Covariation amongst wood traits along the stem axis is important to maintain hydraulic integrity ensuring sufficient sap flow to the canopy. Here, we test how wood traits (co)vary along the trunk... Show moreCovariation amongst wood traits along the stem axis is important to maintain hydraulic integrity ensuring sufficient sap flow to the canopy. Here, we test how wood traits (co)vary along the trunk and whether two seasonally dry Brazilian habitats (cerrado and caatinga) influence this variation in two co-occurring species, Tocoyena formosa (Rubiaceae) and Tabebuia aurea (Bignoniaceae). The samples were collected at five heights along the main trunk of three individuals per species in both sites. We used light, scanning and transmission electron microscopy to observe the wood traits. Out of 13 wood traits, nine show relationships with sampling height: eight traits predict height in T. formosa and five in T. aurea. Contrastingly, only three traits show differences between sites and only for T. formosa. The intratrunk wood variation is reflected by the hydraulically weighted vessel diameter showing a curvilinear relationship, disagreeing with the prediction of a continuous vessel widening from tip to base. In both species, the largest vessels are linked to the thinnest intervessel pit membranes. Wood density increases basipetally for both species, being site-dependent and correlated with vessel traits in T. formosa, and site-independent and determined by fiber wall thickness in T. aurea. Furthermore, the functional role of rays was found to be different for each species, and may be related to the marked difference in ray composition. In conclusion, both species show a unique adaptation to deal with height-related constraints using species-specific co-variation amongst wood traits, while site does not contribute much to the wood variation. Show less
The central theme of this PhD thesis is natural variation in the wing length of the predatory two-spot ladybird beetle, Adalia bipunctata. __Wingless__ individuals of this species occur... Show moreThe central theme of this PhD thesis is natural variation in the wing length of the predatory two-spot ladybird beetle, Adalia bipunctata. __Wingless__ individuals of this species occur occasionally. They possess truncated wing covers and flight wings and cannot fly, but the extent of the reduction is highly variable between individuals. At one hand, I take a multidisciplinary experimental approach to study the causes and consequences of this variation in an evolutionary context. Genetic and developmental studies show that it is regulated by several polymorphic genes, and results from gene-environment interactions affecting the growth of the larval wing discs. Studies on life-history traits and mating behaviour provide no evidence that winglessness is an adaptive trait in this ladybird. However, they reveal a function of the wing covers in survival and mating behaviour. On the other hand, I examine the use of wingless ladybirds in the biological control of aphids, since winged ladybirds are not effective when flying away soon after release. I show that wingless morphs have the potential to improve biocontrol efficacy. I then suggest that mass-rearing of this less fit morph could be improve by manipulation of the wing length. Altogether, this thesis interlinks the fields of fundamental (evolutionary) biology and applied biological control. Show less
