Publications by EEOB faculty to 03 April 2014

April 4, 2014

This wasp parasitizes the eggs of an intertidal spider along the Atlantic coast of South Africa near the Cape of Good Hope. The spider lays its eggs under limpet shells that are attached to the rocks. Every high tide they go under water, but keep that air bubble beneath the shell. Credit: Simon van Noort, Iziko Museums of Cape Town.

Systematics and biology of the aberrant intertidal parasitoid wasp Echthrodesis lamorali Masner (Hymenoptera, Platygastridae s.l.): a parasitoid of spider eggs

van Noort, S., L. Masner, O. Popovici, A.A. Valerio, C. Taekul, N.F. Johnson, N.P. Murphy and A.D. Austin. 2014. Invertebrate Systematics 28, 1-16. DOI: 10.1071/IS13015

Abstract The platygastroid wasp Echthrodesis lamorali has been of considerable interest since its description in 1968, primarily because of its highly modified, densely pilose, wingless body, its distribution and unusual biology. The species is endemic to the Cape Peninsula, South Africa, where it is an endoparasitoid of eggs of the marine spiders Desis formidabilis (Desidae) and Amaurobioides africanus (Anyphaenidae) in the intertidal region. Although a highly aberrant monospecific genus, the phylogenetic relationships of Echthrodesis are confused, in part due to convergence in body form across numerous unrelated platygastroid genera. We used sequence data from the nuclear 28S rRNA and 18S rDNA genes, and the mitochondrial cytochrome oxidase 1 (CO1) gene, to determine the phylogenetic affinities of E. lamorali. We present a revised taxonomic description for the genus and species, as well as new morphological information on the structure of its mouthparts and ovipositor system. Phylogenetic analyses of molecular data place E. lamorali within one of two independent clades of platygastroid wasps that use spider eggs as hosts. Echthrodesis is sister to a group of three genera: Neobaeus (New Zealand; host unconfirmed); Mirobaeoides (Australia; spider eggs); and Embidobia (near cosmopolitan; embiid eggs). Details on the biology, behaviour and morphological adaptations of E. lamorali are provided.

Johnson lab


A taxonomic issue of two species of Trissolcus (Hymenoptera: Platygastridae) parasitic on eggs of the brown-winged green bug, Plautia stali (Hemiptera: Pentatomidae): resurrection of T. plautiae, a cryptic species of T. japonicus revealed by morphology, reproductive isolation and molecular evidence

Matsuo, K., Y. Hirose and N.F. Johnson. 2014. Applied Entomology and Zoology in press. DOI: 10.1007/s13355-014-0260-4

Abstract Trissolcus plautiae (Watanabe) is known as a major egg parasitoid of the brown-winged green bug Plautia stali Scott, which is a serious pest of various fruit trees in Japan. Although T. plautiae was synonymized with T. japonicus (Ashmead) in 1981, both scientific names have been used for the same egg parasitoid of P. stali for about the past 30 years because of their taxonomic confusion. To promote an effective IPM program for P. stali using its egg parasitoids, we attempted to resolve the confusion by the use of a variety of methods. On detailed observation of adult morphology, we found that sublateral setae on the T1 are present in T. plautiae and absent in T. japonicus, and that this morphological difference is corroborated by more subtle differences between the two species. This finding supports the view that they are different species. The view was also supported by the results of mating experiments to determine the reproductive isolation of T. plautiae from T. japonicus and DNA analysis of these two species. We conclude that T. plautiae is a cryptic species of T. japonicus and resurrect T. plautiae from T. japonicus stat. rev.

Johnson lab


Coexistence of minicircular and a highly rearranged mtDNA molecule suggests that recombination shapes mitochondrial genome organization

Mao, M., A.D. Austin, N.F. Johnson and M. Dowton. 2014. Molecular Biology and Evolution 31, 636-644. DOI: 10.1093/molbev/mst255

Abstract Recombination has been proposed as a possible mechanism to explain mitochondrial (mt) gene rearrangements, although the issue of whether mtDNA recombination occurs in animals has been controversial. In this study, we sequenced the entire mt genome of the megaspilid wasp Conostigmus sp., which possessed a highly rearranged mt genome. The sequence of the A+T-rich region contained a number of different types of repeats, similar to those reported previously in the nematode Meloidogyne javanica, in which recombination was discovered. In Conostigmus, we detected the end products of recombination: a range of minicircles. However, using isolated (cloned) fragments of the A+T-rich region, we established that some of these minicircles were found to be polymerase chain reaction (PCR) artifacts. It appears that regions with repeats are prone to PCR template switching or PCR jumping. Nevertheless, there is strong evidence that one minicircle is real, as amplification primers that straddle the putative breakpoint junction produce a single strong amplicon from genomic DNA but not from the cloned A+T-rich region. The results provide support for the direct link between recombination and mt gene rearrangement. Furthermore, we developed a model of recombination which is important for our understanding of mtDNA evolution

Johnson lab


Monograph of the Afrotropical species of Scelio Latreille (Hymenoptera: Platygastridae), egg parasitoids of acridid grasshoppers (Orthoptera: Acrididae)

Yoder, M.J., A.A. Valerio, A. Polaszek, S. van Noort, L. Masner and N.F. Johnson. 2014. ZooKeys 380, 1-188. DOI: 10.3897/zookeys.380.5755

Abstract The genus Scelio is a cosmopolitan and speciose group of solitary parasitoids of the eggs of short-horned grasshoppers (Orthoptera: Acrididae). A number of these hosts are important pests, including plague locusts of the genus Schistocerca. Species of Scelio are recognized as potentially important biological control agents, but this possibility has yet to be fully realized, in part because the species-level taxonomy is still incompletely developed. The species of the pulchripennis group have been recently revised. As a continuation of this effort, here we revise the Afrotropical species of Scelio, excluding the pulchripennis species group. Sixty two (62) species are treated, 48 of which are new. Species are classified into the following species groups: ernstii (12 species, 9 new), howardi (23 species, 19 new), ipomeae (6 species, 5 new), irwini (4 species, 3 new), simoni (3 new species) and walkeri (12 species, 9 new). Keys to species groups and to the species within each group are provided. ... Digital versions of the identification keys are available at http://www.waspweb.org/Platygastroidea/Keys/index.htm.

Johnson lab


Physiological underpinnings associated with differences in pace of life and metabolic rate in north temperate and neotropical birds

Ana Gabriela Jimenez, Clara Cooper-Mullin, Elisabeth A. Calhoon, Joseph B. Williams. 2014. Journal of Comparative Physiology B, in press. DOI: 10.1007/s00360-014-0825-0

Abstract Animal life-history traits fall within limited ecological space with animals that have high reproductive rates having short lives, a continuum referred to as a 'slow-fast' life-history axis. Animals of the same body mass at the slow end of the life-history continuum are characterized by low annual reproductive output and low mortality rate, such as is found in many tropical birds, whereas at the fast end, rates of reproduction and mortality are high, as in temperate birds. These differences in life-history traits are thought to result from trade-offs between investment in reproduction or self-maintenance as mediated by the biotic and abiotic environment. Thus, tropical and temperate birds provide a unique system to examine physiological consequences of life-history trade-offs at opposing ends of the 'pace of life' spectrum. We have explored the implications of these trade-offs at several levels of physiological organization including whole-animal, organ systems, and cells. Tropical birds tend to have higher survival, slower growth, lower rates of whole-animal basal metabolic rate and peak metabolic rate, and smaller metabolically active organs compared with temperate birds. At the cellular level, primary dermal fibroblasts from tropical birds tend to have lower cellular metabolic rates and appear to be more resistant to oxidative cell stress than those of temperate birds. However, at the subcellular level, lipid peroxidation rates, a measure of the ability of lipid molecules within the cell membranes to thwart the propagation of oxidative damage, appear not to be different between tropical and temperate species. Nevertheless, lipids in mitochondrial membranes of tropical birds tend to have increased concentrations of plasmalogens (phospholipids with antioxidant properties), and decreased concentrations of cardiolipin (a complex phospholipid in the electron transport chain) compared with temperate birds.

Williams lab


Obligate insect endosymbionts exhibit increased ortholog length variation and loss of large accessory proteins concurrent with genome shrinkage

Laura J. Kenyon and Zakee L. Sabree. 2014. Genome Biology and Evolution in press. DOI: 10.1093/gbe/evu055

Abstract Extreme genome reduction has been observed in obligate intracellular insect mutualists and is an assumed consequence of fixed, long-term host isolation. Rapid accumulation of mutations and pseudogenization of genes no longer vital for an intracellular lifestyle, followed by deletion of many genes, are factors that lead to genome reduction. Size reductions in individual genes due to small-scale deletions have also been implicated in contributing to overall genome shrinkage. Conserved protein functional domains are expected to exhibit low-tolerance for mutations and therefore remain relatively unchanged throughout protein length reduction while non-domain regions, presumably under less selective pressures, would shorten. This hypothesis was tested using orthologous protein sets from the Flavobacteriaceae (phylum: Bacteroidetes) and Enterobacteriaceae (subphylum: Gammaproteobacteria) families, each of which includes some of the smallest known genomes. Upon examination of protein, functional domain, and non-domain region lengths, we found that proteins were not uniformly shrinking with genome reduction, but instead increased in length variability and variability was observed in both the functional domain and non-domain regions. Additionally, as complete gene loss also contributes to overall genome shrinkage, we found that the largest proteins in the proteomes of non-host-restricted bacteroidetial and gammaproteobacterial species often were inferred to be involved in secondary metabolic processes, extracellular sensing, or of unknown function. These proteins were absent in the proteomes of obligate insect endosymbionts. Therefore, loss of large proteins not required for host-restricted lifestyles in obligate endosymbiont proteomes likely contributes to extreme genome reduction to a greater degree than ortholog shrinkage.

Sabree lab