Skeletogenic heterochronies have gained much attention in comparative developmental biology. The temporal appearance of mineralized individual bones in a species – the species ossification sequence – is an excellent marker in this kind of study. Several publications describe interspecific variation, but only very few detail intraspecific variation. In this study, we describe and analyze the temporal order of ossification of skeletal elements in the zebra finch, Taeniopygia guttata, the Japanese quail, Coturnix coturnix japonica, and the White Pekin duck, a domestic race of the mallard Anas platyrhynchos, and explore patterns of intraspecific variation in these events. The overall sequences were found to be conserved. In the duck, variability is present in the relative timing of ossification in the occipital, the basisphenoid and the otic regions of the skull and the phalanges in the postcranium. This variation appears generally in close temporal proximity. Comparison with previously published data shows differences in ossification sequence in the skull, the feet, and the pelvis in the duck, and especially the pelvis in the quail. This clearly documents variability among different breeds.

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Maternally transmitted reproductive parasites such as Wolbachia and Cardinium can drastically reshape reproduction in their hosts. Beyond skewing sex ratios towards females, these microbes can also cause cytoplasmic incompatibility. Wolbachia probably infects two thirds of insects, but far less is known about the occurrence or action of other bacteria with potentially similar effects. In contrast with the two more widespread reproductive parasites, Wolbachia and Spiroplasma, far less is known of infections with Cardinium (Bacteroidetes) and possible consequences in the Diptera. Here, in an extensive survey, 244 dipteran species from 67 genera belonging to the Dolichopodidae, Empididae, and Hybotidae were assessed for the presence of the microbe Cardinium. Although 130 of the species screened tested positive (ca. 53%), the presence of Cardinium could only be confirmed in 10 species (ca. 4%) based on analysis of sequences. Numerous additional sequences were found to be assignable to known or unknown Bacteroidetes.Considering the known issues concerning specificity of Cardinium primers and the phylogenetic uncertainties surrounding this microbe, the actual prevalence of this symbiont is worthy of further scrutiny. Potential directions for future research on Cardinium-host interactions in Diptera and in general are discussed.

1. In solitary parasitoids, only one individual can complete development in a given host. Therefore, solitary parasitoids tend to prefer unparasitised hosts for oviposition, yet under high parasitoid densities, superparasitism is frequent and results in fierce competition for the host's limited resources. This may lead to selection for the best intra-host competitors. 2. Increased intra-host competitive ability may evolve under a high risk of superparasitism if this trait exhibits genetic variation, and if competitive differences among parasitoid genotypes are consistent across environments, e.g. different host genotypes. 3. These assumptions were addressed in the aphid parasitoid Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) and its main host, the black bean aphid, Aphis fabae (Scopoli) (Hemiptera: Aphididae). Three parthenogenetic lines of L. fabarum were allowed to parasitise three aphid clones singly and in all pairwise combinations (superparasitism). The winning parasitoid in superparasitised aphids was determined by microsatellite analysis. 4. The proportions of singly parasitised aphids that were mummified were similar for the three parasitoid lines and did not differ significantly among host clones. 5. Under superparasitism, significant biases in favour of one parasitoid line were observed for some combinations, indicating that there is genetic variation for intra-host competitive ability. However, the outcome of superparasitism was inconsistent across aphid clones and thus influenced significantly by the host clone in which parasitoids competed. 6. Overall, this study shows that the fitness of aphid parasitoids under superparasitism is determined by complex interactions with competitors as well as hosts, possibly hampering the evolution of improved intra-host competitive ability.