Takeshi Awasaki

Seminal fluid not only assists successful fertilization but also induces changes in female post-mating behavior and physiology. Consequently, males with depleted or inadequate seminal fluid produce fewer offspring. Males of iteroparous species therefore increase seminal fluid production to replenish exhausted supplies. However, it remains unclear how mating-induced replenishment of seminal fluid components is regulated at the molecular and cellular levels. Here, we show that replenishment of Sex peptide (SP) in male Drosophila melanogaster requires both SP and its receptor SPR. Mechanistically, mating-induced SP replenishment in the male accessory gland (MAG) is regulated by MAG-projecting serotonergic neurons, and this regulation depends on SPR, which is likely activated by SP as it passes through the reproductive tract during mating. This inter-tissue signaling pathway is not limited to SP but also coordinates the post-mating upregulation of an additional seminal fluid protein gene. While SP-SPR signaling is a well-known regulator of female post-mating responses, we demonstrate that it also modulates male physiology. Furthermore, comparative analyses across 12 drosophilid species are consistent with the hypothesis that SP-SPR signaling acquired a role in males before its role in canonical female post-mating responses evolved. We therefore propose that the role of SP-SPR signaling as a mating signal in males is ancestral to its more familiar but evolutionarily derived role in females.

In accepting a courting male, Drosophila subobscura females require nuptial gift giving in which a male gives regurgitated crop contents to her mouth to mouth. No similar behavior is found in D. melanogaster . By clonal activation of neurons expressing the male-determinant FruM, we identified insulin-like peptide–producing cells (IPCs) and their putative postsynaptic targets, proboscis-innervating motoneurons, as those critical for gift giving. We demonstrate that loss of FruM from D. subobscura IPCs abrogates neurite extension and gift giving, whereas FruM overexpression in their D. melanogaster counterparts induces overgrowth of neurites that harbor functional synapses, culminating in increased regurgitation. We suggest that the acquisition of FruM expression by IPCs was a key event occurring in an ancestral D. subobscura that conferred a latent capability to perform nuptial gift giving.

In sexually reproducing animals, genital morphology is usually divergent among closely related species, which can lead to a mismatch of genital coupling (i.e. mechanical isolation). The montium species group of the subgenus Sophophora is the largest clade in Drosophila and is a useful model in which to study the evolution of genital morphology. This group includes a pair of sister clades, i.e. the Drosophila auraria and Drosophila rufa species complexes. The former includes four species with overlapping distributions, and the latter consists of five species that are almost allopatric. The previous study on the D. auraria complex suggested genital co-evolution between sexes (female structures accepting for or protecting from male structures). To test the generality, we analysed the D. rufa complex and three outgroup species. In the D. rufa complex, we detected genital structures corresponding between sexes, and copulatory wounds with species-specific positions. Given that approximately the same number of evolutionary changes in the genital traits were detected in both sexes of the two clades, we conclude that selection pressure to avoid interspecific mating (reproductive character displacement) is not a prerequisite for rapid genital co-evolution.

Temperature is one of the most critical environmental factors that influence various biological processes. Species distributed in different temperature regions are considered to have different optimal temperatures for daily life activities. However, how organisms have acquired various features to cope with particular temperature environments remains to be elucidated. In this study, we have systematically analyzed the temperature preference behavior and effects of temperatures on daily locomotor activity and sleep using 11 Drosophila species. We also investigated the function of antennae in the temperature preference behavior of these species. We found that, (1) an optimal temperature for daily locomotor activity and sleep of each species approximately matches with temperatures it frequently encounters in its habitat, (2) effects of temperature on locomotor activity and sleep are diverse among species, but each species maintains its daily activity and sleep pattern even at different temperatures, and (3) each species has a unique temperature preference behavior, and the contribution of antennae to this behavior is diverse among species. These results suggest that Drosophila species inhabiting different climatic environments have acquired species-specific temperature response systems according to their life strategies. This study provides fundamental information for understanding the mechanisms underlying their temperature adaptation and lifestyle diversification.

Temperature is one of the most critical environmental factors that influence various biological processes. Species distributed in different temperature regions are considered to have different optimal temperatures for daily life activities. However, how organisms have acquired various features to cope with particular temperature environments remains to be elucidated. In this study, we have systematically analyzed the temperature preference behavior and effects of temperatures on daily locomotor activity and sleep using 11 Drosophila species. We also investigated the function of antennae in the temperature preference behavior of these species. We found that, (1) an optimal temperature for daily locomotor activity and sleep of each species approximately matches with temperatures it frequently encounters in its habitat, (2) effects of temperature on locomotor activity and sleep are diverse among species, but each species maintains its daily activity and sleep pattern even at different temperatures, and (3) each species has a unique temperature preference behavior, and the contribution of antennae to this behavior is diverse among species. These results suggest that Drosophila species inhabiting different climatic environments have acquired species-specific temperature response systems according to their life strategies. This study provides fundamental information for understanding the mechanisms underlying their temperature adaptation and lifestyle diversification.

Neural remodeling is essential for the development of a functional nervous system and has been extensively studied in the metamorphosis of Drosophila. Despite the crucial roles of glial cells in brain functions, including learning and behavior, little is known of how adult glial cells develop in the context of neural remodeling. Here, we show that the architecture of neuropil-glia in the adult Drosophila brain, composed of astrocyte-like glia (ALG) and ensheathing glia (EG), robustly develops from two different populations in the larva: the larval EG and glial cell missing-positive (gcm⁺) cells. While larval EG dedifferentiate, proliferate, and redifferentiate into adult ALG and EG, gcm⁺ cells also generate the same glial subtypes. Each glial lineage occupies a certain brain area complementary to the other, and together they form the adult neuropil-glia architecture. Both lineages require the FGF receptor Heartless to proliferate, and the homeoprotein Prospero to differentiate into ALG. Lineage-specific inhibition of gliogenesis revealed that each lineage compensates for deficiency in the proliferation of the other. Together, the lineages ensure the robust development of adult neuropil-glia, thereby ensuring a functional brain.

ELYS determines the subcellular localizations of Nucleoporins (Nups) during interphase and mitosis. We made loss-of-function mutations of Elys in Drosophila melanogaster and found that ELYS is dispensable for zygotic viability and male fertility but the maternal supply is necessary for embryonic development. Subsequent to fertilization, mitotic progression of the embryos produced by the mutant females is severely disrupted at the first cleavage division, accompanied by irregular behavior of mitotic centrosomes. The Nup160 introgression from D. simulans shows close resemblance to that of the Elys mutations, suggesting a common role for those proteins in the first cleavage division. Our genetic experiments indicated critical interactions between ELYS and three Nup107–160 subcomplex components; hemizygotes of either Nup37, Nup96 or Nup160 were lethal in the genetic background of the Elys mutation. Not only Nup96 and Nup160 but also Nup37 of D. simulans behave as recessive hybrid incompatibility genes with D. melanogaster. An evolutionary analysis indicated positive natural selection in the ELYS-like domain of ELYS. Here we propose that genetic incompatibility between Elys and Nups may lead to reproductive isolation between D. melanogaster and D. simulans, although direct evidence is necessary.

Macroglial cells in the central nervous system exhibit regional specialization and carry out region-specific functions. Diverse glial cells arise from specific progenitors in specific spatiotemporal patterns. This raises an interesting possibility that glial precursors with distinct developmental fates exist that govern region-specific gliogenesis. Here, we have mapped the glial progeny produced by the Drosophila type II neuroblasts, which, like vertebrate radial glia cells, yield both neurons and glia via intermediate neural progenitors (INPs). Distinct type II neuroblasts produce different characteristic sets of glia. A single INP can make both astrocyte-like and ensheathing glia, which co-occupy a relatively restrictive subdomain. Blocking apoptosis uncovers further lineage distinctions in the specification, proliferation and survival of glial precursors. Both the switch from neurogenesis to gliogenesis and the subsequent glial expansion depend on Notch signaling. Taken together, lineage origins preconfigure the development of individual glial precursors with involvement of serial Notch actions in promoting gliogenesis.

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