Case studies on the genes zerknuellt, decapentaplegic and short gastrulation in the beetle Tribolium illustrate concepts in evolutionary developmental biology

Evolutionary developmental biology (Evo-Devo) attempts to trace modifications in development that have lead to evolutionary novelty. Some important concepts in Evo-Devo are GENE DUPLICATION, SUBFUNCTIONALIZATION, MODULARITY, CO-OPTION, CIS-REGULATORY EVOLUTION, GENE NETWORKS and HUBS. This thesis consists of two case studies on genes in the beetle Tribolium castaneum which is thought to represent a more ancestral mode of development than the well-studied fruit fly Drosophila melanogaster. In the first case study, the expression and function of the two zerknüllt genes (Tc-zen1 and Tc-zen2) were investigated. Drosophila-zen is, initially under control of Dorsal, expressed at the dorsal side and specifies a single extraembryonic membrane, the amnioserosa. Tribolium possesses two extraembryonic membranes: an outer serosa and an inner amnion. Tc-zen1 displays early, anterior expression and specifies the serosa. Tc-zen1 knock-down enlarges the germ rudiment and deletes the serosa, but the remaining dorsal amnion allows relatively normal further development. Thus, in absence of Tc-zen1, Tribolium acquires features of Drosophila development. Tc-zen2 is expressed later and mediates the amnion-serosa fusion necessary for dorsal closure. Tc-zen2 depletion prevents this fusion and leads to completely everted (inside-out) larvae. In the second case study, Decapentaplegic (Dpp, a BMP ligand) and Short gastrulation (Sog, a BMP inhibitor) were examined. In Drosophila and vertebrates, BMP signaling plays a major role in dorsoventral patterning. In contrast to Drosophila, where Dm-dpp expression is restricted to the dorsal side by Dorsal, Tribolium-dpp shows differential expression along the anteroposterior axis. However, Tc-Sog is expressed in a ventral domain and establishes a dorsoventral Dpp activity gradient by transporting Dpp towards the dorsal side. Tc-sog RNAi abolishes neurogenesis and normal dorsoventral polarity in the ectoderm. Tc-dpp RNAi leads to the loss of dorsal cell fates. Surprisingly, similar to vertebrates but in contrast to Drosophila, Tribolium BMP knock-down enlarges the head, while knock-down of BMP antagonism deletes the head. Possibly, Sog/Chordin was already CO-OPTED for head formation in an ancestor of all bilateria. Besides CO-OPTION, the evolutionary implications of these case studies illustrate other concepts of Evo-Devo. For example, the DUPLICATION of zen in an ancestor of Tribolium was followed by SUBFUNCTIONALIZATION. Dpp belongs to a signaling MODULE that is repeatedly employed in different contexts. The CIS-REGULATORY SEQUENCES of dpp and zen acquired binding sites for Dorsal which became a HUB in the dorsoventral regulatory GENE NETWORK of Drosophila

Winter moth adaptation to climate change:Genetic changes in thermal plasticity of embryonic development rate

Timing of winter moth egg hatching shows rapid genetic adaptation to climate change. The reaction norm of egg development rate versus temperature has shifted up compared to 10 years ago. This later hatching for a given temperature has led to a better match with timing of their food source, young oak leaves. To identify the genes underlying the genetic adaptation of winter moth egg hatching, we used an evo-eco-devo approach: eggs collected from the field were used in a split-brood experiment. At different times during development, we measured embryonic development in, and obtained transcriptomes of, eggs before and after transfer to a colder or warmer temperature compared to a baseline. Stages of embryonic development in the winter moth were determined by imagining eggs using epifluorescence microscopy. These images were then used to map the thermal sensitivity of winter moth embryonic development over time, enabling us to focus on the transcriptomes taken during thermally sensitive stages of development. Ultimately, we aim to compare the genes identified this way with genes that show changes in allele frequency over the past 20 years, using our DNA record of four natural populations that adapted to climate change. As winter moths are one of the few species showing genetic adaptation under climate change, this study of winter moth embryonic development can advance our understanding of the genetic basis of adaptive evolutionary change in a natural population

Winter moth adaptation to climate change:Genetic changes in thermal plasticity of embryonic development rate

Timing of winter moth egg hatching shows rapid genetic adaptation to climate change. The reaction norm of egg development rate versus temperature has shifted up compared to 10 years ago. This later hatching for a given temperature has led to a better match with timing of their food source, young oak leaves. To identify the genes underlying the genetic adaptation of winter moth egg hatching, we used an evo-eco-devo approach: eggs collected from the field were used in a split-brood experiment. At different times during development, we measured embryonic development in, and obtained transcriptomes of, eggs before and after transfer to a colder or warmer temperature compared to a baseline. Stages of embryonic development in the winter moth were determined by imagining eggs using epifluorescence microscopy. These images were then used to map the thermal sensitivity of winter moth embryonic development over time, enabling us to focus on the transcriptomes taken during thermally sensitive stages of development. Ultimately, we aim to compare the genes identified this way with genes that show changes in allele frequency over the past 20 years, using our DNA record of four natural populations that adapted to climate change. As winter moths are one of the few species showing genetic adaptation under climate change, this study of winter moth embryonic development can advance our understanding of the genetic basis of adaptive evolutionary change in a natural population