Lõhmus Mare, Björklund Mats
Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
PLoS One. 2009;4(2):e4602. doi: 10.1371/journal.pone.0004602. Epub 2009 Feb 26.
Organisms face trade-offs regarding their life-history strategies, such as decisions of single or multiple broods within a year. In passerines displaying facultative multiple breeding, the probability of laying a second clutch is influenced by several life-history factors. However, information about the mechanistic background of these trade-offs is largely lacking. Leptin is a protein hormone produced by white fat cells, and acts as a signal between peripheral energy depots and the central nervous system. In addition, leptin affects cells at all levels of the reproductive axis and plays a critical role in regulating the allocation of metabolic energy to reproduction. As such, it is possible that leptin levels influence the decision of whether or not to invest time and energy into a second clutch. Accordingly, we expect a treatment with exogenous leptin to result in an increased number of second broods.
METHODOLOGY/PRINCIPAL FINDINGS: At a later stage during the first brood, female great tits were treated either with long-term leptin-filled cholesterol pellets (the experimental birds) or with pellets containing only cholesterol (the control birds). We found that leptin-treated females were significantly more likely to have a second brood and that the earlier females were more likely to lay a second clutch than the late females.
CONCLUSIONS/SIGNIFICANCE: As both timing of first brood and treatment with leptin were important in the decision of having multiple broods, the trade-offs involved in the breeding strategy most likely depend on multiple factors. Presumably leptin has evolved as a signal of energy supply status to regulate the release of reproductive hormones so that reproduction is coordinated with periods of sufficient nutrients. This study investigated the role of leptin as a mediator between energy resources and reproductive output, providing a fundamentally new insight into how trade-offs work on a functional basis.
生物体在其生活史策略方面面临权衡，例如一年中单窝或多窝繁殖的决策。在表现出兼性多窝繁殖的雀形目鸟类中，产第二窝卵的概率受多种生活史因素影响。然而，关于这些权衡的机制背景的信息在很大程度上是缺乏的。瘦素是一种由白色脂肪细胞产生的蛋白质激素，在外周能量储存库和中枢神经系统之间起信号作用。此外，瘦素影响生殖轴各级的细胞，并在调节代谢能量向生殖的分配中起关键作用。因此，瘦素水平有可能影响是否投入时间和精力产第二窝卵的决策。相应地，我们预期外源性瘦素处理会导致第二窝雏鸟数量增加。
方法/主要发现：在第一窝雏鸟发育的后期阶段，雌性大山雀要么接受长期填充瘦素的胆固醇丸剂处理（实验鸟），要么接受仅含胆固醇的丸剂处理（对照鸟）。我们发现，经瘦素处理的雌性更有可能产第二窝卵，并且早期雌性比晚期雌性更有可能产第二窝卵。
结论/意义：由于第一窝繁殖的时间和瘦素处理在产多窝卵的决策中都很重要，繁殖策略中涉及的权衡很可能取决于多种因素。瘦素大概已经进化成为能量供应状态的信号，以调节生殖激素的释放，从而使繁殖与营养充足的时期相协调。本研究调查了瘦素作为能量资源与生殖输出之间的调节因子的作用，为权衡在功能基础上如何发挥作用提供了全新的见解。
