Parthenogenesis: birth of a new lineage or reproductive accident?

Parthenogenesis - the ability to produce offspring from unfertilized eggs - is widespread among invertebrates and now increasingly found in normally sexual vertebrates. Are these cases reproductive errors or could they be a first step in the emergence of new parthenogenetic lineages

Evolution and comparative ecology of parthenogenesis in haplodiploid arthropods.

Changes from sexual reproduction to female-producing parthenogenesis (thelytoky) have great evolutionary and ecological consequences, but how many times parthenogenesis evolved in different animal taxa is unknown. We present the first exhaustive database covering 765 cases of parthenogenesis in haplodiploid (arrhenotokous) arthropods, and estimate frequencies of parthenogenesis in different taxonomic groups. We show that the frequency of parthenogenetic lineages extensively varies among groups (0-38% among genera), that many species have both sexual and parthenogenetic lineages and that polyploidy is very rare. Parthenogens are characterized by broad ecological niches: parasitoid and phytophagous parthenogenetic species consistently use more host species, and have larger, polewards extended geographic distributions than their sexual relatives. These differences did not solely evolve after the transition to parthenogenesis. Extant parthenogens often derive from sexual ancestors with relatively broad ecological niches and distributions. As these ecological attributes are associated with large population sizes, our results strongly suggests that transitions to parthenogenesis are more frequent in large sexual populations and/or that the risk of extinction of parthenogens with large population sizes is reduced. The species database presented here provides insights into the maintenance of sex and parthenogenesis in natural populations that are not taxon specific and opens perspectives for future comparative studies

Niche differentiation among clones in asexual grass thrips.

Many asexual animal populations comprise a mixture of genetically different lineages, but to what degree this genetic diversity leads to ecological differences remains often unknown. Here, we test whether genetically different clonal lineages of Aptinothrips grass thrips differ in performance on a range of plants used as hosts in natural populations. We find a clear clone-by-plant species interactive effect on reproductive output, meaning that clonal lineages perform differently on different plant species and thus are characterized by disparate ecological niches. This implies that local clonal diversities can be driven and maintained by frequency-dependent selection and that resource heterogeneity can generate diverse clone assemblies

Plant Biology: Flower Orientation, Temperature Regulation and Pollinator Attraction.

The reproductive performance of plants depends on the temperature of the flower. A recent study reports the mechanistic basis of flower head orientation in sunflowers and provides intriguing hints as to its functional significance

Non-used sexual traits: handicap or minor appendix? Negative selection plays important role in sexual trait loss in asexual insects

De begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie. The supervisor and/or the author did not authorize public publication of the thesis.

Essay: Flowering, sex and sterility in clonal plants

De begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie. The supervisor and/or the author did not authorize public publication of the thesis.

Research Report 1 : Evolution of parthenogenesis in Aptinothrips (Thysanoptera:Thripinae)

De begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie. The supervisor and/or the author did not authorize public publication of the thesis.

Structural coloured feathers of mallards act by simple multilayer photonics.

The blue colours of the speculum of the mallard (Anas platyrhynchos), both male and female, and the green head feathers of the male arise from light interacting with stacks of melanosomes residing in the feather barbules. Here, we show that the iridescent colours can be quantitatively explained with an optical multilayer model by using a position-dependent effective refractive index, which results from the varying ratio of melanin and keratin. Reflectance spectra obtained by multilayer modelling and three-dimensional finite-difference time-domain calculations were virtually identical. The spectral properties of the barbules' photonic structures are sensitive to variations in the multilayer period and the cortex thickness, but they are surprisingly robust to variations in the spatial parameters of the barbules' melanosome stacks. The blue and green reflectance spectra of the structural-coloured feathers correspond with the sensitivity spectra of the short- and middle-wavelength-sensitive photoreceptors, indicating their biological significance for intraspecific signalling

How to colour a flower: on the optical principles of flower coloration.

The coloration of flowers is due to the wavelength-selective absorption by pigments of light backscattered by structures inside the petals. We investigated the optical properties of flowers using (micro)spectrophotometry and anatomical methods. To assess the contribution of different structures to the overall visual signal of flowers, we used an optical model, where a petal is considered as a stack of differently pigmented and structured layers and we interpreted the visual signals of the model petals with insect vision models. We show that the reflectance depends, in addition to the pigmentation, on the petal's thickness and the inhomogeneity of its interior. We find large between-species differences in floral pigments, pigment concentration and localization, as well as floral interior structure. The fractions of reflected and transmitted light are remarkably similar between the studied species, suggesting common selective pressures of pollinator visual systems. Our optical model highlights that pigment localization crucially determines the efficiency of pigmentary filtering and thereby the chromatic contrast and saturation of the visual signal. The strongest visual signal occurs with deposition of pigments only on the side of viewing. Our systematic approach and optical modelling open new perspectives on the virtues of flower colour