Biomedical subjects

P Mardulyn

Publications and source records attributed to P Mardulyn.

6 recordsLinked to original sources

PubMed2001

Phylogeography of the Vosges mountains populations of Gonioctena pallida (Coleoptera: Chrysomelidae): a nested clade analysis of mitochondrial DNA haplotypes.

The pattern of genetic variation in the leaf beetle Gonioctena pallida was investigated inside the Vosges mountains using a highly variable 363 bp DNA fragment of the mitochondrial control region. Sequencing of 242 individuals, sampled in a geographical area of 100 x 40 km, identified 61 haplotypes whose genealogy was inferred. The resulting haplotype network exhibits four star-like phylogenies, two of which may be indicative of a population having recently expanded in size from a small number of founders. Nested clade analysis suggested multiple past expansion events, but also isolation by distance and possibly past fragmentation events, as the causes of the detected geographical associations of haplotypes. These results indicate the existence of effective barriers to gene flow inside the investigated area. Because the oldest demographic events inferred in the nested clade analysis were identified as expansion events, we hypothesize that a small population of founders have expanded not only in size, but also in geographical range from the south towards the north and east of the Vosges.

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PubMed2001

Multiple molecular data sets suggest independent origins of highly eusocial behavior in bees (Hymenoptera:Apinae).

Different views of the pattern of social evolution among the highly eusocial bees have arisen as a result of discordance between past molecular and morphology-based phylogenies. Here we present new data and taxa for four molecular data sets and reassess the morphological characters available to date. We show there is no significant character incongruence between four molecular data sets (two nuclear and two mitochondrial), but highly significant character incongruence leads to topological incongruence between the molecular and morphological data. We investigate the effects of using different outgroup combinations to root the estimated tree. We also consider various ways in which biases in the sequence data could be misleading, using several maximum likelihood models, LogDet corrections, and spectral analyses. Ultimately, we concede there is strong discordance between the molecular and morphological data partitions and appropriately apply the conditional combination approach in this case. We also find two equally well supported placements of the root for the molecular trees, one supported by 16S and 28S sequences, the other supported by cytochrome b and opsin. The strength of the evidence leads us to accept two equally well supported hypotheses based on analyses of the molecular data sets. These are the most rigorously supported hypotheses of corbiculate bee relationships at this time, and frame our argument that highly eusocial behavior within the corbiculate bees evolved twice independently.

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PubMed2000

Myzostomida: a link between trochozoans and flatworms?

Myzostomids are obligate symbiotic invertebrates associated with echinoderms with a fossil record that extends to the Ordovician period. Due to their long history as host-specific symbionts, myzostomids have acquired a unique anatomy that obscures their phylogenetic affinities to other metazoans: they are incompletely segmented, parenchymous, acoelomate organisms with chaetae and a trochophore larva. Today, they are most often classified within annelids either as an aberrant family of polychaetes or as a separate class. We inferred the phylogenetic position of the Myzostomida by analysing the DNA sequences of two slowly evolving nuclear genes: the small subunit ribosomal RNA and elongation factor-1alpha. All our analyses congruently indicated that myzostomids are not annelids but suggested instead that they are more closely related to flatworms than to any trochozoan taxon. These results, together with recent analyses of the myzostomidan ultrastructure, have significant implications for understanding the evolution of metazoan body plans, as major characters (segmentation, coeloms, chaetae and trochophore larvae) might have been independently lost or gained in different animal phyla.

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PubMed1999

The major opsin in bees (Insecta: Hymenoptera): A promising nuclear gene for higher level phylogenetics.

We report the phylogenetic utility of the nuclear gene encoding the long-wavelength opsin (LW Rh) for tribes of bees. Aligned nucleotide sequences were examined in multiple taxa from the four tribes comprising the corbiculate bees within the subfamily Apinae. Phylogenetic analyses of sequence variation in a 502-bp fragment (approx 40% of the coding region) strongly supported the monophyly of each of the four tribes, which are well established from previous studies of morphology and DNA. Trees estimated from parsimony and maximum likelihood analyses of LW Rh sequences show a strongly supported relationship between the tribes Meliponini and Bombini, a relationship that has been found uniformly in studies of other genes (28S, 16S, and cytochrome b). All of the tribal clades as well as relationships among the tribes are supported by high bootstrap values, suggesting the utility of LW Rh in estimating tribal and subfamily rank for these bees. The sequences exhibit minimal base composition bias. Both 1st + 2nd and 3rd position sites provide information for estimating a reliable tree topology. These results suggest that LW Rh, which has not been reported previously in studies of organismal phylogenetics, could provide important new data from the nuclear genome for phylogeny reconstruction.

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PubMed1999

Phylogenetic signal in the COI, 16S, and 28S genes for inferring relationships among genera of Microgastrinae (Hymenoptera; Braconidae): evidence of a high diversification rate in this group of parasitoids.

The subfamily Microgastrinae is a highly diversified group of parasitoid wasps that attacks all of the different groups of Lepidoptera. We explore here the phylogenetic signal in three gene (mitochondrial COI and 16S, and nuclear 28S) fragments as an assessment of their utility in resolving generic relationships within this species-rich insect group. These genes were chosen because their level of sequence divergence is thought to be appropriate for this study and because they have resolved relationships among other braconid wasps at similar taxonomic levels. True phylogenetic signal, as opposed to random signal or noise, was detected in the 16S and 28S data sets. Phylogenetic analyses conducted on each microgastrine data set, however, have all resulted in poorly resolved trees, with most clades being supported by low bootstrap values. The phylogenetic signal, if present, is therefore concentrated on a few well-supported clades. Some rapidly evolving sites may be too saturated to be phylogenetically useful. Nonetheless, the sequence data (nearly 2300 nucleotides) used here appear to exhibit the appropriate level of variation, theoretically, to resolve the relationships studied. Moreover, the clades that are well supported by the data are usually supported by more than one data set and represent different levels of sequence divergence. We suggest that the lack of phylogenetic signal observed is an indication of the presence of many short internal branches on the phylogeny being estimated, which in turn might be the result of a rapid diversification of the taxa examined. Relative specialization of diet, which is typically associated with parasitic behavior, is believed to result in high radiation rates, which may have been especially high in microgastrine wasps because of the great diversity of their lepidopteran hosts. This hypothesis of a rapid diversification caused by an abundance of host species remains speculative and more data will be needed to test it further.

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PubMed1997

Phylogenetic analyses of DNA and allozyme data suggest that Gonioctena leaf beetles (Coleoptera; Chrysomelidae) experienced convergent evolution in their history of host-plant family shifts.

A phylogenetic analysis of the genus Gonioctena (Coleoptera, Chrysomelidae) based on allozyme data (17 loci) and mitochondrial DNA sequence data (three gene fragments, 1,391 sites) was performed to study the evolutionary history of host-plant shifts among these leaf beetles. This chrysomelid genus is characteristically associated with a high number of different plant families. The diverse molecular data gathered in this study are to a large extent congruent, and the analyses provide a well-supported phylogenetic hypothesis to address questions about the evolution of host-plant shifts in the genus Gonioctena. The most-parsimonious reconstruction of the ancestral host-plant associations, based on the estimated phylogeny, suggests that the Fabaceae was the ancestral host-plant family of the genus. Although most of the host-plant shifts (between different host species) in Gonioctena have occurred within the same plant family or within the same plant genus, at least eight shifts have occurred between hosts belonging to distantly related and chemically dissimilar plant families. In these cases, host shifts may have been simply directed toward plant species available in the environment. Yet, given that two Gonioctena lineages have independently colonized the same three new plant families (Salicaceae, Betulaceae, Rosaceae), including four of the same new genera (Salix, Alnus, Prunus, Sorbus), some constraints are likely to have limited the different possibilities of interfamilial host-plant shifts.

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