Ancient association with Fagaceae in the aphid tribe Greenideini (Hemiptera: Aphididae: Greenideinae)

Aphids are intimately associated with their host plants. Evolutionary lability of host association is common within heteroecious aphid lineages, whereas our knowledge of host‐use evolution in non‐host‐alternating aphids is limited. In the present study, we construct the first detailed molecular phylogeny of the monoecious aphid tribe Greenideini based on three mitochondrial genes (COI, COII and Cytb) and one nuclear gene (EF‐1α), and investigated its history of host association. Maximum likelihood and Bayesian phylogenies strongly support the monophyly of Greenideini and most constituent genera. Divergence time estimates and character reconstructions suggest that Greenideini may have originated during the Late Cretaceous to early Paleogene, which accompanies the origin of its ancestral host, members of the family Fagaceae. Colonisation of novel host plants has occurred multiple times during the evolutionary history of Greenideini, thereby leading to current patterns of host association. We suggest that directly shifting to novel hosts, together with expanding host range onto pre‐existing, unused plants, has probably promoted diversification in this tribe.     

Mitochondrial DNA Phylogeny and the Evolution of Host-Plant Use in Palearctic Chrysolina (Coleoptera, Chrysomelidae) Leaf Beetles

The genus Chrysolina consists of specialized phytophagous leaf-beetles (Coleoptera, Chrysomelidae) with feed on several plant families. There is no explicit phylogenetic hypothesis available for this genus, which includes 65 subgenera and more than 400 species with a wide distribution. We obtained 839-bp sequence data from the 16S rDNA and cytochrome oxidase subunit I (COI) mitochondrial genes. Thirty Chrysolina taxa representing eight host–plant affiliations, two species of the closely related genus Oreina, and two outgroups were sampled. These data sets were used separately and combined to obtain the mitochondrial cladogram of the group using maximum-parsimony and maximum-likelihood criteria. The results were compared to current proposals for Chrysolina systematics that are based on morphological, ecological, and karyological data. The trees obtained were in the most part congruent with the proposed ancestral association of Chrysolina to Lamiaceae based on chromosome number in several lineages. A minimum of five host-plant switches from the ancestral state inferred at the family level and two at the subclass level suggests the absence of parallel evolution of beetles and their host plants. Another switch leading to oligophagy at the family level was deduced to have occurred in the lineage of the subgenus Chrysolina s.str. Received: 22 May 1998 / Accepted: 16 September 1998     

Pattern and process in the evolution of insect-plant associations: Yponomeuta as an example

Phylogenetic studies are increasing our understanding of the evolution of associations between phytophagous insects and their host plants. Sequential evolution, i.e. the shift of insect herbivores onto pre-existing plant species, appears to be much more common than coevolution, where reciprocal selection between interacting insects and plants is thought to induce chemical diversification and resistance in plants and food specialization in insects.Extreme host specificity is common in phytophagous insects and future studies are likely to reveal even more specialization. Hypotheses that assume that food specialists have selective advantages over generalists do not seem to provide a general explanation for the ubiquity of specialist insect herbivores. Specialists are probably committed to remain so, because they have little evolutionary opportunity to reverse the process due to genetically determined constraints on the evolution of their physiology or nervous system. The same constraints might result in phylogenetic conservatism, i.e. the frequent association of related insect herbivores with related plants. Current phylogenetic evidence, however, indicates that there is no intrinsic direction to the evolution of specialization.Historical aspects of insect-host plant associations will be illustrated with the small ermine moth genus Yponomeuta. Small ermine moths show an ancestral host association with the family Celastraceae. The genus seems to be committed to specialization per se rather than to a particular group of plants. Whatever host shift they have made in their evolutionary past (onto Rosaceae, Crassulaceae, and Salicaceae), they remain monophagous. The oligophagous Y. padellus is the only exception. This species might comprise a mosaic of genetically divergent host-associated populations.     

Rhododrilus sexpapillatus n.sp. (Oligochaeta: Megascolecidae) from New Zealand

Abstract

A new earthworm species belonging to the acanthodriline genus Rhododrilus is described from the North Island of New Zealand, elevating the generic total (excluding Australian forms) to 30 species. The new taxon forms part of the species-group with incomplete fusion of the male and prostatic terminalia. Its most closely related congener is the geographically proximate R. papaensis. Though exhibiting great heterogeneity, suggestive of polyphyly, the genus remains taxonomically convenient. It probably encompasses convergent forms, the ancestral affinities of which may never be ascertained.     

Molecular phylogeny of the entomopathogenic fungi of the genus Cordyceps (Ascomycota: Clavicipitaceae) and its evolutionary implications

Abstract Cordyceps is an endoparasite ascomycetous genus containing approximately 450 species with a diversity of insect hosts, traditionally included in the family Clavicipitaceae of Ascomycota. Establishing the relationships among species with a varied range of morphologies and hosts is of importance to our understanding of the phylogeny and co‐evolution of parasites and hosts in entomopathogenic ascomycetes. To this end, we used a combination of molecular index and morphological characters from 40 representative species to carry out comprehensive molecular phylogenetic analyses. Based on the phylogenetic tree, we used the program DISCRETE for inferring the rates of evolution and finding ancestral states of morphological character. The phylogenetic analyses revealed two important points. (i) Types of perithecia attached to stroma reflected an evolutionary trend in Cordyceps. The vertically immersed perithecia form was the ancestral state, superficial and obliquely immersed perithecia were derived characters, obliquely immersed was irreversible. Species with obliquely immersed perithecia were in a closely related group and were the derived group. (ii) A strong correlation between fungal relatedness and the microhabitat supported the hypothesis that the host jumps through commingling in soil microhabitats. Based on the results of these analyses, host switching explains the diversity of entomopathogenic fungi of the genus Cordyceps.     

Sequential evolution of Euphilotes (Lycaenidae: Scolitantidini) on their plant host Eriogonum (Polygonaceae: Eriogonoideae)

The relationship between the butterfly genus Euphilotes and their host plant genus Eriogonum in western North America is suggested to be one of sequential evolution rather than coevolution. Eriogonum, a genus of nearly 250 species, probably had a Miocene origin, but has had its modern distribution significantly influenced by recent Pleistocene glaciation. The evolution of Euphilotes, as a distinct genus of four sibling species, apparently postdates the establishment and recent proliferation of Eriogonum. Successful speciation in Euphilotes has been accomplished mainly through modifications in genitalia of those butterflies using a single species of Eriogonum. The subsequent proliferation of Euphilotes subspecies has been the result of host switching coupled with geographic isolation onto individual species of Eriogonum acting as restricted biogeographic islands. In the first instance, direct evolutionary competition for a limited resource (one species of Eriogonum) leads to partitioning of that resource by the butterflies whose entire life cycle is associated with that plant species. In the second instance, host switching and isolation have permitted establishment of minor subspecies without significant interaction with other subspecies of the same species. In instances where interspecific subspecies competition exists, resource partitioning, coupled with more pronounced genetic isolation, seem to have occurred resulting in more readily distinct subspecies. We speculate that the success of subspeciation in Euphilotes is dependent upon the numeric size and geographic extent of the host species. Euphilotes subspecies on plants of restricted distributions are themselves seemingly limited in their evolutionary potential as the most dynamic evolution of Euphilotes subspecies is that associated with widespread and variable Eriogonum species. In all instances, the tempo and mode of evolution in Euphilotes appears to be sequential as it follows and is seemingly dependent upon what has already occurred in Eriogonum.     

Phylogenetic evidence for the evolution of ecological specialization in Timema walking‐sticks

We used phylogenetic and ecological information to study the evolution of host‐plant specialization and colour polymorphism in the genus Timema, which comprises 14 species of walking‐sticks that are subject to strong selection for cryptic coloration on their host‐plants. Phylogenetic analysis indicated that this genus consists of three main lineages. Two of the lineages include highly generalized basal species and relatively specialized distal species, and one of the lineages comprises four specialized species. We tested for phylogenetic conservatism in the traits studied via randomizing host‐plant use, and the four basic Timema colour patterns, across the tips of the phylogeny, and determining if the observed number of inferred changes was significantly low compared to the distribution of numbers of inferred changes expected under the null model. This analysis showed that (1) host‐plant use has evolved nonrandomly, such that more closely related species tend to use similar sets of hosts and (2) colour pattern evolution exhibits considerable lability. Inference of ancestral states using maximum parsimony, under four models for the relative ease of gain and loss of plant hosts or colour morphs, showed that (1) for all models with gains of host‐plants even marginally more difficult than losses, and for most optimizations with gains and losses equally difficult, the ancestral Timema were generalized, feeding on the chaparral plants Ceanothus and Adenostoma and possibly other taxa, and (2) for all models with gains of colour morphs more difficult than losses, the ancestral Timema were polymorphic for colour pattern. Generation of null distributions of inferred ancestral states showed that the maximum‐parsimony inference of host‐plant generalization was most robust for the most speciose of the three main Timema lineages. Ancestral states were also inferred using maximum likelihood, after recoding host‐plant use and colour polymorphism as dichotomous characters. Likelihood analyses provided some support for inference of generalization in host‐plant use at ancestral nodes of the two lineages exhibiting mixtures of generalists and specialists, although levels of uncertainty were high. By contrast, likelihood analysis did not estimate ancestral colour morph patterns with any confidence, due to inferred rates of change that were high with respect to speciation rates. Information from biogeography, floristic history and the timing of diversification of the genus are compatible with patterns of inferred ancestral host‐plant use. Diversification in the genus Timema appears to engender three main processes: (1) increased specialization via loss of host‐plants, (2) retention of the same, single, host‐plant and (3) shifts to novel hosts to which lineages were ‘preadapted’ in colour pattern. Our evidence suggests that the radiation of this genus has involved multiple evolutionary transitions from individual‐level specialization (multiple‐niche polymorphism) to population‐level and species‐level specialization. Ecological studies of Timema suggest that such transitions are driven by diversifying selection for crypsis. This paper provides the first phylogeny‐based evidence for the macroevolutionary importance of predation by generalist natural enemies in the evolution of specialization.     

A new species Megabruchidius sophorae (Coleoptera, Bruchidae), feeding on seeds of Styphnolobium (Fabaceae) new to Bruchidae

A new species Megabruchidiussophorae (Insecta, Coleoptera) is described from Japan (Honshu). The larval host of this bruchid is the seeds of the tree legume 'enju', or chinese scholar tree, Styphnolobium japonicum (a senior synonym of Sophora japonica), which is a new host genus to Bruchidae. Styphnolobium is positioned basally in molecular phylogeny of the leguminous subfamily Papilionoideae. Other members of Megabruchidius are known to feed on Gleditsia, the tree legumes that belong to the most ancestral subfamily Caesalpinioideae. Therefore, Megabruchidius utilizes ancestral groups of legumes as its host plants. Megabruchidius has been inferred to be ancestral, based on its behavior. The character state of the host for this third Megabruchidius species supports that the genus is ancestral, at least in the subfamily Bruchinae. We also reviewed the genera closely related to Megabruchidius, i.e., Bruchidius and Sulcobruchus in Bruchidini, and wrote a key to the species in the genus Megabruchidius.     

Evolutionary origin of a periodical mass‐flowering plant

The evolutionary origin of periodical mass‐flowering plants (shortly periodical plants), exhibiting periodical mass flowering and death immediately after flowering, has not been demonstrated. Within the genus Strobilanthes (Acanthaceae), which includes more than 50 periodical species, Strobilanthes flexicaulis on Okinawa Island, Japan, flowers gregariously every 6 years. We investigated the life history of S. flexicaulis in other regions and that of closely related species together with their molecular phylogeny to reveal the evolutionary origin of periodical mass flowering. S. flexicaulis on Taiwan Island was found to be a polycarpic perennial with no mass flowering and, in the Yaeyama Islands, Japan, a monocarpic perennial with no mass flowering. Molecular phylogenetic analyses indicated that a polycarpic perennial was the ancestral state in this whole group including S. flexicaulis and the closely related species. No distinctive genetic differentiation was found in S. flexicaulis among all three life histories (polycarpic perennial, monocarpic perennial, and periodical plant). These results suggest that among S. flexicaulis, the periodical mass flowering on Okinawa Island had evolved from the polycarpic perennial on Taiwan Island via the monocarpic perennial in the Yaeyama Islands. Thus, the evolution of life histories could have taken at the level of local populations within a species.     

Chromosome evolution and phylogeny in Ronderosia (Orthoptera,Acrididae, Melanoplinae): clues of survivors to the challenge of sympatry?

In an attempt to unveil the origin of neo‐sex chromosomes in Ronderosia Cigliano grasshoppers, we performed a combined phylogenetic analysis based on morphological (external morphology and male genitalia) and molecular data (COI, COII, 16S and ITS2) to explore the chromosome evolution within the genus. We also analysed the distributional patterns of the various Ronderosia species and considered the possible role of chromosome rearrangements (CRs) in speciation processes within the genus in the light of ‘suppressed‐recombination’ models. We mapped the states of three chromosomal characters on the combined tree topology. The combined evidence supported Ronderosia as a monophyletic group. The cytogenetic analyses of the genus demonstrated the importance of rearranged karyotypes with single, complex and multiples neo‐sex chromosome determination systems in all species. The chromosome character optimisation suggests X‐autosome centric fusion as the mechanism responsible for neo‐sex chromosome formation in most Ronderosia species, except in R. dubia and R. bergii. Similar autosomes were involved in fusions with the ancestral X chromosome in Ronderosia, supporting previous hypotheses on the unique origin of X‐autosome fusion for the sex chromosome in the genus. As a source of chromosome variation, autosome‐autosome centric fusion played a secondary role in Ronderosia compared with other Dichroplini. Given the homogeneity in the morphological features, the sympatric distribution of closely related species and the intrinsic property of centric fusion as suppressors of the crossing over, we suggest that CRs may have played a key role during the speciation process within Ronderosia.     

Comprehensive molecular phylogenetic analysis and evolution of the genus Phyllactinia (Ascomycota: Erysiphales) and its allied genera

Phyllactinia is a unique genus within the Erysiphales (Ascomycota) having a partly endo-parasitic nature of the mycelium within the host plant tissues. We constructed phylogenetic trees for the genus Phyllactinia and its allied genera based on a total of 120 nucleotide sequences of the 28S rDNA and ITS regions to discuss their phylogenetic relationships with special references to host plants, biogeography, evolutionary dating, and taxonomy. The analysis of the Erysiphales confirmed the monophyly of the endo-parasitic genera, i.e. Leveillula, Phyllactinia, and Pleochaeta. Phyllactinia specimens used in this study were divided into six distinctive groups and three subgroups. Interestingly, Leveillula, an obligately endo-parasitic genus of the Erysiphales, grouped together with Phyllactinia, although this was not significantly supported by the Kishino–Hasegawa and Shimodaira–Hasegawa tests. This suggests that the evolution within this group of fungi occurred from partial endo-parasitism to obligate endo-parasitism. The host range of Phyllactinia is mostly confined to woody plants, especially deciduous trees. Betulaceae, Fagaceae, Ulmaceae, Moraceae, and Rosaceae may have close connections to the divergence of the groups and subgroups of Phyllactinia concerned. Most of these plant families are known as major members of the boreotropical flora of the Tertiary, which suggests an early Tertiary origin of this genus. A comparison of the phylogenies of hosts and parasites revealed that host range expansion at higher taxonomic levels (higher than family level) is independent of the phylogeny of plants. Conversely, host range expansions in lower taxonomic levels (infrafamilial or infrageneric) tend to occur within a single family or genus. An estimation of the evolutionary timing using a molecular clock approach suggested that Phyllactinia split from Pleochaeta about 60 M years ago (Ma) in the early Tertiary and divergence of the six major clades of Phyllactinia occurred between 5 and 40 Ma during the Oligocene and Miocene. Divergence within the major clades and within Leveillula occurred maybe from more than 5 Ma onwards during the Pliocene and Quaternary. This is the first comprehensive phylogenetic study of Phyllactinia and other endo-parasitic genera of the Erysiphales.     

OBSERVATIONS ON ROOT-PARASITISM IN CORDYLANTHUS (SCROPHULARIACEAE)

Eight species of Cordylanthus (Scrophulariaeeae: tribe Euphrasieae) representing the three major sections of the genus were successfully grown both with and without a host plant, demonstrating that the plants are facultative hemi-parasites capable of completing their life cycle without a host under the favorable conditions of greenhouse culture. The plants are almost certainly parasitic in the wild. Even though haustorial connections were formed by Cordylanthus on the roots of all host plants provided, most species were more vigorous when growing with certain hosts (Quercus, Pinus, Helianthus) than with others (Plantago, Phleum). This indicates a difference in the ability of the parasite to obtain materials successfully from the various plants used as hosts. Natural hosts are inferred for 15 species of Cordylanthus from the presence of associated species in nature. The haustoria are exogenous in origin, being formed by dedifferentiation of several cells in the hypo-dermal or subhypodermal layers of the rootlets. Anatomically the haustoria differ from those reported for other members of Euphrasieae in having secondary vascular structure and abundant connecting strands. The vascular structure of haustoria is composed mainly of specialized vessel elements. Root-parasitism gives Cordylanthus the ability to grow in arid areas during the summer after most other annuals have died, thus successfully equipping the plants for survival and expansion in western North America.     

Genome size shifts: karyotype evolution in Crepis section Neglectoides (Asteraceae)

Plant genome size evolution is a very dynamic process: the ancestral genome of angiosperms was initially most likely small, which led to a tendency towards genome increase during evolution. However, findings in several angiosperm lineages demonstrate mechanisms that also led to genome size contraction. Recent molecular investigations on the Asteraceae genus Crepis suggest that several genomic reduction events have occurred during the evolution of the genus. This study focuses on the Mediterranean Crepis sect. Neglectoides, which includes three species with some of the smallest genomes within the whole genus. Crepis neglecta has the largest genome in sect. Neglectoides, approximately twice the size of the two species Crepis cretica and Crepis hellenica. Whereas C. cretica and C. hellencia are more closely related to each other than to C. neglecta the karyotypes of the latter species and C. cretica are similar, while that of C. hellenica differs considerably. Here, the karyotypic organisation of the three species is investigated with fluorescence in‐situ hybridisation and studied in a molecular phylogenetic framework based on the nuclear markers Actin, CHR12, CPN60B, GPCR1 and XTH23. Our findings further corroborate the occurrence of genome size contraction in Crepis, and suggest that the difference in genome size between C. neglecta and C. cretica is mostly due to elimination of dispersed repetitive elements, whereas chromosomal reorganisation was involved in the karyotype formation of C. hellenica.     

Genetic differentiation,polyploidization and hybridization in northern EuropeanDactylorhiza (Orchidaceae): Evidence from allozyme markers

Taxa endemic to North-western Europe are rare, but the orchid genusDactylorhiza contains several species restricted to this area. Evidence from morphological and cytological studies have indicated that some species may have arisen recently and may be of hybrid origin. In the present report, I use allozymes to characterize the genomes in various species ofDactylorhiza and evaluate the possibilities for rapid evolutionary change in the genus. Allotetraploid species have evolved repeatedly from two principal diploid ancestral lineages. These lineages include extant diploid and autotetraploid species, from which allotetraploid derivatives may still arise. It is suggested that allotetraploidization dominates over introgression as speciation mechanism in the genus. The more common and widespread allotetraploid species could be characterized by their allozyme characters over considerable distances, indicating that each of them may have a unique origin and that they have spread from their ancestral populations to the present distribution areas. However, it is also possible that some allotetraploid species contain local populations that have been independently derived from the ancestral lineages.     

PHYLOGENY OF THE TRIBE CERATAPHIDINI (HOMOPTERA) AND THE EVOLUTION OF THE HORNED SOLDIER APHIDS

The horned soldier aphids of the Cerataphidini, unlike most social insects that reside in nests, live on the open surface of plants. The lack of a nest and other obvious ecological correlates makes it unclear why secondary-host soldiers might have evolved. Here I present a molecular phylogenetic analysis of 32 species of the Cerataphidini, including 10 species from the genera Ceratovacuna and Pseudoregma that produce horned soldiers. The phylogeny suggests that horned soldiers evolved once and were lost once or twice. Most horned soldiers are a morphologically specialized caste and two species that have unspecialized soldiers are independently derived from species with specialized castes. The genus Ceratovacuna appears to have undergone a relatively rapid radiation. Mapping secondary-host plants and geographic ranges onto the phylogeny suggests that bamboos were the ancestral secondary-host plants and that the Asian tropics and subtropics were the ancestral geographic regions for the genera Astegopteryx, Ceratoglyphina, Ceratovacuna Chaitoregma, and Pseudoregma and possibly for the entire tribe. There is evidence for vicariant events that separate the tropical and subtropical lineages in all of the major lineages of the tribe and for dispersal of some lineages. Based on these results, I present hypotheses for the causes and consequences of horned-soldier evolution.     

Reconstruction of ancestral karyotype illuminates chromosome evolution in the genus Cucumis

Karyotype dynamics driven by complex chromosome rearrangements constitute a fundamental issue in evolutionary genetics. The evolutionary events underlying karyotype diversity within plant genera, however, have rarely been reconstructed from a computed ancestral progenitor. Here, we developed a method to rapidly and accurately represent extant karyotypes with the genus, Cucumis, using highly customizable comparative oligo-painting (COP) allowing visualization of fine-scale genome structures of eight Cucumis species from both African-origin and Asian-origin clades. Based on COP data, an evolutionary framework containing a genus-level ancestral karyotype was reconstructed, allowing elucidation of the evolutionary events that account for the origin of these diverse genomes within Cucumis. Our results characterize the cryptic rearrangement hotspots on ancestral chromosomes, and demonstrate that the ancestral Cucumis karyotype (n = 12) evolved to extant Cucumis genomes by hybridizations and frequent lineage- and species-specific genome reshuffling. Relative to the African species, the Asian species, including melon (Cucumis melo, n = 12), Cucumis hystrix (n = 12) and cucumber (Cucumis sativus, n = 7), had highly shuffled genomes caused by large-scale inversions, centromere repositioning and chromothripsis-like rearrangement. The deduced reconstructed ancestral karyotype for the genus allowed us to propose evolutionary trajectories and specific events underlying the origin of these Cucumis species. Our findings highlight that the partitioned evolutionary plasticity of Cucumis karyotype is primarily located in the centromere-proximal regions marked by rearrangement hotspots, which can potentially serve as a reservoir for chromosome evolution due to their fragility.     

Using chromosomal data in the phylogenetic and molecular dating framework: karyotype evolution and diversification in Nierembergia (Solanaceae) influenced by historical changes in sea level

Karyotype data within a phylogenetic framework and molecular dating were used to examine chromosome evolution in Nierembergia and to infer how geological or climatic processes have influenced in the diversification of this solanaceous genus native to South America and Mexico. Despite the numerous studies comparing karyotype features across species, including the use of molecular phylogenies, to date relatively few studies have used formal comparative methods to elucidate chromosomal evolution, especially to reconstruct the whole ancestral karyotypes. Here, we mapped on the Nierembergia phylogeny one complete set of chromosomal data obtained by conventional staining, AgNOR‐, C‐ and fluorescent chromosome banding, and fluorescent in situ hybridisation. In addition, we used a Bayesian molecular relaxed clock to estimate divergence times between species. Nierembergia showed two major divergent clades: a mountainous species group with symmetrical karyotypes, large chromosomes, only one nucleolar organising region (NOR) and without centromeric heterochromatin, and a lowland species group with asymmetrical karyotypes, small chromosomes, two chromosomes pairs with NORs and centromeric heterochromatin bands. Molecular dating on the DNA phylogeny revealed that both groups diverged during Late Miocene, when Atlantic marine ingressions, called the ‘Paranense Sea’, probably forced the ancestors of these species to find refuge in unflooded areas for about 2 Myr. This split agrees with an increased asymmetry and heterochromatin amount, and decrease in karyotype length and chromosome size. Thus, when the two Nierembergia ancestral lineages were isolated, major divergences occurred in chromosomal evolution, and then each lineage underwent speciation separately, with relatively minor changes in chromosomal characteristics.     

Evolution of the male genitalia in the genus Limnebius Leach, 1815 (Coleoptera,Hydraenidae)

We investigated the evolution of the male genitalia of species of Limnebius (Coleoptera, Hydraenidae). This genus is very homogeneous externally but characterized by highly diverse male genitalia, which are in some cases extraordinarily complex. We reconstructed a molecular phylogeny for 70 of the c. 150 known species of the genus with six fragments of mitochondrial and nuclear genes. We found two main lineages of Miocene origin, largely corresponding to the synonymized subgenera Bilimneus and Limnebius, which are here re‐erected. Within the Holarctic Limnebius s.s. we found four well‐supported lineages, although with poorly supported relationships between them: the L. piceus, L. gracilipes, L. parvulus and L. nitidus species groups. We describe the aedeagus and its different appendages in detail based on the study of 116 species, including serial histological sections to reconstruct the internal structure of seven of them. Using Bayesian methods we reconstructed the ancestral Limnebius as having small males (c. 1.2 ± 0.5 mm), with a small aedeagus (c. 0.4 ± 0.3 mm) with a free left paramere, probably an externally fused right paramere, and a possible additional appendage. The species of Bilimneus experienced a reduction in size and a simplification of their genitalia, without free parameres and with a very simple, homogenous structure. Within Limnebius s.s. several independent increases in male body and genital size took place, with a strong correlation as measured with independent contrasts. There was, however, no overall correlation between genital size and number of appendages, even though smaller genitalia tend to be less complex.     

Evolutionary lability of a complex life cycle in the aphid genus <Emphasis Type="Italic">Brachycaudus</Emphasis>

Background  

Most aphid species complete their life cycle on the same set of host-plant species, but some (heteroecious species) alternate between different hosts, migrating from primary (woody) to secondary (herbaceous) host plants. The evolutionary processes behind the evolution of this complex life cycle have often been debated. One widely accepted scenario is that heteroecy evolved from monoecy on woody host plants. Several shifts towards monoecy on herbaceous plants have subsequently occurred and resulted in the radiation of aphids. Host alternation would have persisted in some cases due to developmental constraints preventing aphids from shifting their entire life cycle to herbaceous hosts (which are thought to be more favourable). According to this scenario, if aphids lose their primary host during evolution they should not regain it. The genus Brachycaudus includes species with all the types of life cycle (monoecy on woody plants, heteroecy, monoecy on herbs). We used this genus to test hypotheses concerning the evolution of life cycles in aphids.