School of Biological Sciences, University of Nebraska-Lincoln, NE 68588, United States.
Department of Entomology, University of Nebraska-Lincoln, NE 68583, United States.
J Insect Physiol. 2018 May-Jun;107:233-243. doi: 10.1016/j.jinsphys.2018.04.003. Epub 2018 Apr 12.
The functional basis of life history adaptation is a key topic of research in life history evolution. Studies of wing-polymorphism in the cricket Gryllus firmus have played a prominent role in this field. However, prior in-depth investigations of morph specialization have primarily focused on a single hormone, juvenile hormone, and a single aspect of intermediary metabolism, the fatty-acid biosynthetic component of lipid metabolism. Moreover, the role of diurnal variation in life history adaptation in G. firmus has been understudied, as is the case for organisms in general. Here, we identify genes whose expression differs consistently between the morphs independent of time-of-day during early adulthood, as well as genes that exhibit a strong pattern of morph-specific diurnal expression. We find strong, consistent, morph-specific differences in the expression of genes involved in endocrine regulation, carbohydrate and lipid metabolism, and immunity - in particular, in the expression of an insulin-like-peptide precursor gene and genes involved in triglyceride production. We also find that the flight-capable morph exhibited a substantially greater number of genes exhibiting diurnal change in gene expression compared with the flightless morph, correlated with the greater circadian change in the hemolymph juvenile titer in the dispersing morph. In fact, diurnal differences in expression within the dispersing morph at different times of the day were significantly greater in magnitude than differences between dispersing and flightless morphs at the same time-of-day. These results provide important baseline information regarding the potential role of variable gene expression on life history specialization in morphs of G. firmus, and the first information on genetically-variable, diurnal change in gene expression, associated with a key life history polymorphism. These results also suggest the existence of prominent morph-specific circadian differences in gene expression in G. firmus, possibly caused by the morph-specific circadian rhythm in the juvenile hormone titer.
生活史适应的功能基础是生活史进化研究的一个关键课题。在这个领域，蟋蟀 Gryllus firmus 的翅型多态性研究发挥了突出的作用。然而，先前对形态特化的深入研究主要集中在一种激素——保幼激素，以及代谢中间物的一个方面——脂质代谢中的脂肪酸生物合成成分。此外，蟋蟀 G. firmus 中昼夜变化在生活史适应中的作用，以及一般生物中的昼夜变化作用，都研究不足。在这里，我们鉴定了一些基因，这些基因的表达在成年早期的不同时间之间始终在形态之间存在差异，以及表现出强烈的形态特异性昼夜表达模式的基因。我们发现，参与内分泌调节、碳水化合物和脂质代谢以及免疫的基因的表达存在强烈、一致、形态特异性的差异——特别是胰岛素样肽前体基因和参与甘油三酯产生的基因的表达。我们还发现，能够飞行的形态表现出与散布形态中血液保幼激素滴度的较大昼夜变化相关的大量表现出昼夜变化的基因表达，而不能飞行的形态则表现出较少的基因表达昼夜变化。事实上，在一天中的不同时间，散布形态内的昼夜差异表达的幅度明显大于同一时间散布形态和不能飞行形态之间的差异。这些结果为蟋蟀 G. firmus 中形态生活史特化的可变基因表达的潜在作用提供了重要的基础信息，也是与一个关键生活史多态性相关的遗传可变、昼夜变化的基因表达的第一份信息。这些结果还表明，蟋蟀 G. firmus 中可能存在明显的形态特异性昼夜差异的基因表达，这可能是由保幼激素滴度的形态特异性昼夜节律引起的。
