Short Clancy A, Hatle John D, Hahn Daniel A
Department of Entomology and Nematology, The University of Florida, Gainesville, FL, United States.
Department of Biology, The University of North Florida, Jacksonville, FL, United States.
Front Physiol. 2020 Aug 6;11:991. doi: 10.3389/fphys.2020.00991. eCollection 2020.
Many animals exhibit reproductive behavior that requires expenditure of valuable nutrients. In males of many species, competitive energetically demanding displays and the development of sexual ornaments require prior accumulation of nutrient stores. Males must coordinate nutrient stores with ornament development and reproductive displays or they risk depleting their resources mid-development or mid-display, reducing their chance of mating. Males may use nutrient stores to regulate their reproductive behavior. Amino acid reserves may be important for reproduction, but the roles of amino acid stores in initiating maturation and reproductive behavior are less studied than fat stores. Insects store amino acids as hexamerin storage proteins. Many fly species use a specific hexamerin, larval serum protein 2 (LSP-2), as both a juvenile storage medium and to store protein consumed after adult eclosion. Protein stored as LSP-2 has previously been suggested to regulate reproduction in females, but no role has been proposed for LSP-2 in regulating male maturation. We use males of the Caribbean fruit fly, , a species with nutrient-intensive male sexual displays to test whether LSP-2 stores regulate male reproductive displays. We fed adult males a diet with or without protein, then assayed these males for transcript abundance via qRT-PCR, LSP-2 protein abundance via Western blot, and reproductive display behavior via observation. We found that adult males with dietary protein had greater transcript and protein abundance, earlier sexual display behavior, and were more likely to exhibit sexual display behavior than protein-deprived adult males. We show that knockdown via RNAi decreases the proportion of males exhibiting reproductive displays, particularly early in the onset of reproductive behavior. Our results suggest circulating LSP-2 protein stores regulate reproductive behavior in males, consistent with protein stores modulating reproduction in males with expensive reproductive strategies. Our results are consistent with hexamerin storage proteins performing dual roles of protein storage and protein signaling. Our work also has substantial practical applications because tephritid flies are a pest group and the timing and expression of male reproductive displays in this group are important for control efforts using the sterile insect technique.
许多动物表现出需要消耗宝贵营养物质的生殖行为。在许多物种的雄性中，竞争性的、能量需求高的展示以及性装饰的发育需要事先积累营养储备。雄性必须协调营养储备与装饰发育和生殖展示，否则它们有可能在发育中期或展示过程中耗尽资源，从而降低交配的机会。雄性可能利用营养储备来调节其生殖行为。氨基酸储备对于繁殖可能很重要，但与脂肪储备相比，氨基酸储备在启动成熟和生殖行为中的作用研究较少。昆虫将氨基酸储存为六聚体储存蛋白。许多果蝇物种使用一种特定的六聚体蛋白，即幼虫血清蛋白2（LSP - 2），作为幼虫储存介质以及储存成虫羽化后消耗的蛋白质。以前有人提出，以LSP - 2形式储存的蛋白质可调节雌性的繁殖，但尚未有人提出LSP - 2在调节雄性成熟方面的作用。我们使用加勒比果蝇的雄性个体，这是一种具有营养密集型雄性性行为展示的物种，来测试LSP - 2储备是否调节雄性生殖展示。我们给成年雄性果蝇喂食含或不含蛋白质的食物，然后通过定量逆转录聚合酶链反应（qRT - PCR）检测这些雄性果蝇中LSP - 2的转录本丰度，通过蛋白质免疫印迹法检测LSP - 2蛋白丰度，并通过观察检测生殖展示行为。我们发现，摄入含蛋白质食物的成年雄性果蝇具有更高的转录本和蛋白丰度，更早出现性行为展示，并且比缺乏蛋白质的成年雄性果蝇更有可能表现出性行为展示。我们表明，通过RNA干扰（RNAi）敲低LSP - 2会降低表现出生殖展示行为的雄性果蝇的比例，尤其是在生殖行为开始的早期。我们的结果表明，循环中的LSP - 2蛋白储备调节加勒比果蝇雄性的生殖行为，这与蛋白质储备调节具有昂贵生殖策略的雄性的繁殖情况一致。我们的结果与六聚体储存蛋白具有蛋白质储存和蛋白质信号传导的双重作用相符。我们的工作还具有重要的实际应用价值，因为实蝇是害虫群体，该群体中雄性生殖展示的时间和表达对于使用昆虫不育技术进行防治工作很重要。
