Sex and tissue-specific evolution of developmental plasticity in Drosophila melanogaster.

Developmental plasticity influences the size of adult tissues in insects. Tissues can have unique responses to environmental perturbation during development; however, the prevalence of within species evolution of tissue-specific developmental plasticity remains unclear. To address this, we studied the effects of temperature and nutrition on wing and femur size in D. melanogaster populations from a temperate and tropical region. Wings were more sensitive to temperature, while wings and femurs were equally responsive to nutrition in both populations and sexes. The temperate population was larger under all conditions, except for femurs of starved females. In line with this, we observed greater femur size plasticity in response to starvation in temperate females, leading to differences in sexual dimorphism between populations such that the slope of the reaction norm of sexual dimorphism in the tropical population was double that of the temperate population. Lastly, we observed a significant trend for steeper slopes of reaction norms in temperate than in tropical females, but not in males. These findings highlight that plasticity divergence between populations can evolve heterogeneously across sexes and tissues and that nutritional plasticity can alter sexual dimorphism in D. melanogaster.

Phenotypic coupling of sleep and starvation resistance evolves in D. melanogaster.

BACKGROUND: One hypothesis for the function of sleep is that it serves as a mechanism to conserve energy. Recent studies have suggested that increased sleep can be an adaptive mechanism to improve survival under food deprivation in Drosophila melanogaster. To test the generality of this hypothesis, we compared sleep and its plastic response to starvation in a temperate and tropical population of Drosophila melanogaster. RESULTS: We found that flies from the temperate population were more starvation resistant, and hypothesized that they would engage in behaviors that are considered to conserve energy, including increased sleep and reduced movement. Surprisingly, temperate flies slept less and moved more when they were awake compared to tropical flies, both under fed and starved conditions, therefore sleep did not correlate with population-level differences in starvation resistance. In contrast, total sleep and percent change in sleep when starved were strongly positively correlated with starvation resistance within the tropical population, but not within the temperate population. Thus, we observe unexpectedly complex relationships between starvation and sleep that vary both within and across populations. These observations falsify the simple hypothesis of a straightforward relationship between sleep and energy conservation. We also tested the hypothesis that starvation is correlated with metabolic phenotypes by investigating stored lipid and carbohydrate levels, and found that stored metabolites partially contributed towards variation starvation resistance. CONCLUSIONS: Our findings demonstrate that the function of sleep under starvation can rapidly evolve on short timescales and raise new questions about the physiological correlates of sleep and the extent to which variation in sleep is shaped by natural selection.

Reproductive Capacity Evolves in Response to Ecology through Common Changes in Cell Number in Hawaiian Drosophila.

Lifetime reproductive capacity is a critical fitness component. In insects, female reproductive capacity is largely determined by the number of ovarioles, the egg-producing subunits of the ovary [e.g., 1]. Recent work has provided insights into ovariole number regulation in Drosophila melanogaster. However, whether mechanisms discovered under laboratory conditions explain evolutionary variation in natural populations is an outstanding question. We investigated potential effects of ecology on the developmental processes underlying ovariole number evolution among Hawaiian Drosophila, a large adaptive radiation wherein the highest and lowest ovariole numbers of the family have evolved within 25 million years. Previous studies proposed that ovariole number correlated with oviposition substrate [2-4] but sampled largely one clade of these flies and were limited by a provisional phylogeny and the available comparative methods. We test this hypothesis by applying phylogenetic modeling to an expanded sampling of ovariole numbers and substrate types and show support for these predictions across all major groups of Hawaiian Drosophila, wherein ovariole number variation is best explained by adaptation to specific substrates. Furthermore, we show that oviposition substrate evolution is linked to changes in the allometric relationship between body size and ovariole number. Finally, we provide evidence that the major changes in ovarian cell number that regulate D. melanogaster ovariole number also regulate ovariole number in Hawaiian drosophilids. Thus, we provide evidence that this remarkable adaptive radiation is linked to evolutionary changes in a key reproductive trait regulated at least partly by variation in the same developmental parameters that operate in the model species D. melanogaster.

Ex vivo culture of pre-placental tissues reveals that the allantois is required for maintained expression of Gcm1 and Tpbpα.

INTRODUCTION: Chorioallantoic fusion is essential for development of the labyrinth layer of the mouse placenta. However, events that occur after chorioallantoic attachment remain poorly described, partly due to difficulties of conducting ex vivo analysis of the placenta. Herein, we report conditions for ex vivo culture of the developing murine placenta. METHODS: Mesometrial halves of decidua containing pre-attachment chorions were cultured alone or with explants of allantoides from stage-matched controls and analyzed by confocal and immunofluorescence microscopy. Expression and levels of marker genes associated with specific placental cell types were measured by in situ hybridization and qRT-PCR, respectively. RESULTS: After 24 h (hr) of co-culture, a mosaic pattern of eGFP+ and eGFP- cells were found when explants of pre-attachment chorions from eGFP+ embryos were co-cultured with stage-matched allantoides from eGFP- embryos or vice versa. In addition, proliferation increased in the allantoic region and folds formed on the chorionic plate. PECAM positive cells derived from the allantois were found in the chorionic region. Levels of the SynT-II marker, Gcm1, significantly increased at 24 h, although expression of Gcm1, was only found in explants co-cultured with an allantois at 12 h and 24 h. In addition, though levels of Tpbpα was not altered by co-culture with an allantois, Tpbpα was only detected in explants co-cultured with an allantois for 24 h. DISCUSSION: Our data show that chorioallantoic fusion and events associated with initiation of labyrinth layer formation can be modeled ex vivo, and reveal a previously unsuspected requirement of chorioallantoic fusion for Tpbpα expression.

The Hippo pathway regulates homeostatic growth of stem cell niche precursors in the Drosophila ovary.

The Hippo pathway regulates organ size, stem cell proliferation and tumorigenesis in adult organs. Whether the Hippo pathway influences establishment of stem cell niche size to accommodate changes in organ size, however, has received little attention. Here, we ask whether Hippo signaling influences the number of stem cell niches that are established during development of the Drosophila larval ovary, and whether it interacts with the same or different effector signaling pathways in different cell types. We demonstrate that canonical Hippo signaling regulates autonomous proliferation of the soma, while a novel hippo-independent activity of Yorkie regulates autonomous proliferation of the germ line. Moreover, we demonstrate that Hippo signaling mediates non-autonomous proliferation signals between germ cells and somatic cells, and contributes to maintaining the correct proportion of these niche precursors. Finally, we show that the Hippo pathway interacts with different growth pathways in distinct somatic cell types, and interacts with EGFR and JAK/STAT pathways to regulate non-autonomous proliferation of germ cells. We thus provide evidence for novel roles of the Hippo pathway in establishing the precise balance of soma and germ line, the appropriate number of stem cell niches, and ultimately regulating adult female reproductive capacity.

Counting in oogenesis.

The determination of a precise number of cells within a structure and of a precise number of cellular structures within an organ is critical for correct development in animals and plants. However, relatively little is known about the molecular mechanisms that ensure that these numbers are achieved. We discuss counting mechanisms that operate during ovarian development and oogenesis.