Reproductive interference and fecundity affect competitive interactions of sibling species with low mating barriers: experimental and theoretical evidence.

When allopatric species with incomplete prezygotic isolation come into secondary contact, the outcome of their interaction is not easily predicted. The parasitoid wasp Encarsia suzannae (iES), infected by Cardinium inducing cytoplasmic incompatibility (CI), and its sibling species E. gennaroi (EG), not infected by bacterial endosymbionts, may have diverged because of the complementary action of CI and asymmetric hybrid incompatibilities. Whereas postzygotic isolation is now complete because of sterility of F1 hybrid progeny, prezygotic isolation is still incipient. We set up laboratory population cage experiments to evaluate the outcome of the interaction between ES and EG in two pairwise combinations: iES vs EG and cured ES (cES, where Cardinium was removed with antibiotics) vs EG. We also built a theoretical model aimed at exploring the role of life-history differences and asymmetric mating on competitive outcomes. In three of four cages in each treatment, ES dominated the interaction. We found evidence for reproductive interference, driven by asymmetric mating preferences, that gave a competitive edge to ES, the species that better discriminated against heterospecifics. However, we did not find the fecundity cost previously shown to be associated with Cardinium infection in iES. The model largely supported the experimental results. The finding of only a slight competitive edge of ES over EG in population cages suggests that in a more heterogeneous environment the species could coexist. This is supported by evidence that the two species coexist in sympatry, where preliminary data suggest reproductive character displacement may have reinforced postzygotic isolation.

Characterization, distribution, biology and impact on Italian walnut orchards of the invasive North-American leafminer Coptodisca lucifluella (Lepidoptera: Heliozelidae).

The leafminer Coptodisca sp. (Lepidoptera: Heliozelidae), recently recorded for the first time in Europe on Italian black and common walnut trees, is shown to be the North-American Coptodisca lucifluella (Clemens) based on morphological (forewing pattern) and molecular (cytochrome oxidase c subunit I sequence) evidence. The phylogenetic relatedness of three species feeding on Juglandaceae suggests that C. lucifluella has likely shifted, within the same host plant family, from its original North-American hosts Carya spp. to Juglans spp. Over the few years since its detection, it has established in many regions in Italy and has become a widespread and dominant invasive species. The leafminer completes three to four generations per year, with the first adults emerging in April-May and mature larvae of the last generation starting hibernation in September-October. Although a high larval mortality was recorded in field observations (up to 74%), the impact of the pest was substantial with all leaves infested at the end of the last generation in all 3 years tested. The distribution of the leafminer in the canopy was homogeneous. The species is redescribed and illustrated, a lectotype is designated and a new synonymy is established.

Integration of molecular, ecological, morphological and endosymbiont data for species delimitation within the Pnigalio soemius complex (Hymenoptera: Eulophidae).

Integrative taxonomy is a recently developed approach that uses multiple lines of evidence such as molecular, morphological, ecological and geographical data to test species limits, and it stands as one of the most promising approaches to species delimitation in taxonomically difficult groups. The Pnigalio soemius complex (Hymenoptera: Eulophidae) represents an interesting taxonomical and ecological study case, as it is characterized by a lack of informative morphological characters, deep mitochondrial divergence, and is susceptible to infection by parthenogenesis-inducing Rickettsia. We tested the effectiveness of an integrative taxonomy approach in delimiting species within the P. soemius complex. We analysed two molecular markers (COI and ITS2) using different methods, performed multivariate analysis on morphometric data and exploited ecological data such as host-plant system associations, geographical separation, and the prevalence, type and effects of endosymbiont infection. The challenge of resolving different levels of resolution in the data was met by setting up a formal procedure of data integration within and between conflicting independent lines of evidence. An iterative corroboration process of multiple sources of data eventually indicated the existence of several cryptic species that can be treated as stable taxonomic hypotheses. Furthermore, the integrative approach confirmed a trend towards host specificity within the presumed polyphagous P. soemius and suggested that Rickettsia could have played a major role in the reproductive isolation and genetic diversification of at least two species.

A karyological study of the genus Pnigalio Schrank (Hymenoptera: Eulophidae): assessing the taxonomic utility of chromosomes at the species level.

We provide a karyological study of 12 species of the genus Pnigalio in an attempt to evaluate the taxonomic utility of karyotypes at the species level. For all species of Pnigalio examined the number of chromosome was 2n=12. Karyotype formulae presented mainly metacentric and submetacentric chromosomes, although a pair of acrocentrics or subtelocentrics, shorter than biarmed chromosomes, was present in some species. The analysis of karyotypes of Pnigalio showed frequent but not general interspecific variability of the chromosome traits. Although most of the studied species revealed concordance between morphological and karyological characters (centromeric index and relative length), two other categories have been identified: morphologically distinct species without reciprocal differences in karyotype structure, and morphologically similar species that strongly differ in chromosomal characters.

Rickettsia symbionts cause parthenogenetic reproduction in the parasitoid wasp Pnigalio soemius (Hymenoptera: Eulophidae).

Bacteria in the genus Rickettsia are intracellular symbionts of disparate groups of organisms. Some Rickettsia strains infect vertebrate animals and plants, where they cause diseases, but most strains are vertically inherited symbionts of invertebrates. In insects Rickettsia symbionts are known to have diverse effects on hosts ranging from influencing host fitness to manipulating reproduction. Here we provide evidence that a Rickettsia symbiont causes thelytokous parthenogenesis (in which mothers produce only daughters from unfertilized eggs) in a parasitoid wasp, Pnigalio soemius (Hymenoptera: Eulophidae). Feeding antibiotics to thelytokous female wasps resulted in production of progeny that were almost all males. Cloning and sequencing of a fragment of the 16S rRNA gene amplified with universal primers, diagnostic PCR screening of symbiont lineages associated with manipulation of reproduction, and fluorescence in situ hybridization (FISH) revealed that Rickettsia is always associated with thelytokous P. soemius and that no other bacteria that manipulate reproduction are present. Molecular analyses and FISH showed that Rickettsia is distributed in the reproductive tissues and is transovarially transmitted from mothers to offspring. Comparison of antibiotic-treated females and untreated females showed that infection had no cost. Phylogenetic analyses of 16S rRNA and gltA gene sequences placed the symbiont of P. soemius in the bellii group and indicated that there have been two separate origins of the parthenogenesis-inducing phenotype in the genus Rickettsia. A possible route for evolution of induction of parthenogenesis in the two distantly related Rickettsia lineages is discussed.