Publications

2004
Megens HJ, Van Nes WJ, Van Moorsel CHM, Pierce NE, de Jong R. Molecular phylogeny of the Oriental butterfly genus Arhopala (Lycaenidae, Theclinae) inferred from mitochondrial and nuclear genes. Systematic Entomology. 2004;29 :115-131.Abstract

We present a phylogeny for a selection of species of the butterfly genus Arhopala Boisduval, 1832 based on molecular characters. We sequenced 1778 bases of the mitochondrial genes Cytochrome Oxidase 1 and 2 including tRNA(Leu), and a 393-bp fragment of the nuclear wingless gene for a total of 42 specimens of 33 species, representing all major species groups. Analyses of mtDNA and wingless genes show congruent phylogenetic signal. The phylogeny presented here confirms the monophyly of the centaurus, eumolphus, camdeo and epimuta groups and the amphimuta subgroup. It confirms close relationships between species within the agelastus group, that together with the amphimuta subgroup, centaurus and camdeo groups form a monophyletic group. However, incongruencies with previous taxonomic studies also occur; the amphimuta and silhetensis groups are not monophyletic, as is the genus Arhopala itself. One enigmatic species, A. kinabala, was evaluated further for topology and the support for basal placement of this species is due mainly to the wingless gene. However, in the Parsimony analysis, and subsequent Maximum Likelihood evaluations, certain nodes could not be resolved due to insufficient support. The mtDNA shows extreme AT bias with compositional heterogeneity at 3rd codon positions, which may result in saturation. By contrast, the wingless gene does not show compositional bias, suggesting that poor support is not due solely to saturation. The evaluation of morphological characters used in previous studies on Arhopala systematics on the molecular tree indicates that the macular pattern and the absence of tails at the hind wings show extensive homoplasy. A significant phylogenetic signal (as indicated by T-PTP tests) is present in several of these morphological characters, which are nevertheless of limited use in phylogenetic studies due to their labile nature.

megens_et_al_2004.pdf
Kandul NP, Lukhtanov VA, Dantchenko AV, Coleman JWS, Sekercioglu CH, Haig D, Pierce NE. Phylogeny of Agrodiaetus Hubner 1822 (Lepidoptera : Lycaenidae) inferred from mtDNA sequences of COI and COII and nuclear sequences of EF1-alpha: Karyotype diversification and species radiation. Systematic Biology. 2004;53 :278-298.Abstract

Butterflies in the large Palearctic genus Agrodiaetus ( Lepidoptera: Lycaenidae) are extremely uniform and exhibit few distinguishing morphological characters. However, these insects are distinctive in one respect: as a group they possess among the greatest interspecific karyotype diversity in the animal kingdom, with chromosome numbers (n) ranging from 10 to 125. The monophyly of Agrodiaetus and its systematic position relative to other groups within the section Polyommatus have been controversial. Characters from the mitochondrial genes for cytochrome oxidases I and II and from the nuclear gene for elongation factor 1alpha were used to reconstruct the phylogeny of Agrodiaetus using maximum parsimony and Bayesian phylogenetic methods. Ninety-one individuals, encompassing most of the taxonomic diversity of Agrodiaetus, and representatives of 14 related genera were included in this analysis. Our data indicate that Agrodiaetus is monophyletic. Representatives of the genus Polyommatus ( sensu stricto) are the closest relatives. The sequences of the Agrodiaetus taxa in this analysis are tentatively arranged into 12 clades, only 1 of which corresponds to a species group traditionally recognized in Agrodiaetus. Heterogeneous substitution rates across a recovered topology were homogenized with a nonparametric rate-smoothing algorithm before the application of a molecular clock. Two published estimates of substitution rates dated the origin of Agrodiaetus between 2.51 and 3.85 million years ago. During this time, there was heterogeneity in the rate and direction of karyotype evolution among lineages within the genus. Karyotype instability has evolved independently three times in the section Polyommatus, within the lineages Agrodiaetus, Lysandra, and Plebicula. Rapid karyotype diversification may have played a significant role in the radiation of the genus Agrodiaetus.

kandul_phylo.pdf
Megens HJ, Van Moorsel CHM, Piel WH, Pierce NE, de Jong R. Tempo of speciation in a butterfly genus from the Southeast Asian tropics, inferred from mitochondrial and nuclear DNA sequence data. Molecular Phylogenetics and Evolution. 2004;31 :1181-1196.Abstract

Molecular systematics is frequently beset with phylogenetic results that are not fully resolved. Researchers either state that the absence of resolution is due to character conflict, explosive speciation, or some combination of the two, but seldom do they carefully examine their data to distinguish between these causes. In this study, we exhaustively analyze a set of nuclear and mitochondrial nucleotide data for the Asian tropical butterfly genus Arhopala so as to highlight the causes of polytomies in the phylogenetic trees, and, as a result, to infer important biological events in the history of this genus. We began by using non-parametric statistical methods to determine whether the ambiguously resolved regions in these trees represent hard or soft polytomies. In addition we determined how this correlated to number of inferred changes on branches, using parametric maximum likelihood estimations. Based on congruent patterns in both mitochondrial and nuclear DNA sequences, we concluded that at two stages in the history of Arhopala there have been accelerated instances of speciation. One event, at the base of the phylogeny, generated many of the groups and subgroups currently recognized in this genus, while a later event generated another major clade consisting of both Oriental and Papuan species groups. Based on comparisons of closely related taxa, the ratio of instantaneous rate of evolution between mitochondrial and nuclear DNA evolution is established at approximately 3:1. The earliest radiation is dated between 7 and 11 Ma by a molecular clock analysis, setting the events generating much of the diversity of Arhopala at well before the Pleistocene. Periodical flooding of the Sunda plateau during interglacial periods was, therefore, not responsible for generating the major divisions in the genus Arhopala. Instead, we hypothesize that large-scale climatic changes taking place in the Miocene have induced the early acceleration in speciation. (C) 2003 Elsevier Inc. All rights reserved.

megens_speciation.pdf
2003
Campbell DL, Pierce NE. Phylogenetic relationships of the Riodinidae: Implications for the evolution of ant association. In: Butterflies as Model Systems. Chicago University Press ; 2003. pp. 395-408. 2003_campbell_and_pierce.pdf
2002
Pierce NE, Braby MF, Heath A, Lohman DJ, Mathew J, Rand DB, Travassos MA. The ecology and evolution of ant association in the Lycaenidae (Lepidoptera). Annual Review of Entomology. 2002;47 :733-771.Abstract

The estimated 6000 species of Lycaenidae account for about one third of all Papilionoidea. The majority of lycaenids have associations with ants that can be facultative or obligate and range from mutualism to parasitism. Lycaenid larvae and pupae employ complex chemical and acoustical signals to manipulate ants. Cost/benefit analyses have demonstrated multiple trade-offs involved in myrmecophily. Both demographic and phylogenetic evidence indicate that ant association has shaped the evolution of obligately associated groups. Parasitism typically arises from mutualism with ants, arid entomophagous species are disproportionately common in the Lycaenidae compared with other Lepidoptera. Obligate associations are more common in the Southern Hemisphere, in part because highly ant-associated lineages make up a larger proportion of the fauna in these, regions. Further research on phylogeny and natural history, particularly of the Neotropical fauna, will be necessary to understand the rote ant association has played in the evolution of the Lycaenidae.

2002_pierce_et_al.pdf
Fraser AM, Tregenza T, Wedell N, Elgar MA, Pierce NE. Oviposition tests of ant preference in a myrmecophilous butterfly. Journal of Evolutionary Biology. 2002;15 :861-870.Abstract

Butterflies in the family Lycaenidae that have obligate associations with ants frequently exhibit ant-dependent egg laying behaviour. In a series of field and laboratory choice tests, we assessed oviposition preference of the Australian lycaenid Jalmenus evagoras in response to different species and populations of ants. Females discriminated between attendant and nonattendant ant species, between attendant ant species, and to some extent, between populations of a single ant species. When preferences were found, ovipositing butterflies preferred their locally predominant attendant ant species and geographically proximate attendant ant populations. A reciprocal choice test using adults from a generation of butterflies reared in the absence of ants indicated a genetic component to oviposition preference. Individual females were flexible with respect to oviposition site choice, often ovipositing on more than one treatment during a trial. Preferences arose from a hierarchical ranking of ant treatments. These results are discussed in terms of local adaptation and its possible significance in the diversification of ant-associated lycaenids.

2002_fraser_et_al.pdf
Cui JP, Jander G, Racki LR, Kim PD, Pierce NE, Ausubel FM. Signals involved in Arabidopsis resistance to Trichoplusia ni caterpillars induced by virulent and avirulent strains of the phytopathogen Pseudomonas syringae. Plant Physiology. 2002;129 :551-564.Abstract

Plants have evolved different but interconnected strategies to defend themselves against herbivorous insects and microbial pathogens. We used an Arabidopsis/Pseudomonas syringae pathosystem to investigate the impact of pathogen-induced defense responses on cabbage looper (Trichoplusia ni) larval feeding. Arabidopsis mutants [npr1, pad4, eds5, and sid2(eds16)] or transgenic plants (nahG) that are more susceptible to microbial pathogens and are compromised in salicylic acid (SA)-dependent defense responses exhibited reduced levels of feeding by T. ni compared with wild-type plants. Consistent with these results, Arabidopsis mutants that are more resistant to microbial pathogens and have elevated levels of SA (cpr1 and cpr6) exhibited enhanced levels of T. ni feeding. These experiments suggested an inverse relationship between an active SA defense pathway and insect feeding. In contrast to these results, there was increased resistance to T. ni in wild-type Arabidopsis ecotype Columbia plants that were infected with P. syringae pv. maculicola strain ES4326 (Psm ES4326) expressing the avirulence genes avrRpt2 or avrB, which elicit a hypersensitive response, high levels of SA accumulation, and systemic acquired resistance to bacterial infection. Similar results were obtained with other ecotypes, including Landsberg erecta, Cape Verdi Islands, and Shakdara. When infected with Psm ES4326(avrRpt2) or Psm ES4326(avrB), nahG transgenic and npr1 mutant plants (which are more susceptible to virulent and avirulent P. syringae strains) failed to show the increased insect resistance exhibited by wild-type plants. It was surprising that wild-type plants, as well as nahG and npr1 plants, infected with Psm ES4326 not expressing avrRpt2 or avrB, which elicits disease, became more susceptible to T. ni. Our results suggest two potentially novel systemic signaling pathways: a systemic response elicited by HR that leads to enhanced T. ni resistance and overrides the SA-mediated increase in T. ni susceptibility, and a SA-independent systemic response induced by virulent pathogens that leads to enhanced susceptibility to T. ni.

2002_cui_et_al.pdf
2001
Pierce NE. Peeling the onion: Symbioses between ants and blue butterflies. In: Model systems in behavioral ecology. Princeton: Princeton University Press ; 2001. pp. 41-56. 2001_pierce_peeling_the_onion.pdf
Fraser AM, Axen AH, Pierce NE. Assessing the quality of different ant species as partners of a myrmecophilous butterfly. Oecologia. 2001;129 :452-460.Abstract

We assessed the quality of different ant species as partners of the facultatively myrmecophilous lycaenid butterfly Glaucopsyche lygdamus. We compared disappearance and parasitism rates of G. lygdamus larvae in the field, and development of non-feeding pre-pupae in the laboratory, when individuals were untended or tended by one of four ant species. Formica podzolica was the only ant species to provide a clear benefit to G. lygdamus, in the form of reduced larval parasitism relative to untended larvae. F. 'neogagates' (F. neogagates + F. lasioides) and Tapinoma sessile were essentially neutral partners, providing no significant cost or benefit for any of the parameters measured. Relative to untended individuals, association with F. obscuripes significantly increased larval disappearance and significantly decreased pupal mass. Thus, F. obscuripes may act as a parasite of the general association between G. lygdamus and ants under certain conditions. Ant species also differed in their persistence as tenders of G. lygdamus larvae once an interaction was established. Over the lifetime of a larva, F. podzolica and F. obscuripes usually remained as the attendant ant species on plants over consecutive census dates, while F. 'neogagates' and T. sessile were frequently replaced, most commonly by F. obscuripes. It remains to be determined if disappearance and developmental outcomes reported here reflect true fitness costs (i.e. reduced survivorship and lower reproductive success) for G. lygdamus. The potential and limitations for specialization in association between G. lygdamus and high quality ant partners are discussed.

2001_fraser_et_al.pdf
Pratt SC, Pierce NE. The cavity-dwelling ant Leptothorax curvispinosus uses nest geometry to discriminate between potential homes. Animal Behaviour. 2001;62 :281-287.Abstract

Nest site selection is a frequent context for decision making in ants, but little is known of the criteria used to make a choice. We tested the nest site preferences of Leptothorax curvispinosus, both by measuring hollow acorn nests occupied in nature, and by inducing laboratory colonies to choose between artificial nests of different design. Three criteria were examined. (1) Entrance size: the ants preferred small entrance holes, presumably for their greater defensibility and crypsis. Natural nest entrances were small, and 52% of them were reduced still further by the addition of rims of soil and leaf litter. In choice tests, colonies selected nest entrances near the median size of rimmed natural holes, rejecting those near the larger end of the distribution of raw natural holes. (2) Cavity volume: acorn cavity volume was weakly correlated with the size of the occupying colony. In choice tests, colonies rejected cavities near the median size of natural nests, preferring instead larger cavities near the upper end of the natural size distribution. This may reflect active size matching of colonies to nests, because the colonies used in the choice test were bigger than those from the natural nest sample. Alternatively, all colonies may prefer big nests, but face limited availability of large cavities in nature. (3) Cavity shape: colonies preferred shapes roughly similar to that of an acorn interior, rejecting thin crevices in favour of compact, high-ceilinged cavities. (C) 2001 The Association for the Study of Animal Behaviour.

2001_pratt_pierce.pdf
Yu DW, Wilson HB, Pierce NE. An empirical model of species coexistence in a spatially structured environment. Ecology. 2001;82 :1761-1771.Abstract

Ecological theory has long supported the idea that species coexistence in a homogeneous habitat is promoted by spatial structure, but empirical evidence for this hypothesis has lagged behind theory. Here we describe a Neotropical ant-plant symbiosis that is ideally suited for testing spatial models of coexistence. Two genera of ants, Allomerus cf. demerarae and three species of Azteca are specialized to live on a single species of ant-plant, Cordia nodosa, in a Western Amazonian tropical rain forest. Empirically, using census data from widely separated localities, we show that the relative colonization abilities of the two ant genera are a function of plant density. A parameterized model shows that this pattern alone is sufficiently robust to explain coexistence in;the system. Census and experimental data suggest that Azteca queens are better long-distance flyers, but that Allomerus colonies are more fecund. Thus, Azteca can dominate in areas where host-plant densities are low land parent colony-sapling distances are long), and Allomerus can dominate in areas where host-plant densities are high. Existing spatial heterogeneity in host-plant densities therefore can allow regional coexistence, and intersite dispersal can produce local mixing. In conclusion, a dispersal-fecundity trade-off appears to allow the two genera to treat spatial heterogeneity in patch density as a niche axis. This study further suggests that a spatially structured approach is essential in understanding the persistence of some mutualisms in the presence of parasites.

2001_yu_et_al.pdf
Hsu R, Briscoe AD, Chang BSW, Pierce NE. Molecular evolution of a long wavelength-sensitive opsin in mimetic Heliconius butterflies (Lepidoptera : Nymphalidae). Biological Journal of the Linnean Society. 2001;72 :435-449.Abstract

This study examines the pattern of opsin nucleotide and amino acid substitution among mimetic species 'rings' of Heliconius butterflies that are characterized by divergent wing colour patterns. A long wavelength opsin gene, OPS1, was sequenced from each of seven species of Heliconius and one species of Dryas (Lepidoptera: Nymphalidae). A parsimony analysis of OPS1 nucleotide and amino acid sequences resulted in a phylogeny that was consistent with that presented by Brewer & Egan in 1997, which was based on mitochondrial cytochrome oxidase I and II as well as nuclear wingless genes. Nodes in the OPS1 phylogeny were well supported by bootstrap analysis and decay indices. An analysis of specific sites within the gene indicates that the accumulation of amino acid substitutions has occurred independently of the morphological diversification of Heliconius wing colour patterns. Amino acid substitutions were examined with respect to their location within the opsin protein and their possible interactions with the chromophore and the G-protein. Of the 15 amino acid substitutions identified among the eight species, one nonconservative replacement (A226Q) was identified in a position that may be involved in binding with the G-protein. (C) 2001 The Linnean Society of London.

2001_hsu_et_al.pdf
Monteiro A, Pierce NE. Phylogeny of Bicyclus (Lepidoptera : Nymphalidae) inferred from COI, COII, and EF-1 alpha gene sequences. Molecular Phylogenetics and Evolution. 2001;18 :264-281.Abstract

Despite the fact that Bicyclus anynana has become an important model species for wing-pattern developmental biology and studies of phenotypic plasticity, little is known of the evolutionary history of the genus Bicyclus and the position of B. anynana. Understanding the evolution of development as well as the evolution of plasticity can be attempted in this species-rich genus that displays a large range of wing patterns with variable degrees of phenotypic responses to the environment. A context to guide extrapolations from population genetic studies within B. anynana to those between closely related species has been long overdue. A phylogeny of 54 of the 80 known Bicyclus species is presented based on the combined 3000-bp sequences of two mitochondrial genes, cytochrome oxidase I and II, and the nuclear gene, elongation factor I alpha. A series of tree topologies, constructed either from the individual genes or from the combined data, using heuristic searches under a variety of weighting schemes were compared under the best maximum-likelihood models fitted for each gene separately. The most likely tree topology to have generated the three data sets was found to be a tree resulting from a combined MP analysis with equal weights. Most phylogenetic signal for the analysis comes from silent substitutions at the third position, and despite the faster rate of evolution and higher levels of homoplasy of the mitochondrial genes relative to the nuclear gene, the latter does not show substantially stronger support for basal clades. Finally, moving branches from the chosen tree topology to other positions on the tree so as to comply better with a previous morphological study did not significantly affect tree length. (C) 2001 Academic Press.

2001_monteiro_and_pierce.pdf
Jander G, Cui JP, Nhan B, Pierce NE, Ausubel FM. The TASTY locus on chromosome 1 of Arabidopsis affects feeding of the insect herbivore Trichoplusia ni. Plant Physiology. 2001;126 :890-898.Abstract

The generalist insect herbivore Trichoplusia ni (cabbage looper) readily consumes Arabidopsis and can complete its entire life cycle on this plant. Natural isolates (ecotypes) of Arabidopsis are not equally susceptible to T. ni feeding. While some are hardly touched by T. ni, others are eaten completely to the ground. Comparison of two commonly studied Arabidopsis ecotypes in choice experiments showed that Columbia is considerably more resistant than Landsberg erecta. In no-choice experiments, where larvae were confined on one or the other ecotype, weight gain was more rapid on Landsberg erects than on Columbia. Genetic mapping of this difference in insect susceptibility using recombinant inbred lines resulted in the discovery of the TASTY locus near 85 cM on chromosome 1 of Arabidopsis. The resistant allele of this locus is in the Columbia ecotype, and an F, hybrid has a sensitive phenotype that is similar to that of Landsberg erecta. The TASTY locus is distinct from known genetic differences between Columbia and Landsberg erecta that affect glucosinolate content, trichome density, disease resistance, and flowering time.

2001_jander_et_al.pdf
2000
Rand DB, Heath A, Suderman T, Pierce NE. Phylogeny and life history evolution of the genus Chrysoritis within the Aphnaeini (Lepidoptera: Lycaenidae), inferred from mitochondrial cytochrome oxidase I sequences. Molecular Phylogeny and Evolution. 2000;17 :85-96.Abstract

Phylogenetic relationships among 26 South African species in the tribe Aphnaeini (Lepidoptera: Lycaenidae) were inferred from DNA characters of the mitochondrial gene cytochrome oxidase I (COI), using maximum-parsimony methods. The resulting phylogenetic estimate supports the systematic hypothesis made by Heath (1997, Metamorphosis, supplement 2), based on morphological characters, that at least three preexisting genera (Chrysoritis, Poecilmitis, and Oxychaeta) should be collapsed into the single monophyletic genus Chrysoritis. Two of the species groups described by Heath within Chrysoritis are also monophyletic, while one is paraphyletic and thus unsupported by the molecular data. Strong node support and skewed transition/transversion ratios suggest that two Chrysoritis clades contain synonymous species. Aphytophagy appears as a derived feeding strategy. Evolutionary patterns of ant association indicate lability at the level of ant genus, while association with different ant subfamilies may have played an ancestral and chemically mediated role in the diversification of South African aphnaeines. ©

rand_et_al._2000.pdf
Travassos MA, Pierce NE. Acoustics, context and function of vibrational signalling in a lycaenid butterfly-ant mutualism. Animal Behaviour. 2000;60 :13-26.Abstract

Juveniles of the Australian common imperial blue butterfly, Jalmenus evagoras, produce substrate-borne vibrational signals in the form of two kinds of pupal calls and three larval calls. Pupae stridulate in the presence of conspecific larvae, when attended by an ant guard, and as a reaction against perturbation. Using pupal pairs in which one member was experimentally muted, pupal calls were shown to be important in ant attraction and the maintenance of an ant guard. A pupa may use-calls to regulate levels of its attendant ants and to signal its potential value in these mutualistic interactions. Therefore substrate-borne vibrations play a significant role in the communication between J. evagoras and its attendant ants and pupal calls appear to be more than just signals acting as a predator deterrent. Similarly, caterpillars make more sound when attended by Iridomyrmex anceps, suggesting that larval calls may be important in mediating ant symbioses. One larval call has the same mean dominant frequency, pulse rate, bandwidth and pulse length as the primary signal of a pupa, suggesting a similarity in function. (C) 2000 The Association for the Study of Animal Behaviour.

2000_travassos_pierce.pdf
Hughes L, Chang BSW, Wagner D, Pierce NE. Effects of mating history on ejaculate size, fecundity, longevity, and copulation duration in the ant-tended lycaenid butterfly, Jalmenus evagoras. Behavioral Ecology and Sociobiology. 2000;47 :119-128.Abstract

The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an 'explosive mating strategy,' include the formation of an intensely competitive mating aggregation of males, a highly male biased operational sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy. In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores, and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second mating and the dry weight by 29%, and an intermating interval of 5-9 days was needed for the ejaculate to return to the size at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number.

2000_hughes_et_al.pdf
Campbell DL, Brower AVZ, Pierce NE. Molecular evolution of the Wingless gene and its implications for the phylogenetic placement of the butterfly family riodinidae (Lepidoptera : Papilionoidea). Molecular Biology and Evolution. 2000;17 :684-696.Abstract

The sequence evolution of the nuclear gene wingless was investigated among 34 representatives of three lepidopteran families (Riodinidae, Lycaenidae, and Nymphalidae) and four outgroups, and its utility for inferring phylogenetic relationships among these taxa was assessed. Parsimony analysis yielded a well-resolved topology supporting the monophyly of the Riodinidae and Lycaenidae, respectively, and indicating that these two groups are sister lineages, with strong nodal support based on bootstrap and decay indices. Although, wingless provides robust support for relationships within and between the riodinids and the lycaenids, it is less informative about nymphalid relationships. Wingless does not consistently recover nymphalid monophyly or traditional subfamilial relationships within the nymphalids, and nodal support for all but the most recent branches in this family is low. Much of the phylogenetic information in this data set is derived from first- and second-position substitutions. However third positions, despite showing uncorrected pairwise divergences up to 78%, also contain consistent signal at deep nodes within the family Riodinidae and at the node defining the sister relationship between the riodinids and lycaenids. Several hypotheses about how third-position signal has been retained in deep nodes are discussed. These include among-site rate variation, identified as a significant factor by maximum likelihood analyses, and nucleotide bias, a prominent feature of third positions in this data set. Understanding the mechanisms which underlie third-position signal is a first step in applying appropriate models to accommodate the specific evolutionary processes involved in each lineage.

2000_campbell_et_al.pdf
Moran N, Pierce N, Seger J. W.D. Hamilton, 1936-2000 - Obituary. Nature Medicine. 2000;6 :367-367. pierce_hamilton.pdf
Haig D, Pierce NE, Wilson EO. William Hamilton (1936-2000). Science. 2000;287 :2438-2438. haig_hamilton.pdf

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