Kazunori Yoshizawa

Mitochondrial genome deletions and minicircles are common in lice (Insecta: Phthiraptera)

BackgroundThe gene composition, gene order and structure of the mitochondrial genome are remarkably stable across bilaterian animals. Lice (Insecta: Phthiraptera) are a major exception to this genomic stability in that the canonical single chromosome with 37 genes found in almost all other bilaterians has been lost in multiple lineages in favour of multiple, minicircular chromosomes with less than 37 genes on each chromosome.ResultsMinicircular mt genomes are found in six of the ten louse species examined to date and three types of minicircles were identified: heteroplasmic minicircles which coexist with full sized mt genomes (type 1); multigene chromosomes with short, simple control regions, we infer that the genome consists of several such chromosomes (type 2); and multiple, single to three gene chromosomes with large, complex control regions (type 3). Mapping minicircle types onto a phylogenetic tree of lice fails to show a pattern of their occurrence consistent with an evolutionary series of minicircle types. Analysis of the nuclear-encoded, mitochondrially-targetted genes inferred from the body louse, Pediculus, suggests that the loss of mitochondrial single-stranded binding protein (mtSSB) may be responsible for the presence of minicircles in at least species with the most derived type 3 minicircles (Pediculus, Damalinia).ConclusionsMinicircular mt genomes are common in lice and appear to have arisen multiple times within the group. Life history adaptive explanations which attribute minicircular mt genomes in lice to the adoption of blood-feeding in the Anoplura are not supported by this expanded data set as minicircles are found in multiple non-blood feeding louse groups but are not found in the blood-feeding genus Heterodoxus. In contrast, a mechanist explanation based on the loss of mtSSB suggests that minicircles may be selectively favoured due to the incapacity of the mt replisome to synthesize long replicative products without mtSSB and thus the loss of this gene lead to the formation of minicircles in lice.

Monophyletic Polyneoptera recovered by wing base structure

Phylogenetic relationships among the winged orders of Polyneoptera [Blattodea, Dermaptera, Embiodea (=Embioptera), Isoptera, Mantodea, Orthoptera, Phasmatodea, Plecoptera and Zoraptera] were estimated based on morphological data selected from the hindwing base structure. Cladistic analyses were carried out using hindwing base data alone and in combination with other, more general, morphological data. Both datasets resulted in similar trees and recovered the monophyly of Polyneoptera. Deepest phylogenetic relationships among the polyneopteran orders were not confidently estimated, but the monophyly of Mystroptera (= Embiodea + Zoraptera), Orthopterida (= Orthoptera + Phasmatodea) and Dictyoptera (= Blattodea + Mantodea + Isoptera) was supported consistently. In contrast, placements of Plecoptera and Dermaptera were unstable, although independent analysis of the wing base data supported their sister‐group relationship with two nonhomoplasious synapomorphies (unique conditions in the ventral basisubcostale, and in the articulation between the antemedian notal wing process and first axillary sclerite). Results from the combined wing base plus general morphology data were consistent, even if the wingless orders Grylloblattodea and Mantophasmatodea were included in the analysis. Generally, trees obtained from the present analyses were concordant with the results from other morphological and molecular analyses, but Isoptera were placed inappropriately to be the sister of Blattodea + Mantodea by the inclusion of the wing base data, probably as a result of morphological regressions of the order.

How stable is the "Polyphyly of Lice" hypothesis (Insecta: Psocodea)?: a comparison of phylogenetic signal in multiple genes.

Recent molecular phylogenetic analyses of 18S rDNA have indicated that parasitic lice (order Phthiraptera) are possibly polyphyletic. These analyses recovered one of the parasitic louse suborders, Amblycera, as the sister group to the free-living booklouse family Liposcelididae. We further tested this hypothesis using DNA sequences from five genes: nuclear 18S rDNA, Histone 3, and wingless and mitochondrial 16S rDNA and COI. Combined analyses of these five genes provided reasonably strong support for the Amblycera+Liposcelididae clade, supporting the polyphyly of lice hypothesis. To explore the robustness of this result, we examined the phylogenetic signal contained in each gene independently (except for wingless, which could not be readily amplified in many target taxa). Analyses of each gene separately and in various combinations with other genes revealed that clear signal supporting Amblycera+Liposcelididae only existed in the 18S data, although no analysis supported monophyly of parasitic lice. Nevertheless, combined analyses of all genes provided stronger support for this relationship than that obtained from 18S data alone. The increase in support for this clade was mostly explained by the stabilization of other parts of the tree and potentially inappropriate substitution modeling. These findings demonstrate that the increased support values provided by combined data set does not always indicate corroboration of the hypothesis.

Morphology of male genitalia in lice and their relatives and phylogenetic implications

Abstract.  Lice (Insecta: Phthiraptera) have long been considered to compose a monophyletic group of insects on the basis of external morphological characteristics. However, a recent phylogenetic analysis of 18S rDNA sequences suggested that ‘Phthiraptera’ have arisen twice within the order Psocoptera (booklice and barklice). The external features of lice are highly specialized to a parasitic lifestyle, and convergence may be frequent for such characters. To provide a further test between traditional and recent molecular‐based phylogenetic hypotheses, a phylogenetic analysis of lice and relatives based on morphological characters that are independent from the selective pressures of a parasitic lifestyle is needed. Here, we examined the morphology of the male phallic organ in lice and relatives (‘Psocoptera’: suborders Troctomorpha and Psocomorpha) and detected some novel modifications that were stable within each group and useful for higher level phylogenetic reconstruction. Phylogenetic analysis based on these characters provided a concordant result with the 18S‐based phylogeny. In particular, the apomorphic presence of articulations between the basal plate, mesomere and ventral plate (= sclerite on the permanently everted endophallus) is observed consistently throughout the psocid families Pachytroctidae and Liposcelididae and the louse suborder Amblycera, providing support for a clade composed of these three groups, although possible homoplasy was detected in some Ischnocera. This is the first study to provide morphological support for the polyphyly of lice.

The Zoraptera problem : evidence for Zoraptera + Embiodea from the wing base

Abstract The order Zoraptera is one of the most enigmatic insect groups. Its phylogenetic position is far from settled, and more than ten different placements have been discussed since the insects were first discovered. This problem is also difficult to resolve with molecular studies because of the unusual characteristics of zorapteran 18S rDNA sequences, which are the most widely used genetic markers for the estimation of the deep phylogeny of insects. In this study, the wing base structures of Zoraptera and various potential sister taxa were examined. Numbers of unique modifications were detected in the wing base structure of Zoraptera, and six were also observed in the wing base of Embiodea (Embioptera, Embiidina; webspinners). No possible synapomorphies supporting the other relationships were detected. This is the second unambiguous morphological synapomorphy providing strong evidence for the phylogenetic position of Zoraptera.

Multiple lineages of lice pass through the K-Pg boundary

For modern lineages of birds and mammals, few fossils have been found that predate the Cretaceous–Palaeogene (K–Pg) boundary. However, molecular studies using fossil calibrations have shown that many of these lineages existed at that time. Both birds and mammals are parasitized by obligate ectoparasitic lice (Insecta: Phthiraptera), which have shared a long coevolutionary history with their hosts. Evaluating whether many lineages of lice passed through the K–Pg boundary would provide insight into the radiation of their hosts. Using molecular dating techniques, we demonstrate that the major louse suborders began to radiate before the K–Pg boundary. These data lend support to a Cretaceous diversification of many modern bird and mammal lineages.

Direct optimization overly optimizes data

Direct optimization is a criterion that recognizes sequence alignment and tree search as a single epistemological problem and performs them simultaneously. When multiple datasets are analysed under the direct optimization criterion, all data partitions are combined and optimized simultaneously, along with one and the same tree topology (Wheeler & Hayashi, 1998; Wheeler, 2003). Each data partition of the combined data is independent in the sense that the homologies are not shifted between partitions, but every data partition has the potential to influence the optimizations of other partitions (Simmons, 2004). The criterion has been adopted mainly for analyses of DNA sequences but has also been used for behavioural (Robillard et al., 2006) and morphological (Agolin & D’Haese, 2009) characters for which homology assessment between taxa is ambiguous (dynamic homology). Systematic Entomology has published many important contributions to insect systematics partly or fully based on the direct optimization criterion, with little or no discussion of the procedures and methodological assumptions (Edgecombe et al., 2002; Hebsgaard et al., 2004; Robertson et al., 2004; Whiting & Whiting, 2004; Damgaard et al., 2005; Jarvis et al., 2005; Schuh et al., 2009; Kehlmaier & Assmann, 2010). One of the most important contributions to systematic entomology based on the direct optimization criterion is that by Terry & Whiting (2005a), who provided new insights into the very poorly understood phylogenetic relationships among orthopteroid insect orders. Among the many gene sequences presented in that paper, the 18S sequence of Zorotypus hubbardi (order Zoraptera: AY521890; voucher BYU ACZO001) was used subsequently by Xie et al. (2009), who analysed its secondary structure. This analysis showed that the 18S of Zoraptera had a secondary structure similar to that of other insects. By contrast, previous studies had shown that the 18S of zorapterans contains unusual evolutionary motifs, including modifications of secondary structure (Kjer, 2004; Yoshizawa & Johnson, 2005). The sequence was used here for a BLAST search (http://blast.ddbj.nig.ac.jp/: Sept. 24,

Differential introgression causes genealogical discordance in host races of Acrocercops transecta (Insecta: Lepidoptera).

Recently diverged populations often exhibit incomplete reproductive isolation, with a low level of gene flow continuing between populations. Previous studies have shown that, even under a low level of gene flow, genetic divergence between populations can proceed at the loci governing local adaptation and reproductive isolation but not at other neutral loci. A leaf‐mining moth, Acrocercops transecta, consists of Juglans‐ and Lyonia‐associated host races. The two host races differ in host preferences of ovipositing females and in larval adaptation to host plants but mate readily in the laboratory, producing fertile hybrids. The Juglans and Lyonia races are often sympatric in the wild, implying that gene introgression could occur in nature between the two host races. We tested this hypothesis by combining phylogenetic analyses with coalescent simulations, focusing on mitochondrial genes (COI and ND5) and the nuclear Tpi, Per and Ldh genes located on the Z‐chromosome. The mitochondrial genes clearly distinguished the Lyonia race from the Juglnas race, whereas the Tpi, Per and Ldh genealogies did not reflect the two host races. Coalescent simulations indicated gene flow at the three Z‐linked genes in both directions, whereas there was no introgression in the mitochondrial genes. The lack of introgression in mitochondrial genes suggests that female host preference is the primary force leading to the bifurcation of maternally inherited loci. Thus, the results show that a low level of gene flow coupled with the inflexible female host preference differentiates histories of divergence between maternally and biparentally inherited genes in this host race system.

The treehopper's helmet is not homologous with wings (Hemiptera: Membracidae)

The helmet-like structure of membracid treehoppers (Hemiptera: Membracidae) has long been recognized as the modified tergum of the first thoracic segment (T1) (Buckton, 1903; Kramer, 1950; Hasenoehrl & Cook, 1965; Boulard, 1973; Rietschel, 1987; Stegmann, 1998). In challenging this widely accepted interpretation, Prud’homme et al. (2011) proposed a novel hypothesis: that the helmet is homologous with the wings of T1. No extant winged insects possess T1 wings; these structures have apparently been suppressed for over 250 Myr (e.g. Grimaldi & Engel, 2005). Morphological, developmental and gene expression evidence purported to support the helmet-wing hypothesis. The presence of a jointed articulation between the helmet and T1, analogous to the wing base joint, was considered as key evidence (Prud’homme et al., 2011). ‘Wing base’ is a keyword of my research (e.g. Yoshizawa & Saigusa, 2001; Yoshizawa, 2011), so I read Prud’homme et al. (2011) with great interest. However, I realized immediately that the morphological interpretations were problematic, and concluded that the interpretation of the treehopper’s helmet as the modified T1 tergum should be maintained. Here I point out the problems in the morphological interpretations of Prud’homme et al. (2011) based on published data and my morphological examination of Publilia modesta, the treehopper analysed by Prud’homme et al. (2011). Comparison was also made with a closely related but less specialized insect: a leafhopper (Pagaronia sp.).

Homology of the internal sac components in the leaf beetle subfamily criocerinae and evolutionary novelties related to the extremely elongated flagellum

Extremely elongated intromittent organs are found in a wide range of taxa, especially among insects. This phenomenon is generally thought to result from sexual selection, but it is predicted that limited storage space in the body cavity and the difficulty of using the elongated organs should have constrained the evolution of extreme elongation, neutralizing any selective advantage. Therefore, in groups with long intromittent organs, features that overcome these constraints may have evolved or coevolved together with intromittent organ elongation. Using a comparative morphological approach and outgroup comparisons, we identified potential constraints and key novelties that may neutralize such constraints in the leaf beetle subfamily Criocerinae. Observations of the internal sac structure throughout Criocerinae were performed. Comparing the results with preceding studies from outgroups, a ground plan of the criocerine internal sac was constructed. Our analysis also identified specific features that are always correlated with extreme elongation: the rotation of whole internal‐sac sclerites and the possession of a pocket in which to store the elongated flagellum. The pocket is thought to be formed by the rotation of the sclerites, markedly altering internal sac shape from the criocerine ground plan. Onlythe clades that have acquired this derived state contain species with an elongated flagellum that distinctly exceeds the median lobe length. It is presumed that these character correlations evolved independently three times. The detected character correlations corroborate the hypothesis that there are latent adaptive constraints for the evolution of extremely elongated intromittent organs. The constraints may have been neutralized by the alteration from the criocerine ground plan resulting in the formation of a storage pocket. In conclusion, deviation from the criocerine ground plan isconsidered to be the evolutionary innovation that neutralized the latent adaptive constraints of flagellum elongation in the subfamily Criocerinae. J. Morphol., 2012.