The Developmental Basis of Caste Evolution in Ants

Tese de doutoramento do programa conjunto de Doutoramento em Economia da Faculdade de Economia da Universidade de Coimbra e da Escola de Economia e Gestão da Universidade do Minho, apresentada à Faculdade de Economia da Universidade de CoimbraEste estudo teve como principal objetivo a análise das políticas monetária e orçamental e ciclos económicos nos mercados emergentes. Primeiro, analisou-se a importância destas políticas através de um modelo teórico, numa situação em que os gastos públicos variam de acordo com os ciclos económicos e o país emergente enfrenta barreiras no acesso ao capital externo. A análise do modelo mostrou os resultados esperados: a política orçamental pro-cíclica aumenta, em geral, a volatilidade da economia. Contudo, o contrário acontece para variáveis como o consumo, a taxa de juro e a posição de investimento internacional. De seguida estimaram-se os efeitos destas políticas na economia, através de diferentes modelos de Vectores Auto-Regressivos (VAR), para 11 países emergentes europeus e os principais resultados mostraram que tanto a política monetária como a política orçamental têm um importante efeito na economia destes países. Se, por um lado, um choque na política monetária apresenta um importante efeito negativo no produto destas economias, assim como na procura interna privada, já o impacto de um choque na política orçamental depende de país para país. Por último, estimaram-se as regras de políticas para os mesmos países, usando a metodologia das variáveis instrumentais e os resultados confirmaram que, para além das variáveis internas, o setor externo tem um importante efeito na dinâmica dos dois tipos de política económica.This study had as the main objective the analysis of monetary and fiscal policies and business cycles in emerging markets. First, we analyzed the importance of these policies through a theoretical model, in a situation where public expenditure varies with business cycles and the emerging country faces barriers in access to external capital. The analysis of the model showed the expected results: the pro-cyclical fiscal policy increases, in general, the volatility of the economy. However, the opposite happens for variables such as consumption, the interest rate and the international investment position. Then we estimated the effects of these policies on the economy, through different VAR models, for 11 emerging European countries, and the main results showed that both monetary policy and fiscal policy have an important effect on the economy in these countries. If on the one hand, in general, a shock in monetary policy has a significantly negative effect on the output of these countries as well as on private domestic demand, on the other hand, the impact of a shock in fiscal policy is heterogeneous across countries. Finally, policy rules were estimated for these countries using the instrumental variables approach and the results confirmed that in addition to the internal variables, the external sector has an important effect on the dynamics of the two types of economic policy.Fundação para a Ciência e Tecnologi

A comparative analysis of the allometry for sexual size dimorphism : testing Rensch's Rule

Tests the validity and generality of Rensch's Rule within 21 independent animal taxa, using the recently developed independent contrasts method

Desert and tropical ecosystems of the world harbour the most complex ant societies

Morphological diversity in the worker caste is present in ants, wasps, termites and thrips, but is particularly striking in ants, as they can produce distinct or continuous worker subcastes. This is referred to as worker caste polymorphism, which has enabled efficient division of labour and consequently, ecological dominance. Previous research shows that nutrition and colony demography during larval development are important determinants of worker polymorphism, which in turn can be mediated by the abiotic environment. However, little is known about the influence of environmental gradients on the geographic distribution of worker caste polymorphism. Here, I developed and tested three hypotheses explaining the global distribution of worker polymorphism: (1) The Tropical Polymorphism Hypothesis, (2) The Desert Polymorphism Hypothesis and (3) The Extreme Climate Hypothesis. I therefore investigated the influence of geographic variation in temperature and precipitation on the distribution of worker polymorphism worldwide using 680 000 ant occurrences and identifying each occurrence point as polymorphic or not. Previous estimates suggested that 13% of ant species are polymorphic whereas my results show this number to be as high as 29%. Moreover, I found that the occurrence of polymorphism was highest in the most arid and tropical ecosystems, suggesting that it may be an adaptation to regions with extremely scarce or diverse resources. Additionally, warm climate is a pre-requisite for the evolution of worker caste polymorphism. Taken together, my work sheds light on the factors promoting complex social lifestyle in insects, and reveals that it is more common in ants than previously believed

Evolution of a Novel Appendage Ground Plan in Water Striders Is Driven by Changes in the Hox Gene Ultrabithorax

Water striders, a group of semi-aquatic bugs adapted to life on the water surface, have evolved mid-legs (L2) that are long relative to their hind-legs (L3). This novel appendage ground plan is a derived feature among insects, where L2 function as oars and L3 as rudders. The Hox gene Ultrabithorax (Ubx) is known to increase appendage size in a variety of insects. Using gene expression and RNAi analysis, we discovered that Ubx is expressed in both L2 and L3, but Ubx functions to elongate L2 and to shorten L3 in the water strider Gerris buenoi. Therefore, within hemimetabolous insects, Ubx has evolved a new expression domain but maintained its ancestral elongating function in L2, whereas Ubx has maintained its ancestral expression domain but evolved a new shortening function in L3. These changes in Ubx expression and function may have been a key event in the evolution of the distinct appendage ground plan in water striders

The Phylogenetic Origin of oskar Coincided with the Origin of Maternally Provisioned Germ Plasm and Pole Cells at the Base of the Holometabola

The establishment of the germline is a critical, yet surprisingly evolutionarily labile, event in the development of sexually reproducing animals. In the fly Drosophila, germ cells acquire their fate early during development through the inheritance of the germ plasm, a specialized maternal cytoplasm localized at the posterior pole of the oocyte. The gene oskar (osk) is both necessary and sufficient for assembling this substance. Both maternal germ plasm and oskar are evolutionary novelties within the insects, as the germline is specified by zygotic induction in basally branching insects, and osk has until now only been detected in dipterans. In order to understand the origin of these evolutionary novelties, we used comparative genomics, parental RNAi, and gene expression analyses in multiple insect species. We have found that the origin of osk and its role in specifying the germline coincided with the innovation of maternal germ plasm and pole cells at the base of the holometabolous insects and that losses of osk are correlated with changes in germline determination strategies within the Holometabola. Our results indicate that the invention of the novel gene osk was a key innovation that allowed the transition from the ancestral late zygotic mode of germline induction to a maternally controlled establishment of the germline found in many holometabolous insect species. We propose that the ancestral role of osk was to connect an upstream network ancestrally involved in mRNA localization and translational control to a downstream regulatory network ancestrally involved in executing the germ cell program

The Genome Sequence of the Leaf-Cutter Ant Atta cephalotes Reveals Insights into Its Obligate Symbiotic Lifestyle

Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the formation of their massive colonies. Mature leaf-cutter ant colonies contain millions of workers ranging in size from small garden tenders to large soldiers, resulting in one of the most complex polymorphic caste systems within ants. To begin uncovering the genomic underpinnings of this system, we sequenced the genome of Atta cephalotes using 454 pyrosequencing. One prediction from this ant's lifestyle is that it has undergone genetic modifications that reflect its obligate dependence on the fungus for nutrients. Analysis of this genome sequence is consistent with this hypothesis, as we find evidence for reductions in genes related to nutrient acquisition. These include extensive reductions in serine proteases (which are likely unnecessary because proteolysis is not a primary mechanism used to process nutrients obtained from the fungus), a loss of genes involved in arginine biosynthesis (suggesting that this amino acid is obtained from the fungus), and the absence of a hexamerin (which sequesters amino acids during larval development in other insects). Following recent reports of genome sequences from other insects that engage in symbioses with beneficial microbes, the A. cephalotes genome provides new insights into the symbiotic lifestyle of this ant and advances our understanding of host–microbe symbioses

The genome of the water strider Gerris buenoi reveals expansions of gene repertoires associated with adaptations to life on the water.

BACKGROUND: Having conquered water surfaces worldwide, the semi-aquatic bugs occupy ponds, streams, lakes, mangroves, and even open oceans. The diversity of this group has inspired a range of scientific studies from ecology and evolution to developmental genetics and hydrodynamics of fluid locomotion. However, the lack of a representative water strider genome hinders our ability to more thoroughly investigate the molecular mechanisms underlying the processes of adaptation and diversification within this group. RESULTS: Here we report the sequencing and manual annotation of the Gerris buenoi (G. buenoi) genome; the first water strider genome to be sequenced thus far. The size of the G. buenoi genome is approximately 1,000 Mb, and this sequencing effort has recovered 20,949 predicted protein-coding genes. Manual annotation uncovered a number of local (tandem and proximal) gene duplications and expansions of gene families known for their importance in a variety of processes associated with morphological and physiological adaptations to a water surface lifestyle. These expansions may affect key processes associated with growth, vision, desiccation resistance, detoxification, olfaction and epigenetic regulation. Strikingly, the G. buenoi genome contains three insulin receptors, suggesting key changes in the rewiring and function of the insulin pathway. Other genomic changes affecting with opsin genes may be associated with wavelength sensitivity shifts in opsins, which is likely to be key in facilitating specific adaptations in vision for diverse water habitats. CONCLUSIONS: Our findings suggest that local gene duplications might have played an important role during the evolution of water striders. Along with these findings, the sequencing of the G. buenoi genome now provides us the opportunity to pursue exciting research opportunities to further understand the genomic underpinnings of traits associated with the extreme body plan and life history of water striders