Identity and phylogenetic placement of Spirogyra species (Zygnematophyceae,Charophyta) from California streams and elsewhere1

Diversity of the filamentous green algae in the genus Spirogyra (Zygnematophyceae) was investigated from more than 1,200 stream samples from California. We identified 12 species of Spirogyra not previously known for California (CA), including two species new to science, Spirogyra californica sp. nov. and Spirogyra juliana sp. nov. Environmental preferences of the Californian species are discussed in the light of their restricted distribution to stream habitats with contrasting nutrient levels. We also investigated the systematic relationships of Spirogyra species from several continents using the chloroplast‐encoded genes ribulose‐1,5‐bisphosphate carboxylase/hydrogenase large subunit (rbcL) and the beta subunit of the ATP synthase (atpB). Californian species were positioned in most major clades of Spirogyra. The phylogeny of Spirogyra and its taxonomic implications are discussed, such as the benefits of combining structural and molecular data for more accurate and consistent species identification. Considerable infraspecific genetic variation of globally distributed Spirogyra species was observed across continental scales. This finding suggests that structurally similar species from distant regions may be genetically dissimilar and that Spirogyra may contain a large number of cryptic species. Correlating the morphological and genetic variation within the genus will be a major challenge for future researchers.     

Phylogenetic congruence between subtropical trees and their associated fungi

Recent studies have detected phylogenetic signals in pathogen–host networks for both soil‐borne and leaf‐infecting fungi, suggesting that pathogenic fungi may track or coevolve with their preferred hosts. However, a phylogenetically concordant relationship between multiple hosts and multiple fungi in has rarely been investigated. Using next‐generation high‐throughput DNA sequencing techniques, we analyzed fungal taxa associated with diseased leaves, rotten seeds, and infected seedlings of subtropical trees. We compared the topologies of the phylogenetic trees of the soil and foliar fungi based on the internal transcribed spacer (ITS) region with the phylogeny of host tree species based on matK, rbcL, atpB, and 5.8S genes. We identified 37 foliar and 103 soil pathogenic fungi belonging to the Ascomycota and Basidiomycota phyla and detected significantly nonrandom host–fungus combinations, which clustered on both the fungus phylogeny and the host phylogeny. The explicit evidence of congruent phylogenies between tree hosts and their potential fungal pathogens suggests either diffuse coevolution among the plant–fungal interaction networks or that the distribution of fungal species tracked spatially associated hosts with phylogenetically conserved traits and habitat preferences. Phylogenetic conservatism in plant–fungal interactions within a local community promotes host and parasite specificity, which is integral to the important role of fungi in promoting species coexistence and maintaining biodiversity of forest communities.     

A review of iguanian and anguimorph lizard genitalia (Squamata: Chamaeleonidae; Varanoidea, Shinisauridae, Xenosauridae, Anguidae) and their phylogenetic significance: comparisons with molecular data sets

We compare phylogenetic hypotheses for iguanian (chameleonids) and anguimorph lizard groups (varanoids, xenosauroids, anguids) which were generated from analyses of genital (hemipenial) morphology, with recent molecular phylogenetic approaches towards the same groups. Taxa with infraspecific communication by means of visible, sexually dimorphic epigamic characters usually have less diverse genital structures than taxa with less developed visible epigamic characters but with a more highly developed chemical intersexual communication. Generally, it turned out in the cases considered here, that phylogenetic hypotheses based on hemipenial characters coincide much better with molecular-genetic phylogenies than with earlier concepts based solely on external morphology. It seems that genital morphological characters are phylogenetically more informative – on both the species and the supraspecific level – than external morphological characters at least in these examples, because the former seem not to be affected by environmental selective pressures but seem to be only subject to sexual selection. Our data suggest that sexual selective pressure on genital structural diversity is higher the less sexually dimorphic, optical cues for infraspecific communication have evolved. They further suggest a correlation with the mating system (single versus multiple matings).     

Fitting models of continuous trait evolution to incompletely sampled comparative data using approximate Bayesian computation

In recent years, a suite of methods has been developed to fit multiple rate models to phylogenetic comparative data. However, most methods have limited utility at broad phylogenetic scales because they typically require complete sampling of both the tree and the associated phenotypic data. Here, we develop and implement a new, tree-based method called MECCA (Modeling Evolution of Continuous Characters using ABC) that uses a hybrid likelihood/approximate Bayesian computation (ABC)-Markov-Chain Monte Carlo approach to simultaneously infer rates of diversification and trait evolution from incompletely sampled phylogenies and trait data. We demonstrate via simulation that MECCA has considerable power to choose among single versus multiple evolutionary rate models, and thus can be used to test hypotheses about changes in the rate of trait evolution across an incomplete tree of life. We finally apply MECCA to an empirical example of body size evolution in carnivores, and show that there is no evidence for an elevated rate of body size evolution in the pinnipeds relative to terrestrial carnivores. ABC approaches can provide a useful alternative set of tools for future macroevolutionary studies where likelihood-dependent approaches are lacking.     

Molecular phylogenies reveal host-specific divergence of Ophiocordyceps unilateralis sensu lato following its host ants

Ophiocordyceps unilateralis (Hypocreales, Ascomycetes) is an entomopathogenic fungus specific to formicine ants (Formicinae, Hymenoptera). Previous works have shown that the carpenter ant Camponotus leonardi acts as the principal host with occasional infections of ants from the genus Polyrhachis (sister genus of Camponotus). Observations were made on the permanent plots of Mo Singto, Khao Yai National Park of Thailand according to which O. unilateralis was found to occur predominantly on three host species: C. leonardi, C. saundersi and P. furcata. Molecular phylogenies of the elongation factor 1-α and β-Tubulin genes indicate a separation of O. unilateralis samples into three clades, reflecting specificity to each of the three different ant species. Samples collected from P. furcata and from C. leonardi were found to form sister groups with samples from C. saundersi forming an outgroup to the latter. Additional samples collected from unidentified ant species of Camponotus and Polyrhachis were positioned as outgroups to those samples on identified species. These results demonstrate that O. unilateralis is clearly not a single phylogenetic species and comprises at least three species that are specific to different host ant species. These cryptic species may arise through recent events of speciation driven by their specificity to host ant species.     

Molecular phylogeny and historical biogeography of the large carpenter bees, genus Xylocopa (Hymenoptera: Apidae)

The biogeographical history of major groups of bees with worldwide distributions have often been explained through hypotheses based on Gondwanan vicariance or long distance dispersal events, but until recently these hypotheses have been very difficult, if not impossible, to distinguish. New fossil data, comprehensive information on Mesozoic and Cenozoic coastline positions and the availability of phylogenetically informative DNA markers now makes it feasible to test these hypotheses for some groups of bees. This paper presents historical biogeographical analyses of the genus Xylocopa Latreille, based on phylogenetic analyses of species belonging to 22 subgenera using molecular data from two nuclear genes, elongation factor‐1α (EF‐1α) and phosphoenolpyruvate carboxykinase (PEPCK), combined with previously published morphological and mitochondrial data sets. Phylogenetic analyses based on parsimony and likelihood approaches resulted in several groups of subgenera supported by high bootstrap values (>85%): an American group with the Oriental/Palaearctic subgenera Nyctomelitta and Proxylocopa as sister taxa; a geographically diverse group (Xylocopa s.l); and a group consisting of African and Oriental subgenera. The relationships among these three clades and the subgenus Perixylocopa remained unresolved. The Oriental subgenus Biluna was found to be the sister group of all other carpenter bee subgenera included in this study. Using a relaxed molecular clock calibrated using fossil carpenter bees, we show that the major splits in the carpenter bee phylogeny occurred well after the final breakup of Gondwanaland (the separation of South America and Africa, 100 Mya), but before important Miocene fusion events. Ancestral area analysis showed that the genus Xylocopa most likely had an Oriental‐Palaearctic origin and that the present world distribution of Xylocopa subgenera resulted mainly from independent dispersal events. The influence of Pleistocene glaciations on carpenter bee distributions is also discussed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77 , 249–266.     

MITOCHONDRIAL DNA PHYLOGENIES FOR THE DROSOPHILA OBSCURA GROUP

Species belonging to the obscura group of the genus Drosophila have long held a central position in evolutionary studies, especially in experimental population genetics. Despite the considerable amount of accumulated knowledge, many of the phylogenetic relationships of the species in the group remain unclear. Here we present DNA sequence data for the mitochondrial gene cytochrome oxidase I (COI) for 13 species native to both the Old and New Worlds. We combine these data with seven other mitochondrial gene sequences from previous studies, for a total of over 3 kb per species. Strongly supported conclusions include: (1) the two North American subgroups, pseudoobscura and affinis, are each monophyletic; and (2) among Eurasian species two unambiguous clades are identified, one containing D. tristis, D. ambigua, and D. obscura and the other containing D. guanche, D. subobscura, and D. madeirensis. Constructing firm hypotheses connecting these four major clades is problematic with all datasets. Major ambiguities are the number of invasions giving rise to the North American obscura species and the relationships among the Eurasian species. The inadequacy of the mtDNA data to resolve these ambiguities does not reside in lack of changes; the transversions-only parsimony tree has 283 informative characters. Rather, the problems are likely intrinsic to the history of the group: while radiating in temperate Eurasia, North America was colonized once or twice, followed by one or two radiations in the New World.     

Morphological evolution and genetic differentiation in Daphnia species complexes

Despite many ecological and evolutionary studies, the history of several species complexes within the freshwater crustacean genus Daphnia (Branchiopoda, Anomopoda) is poorly understood. In particular, the Daphnia longispina group, comprising several large-lake species, is characterized by pronounced phenotypic plasticity, many hybridizing species and backcrossing. We studied clonal assemblages from lakes and ponds comprising daphnids from several species complexes. In order to reveal patterns of reticulate evolution and introgression among species, we analysed three data sets and compared nuclear, mtDNA and morphological divergence using animals from 158 newly established clonal cultures. By examining 15 nuclear and 11 mitochondrial (12S/16S rDNA) genetic characters (allozymes/restriction enzymes), and 48 morphological traits, we found high clonal diversity and discontinuities in genotypic and morphological space which allowed us to group clones by cytonuclear differentiation into seven units (outgroup D. pulex). In contrast to six groups emerging from nuclear divergence (related to three traditional species, D. cucullata, D. galeata, D. hyalina and three pairwise intermediate hybrids), a seventh group of clones was clearly resolved by morphological divergence: distinct mtDNA haplotypes within one nuclear defined cluster, ‘D. hyalina’, resembled traditional D. hyalina and D. rosea phenotypes, respectively. In other nuclear defined clusters, association between mtDNA haplotype and morphology was low, despite hybridization being bidirectional (reciprocal crosses). Morphological divergence was greatest between young sister species which are separated on the lake/pond level, suggesting a significant role for divergent selection during speciation along with habitat shifts. Phylogenetic analyses were restricted to four cytonuclear groups of clones related to species. mtDNA and nuclear phylogenies were consistent in low genetic divergence and monophyly of D. hyalina and D. rosea. Incongruent patterns of phylogenies and different levels of genetic differentiation between traditional species suggest reticulate evolutionary processes.