Reznick D N, Braun B
Department of Biology, University of California, 92521, Riverside, CA, USA.
Department of Biochemistry, University of Pennsylvania, 19104, Philadelphia, PA, USA.
Oecologia. 1987 Sep;73(3):401-413. doi: 10.1007/BF00385257.
We argue, based on reviewed literature covering reptiles, amphibians, birds, and fish, that fat storage may represent a life history adaptation because it enables an organism to shift in time when resources are allocated to reproduction. We applied these arguments to fat and population cycles in three populations of the mosquito fish, Gambusia affinis. For males, there appeared to be a constant size at maturation during the reproductive season. Mature males became scarce late in the summer. At the same time, immature males delayed maturity and attained much larger sizes; they matured in large numbers in the fall. The amount of stored fat tended to be equal for immature and mature males at all times except in the late summer. In the August samples, when mature males were relatively rare, they also had the lowest level of fat reserves. It appears that the older generation of mature males did not store fat and did not overwinter. At the same time, immature males registered a two to three fold increase in fat reserves. These differences in fat content between mature and immature males disappeared by September, probably because of the recruitment of a new generation of mature males. The reserves were gradually utilized during the winter. Females reproduced from the late spring through mid- to late-summer. They stopped reproducing in the late summer, when there was ample time to produce an additional litter of young. There was an inverse relationship between resources devoted to reproduction and fat reserves. As reproductive allotment decreased in the late summer, fat reserves increased. The magnitude of the change in fat reserves was similar to that displayed by males. The reserves were depleted over the winter. Significant reserves remained at the beginning of the reproductive season the following spring. Reproducing females utilized the remaining reserves significantly more rapidly than non-reproducing females. An analysis of resource availability revealed an overall decrease in food availability in the late summer, coincident with the increase in fat reserves. These cycles are therefore not attributable to changes in resource availability. They instead indicate a change in how resources are allocated by the fish. The trends in the data indicate that fat reserves are used to shift investment in reproduction from the late summer to the following spring. In males, deferring maturity, rather than maturing in August, allows them to store the necessary reserves to survive the winter so that they can mate the following spring. In females, a subset of the fat reserves is intended for producing the first clutch of eggs the following spring. The female pattern corresponds to those reported for a diversity of organisms. The possible advantages of shifting reproductive effort from the fall to the following spring include higher fecundity and higher offspring fitness. The limitations of the methodology and potential directions for future research are discussed.
基于对爬行动物、两栖动物、鸟类和鱼类的文献综述，我们认为脂肪储存可能代表一种生活史适应，因为它使生物体能够在资源分配给繁殖的时间上进行转移。我们将这些观点应用于食蚊鱼（Gambusia affinis）三个种群的脂肪和种群周期。对于雄性食蚊鱼，在繁殖季节成熟时似乎有一个恒定的体型。成熟雄性在夏末变得稀少。与此同时，未成熟雄性延迟成熟并长得大得多；它们在秋季大量成熟。除了夏末，未成熟和成熟雄性的储存脂肪量在任何时候都趋于相等。在8月的样本中，当成熟雄性相对稀少时，它们的脂肪储备水平也最低。似乎老一代成熟雄性不储存脂肪，也不过冬。与此同时，未成熟雄性的脂肪储备增加了两到三倍。成熟和未成熟雄性之间的脂肪含量差异在9月消失，可能是因为新一代成熟雄性的补充。这些储备在冬季逐渐被利用。雌性从春末到夏中至夏末进行繁殖。它们在夏末停止繁殖，此时有足够的时间产下另一窝幼鱼。用于繁殖的资源与脂肪储备之间存在反比关系。随着夏末繁殖分配的减少，脂肪储备增加。脂肪储备变化的幅度与雄性表现出的相似。这些储备在冬季被耗尽。在次年春季繁殖季节开始时仍有大量储备。繁殖的雌性比不繁殖的雌性更快地利用剩余储备。对资源可用性的分析表明，夏末食物可用性总体下降，与脂肪储备增加同时发生。因此，这些周期并非归因于资源可用性的变化。相反，它们表明鱼类分配资源的方式发生了变化。数据趋势表明，脂肪储备用于将繁殖投资从夏末转移到次年春季。对于雄性来说，推迟成熟而不是在8月成熟，使它们能够储存必要的储备以度过冬天，从而能够在次年春天交配。对于雌性来说，一部分脂肪储备用于次年春季产下第一窝卵。雌性的模式与报道的多种生物体的模式一致。将繁殖努力从秋季转移到次年春季的可能优势包括更高的繁殖力和更高的后代适应性。讨论了该方法的局限性和未来研究的潜在方向。
