is some evidence that switches between unrelated host plants may be more likely in sympatry. Only one sister pair (Arytainilla cytisi and A. telonicola) and the putative host races of Arytinnis modica are sympatric but on unrelated hosts, which may be a necessary condition for sympatric speciation in these insects. Where several psyllids share the same host, resources appear to be partitioned by ecological specialization and differing psyllid phenology.

Key words. Biogeography, Fabaceae, host-plant speci®city, insect-plant interactions, island colonization, island ra- diation, Psylloidea.

Received September 21, 2002. Accepted June 27, 2003.

Recent radiations of species in which many of the taxa are 1997; Gillespie et al. 2001) or insuf®cient molecular diver- still extant can provide valuable information about the type gence if the evolution of species was rapid (Brower 1994; and repetition of speciation mechanisms. Processes in adap- Richardson et al. 2001; Malcomber 2002). Phylogenetic stud- tive radiations may be related to key innovations, opportu- ies that combine analyses of environmental factors, species nistic expansion in novel environments, changes in repro- interactions, ecology, biogeography, and geological history ductive behavior, or a combination of multiple factors de- may better estimate the conditions that could have promoted pending on the organisms and habitats (Wagner and Funk an increase in speciation and diversity at the time of radiation 1995; Givnish and Sytsma 1997; Grant 1998; Schluter 2000; (Thorpe et al. 1994, 1995; Orr and Smith 1998; Roderick and Gillespie et al. 2001). Shared patterns of evolution in asso- Gillespie 1998). In this study, I interpret observed patterns ciated insects and plants have been explored in recent phy- by extrapolating from morphological, molecular, geograph- logenetic studies of phytophagous insects (e.g. Becerra 1997; ical, and ecological data. Farrell 2001; Janz et al. 2001). However, it is often dif®cult Archipelagos are productive environments for studying ra- to determine how processes of insect diversi®cation are diations, and an increasing number of studies are using these linked to processes of diversi®cation in their host plants (Mit- ``natural laboratories'' to investigate speciation in various ter and Farrell 1991; Futuyma and Mitter 1996; Becerra and biological groups (reviewed in Roderick and Gillespie 1998; Venable 1999), and the interpretation of historical insect- Juan et al. 2000; Emerson 2002; Gillespie and Roderick plant associations, historical host shifts, and ancestral host 2002). However, research in both Paci®c and Atlantic island preferences has proved particularly challenging (Janz and archipelagos has mainly focused on plant and animal groups Nylin 1998; von Dohlen and Moran 2000; Ronquist and Lil- independently. The interactions between plants and animals jeblad 2001; Sequeira and Farrell 2001). The study of com- are the subject of far fewer studies (Kambysellis and Crad- plex insect-plant interactions on islands has many advantages dock 1997; Percy and Cronk 1997; Barrett 1998; Givnish for better understanding the role of these interactions in spe- 1998; Nogales et al. 2001). Research on islands has only ciation. For instance, multiple colonization and speciation rarely focused on herbivorous insects and their host plants, events within island systems provide natural replicates for and these studies have mainly been undertaken in Paci®c testing ideas about host shifts. islands (e.g. Asquith 1995; Gagne 1997, and Roderick 1997). The detection of species radiations may require multiple In the central Macaronesian islands (Madeira and Canary approaches because of problems arising from either pro- Islands, Fig. 1), there are many recent independent evolu- nounced morphological convergence or divergence (Givnish tionary studies of plants and insects (e.g. Francisco-Ortega et al. 1996; Mes and 'T Hart 1996; Pinto et al. 1997; Brunton 1 Present address: Faculty of Agricultural Sciences, University and Hurst 1998; Emerson et al. 2000), but only one study, of British Columbia, 302-2357 Main Mall, Vancouver, British Co- using a predominantly continental phytophagous beetle lumbia V6T 1Z4, Canada; E-mail: [email protected]. group, has addressed the question of island colonization in 2540 ᭧ 2003 The Society for the Study of Evolution. All rights reserved. PHYTOPHAGOUS INSECT SPECIATION 2541

FIG. 1. Map of the Macaronesian islands and adjacent continental areas surveyed for this study. Boxes give the number of native legume species (Genisteae) and psyllids (Arytaininae) on Madeira and each of the central and western Canary Islands (number of endemic species in parenthesis), and the number of Genisteae species on which psyllids are found. The Appendix indicates speci®c collection locations for each taxon. The Canary Islands are probably derived from an oceanic hot spot (Carracedo et al. 1998) and have established geological ages (Ancochea et al. 1990; Ancochea et al. 1994; Guillou et al. 1996, 1998; Carracedo et al. 1999). conjunction with host-plant selection (Garin et al. 1999). This psyllids. Both the plant and insect groups in this study (gen- study of legume-feeding psyllids represents the ®rst use of istoid legumes and arytainine psyllids) reach their greatest phylogenetic analyses to examine evolution in a highly host- diversity in the Mediterranean basin and the Macaronesian speci®c group of phytophagous insects in the Atlantic Ma- islands (Hodkinson and Hollis 1987; Cristofolini 1991; Percy caronesian islands. 2002, 2003; Percy and Cronk 2002). I use the phylogenetic The aim of this study is to understand how processes of analyses to assess the monophyly of groups within the Gen- geographic and host-plant colonization affect speciation in isteae-feeding psyllids, and to establish the number of times 2542 DIANA M. PERCY the Macaronesian islands and different host groups were col- feeds on a much wider range of papilionoid legume tribes onized by ayrtainine psyllids. One weakness that has been (Hodkinson and Hollis 1987). highlighted in evolutionary studies of phytophagous insects, The ingroup includes representatives of all Arytaininae particularly host-associated speciation processes, is the pau- genera that feed on legumes in the west Palearctic region city of complete taxon sampling (Berlocher 1998). This study (Arytaina, Arytainilla, Arytinnis, Cyamophila, Livilla, and uses sister taxon comparisons in a species-rich, comprehen- Pseudacanthopsylla; see Appendix). Multiple individuals are sively sampled, monophyletic island group (Percy 2003). I included where species are found on different islands/con- compare island and continental patterns to infer processes tinental regions and/or different host plants. Two subfamilies, involved in host selection and host switching. I examine how Psyllinae and Acizziinae, were initially selected as possible diversi®cation in the host-plant group may have both con- outgroups for the subfamily Arytaininae. Members of Ac- strained and promoted insect diversity, and I assess which izziinae feed on mimosoid legumes in the tribes Acaciae and factors (e.g. opportunism and ecological specialization) could Ingae, whereas members of Psyllinae feed on a wide variety have contributed to a species radiation. of predominantly nonleguminous plant families. However, As psyllids are predominantly monophagous (feeding on the Psyllinae species were found to be af®liated with Cy- a single host plant), or sometimes oligophagous (feeding on amophila (which is in the Arytaininae but is not Genisteae- a few closely related host plants; Hodkinson 1974, 1980), feeding) in the early stages of the molecular analysis, when acceptance of a new host on colonization of a geographical more distantly related members of the family Psyllidae, the region (such as an island) would test host speci®city where family Triozidae and an aphid, were included. This indicated the original host is absent. Host switches to distantly related that the Psyllinae would be an unsuitable outgroup for the hosts during geographic colonization events (i.e., allopatri- Arytaininae. Two species of Acizziinae were subsequently cally) would indicate an inherently broad host preference. If used as the outgroup: one species native to North Africa and island species are only found on plants closely related to the the Middle East (Acizzia hollisi) and one Australian species hosts of continental sister taxa (or sister taxa on different (Acizzia uncatoides). The two Psyllinae species (Cacopsylla islands) an inherently narrow host speci®city might be as- alaterni, C. mali) were included to analyze the monophyly sumed, with the success of geographical colonization ulti- of the Arytaininae, but not de®ned as an outgroup. mately dependent on the presence or absence of familiar The datasets (morphological and molecular) in which each plants in the new region. If constraints on host selection are taxon is included are indicated in the Appendix. Morpho- strict, host switches between more distantly related plants logical characters were obtained from alcohol-, slide-, and might be expected only rarely when opportunities allowed capillary-mounted material. A total of 67 characters, 43 de- for adaptations to new hosts to develop, such as increased rived from adults and 24 derived from ®fth instar nymphs, contact with new hosts through sympatry and the formation were compiled for phylogenetic analysis using the program of host races. Nexus Data Editor (NDE; Page 2000). Seventeen (39%) of the adult characters and ®ve (21%) of the nymphal characters MATERIALS AND METHODS were based on morphometric data. These data were parti- tioned into discrete character states by eye from graph-plotted Selection of Ingroup/Outgroup Taxa and Data Sources data that incurred minimal polymorphism. The list of char- Psyllids, or ``jumping plant lice'' (Psylloidea) are one of acters, character states, and notes on character scoring are four superfamilies in the monophyletic hemipteran suborder available from the author, and online at http://taxonomy. Sternorrhyncha (Campbell et al. 1995; Sorenson et al. 1995; zoology.gla.ac.uk/ϳdpercy/psyllids.htm. Two mitochondrial von Dohlen and Moran 1995), all members of which are regions were sequenced: the more conserved small subunit phytophagous sap-feeders. Psyllids are small (about 1±7 mm) rRNA (12S) region, and the more rapidly evolving cyto- insects that typically carry out their entire life cycle on a chrome oxidase I (5Ј end) plus cytochrome oxidase II (3Ј single host. Although all six psyllid families are cosmopol- end) and the intervening tRNA leucine (COI-tRNA-COII) itan, many genera have restricted distributions (Hodkinson region. The taxon sampling includes 84 individuals repre- 1980; White and Hodkinson 1985; Burckhardt 1987a,b). The senting 62 taxa (61 species and one subspecies). A total of west Palearctic legume-feeding psyllids belong to two sub- 46 taxa were sampled for the morphological analysis. For the families (Acizziinae and Arytaininae) in the family Psyllidae two mitochondrial regions, 68 individuals from 61 taxa were (Hodkinson and Hollis 1987). Acizziinae is predominantly a sampled for the 12S region, and 73 individuals from 50 taxa southern hemisphere group (with only four native species in for the COI-tRNA-COII region. Most of the samples were the west Palearctic), and the Arytaininae is predominantly a collected by the author during ®eldwork from 1997 to 2000 northern hemisphere group with six genera in the west Pa- in the Canary Islands, Madeira, and adjacent continental areas learcticÐArytaina, Arytainilla, Arytinnis, Livilla, Pseudacan- (material supplied by others is indicated in the Appendix). thopsylla, and Cyamophila (Hodkinson and Hollis 1987; Per- Insects were collected into 100% ethanol in the ®eld and cy 2003). The ®rst ®ve of these genera are mostly restricted stored at Ϫ20ЊC. to the Mediterranean basin, and feed on papilionoid legume Observations of psyllid ecology and distributions were shrubs in the tribe Genisteae (e.g. brooms, gorse and rela- made during June to July and December 1997, March to July tives; Hodkinson and Hollis 1987; Burckhardt 1989; Conci 1998, March to May 1999, and July to August 2000 (Percy et al. 1993; Percy 2002, 2003). There are no nongenistoid 2002, 2003). Geographical and host-preference ranges were host records for these genera. The sixth genus, Cyamophila, determined by extensive sampling from different host pop- is more widespread from Western Europe to central Asia and ulations and by sampling from the same population in dif- PHYTOPHAGOUS INSECT SPECIATION 2543 ferent years and different times of the year. Each host-plant Phylogenetic Analyses species was sampled between one and 34 times, with only Molecular and morphological phylogenies were construct- the most rare species sampled once or twice. For each psyllid ed using PAUP* (ver. 4.0b3; Swofford 1999) and MrBayes taxon, samples were collected from between one and 18 dif- (ver. 2.01; Huelsenbeck and Ronquist 2001). In PAUP*, the ferent localities. Details of ®eld sampling procedures and following heuristic search parameters were employed for the localities are given in Percy (2002, 2003). The species de- parsimony analyses: 100 random stepwise addition replicates limitations follow current taxonomic accounts (Hodkinson with tree bisection-reconnection (TBR) branch swapping, and Hollis 1987; Burckhardt 1989; Conci et al. 1993; Percy saving multiple trees (MULTREES) and collapsing zero- 2002, 2003). length branches (COLLAPSE). For the analysis of the mor- phological data, characters were treated as unordered, with DNA Extraction, Ampli®cation, and Sequencing the exception of the morphometric characters, which were One to three insects (abdomens and wings removed and treated as ordered with multiple states as polymorphisms in retained as vouchers) were either ground in 50 ␮l of 80% order to preserve information on the relative similarity be- SDS lysis buffer and 20% Proteinase K (Qiagen, Crawley, tween taxa and overlapping states. Bootstrap analyses (2000 U.K.) (10mg/ml); or alternatively whole insects were bisected replicates) were performed using simple addition sequence and placed, with Proteinase K, in the buffer provided in the of taxa with TBR branch swapping. Parameters and assump- Qiagen DNeasy Tissue Kit (in which case, the whole insect tions used in the maximum-likelihood (ML) searches were was retained as a voucher after incubation). Specimens were selected using program Modeltest (Posada and Crandall incubated for 24 h at 55ЊC. The remainder of the extraction 1998) and based on the Akaike Information Criterion (AIC). was performed with either the Geneclean II kit (Bio 101, The model selected for the 12S data was HKY85 with in- Carlsbad, CA) in the ®rst protocol, or the Qiagen DNeasy variable sites and gamma distribution. The model selected Tissue Kit in the second. Specimens collected by the author for the CO data was general time-reversible (GTR) with in- were processed within three years; however, dry mounted variable sites and gamma distribution. Maximum likelihood specimens and alcohol preserved material up to 20 years old heuristic search parameters were simple addition sequence (supplied by D. Burckhardt and I. Hodkinson) ampli®ed suc- of taxa with TBR branch swapping, MULTREES, and COL- cessfully for the shorter 12S region (probably aided by highly LAPSE. Distance neighbor-joining (NJ) analyses were used conserved primers) but did not, or only poorly, ampli®ed for to provide a comparison of topology and bootstrap. A ML the longer CO region. analysis of the combined molecular data (12S and CO-tRNA) The primers used to amplify 12S were SR-N-14588 and was performed using Bayesian methods and a GTR model SR-J-14233 (Simon et al. 1994). The COI-tRNA-COII region in MrBayes. For this analysis four simultaneous Monte Carlo was ampli®ed for some taxa using primers UEA9 (Lunt et Markov chains (MCMC) were run for one million genera- al. 1996) and C2-N-3389 (Simon et al. 1994). These CO tions, saving a tree every 100 generations. The partition ho- primers ampli®ed 68% of the taxa, and additional primers mogeneity test (ILD test of Farris et al. 1994) implemented were designed to amplify the remaining taxa: DP1: 5Ј GTT in PAUP* was used to assess congruence between the dif- AGTAGTGGGTTATTAAGTTCRTC 3Ј (positioned in COII ferent data sets (12S, CO-tRNA, and morphology). Biogeo- and used as an antisense primer to UEA9); DP2: 5Ј CGAT graphic assumptions (i.e. derivation of continental species AATTTTAATTGTTAGTAGYGG 3Ј (positioned in COII as from the Macaronesian islands) in the genus Arytinnis were an antisense primer to UEA9); UEA9-MOD: 5Ј GGTATG tested using constraint trees and the nonparametric Temple- CCTCGTCGTTATTCTAAYTAYC 3Ј (positioned in COI ton's Wilcoxon signed-rank test implemented in PAUP*. and used as a sense primer to C2-N-3389). Genistoid host-plant groups were optimized onto the com- Each PCR cycle comprised denaturation at 94ЊC for one bined molecular phylogeny using MacClade 3.07 (Maddison min., 41 cycles of denaturation at 92ЊC for 30 sec, annealing and Maddison 1992). Host-plant associations were treated as at 45ЊC for 40 sec and an extension of 65ЊC for 90 sec, with an unordered character with delayed and accelerated trans- a ®nal extension of 72ЊC for 10 min. Ampli®ed PCR products formation (DELTRAN and ACCTRAN) optimization. were either run on agarose gels and puri®ed with a Qiagen QIAquick Gel Extraction Kit or were puri®ed with a Qiagen RESULTS QIAquick PCR Puri®cation Kit, in both cases resuspension Phylogenetic Analyses was in 30 ␮l of water for direct sequencing using an auto- mated Perkin-Elmer ABI 377 sequencer with ABI Prism Dye Molecular and morphological analyses recover the same Terminator Cycle Ready Reaction Kit (Applied Biosystems, major groups although signi®cant incongruence was found Washington, U.K.) Sequences were aligned manually using between morphological and molecular data. The length of the the program Se-Al (ver. 1.0a1; Rambaut 1998). All the se- 12S alignment is 342 characters (mean of 331 bp, 168 var- quences referred to here have been deposited in GenBank: iable sites with 134 parsimony informative, and A ϩ T con- the 12S sequences under the accession numbers AF367776± tent is 74±80%). The length of the COI-tRNA-COII align- AF36784, and the COI-tRNA-COII sequences under the ac- ment is 639 characters (mean of 618 bp, 352 variable sites cession numbers AY100373±AY100445. Both the aligned with 297 parsimony informative, the tRNA is 65±71bp, and matrices are available from GenBank, and these matrices plus A ϩ T content is 67±83%). The results of the partition ho- the morphological matrix, and trees (Figs. 2, 3) are available mogeneity test implemented in PAUP* indicated that the two from TreeBASE (http://www.treebase.org/). molecular datasets (12S and CO-tRNA) were compatible (P 2544 DIANA M. PERCY

ϭ 0.99), but that the molecular and morphological data were analyses place Pseudacanthopsylla within the Genisteae- signi®cantly incongruent with one another (P ϭ 0.01). There- feeding Arytaininae. An inclusive position for Pseudacan- fore, a maximum-parsimony (MP) tree for each of the three thopsylla suggests a single evolution of the Genisteae-feeding data sets (12S, CO-tRNA, and morphology) is presented in- habit and the MP strict consensus presents a monophyletic dependently (Fig. 2), and a combined molecular analysis (12S Genisteae-feeding group (Fig. 3). Nevertheless, the place- and CO-tRNA) is presented in Figure 3. ment of Pseudacanthopsylla needs to be tested further, with The MP search of the 12S data found 750 trees, and ®ve additional sampling of Afrotropical genera considered related islands of trees. The 12S tree presented in Figure 2A is one to this genus (Hodkinson and Hollis 1987). of the 750 MP trees, which was selected from the one island The phylogenies in Figures 2 and 3 clearly show that three of trees with the most similar topology to that recovered after major generic clades are present in all analyses: AI (Ary- successive reweighting of the 12S data using the mean re- tinnis), an almost exclusively Macaronesian island genus with scaled consistency index in PAUP*; the 22 nodes that col- 16 endemic Canary Island species, two endemic Madeiran lapse in a strict consensus of all 750 MP trees reveals the species, and three continental species (generic sampling is lack of resolution present in the 12S data. The MP search of complete); AR (Arytaina), a genus of 14 species (®ve species the CO-tRNA data found a single island of six trees. The MP including the type species, Ar. genistae, are sampled), three CO-tRNA tree presented in Figure 2B is one of the six trees of which are endemic to the Canary Islands; L (main Livilla that differs only in minor respects to the other ®ve trees as group), which, although representing the majority of Livilla shown by the three nodes in the genus Arytinnis that collapse species (about 32, of which 12 are included here), does not in a strict consensus of all six trees. The MP search of the include the somewhat anomalous type species group (four morphological data found a single island of 18 trees. The MP species, represented in this analysis by L. vicina). This main morphology tree presented in Figure 2C is one of the 18 group of Livilla includes neither the single endemic Canary trees, and as with the CO analysis, the ®ve nodes that collapse Island species (L. monospermae) and its continental sister in the strict consensus of all 18 trees are all within the mor- taxon (L. retamae), nor L. nervosa, nor a small group of phologically homogeneous genus Arytinnis. The combined exclusively Adenocarpus-feeding species. A fourth generic molecular phylogenies presented in Figure 3 are the strict group, A (Arytainilla sensu stricto), is a group of nine species consensus of eight trees derived from a MP analysis (large (six taxa including the type species, A. delarbrei, are sampled) tree) and an ML Bayesian analysis (small tree), the topologies which is characterized morphologically by a massive ovi- of which are very similar. A majority rule consensus of 9600 positor; only one member of this group (A. serpentina)is trees from the ML Bayesian analysis (the ln likelihood score endemic to the Canary Islands. Arytainilla sensu stricto is stabilized after 4000 generations and therefore the ®rst 400 recovered as a monophyletic group in the CO-tRNA, mor- trees were discarded) produced posterior probability values phological, and the combined molecular analyses, though not considerably higher for many of the same nodes than in either in the 12S analysis. All three datasets (12S, CO-tRNA, and the MP or NJ bootstrap analyses (Fig. 3). The optimization morphology) suggest that the genera Livilla and Arytainilla of the host groups onto the tree (Fig. 3) differed between sensu lato are paraphyletic as currently delimited, whereas DELTRAN and ACCTRAN only at the base of the Adeno- Arytinnis and Arytaina are monophyletic genera. carpus-feeding Livilla plus Pseudacanthopsylla group. Island and Continental Colonizations Monophyly of Genisteae-Feeding Arytaininae and The phylogenetic analyses can be used to infer the number Genisteae-Feeding Genera and direction of geographic colonization events. There are To assess patterns and directions of host-plant and geo- 23 native legume-feeding psyllids in the Macaronesian is- graphical colonization it is important to establish whether the lands, two in Madeira, and 21 in the Canary Islands, all of traditional classi®cation is supported by the phylogenetic which are endemic (Loginova 1976; Percy 2003). The 21 analysis. Cyamophila is the only non-Genisteae-feeding ge- Canary Island species are found on the ®ve central and west- nus among the papilionoid legume feeders in the west Pa- ern islands (Fig. 1; there are no native genistoid legumes on learctic Arytaininae. The molecular analyses suggest that Cy- the two much drier, eastern islands, Fuerteventura and Lan- amophila is distinct from the Genisteae feeders, and is more zarote). At least four, possibly ®ve, independent coloniza- closely related to the subfamily Psyllinae (whose members tions of the Canary Islands are suggested by the data (Fig. feed on a wide variety of hosts including species in the Ro- 3): one colonization resulted in a radiation of 16 species in saceae, Rhamnaceae, Salicaceae, and the Caesalpinioideae) Arytinnis; two separate colonizations are each represented by than to other Arytaininae. This placement suggests that pap- single species in Arytainilla (A. serpentina), and Livilla (L. ilionoid legumes may have been colonized at least twice with- monospermae); and there have been at least one, possibly in the west Palearctic region. The placement of the genus two, independent colonizations in the genus Arytaina (the Pseudacanthopsylla has been considered problematic (Hod- ambiguity is due to the lack of support for the monophyly kinson and Hollis 1987). An outlying position for Pseuda- of the three Canary Island Arytaina species, Ar. devia, Ar. canthopsylla is supported by the morphological data (Fig. nubivaga, and Ar. vittata). The two endemic Madeiran species 2C), and partly by the 12S data (ML analysis) and would and three continental species form a well-supported subclade imply two or more origins of the Genisteae-feeding habit. within Arytinnis. The possibility of one or two back colo- However, a NJ analysis of the 12S data, all analyses of the nizations to the continent (i.e., one colonization of the con- CO-tRNA data, and the combined molecular MP and ML tinent from the Canary Islands and one from Madeira; see PHYTOPHAGOUS INSECT SPECIATION 2545 rmative ain. ters, RI 0.613); ). Thick branches . 2, 3): Canary Islands: group. Where taxa are sampled from different host plants, these have been indicated and abbreviated Livilla ;L,main Arytaina 75%, and dotted branches indicate the nodes that collapse in the strict consensus of all trees for each dataset. Labeled nodes: A, ; AR, Ͼ Arytinnis sensu stricto; AI, . 2. Phylograms for each dataset. (A) 12S: one of the 750 maximum-parsimony (MP) trees based on 12S rRNA sequences (length 807, CI 0.32 excluding uninfo IG from host-plant names inC, the Gran Appendix. Canaria; Continental, T, Canary Tenerife; Island, G, and La Madeiran Gomera; distributions P, are La shown. Palma; Abbreviated H, codes El for Hierro; sample MAD, origin Madeira; (Figs MED, Mediterranean; MO, Morocco; PO, Portugal; SC, Scotland; SP, Sp Arytainilla F characters, RI 0.614);(C) (B) Morphology: CO: one oneindicate of of the nodes the 18 with six MP MP bootstrap trees trees values based based on on 67 COI-tRNA morphological leucine-COII characters sequences (length (length 554, CI 2280, 0.484 CI excluding 0.248 a excluding single uninformative uninformative charac character, RI 0.612 2546 DIANA M. PERCY

FIG. 3. Host-plant distributions, geographic locations, and tree architecture. The large tree is the strict consensus of the combined molecular maximum-parsimony (MP) analysis; numbers at nodes indicate support for major groups and subclades (left to right: MP bootstrap; MP bootstrap excluding the two Acizzia species, and with Cacopsylla and Cyamophila speci®ed as the outgroup [bold]; NJ neigbor-joining bootstrap [italic]; maximum-likelihood (ML) Bayesian posterior probability value [underlined]; the remaining nodes with PHYTOPHAGOUS INSECT SPECIATION 2547

Fig. 3) remains equivocal (indicated by a question mark) due may have provided glacial refugia, with more recent dispersal to a nonsigni®cant (P ϭ 0.06) additional tree length (10 steps) through Europe in the continental species. In the Canary Is- required to constrain the subclade of Madeiran and conti- lands, nine of the 21 species (43%) inhabit more than one nental species as sister to the Canary Island species. island (L. monospermae, Ar. devia, Ar. vittata, Ai. dividens, Only one colonization of the islands has resulted in a sig- Ai. diluta, Ai. modica, Ai. nigralineata, Ai. proboscidea, and ni®cant radiation (18 species in Arytinnis). In contrast, col- Ai. occidentalis). All but one (Ai. modica) of these species is onizations by Arytaina, Arytainilla, and Livilla have resulted speci®c to a single host plant, or feeds on two closely related in only one or two psyllid species after each colonization hosts. There is no evidence of major host switches coinciding event. Among the island Arytinnis, the ``basal'' taxa, which with interisland colonizations. About half of these species on may be ancestral in the island radiation (Ai. diluta, Ai. prog- multiple islands shows low intraspeci®c molecular diver- nata, and Ai. romeria), are found on the oldest island (Gran gence (maximum 0.02±2.0%), suggesting recent interisland Canaria), whereas some more recently derived taxa (e.g. Ai. dispersal, but four species (all speci®c to a single host) show occidentalis and Ai. modica) only exist on the youngest is- considerably greater divergence (maximum 4±10%), which lands (La Palma and El Hierro). However, to determine can be compared to the maximum divergence in the genus whether colonization of the Canary Islands matches a ``step- Arytinnis (13%) as a whole. Sequence divergence is therefore ping stone'' model, which is the case in some island groups not always related to the morphological divergence on which (Roderick and Gillespie 1998; Juan et al. 2000), more intra- the species delimitations are based, and appears to be greatest speci®c sampling and resolution within Arytinnis is needed. (possibly via a process of drift) in putatively older popula- tions that have been isolated on different islands but have Diversity among Island and Continental Species not undergone ecological or host shifts. A comparison of sequence divergence with morphological Host Switching by the Genisteae Feeders divergence and geographic distributions can provide an in- dication of dispersal patterns and gene ¯ow. Sequence di- The mapping of host preference onto the phylogenetic anal- vergence (estimated using uncorrected pairwise distances ysis provides an indication of the frequency of host switching from the CO-tRNA data) between individuals from different and can be used to infer whether, and under what conditions, geographic regions or hosts provides a comparative measure host switching is related to speciation. When the host genera of intraspeci®c divergence in continental and island taxa. are mapped onto the psyllid tree, four of the ®ve colonizations Three continental species (Ar. adenocarpi, Ar. genistae, and of the Canary Islands and two continental and Madeiran col- A. spartiophila) are widespread, found on several closely re- onizations coincide with a host switch to a different genistoid lated host species in different geographical regions. Individ- genus. Only one Canary Island species (L. monospermae) and uals of these taxa were sampled from Morocco, Spain, Por- one Madeiran species (Ai. incuba) are found on the same host tugal, and Scotland (Figs. 2, 3, and Appendix). Among the genus as their continental sister taxa (L. retamae and Ai. island species, individuals were sampled from populations hakani respectively). However, when the host genera are cat- that were found either on different islands and/or different egorized according to af®liations within the Genisteae (gen- host plants. Intraspeci®c genetic divergence was greatest istoid groups from Polhill 1976; Bisby 1981; KaÈss and Wink within the four Canary Island species that existed on different 1997), host switches between genera that coincide with geo- islands but on the same host plant (L. monospermae from graphical colonization events are all switches to related gen- three islands, 4±5%; Ar. devia from four islands, 1±10%; Ai. era within the same major genistoid groups (Fig. 3). In ad- dividens from three islands, 1±4%; and Ai. occidentalis from dition, the majority of species within each of the well-sup- two islands, 5%). Divergence within the widespread conti- ported psyllid genera or clades, are found on related hosts nental species that were sampled from different hosts was in the same genistoid group. Of the 18 island Arytinnis spe- less than 3%, and in each case divergence between Moroccan cies, 13 feed on Teline, two on Adenocarpus, one on Cha- and European samples was double or more than double the maecytisus, one on both Teline and Chamaecytisus, and one divergence within Europe (e.g. Ar. genistae from Portugal on Genista (Table 1). In the genus Arytinnis, Teline appears and Scotland showed 0.8% sequence divergence, but 2.8% to be the ancestral island host group with switching to other divergence from the Moroccan individual). This pattern could host genera occurring within the islands. The legume genera result either from greater gene ¯ow on the continent than Adenocarpus, Chamaecytisus, Genista, Retama, and Sparto- between islands, or by the establishment of recent continental cytisus each have one or two island species. The colonization distributions. Extensive continental gene ¯ow is probably of these legumes by Arytinnis (one species on Genista, two unlikely, whereas both northern Africa and the Canary Islands species on Adenocarpus), Arytaina (one species on Chamae-

← bootstrap values Ͼ75% in either, but usually both, the MP or NJ analyses are indicated by a black dot; host groups are mapped as an unordered character using ACCTRAN optimization; colonizations of the Canary Islands are indicated by an asterisk; equivocal colo- nizations (question mark) of Madeira and the continent, from the Canary Islands, are indicated by a cross (Madeira), and open circles (continent; see text); distributions for the Canary Island taxa and subclades are indicated with island codes (abbreviated as for Fig. 2) and maps; island letters in parenthesis indicate taxon distribution that was unsampled. The dividens-modica subclade of Arytinnis is explored further in Figure 4. The small tree is the single ML Bayesian tree with the best ln score; this shows the short internal branches along the backbone of the tree, which suggest an initial radiation (1) when the Genisteae were ®rst colonized, and a second radiation (2) when the Canary Islands were colonized by Arytinnis. 2548 DIANA M. PERCY cytisus, two species on Spartocytisus), Arytainilla (one spe- TABLE 1. Summary of distribution and host associations for the cies on Spartocytisus), and Livilla (one species on Retama), 23 Macaronesian island taxa (abbreviated psyllid genera and island codes are given in the Fig. 2 caption). Multiple psyllids on a single with only one or two psyllid species derived from each col- host often occur on different host subspecies (e.g. the ®ve subspe- onization, re¯ects the low diversity of the hosts. cies of Teline stenopetala; Percy 2003). Hybrids between host plants A comparison of host-plant associations and geographical are indicated where these have been recorded (Lems 1958; Arco distributions in sister species pairs (Table 2) indicates that Aguilar 1983; SuaÂrez RodgrõÂguez 1991). the majority (seven pairs) are found on the same or related hosts, but on different islands/geographical regions, whereas one species pair and the putative host races of Ai. modica are sympatric but on unrelated hosts. The remaining two pairs exist on the same island, in one case on the same host (Ai. diluta and prognata) and in the other case on sister host taxa (Ai. nigralineata and proboscidea), but these taxa exist in different localities and habitats, and may have diverged through ecological shifts (discussed below). In addition, re- lationships within six well-supported subclades of psyllids also indicate that where taxa are sympatric the host plants are unrelated (e.g. Ai. dividens and hupalupa on Chamaecy- tisus and Teline) or moderately closely related (e.g. Ai. incuba and umbonata on Teline and Genista), and that where hosts are closely related, taxa are allopatric (e.g. Ai. equitans, gom- erae, occidentalis, and canariensis, which are all found on a subgroup of hosts in the genus Teline, but on separate islands; and L. baetica, caprifuga, and ima on a subgroup of Aden- ocarpus hosts in different mountain ranges of Morocco and southern Spain).

DISCUSSION Causes of Radiation The psyllid phylogeny suggests two periods of radiation: (1) when the Genisteae were ®rst colonized, and (2) when the Canary Islands were colonized by Arytinnis (Fig. 3). In the ®rst case, a key innovation may have allowed for the initial exploitation of genistoid hosts (e.g. tolerance of quin- olizidine alkaloids). In the second case, colonization of a of establishment and radiation in regions where there are no, novel geographical region with a high diversity of hosts and or few, familiar plants. Similar constraints are apparent in habitats appears to have been important in promoting psyllid some Canary Island colonizing leaf beetles (Garin et al. diversity. Both the breach of plant chemical defenses and the 1999), but in studies of Hawaiian hoppers, unexpected host exploitation of unoccupied niches may precipitate an eco- shifts appear to have taken place in conjunction with island logical release in phytophagous insects (Ehrlich and Raven colonization (Roderick 1997; Roderick and Gillespie 1998). 1964; Gillespie and Roderick 2002). Recent studies in the (2) The role of legume diversity in promoting or con- Canary Islands have found factors such as proximity to a straining psyllid diversi®cation in the Canary Islands is ev- continental landmass, geological chronology of island for- ident in a comparison of the diversity of psyllids on Teline mation, and the exploitation of ecological opportunities to (the main host genus of Arytinnis) with the diversity of psyl- be important in determining the character of the insular fauna lids on other host genera. The legume genus Teline has un- and ¯ora (Juan et al. 2000; Emerson 2002). There have been dergone two separate radiations in the Canary Islands, re- multiple colonizations of the Canary Islands by psyllids, but sulting in 10 species (Percy and Cronk 2002), whereas the the presence or absence of radiation in each of the island other ®ve Canary Island genistoid legume genera have un- psyllid genera is apparently determined by three factors: (1) dergone little or no diversi®cation. None of the psyllid genera constraints on host acceptance, (2) the diversity of the host that are associated only with these less diverse legumes has group and, (3) abundance and distribution of the host group. undergone a radiation. This shared diversity in island psyllids Island size (both elevation and area) is indicative of the va- and legumes, together with the absence of host switches to riety of habitats, and better predicts legume diversity than unrelated genera during colonization of the islands and the psyllid diversity, whereas psyllid diversity is more closely greater number of in situ host switches to related hosts, sug- related to legume diversity than to either island size or num- gests that narrow host speci®city coupled with opportunistic ber of habitats per island. host switching determines the observed patterns of psyllid (1) Constraints on host acceptance are evident in the Gen- diversity and host associations. Opportunistic host switching isteae-feeding psyllids and appear to result from an inherently has clearly promoted diversi®cation in Hawaiian Hemiptera narrow host preference that effectively limits the possibilities (Asquith 1995; Gagne 1997), and it is central to ``escape and PHYTOPHAGOUS INSECT SPECIATION 2549

TABLE 2. A comparison of host associations and geographic distributions in ten sister species pairs (and the putative host races of Arytinnis modica) with inferred modes of divergence. Each taxon pair is well supported in the combined molecular analysis (Fig. 3). The species pair Ai. equitans and gomerae is recovered in the combined molecular analysis, but an alternative pairing (indicated by an asterisk) of Ai. gomerae and occidentalis, though not recovered in the combined molecular and CO-tRNA analyses, is not inconsistent with the 12S data and is supported by a unique morphological synapomorphy (eight nymphal antennal segments). Positive/negative symbols indicate whether the taxa in each pair share/do not share host preferences and geographic distributions. The same host subspecies category is not applicable (NA) unless sister taxa are found on a single host that has been classi®ed into subspecies. The majority of pairs (seven) are found on similar hosts but different geographical regions. Two species pairs are found on the same or closely related hosts on the same island. One species pair and the putative host races of Ai. modica, are sympatric but on unrelated hosts.

Same Same island or Species genistoid Same host Same host Same host geographical Same Putative speciation/ pair no. Sister taxa group genus species subspecies region locality divergence mode Ai. modica Cham. ϩ ϪϪϪNA ϩϩsympatric with switch modica Teline to unrelated host 1 Ai. hupalupa ϩ ϩϩϩϪ Ϫ Ϫallopatric without host modica switch 2 Ai. hakani ϩ incuba ϩϩϪNA ϪϪallopatric with switch to related host 3 Ai. berber ϩ cogna- ϩϩϪNA ϪϪallopatric with switch ta to related host 4 Ai. nigralineata ϩ ϩϩϩ/ϪϪ ϩ/ϪϪallopatric? with switch proboscidea to related host and ecological speciali- zation 5 Ai. equitans ϩ gom- ϩϩϪNA ϪϪallopatric with switch erae to related host *Ai. gomerae ϩ oc- ϩϩϩϩ/ϪϪϪallopatric without host cidentalis switch 6 Ai. diluta ϩ progna- ϩϩϩNA ϩϪallopatric? without ta host switch but with ecological speciali- zation 7 L. monospermae ϩ ϩϩϩNA ϪϪallopatric without host retamae switch 8 A. delarbrei ϩ ser- ϩϪϪNA ϪϪallopatric with switch pentina to related host 9 A. cytisi ϩ telonico- ϪϪϪNA ϩϩsympatric with switch la to unrelated host 10 Ar. nubivaga ϩ vit- ϩϩϩ/Ϫ NA ϪϪallopatric with switch tata to related host radiate'' models of evolution in plant-insect interactions although host diversity is important, it is not the only de- (Ehrlich and Raven 1964; Thompson 1994). terminant of psyllid diversity. Other factors, including the (3) Nevertheless, a one-to-one psyllid-to-legume ratio is relative age of legume and psyllid groups (island groups may only evident in some groups and regions. Several psyllid be more contemporaneous than continental groups), host species occupy localized habitats within a single widespread abundance, habitat diversity, and the presence or absence of host range. This is consistent with increased colonization competitors and predators may also in¯uence observed pat- opportunities (via more frequent encounter) and a greater terns of psyllid diversity. diversity of localized habitats provided by widespread and Interestingly, this study encountered the highest within- abundant hosts, as proposed by Opler (1974). Examples in species sequence divergence in island taxa that exist on dif- this study include the legume Teline stenopetala, which has ferent islands but the same host. In contrast, sequence di- ®ve subspecies on four islands and is host to six psyllid vergence within continental species that are much more wide- species; and, within a single island, T. canariensis (on Ten- spread and exist on several different but closely related hosts erife) and T. microphylla (on Gran Canaria) are widespread was considerably less. These results suggest there are dif- found in diverse ecological zones, and each host three to four ferent patterns of dispersal and gene ¯ow among island and psyllids (Table 1). In the Macaronesian islands there are more continental species, with perhaps more recent dispersal in Genisteae-feeding psyllids than Genisteae (23 psyllids and continental areas (e.g. northward postglacial expansion), and 21 genistoid legumes), in contrast to the continent (about 230 more complete genetic isolation of island populations. In the species of Genisteae and only about 70 species of psyllid on Hawaiian Islands, similarly structured arthropod populations these legumes). On Madeira there are two native genistoid also display morphological stasis despite considerable ge- legumes and two endemic psyllids (one on each legume), but netic divergence (Roderick and Gillespie 1998). in the Canary Islands, 21 psyllids occur on just 12 legumes. In the Canary Islands and other archipelagos, the historical Furthermore, up to one third of the legumes (17±33%) per time frame provided by the geological formation of islands island in the Canary Islands do not host psyllids, and on each has been useful for interpreting island colonization sequences island there are multiple psyllids on at least one host. Thus, (e.g. Juan et al. 1995; Hormiga et al. 2003). This study sug- 2550 DIANA M. PERCY gests only partial association between island age and colo- of the localized species are more recently derived than the nization sequence (e.g. three putatively basal Arytinnis spe- widespread species, but on Gran Canaria the widespread spe- cies are found on the older island of Gran Canaria, and some cies appears to be more recently derived than the localized more recently derived taxa are only found on younger is- species. Notably, both widespread species develop later in lands). Preliminary results from dating the legume and psyllid the season than the localized species. This scenario agrees phylogenies suggest that, in both groups, initial colonization with studies that show ecological shifts between specialist of the islands occurred well after most of the islands were and generalist to be bi-directional and not limited to unidi- already formed (D. M. Percy et al. 2004). In contrast, other rectional shifts from generalist to specialist (Gillespie and island groups (e.g. ¯ightless insects) may be older than the Roderick 2002). presently emerged islands on which they are found (Sequeira In the Canary Islands, where it is common to ®nd multiple et al. 2000). For psyllids, which are moderately mobile, island psyllids on a single host, temporal divisions between closely distance to source populations may be more important in related species that are sympatric could be an important determining colonization patterns than island age. However, mechanism to facilitate the sharing of host resources and in the Canary Islands, patterns indicative of both processes avoidance of competition. There is also a temporal division may be found because older islands are nearer the continent in two unrelated species that are both widespread throughout than younger islands. the shared host range (Ar. devia develops later than Ai. div- idens on Chamaecytisus proliferus). In addition, there is an Host Speci®city and Speciation example of apparently phenologically driven competitive ex- clusion in the two Adenocarpus-feeding species (Ai. nigral- Host speci®city is a dominant element in psyllid-legume ineata and proboscidea). Oviposition in these species is on interactions, but ecological specialization and host switching the in¯orescences of Adenocarpus. Adenocarpus foliolosus on may be more important in promoting psyllid speciation. Of two islands (Tenerife and La Palma) is found at lower alti- the 23 Macaronesian species, 16 (70%) are found on a single tudes and ¯owers earlier than A. viscosus at higher altitudes. host plant, six species (26%) are found on two hosts, and Host phenology may therefore be the mechanism maintaining one species is found on three hosts. A comparison of the host speci®city on Tenerife where sympatry could have re- psyllid phylogeny with host use and ecological and geo- sulted in competition between psyllids. On La Palma, only graphic patterns from ®eld observations during 1997±2000 one of these psyllids occurs, but on this island host speci®city (Percy 2003) suggests that the majority of sister species are is not maintained and the species is found throughout both both ecologically and geographically allopatric. There is only host-plant ranges. Differences in host-plant phenology can one sister species pair that exists both on the same host and result in reproductive barriers and lead to speciation in sym- the same island (Ai. diluta and prognata). These species are patric host races (Berlocher and Feder 2002), but whether separated ecologically, either on northern mesic or dry south- host-plant phenology could have played a role in the spe- ern habitats of the widespread host, Teline microphylla, sug- ciation of these psyllid taxa is not yet determined. gesting that there has been an ecological shift to different There are some Genisteae that apparently do not have any host habitats. Geographically separated sister taxa on differ- associated psyllids. In the Canary Islands, the Genisteae spe- ent islands but on the same host sometimes show similar cies that do not host psyllids are all rare species, and in many ecological specialization. For example, Ai. occidentalis and cases these are rare because of human disturbance. Frag- gomerae are more common on the xerically adapted host mentation of host populations may also be critical. In con- subspecies of Teline stenopetala on La Palma (ssp. sericea) trast, cultivation of some native host plants for animal fodder and La Gomera (ssp. pauciovulata) respectively, whereas Ai. (Chamaecytisus proliferus and Teline stenopetala) and the ad- modica and hupalupa are more common on the mesically aptation of other native hosts to disturbed or grazed land- adapted host subspecies on each island (ssp. stenopetala and scapes (e.g., Adenocarpus viscosus) appears to have increased ssp. microphylla, respectively). However, ecological prefer- the abundance of psyllid species associated with these hosts ences may have shifted over time, so that observed prefer- (Percy 2003). Another effect of human disturbance is the ences may not re¯ect historical preferences at the time of breakdown of ecological barriers between plant species re- speciation. sulting in hybridization (Lems 1958; Francisco-Ortega et al. The psyllid phylogeny also allows a comparison of the 2000). Several psyllid species (Ai. diluta, equitans, pileolata, relationships between ecologically more specialized and proboscidea, and menceyata) are found on multiple hosts be- more generalist taxa. A widespread legume exists in several tween which hybrids have been recorded (Table 1). On Ten- types of habitat, and a widespread psyllid on this legume may erife, hybrids between three host species (Teline canariensis, therefore be considered an ecological generalist, whereas T. stenopetala, and T. osyroides) are found around the Ladera psyllids restricted to localized host habitats may be ecological de GuÈõÂmar (Arco Aguilar 1983; M. Arco Aguilar, pers. comm. specialists. On Tenerife, four psyllid species occur on Teline 1998), an area that was disturbed by early settlements of canariensis, but only one psyllid is found throughout the host aboriginal Guanches. The most widespread psyllid on Ten- range (Ai. pileolata), whereas the other species (Ai. diluta, erife (Ai. pileolata) is found on these three hosts. As hybrids canariensis, and menceyata) occur in localized regions or are more likely to occur between closely related legumes, it habitats. A similar pattern is found on Gran Canaria, where is not clear whether the host range expansions occurred be- three psyllid species are found on T. microphylla, one wide- cause the hosts were related (and therefore familiar), or spread (Ai. equitans) and two localized species (Ai. diluta and whether hybridization could have promoted host shifts via a prognata). The phylogeny suggests that on Tenerife, some ``hybrid bridge'' effect (Floate and Whitham 1993; Roderick PHYTOPHAGOUS INSECT SPECIATION 2551

FIG. 4. Distributions and mapped host-plant associations in the dividens-modica subclade of Arytinnis (the uppermost clade in Fig. 3). The dashed boxes delimit Ai. dividens and Ai. modica based on a morphological analysis. Three independent colonizations of Chamaecytisus from Teline are numbered. The nodes marked A or B denote where possible ancestral polyphagy at the base of the subclade could account for a propensity to switch between the same unrelated hosts through the retention of dual host acceptance such as is evident in the repeated shift between Teline and Chamaecytisus in Ai. modica on La Palma and El Hierro.

1997). Recent molecular analysis of the host-plant group us- i®city would have been derived from an initial condition of ing the nuclear region ITS1±5.8S-ITS2 (Percy and Cronk ancestral polyphagy. Similar unspecialized ``bridge species'' 2002) found minimal genetic divergence between many of from which specialists evolve have been proposed for lepi- the Macaronesian host plants. Notably, the three host plants dopteran taxa (Menken and Roessingh 1998). Figure 4 il- of Ai. pileolata, which are distinguished using morphological lustrates an example where an atypical host switch between characters, had either identical ITS sequences or a single indel the same unrelated hosts (three independent colonizations of difference (Percy and Cronk 2002), and could therefore con- Chamaecytisus: Cytisus group, from Teline: Genista group) stitute a single species. has apparently occurred repeatedly in a small subclade of The host association patterns in the island groups, as with closely related species (the dividens-modica subclade). The other phytophagous insects on islands (Roderick and Gilles- propensity to switch between Chamaecytisus and Teline in pie 1998), suggest that either ecological or geographical sep- this subclade could re¯ect an earlier period of ancestral po- aration alone may be suf®cient to promote psyllid speciation, lyphagy, after which the formation of host races (which is but both mechanisms are apparent in the majority of sister possibly occurring in Ai. modica) may have led to speciali- species relationships. zation and speciation. This scenario is not inconsistent with the topology and current distributions. The retention of an Host Switches between Unrelated Hosts ancestral host preference is present in a number of phytoph- Although there is evidence that preadaptation is operating agous insects (Keese 1998; Janz and Nylin 1998; Dobler and on selection and acceptance of host plants during colonization Farrell 1999; Janz et al. 2001), and could explain the repeated of a new region, it remains to be answered how host switches host switch between Teline and Chamaecytisus in Ai. modica. have occurred between unrelated genera (in the Canary Is- Despite a capacity for polyphagy, host speci®city may max- lands these are between Teline in the Genista group and Ad- imize reproductive output because of the greater likelihood enocarpus, and Teline and Chamaecytisus in the Cytisus of ®nding conspeci®cs on the preferred host (Feder et al. group). Because there are no apparent host switches to un- 1997). Yet, retention of the capacity for polyphagy may be related hosts during colonization events, successful coloni- advantageous when ¯uctuations in the host lineage (long zation of a new region is apparently dependent on encoun- term) or host density (short term) favor survival on alternate tering familiar plants. Host switches between unrelated plant hosts (Futuyma et al. 1995; Janz et al. 2001). Although re- genera may therefore be facilitated by longer periods of con- tention of a historically broader host preference may remain tact, which allow acclimatization to novel plants and/or host in the ``memory bank'' of an insect lineage for a limited race formation, as has been proposed to explain intergeneric period of time (Futuyma et al. 1993, 1995), it could be an host switching in host speci®c Hawaiian Hemiptera (Gagne important evolutionary mechanism to the survival of an insect 1997). lineage. If the formation of host races subsequently leads to spe- Sympatric divergence is suggested by present day host ciation via specialization on one or other host, observed spec- distributions for one continental species pair (A. cytisi and 2552 DIANA M. PERCY telonicola), and possibly Ai. modica if populations on dif- Canary Island, and genesis of the Caldera de Taburiente. J. Vol- ferent hosts are indeed diverging into distinct host races. canol. Geotherm. Res. 60:243±262. Arco Aguilar, M. D. 1983. Catalogo actualizado de los taxones del However, it is also possible that changes in vegetation struc- genero Teline Medicus en la region Macaronesica adiciones y ture in the past (e.g. during the Pleistocene) resulted in ini- nuevas combinaciones. Viraea 12:193±232. tially allopatric divergence in the continental species. If un- Asquith, A. 1995. Evolution of Sarona (Heteroptera, Miridae). Spe- related hosts in sympatry do provide a mechanism for spe- ciation on geographic and ecological islands. Pp. 90±120 in W. L. Vagner and V. A. Funk, eds. Hawaiian biogeography: evo- ciation, it may be that divergent selection pressures (caused lution on a hot spot archipelago. Smithsonian Inst. Press, Wash- by chemical or physical differences) are greater than between ington, DC. related hosts, providing a stronger barrier to gene ¯ow be- Barrett, S. C. H. 1998. The reproductive biology and genetics of tween populations that are adapting to distinct hosts. The island plants. Pp. 18±34 in P. R. Grant, ed. Evolution on islands. Oxford Univ. Press, Oxford, U.K. identi®cation of distinct host races in Ai. modica could sup- Becerra, J. X. 1997. Insects on plants: macroevolutionary chemical port this scenario but will require more extensive genetic trends in host use. Science 276:253±256. sampling as well as ecological (e.g., host-transplant experi- Becerra, J. X., and D. L. Venable. 1999. Macroevolution of insect- ments) and behavioral studies (e.g., phenology and mating plant associations: the relevance of host biogeography to host behavior). af®liation. Proc. Natl. Acad. Sci. USA 96:12626±12631. Berlocher, S. H. 1998. Can sympatric speciation via host or habitat The interpretations of speciation, colonization patterns, shift be proven from phylogenetic and biogeographic evidence? and host-plant shifts are dependent on correct estimates of Pp. 99±113 in D. J. Howard and S. H. Berlocher, eds. Endless phylogenetic relationships. In this study the molecular phy- forms. Species and speciation. Oxford Univ. Press, New York. logenies are based on a single nonrecombining molecule Berlocher, S. H., and J. L. Feder. 2002. Sympatric speciation in phytophagous insects: Moving beyond controversy? Annu. Rev. (mtDNA). There are an increasing number of studies that Entomol. 47:773±815. have shown this to be a potentially unreliable means of es- Bisby, F. A. 1981. Genisteae (Adans.) Benth. (1865). Pp. 409±425 timating species relationships (Weinreich and Rand 2000), in R. M. Polhill and P. H. Raven, eds. Advances in legume particularly in recently diverged groups (Giannasi et al. 2001; systematics. Kew, Royal Botanical Garden, London. Shaw 2002). These studies emphasize the need to use nuclear Brower, A. V. Z. 1994. Rapid morphological radiation and con- vergence among races of the butter¯y Heliconius erato inferred markers as an alternative and independent estimate of phy- from patterns of mitochondrial DNA evolution. Proc. Natl. Acad. logeny. The addition of nuclear data for the psyllids may also Sci. USA 91:6491±6495. shed light on the apparent incongruence between the mito- Brunton, C. F. A., and G. D. D. Hurst. 1998. Mitochondrial DNA chondrial and morphological analyses. phylogeny of Brimstone butter¯ies (genus Gonepteryx) from the Canary Islands and Madeira. Biol. J. Linn. Soc. 63:69±79. Burckhardt, D. 1987a. Jumping plant lice (Homoptera: Psylloidea) ACKNOWLEDGMENTS of the temperate Neotropical region. Part 1: Psyllidae (Subfam- ilies Aphalarinae, Rhinocolinae and Aphalaroidinae). Zool. J. This research was supported by the Natural Environment Linn. Soc. 89:299±392. Research Council (NERC GT04/97/109/TS doctoral stu- ÐÐÐ. 1987b. Jumping plant lice (Homoptera: Psylloidea) of the dentship and NERC GR3/11075 to R. Page). Additional fund- temperate Neotropical region. Part 2: Psyllidae (Subfamilies ing for ®eldwork was provided by the Carnegie Trust for the Diaphorininae, Acizziinae, Ciriacreminae and Psyllinae). Zool. Universities of Scotland and the Louise Hiom Award (Uni- J. Linn. Soc. 90:145±205. ÐÐÐ. 1989. Les psylles (Insecta, Homoptera, Psylloidea) de l' versity of Glasgow), which together supported two expedi- algeÂrie. Arch. Sci. Geneva 42:367±424. tions to Morocco. Permission to work and collect in the Ca- Campbell, B. C., J. D. Steffen-Campbell, J. T. Sorensen, and R. J. nary Islands was received from ViceconsejerõÂa de Medio Am- Gill. 1995. Paraphyly of Homoptera and Auchenorrhynca in- biente (Gobierno de Canarias), Parque Nacional del Teide ferred from 18S rDNA nucleotide sequences. Syst. Entomol. 20: 175±194. (Tenerife), Parque Nacional de Garajonay (La Gomera), and Carracedo, J. C., S. Day, H. Guillou, E. RodrõÂguez Badiola, J. A. Parque Nacional Caldera de la Taburiente (La Palma). Gen- Canas, and F. J. PeÂrez Torrado. 1998. Hotspot volcanism close erous assistance and support in the Canary Islands was pro- to a passive continental margin: the Canary Islands. Geol. Mag. vided by P. Oromõ (Universidad de La Laguna), in Madeira 135:591±604. by H. Costa Neves (Parque Natural da Madeira), and in An- Carracedo, J. C., S. Day, H. Guillou, and P. Gravestock. 1999. Later stages of volcanic evolution of La Palma, Canary Islands: rift dalusia and Morocco by B. 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APPENDIX Distribution of taxa and location of 84 samples from 62 taxa (61 species and one subspecies) included in this study. The datasets in which each sample was included are indicated: 12S, small subunit rRNA; CO, cytochrome oxidase I, tRNA leucine, and cytochrome oxidase II; M, morphological (adult and nymph; M* adult only). Material supplied by D. Burckhardt (DB), D. Hollis (DH), and I. Hodkinson (IH) is indicated, all other material was collected by D. Percy in 1997±2000.

Plant species from which DNA voucher number sample was collected [collection no. Datasets Taxon Origin of sample [host plant if different] if different] 12S CO Acizzia hollisi High Atlas, Morocco Genista ¯orida [Acacia spp.] DP325.1B 12S CO M Acizzia uncatoides La Palma, Canary Islands Acacia spp. (cultivated) DP194 12S CO M Arytaina adenocarpi Coimbra, Portugal Adenocarpus complicatus DP262.3A 12S CO M Arytaina adenocarpi MaÂlaga, Spain Adenocarpus telonensis DP233 12S CO M Arytaina adenocarpi Middle Atlas, Morocco Adenocarpus boudyi DP243 CO M Arytaina devia Tenerife, Canary Islands Chamaecytisus proliferus DP188.1 CO M Arytaina devia La Gomera, Canary Islands Chamaecytisus proliferus DP68 12S CO M Arytaina devia ssp. insularis Gran Canaria, Canary Is- Chamaecytisus proliferus DP161 lands 12S CO M Arytaina devia ssp. insularis La Palma, Canary Islands Chamaecytisus proliferus DP189 12S CO M Arytaina genistae Edinburgh, Scotland Cytisus scoparius none [DP285] 12S CO M Arytaina genistae Coimbra, Portugal Cytisus striatus DP263 CO M Arytaina genistae High Atlas, Morocco Cytisus grandi¯orus DP325.2 12S CO M Arytaina nubivaga Tenerife, Canary Islands Spartocytisus supranubius DP154 12S CO M Arytaina vittata La Gomera, Canary Islands Spartocytisus ®lipes DP69 ϩ 220 12S CO M Arytainilla cytisi Rif mountains, Morocco Calicotome villosa DP319 12S CO M* Arytainilla delarbrei Coimbra, Portugal Cytisus purgans DP265.2 12S M Arytainilla gredi DH Picos de Europa, Spain Genista hispanica DH336 12S CO M Arytainilla ima High Atlas, Morocco Adenocarpus anagyrifolius DP239 12S CO M Arytainilla serpentina La Palma, Canary Islands Spartocytisus ®lipes DP198 12S CO M Arytainilla spartiophila Coimbra, Portugal Cytisus striatus DP265 12S CO M Arytainilla spartiophila MaÂlaga, Spain Cytisus grandi¯orus DP133 CO M Arytainilla spartiophila High Atlas, Morocco Cytisus fontanesii DP327 12S CO M Arytainilla sulci southwestern coast, Morocco Retama raetam DP297 12S CO M Arytainilla atlantica southwestern coast, Morocco Cytisus albidus DP296 12S CO M Arytainilla telonicola MaÂlaga, Spain Adenocarpus telonensis DP134 12S CO M Arytainilla montivaga Granada, Spain Adenocarpus decorticans DP128 CO M Arytainilla montivaga Rif mountains, Morocco Adenocarpus decorticans DP249 12S CO M Arytinnis berber Anti-Atlas, Morocco Genista segonnei DP332 12S CO M* Arytinnis canariensis Tenerife, Canary Islands Teline canariensis DP179 12S CO M Arytinnis cognata High Atlas, Morocco Genista ¯orida DP238 12S CO M Arytinnis diluta Gran Canaria, Canary Is- Teline microphylla DP172 lands CO M Arytinnis diluta Tenerife, Canary Islands Teline canariensis DP152 12S CO M Arytinnis dividens Gran Canaria, Canary Is- Chamaecytisus proliferus DP168 lands CO M Arytinnis dividens Tenerife, Canary Islands Chamaecytisus proliferus DP188.2 12S CO M Arytinnis dividens La Gomera, Canary Islands Chamaecytisus proliferus DP244 12S CO M Arytinnis equitans Gran Canaria, Canary Is- Teline microphylla DP163 lands 12S CO M Arytinnis fortunata La Palma, Canary Islands Teline splendens DP203 12S CO M Arytinnis gomerae La Gomera, Canary Islands Teline stenopetala DP221 12S CO M Arytinnis hakani Rif mountains, Morocco Teline monspessulana DP256 12S CO M Arytinnis hupalupa La Gomera, Canary Islands Teline stenopetala DP219 12S CO M Arytinnis incuba Encumeada, Madeira Teline maderensis DP271 ϩ 274 12S CO M Arytinnis menceyata Tenerife, Canary Islands Teline canariensis DP182 12S CO M Arytinnis modica La Palma, Canary Islands Teline stenopetala DP192 12S CO M Arytinnis modica La Palma, Canary Islands Chamaecytisus proliferus DP201 CO M Arytinnis modica El Hierro, Canary Islands Teline stenopetala DP212 CO M Arytinnis modica El Hierro, Canary Islands Chamaecytisus proliferus DP211 12S CO M Arytinnis nigralineata Gran Canaria, Canary Is- Adenocarpus foliolosus DP173 lands CO M Arytinnis nigralineata Tenerife, Canary Islands Adenocarpus foliolosus DP156 CO M Arytinnis nigralineata La Gomera, Canary Islands Adenocarpus foliolosus DP67 12S CO M Arytinnis ochrita Tenerife, Canary Islands Teline osyroides DP153 12S CO M Arytinnis occidentalis La Palma, Canary Islands Teline stenopetala DP190 CO M Arytinnis occidentalis El Hierro, Canary Islands Teline stenopetala DP214 12S CO M Arytinnis pileolata Tenerife, Canary Islands Teline canariensis DP178 CO M Arytinnis pileolata Tenerife, Canary Islands Teline osyroides DP184 12S CO M Arytinnis proboscidea Tenerife, Canary Islands Adenocarpus viscosus DP5 CO M Arytinnis proboscidea La Palma, Canary Islands Adenocarpus foliolosus DP204 12S CO M Arytinnis prognata Gran Canaria, Canary Is- Teline microphylla DP160 lands 12S CO M Arytinnis romeria Gran Canaria, Canary Is- Teline rosmarinifolia DP165 lands 2556 DIANA M. PERCY

APPENDIX. Continued.

Plant species from which DNA voucher number sample was collected [collection no. Datasets Taxon Origin of sample [host plant if different] if different] 12S CO M Arytinnis umbonata Encumeada, Madeira Genista tenera DP273 12S CO Cacopsylla alaterni MaÂlaga, Spain Rhamnus alaternus DP112 12S CO Cacopsylla mali Edinburgh, Scotland Malus sp. DP293 12S CO Cyamophila prohaskai DB AemsigeÂn, Switzerland Coniferae [Anthyllis vulner- DB341 aria] 12S CO M* Livilla adusta MaÂlaga, Spain Genista cinerea DP132 12S CO M Livilla blandula Southwestern coast, Morocco Cytisus albidus DP296 12S Livilla horvathi DB Kars, Turkey ? [Chamaecytisus austriacus] DB1 12S Livilla maculipennis IH El Gor, Algeria ? [Genista sp.] IH8 12S CO Livilla maura Rif mountains, Morocco Chamaespartium tridentatum DP250 12S CO M Livilla monospermae Tenerife, Canary Islands Retama monosperma DP28 CO M Livilla monospermae La Gomera, Canary Islands Retama monosperma DP70 CO M Livilla monospermae La Palma, Canary Islands Retama monosperma DP196 12S M* Livilla nervosa Granada, Spain Genista umbellata DP124 12S Livilla pseudoretamae IH Grand Kabylie, Algeria ? [host plant unknown] IH7 12S Livilla pyrenaea DB Zaragoza, Spain ``Genista scoparius'' [Genista DB4 sp.] 12S Livilla radiata DB Peloponnese, Greece ``Genistae?'' [Chamaecytisus DB6 spp.] 12S CO M Livilla retamae CaÂdiz, Spain Retama monosperma DP94 12S Livilla spectabilis IH Liguria, Italy Spartium junceum IH6 12S Livilla syriaca DB Carmel, Israel Genista fasselata DB3 12S CO Livilla variegata Glasgow, Scotland Laburnum anagyroides DP337 12S Livilla vicina DB Vermala, Switzerland Genista radiata DB5 12S Livilla vittipennella IH Trentino, Italy Genista radiata IH5 12S CO M* Livilla caprifuga Middle Atlas, Morocco Adenocarpus bacquei DP309 12S CO M* Livilla baetica Granada, Spain Adenocarpus decorticans DP129 12S CO M* Livilla complexa Coimbra, Portugal Adenocarpus complicatus DP262.3B 12S CO M Pseudacanthopsylla southwestern coast, Morocco Retama raetam DP301 improvisa