Zera A J, Bottsford J
School of Biological Sciences, University of Nebraska, Lincoln 68588, USA.
Evolution. 2001 Mar;55(3):538-49. doi: 10.1554/0014-3820(2001)055[0538:tegbol]2.0.co;2.
The hormonal basis of variation in life-history traits is a poorly studied topic in life-history evolution. An important step in identifying the endocrine-genetic causes of life-history variation is documenting statistical and functional associations between hormone titers and genotypes/phenotypes that vary in life-history traits. To this end, we compared the blood ecdysteroid titer and the mass of the ovaries during the first week of adulthood among a flight-capable morph and two flightless morphs of the wing-polymorphic cricket Gryllus firmus. Ecdysteroids are a group of structurally related hormones that regulate many important aspects of reproduction in insects. Both the ecdysteroid titer and ovarian mass were significantly higher in each of two flightless morphs compared with the flight-capable morph throughout the first week of adulthood. Genetically based differences in the ecdysteroid titer and ovarian mass between morphs from different selected lines were similar to phenotypically based differences among morphs from the same control (unselected) lines. By day 7 of adulthood, ovaries were typically 200-400% larger and the ecdysteroid titer was 60-300% higher in flightless versus the flight-capable morph. In addition, highly significant, positive, phenotypic correlations were observed between the ecdysteroid titer and ovarian mass in pooled samples of the two flightless and flight-capable crickets from control lines or from selected lines. The ecdysteroid titer was sufficiently elevated in the flightless morphs to account for their elevated ovarian growth. This is the first direct documentation that naturally occurring phenotypes/genotypes that differ in early fecundity, a key life-history trait, also differ phenotypically and genetically in the titer of a key reproductive hormone that potentially regulates that trait.
在生活史进化中，生活史性状变异的激素基础是一个研究较少的课题。识别生活史变异的内分泌 - 遗传原因的一个重要步骤是记录激素滴度与生活史性状不同的基因型/表型之间的统计和功能关联。为此，我们比较了具有飞行能力的形态和翅多型蟋蟀Gryllus firmus的两种无飞行能力形态在成年第一周的血蜕皮甾体滴度和卵巢质量。蜕皮甾体是一组结构相关的激素，可调节昆虫繁殖的许多重要方面。在成年后的第一周，两种无飞行能力形态中的每一种的蜕皮甾体滴度和卵巢质量均显著高于具有飞行能力的形态。来自不同选择品系的形态之间，蜕皮甾体滴度和卵巢质量基于遗传的差异与来自相同对照（未选择）品系的形态之间基于表型的差异相似。到成年第7天，无飞行能力形态的卵巢通常比具有飞行能力的形态大200 - 400%，蜕皮甾体滴度高60 - 300%。此外，在来自对照品系或选择品系的两种有飞行能力和无飞行能力蟋蟀的混合样本中，观察到蜕皮甾体滴度与卵巢质量之间存在高度显著的正表型相关性。无飞行能力形态中的蜕皮甾体滴度充分升高，足以解释其卵巢生长的增加。这是首次直接证明，在早期繁殖力这一关键生活史性状上存在差异的自然发生的表型/基因型，在可能调节该性状的关键生殖激素滴度上也存在表型和遗传差异。
