Fit females and fat polygynous males: seasonal body mass changes in the grey-headed flying fox
Fit females and fat polygynous males: seasonal body mass changes in the grey-headed flying fox
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健康的雌性和肥胖的一夫多妻制雄性：灰头狐蝠的季节性体重变化
作者：
J. Welbergen
当女性和男性在最大生殖努力的时间上不同时，这可能导致体重的性别特异性季节性周期。毫无疑问，这样的周期是在强烈的选择，特别是在蝙蝠，在那里他们影响飞行能力。狐蝠（旧大陆果蝠，狐蝠属）是最大的哺乳动物，可以维持动力飞行，因此面临着关键的权衡，在管理身体储备繁殖，但鲜为人知的是，在这一组的身体质量动态。我调查了体重变化与繁殖行为在一个大的殖民地的灰头狐蝠（Pteropus poliocephalus）。在这种一夫多妻制的哺乳动物中，女性在哺乳期和男性在繁殖季节预计将最大限度地提高生殖努力。正如所预测的那样，女性的身体状况下降，在哺乳期，但没有变化的性活动。相比之下，雄性在繁殖季节之前积累了身体储备，但随后失去了超过20%的身体质量的领土防御和求偶，并失去了觅食的机会，因为他们也在夜间捍卫他们的白天栖息领土。条件较好的男性睾丸较大，特别是在领土建立期间，在最大限度的性活动之前。因此，女性质量的季节性反映了高代谢负荷，哺乳强加给母亲。然而，雄性群体遵循类似于“肥胖雄性现象”的模式，这通常在季节性繁殖的大型一夫多妻哺乳动物中观察到，但不在蝙蝠中。这表明了身体储备的重要性，为繁殖的狐蝠，尽管他们的身体质量的严重限制。
When females and males differ in their timing of maximum reproductive effort, this can result in sex-specific seasonal cycles in body mass. Such cycles are undoubtedly under strong selection, particularly in bats, where they affect flying ability. Flying foxes (Old World fruit bats, Pteropus spp.) are the largest mammals that can sustain powered flight and therefore face critical trade-offs in managing body reserves for reproduction, yet little is known about body mass dynamics in this group. I investigated body mass changes in relation to reproductive behaviour in a large colony of grey-headed flying foxes (Pteropus poliocephalus). In this polygynous mammal, females were predicted to maximise reproductive effort during lactation and males during the breeding season. As predicted, female body condition declined during the nursing period, but did not vary in relation to sexual activity. By contrast, males accumulated body reserves prior to the breeding season, but subsequently lost over 20% of their body mass on territory defence and courtship, and lost foraging opportunities as they also defended their day roost territories at night. Males in better condition had larger testes, particularly during territory establishment, prior to maximum sexual activity. Thus, the seasonality of female mass reflected the high metabolic load that lactation imposes on mothers. However, male mass followed a pattern akin to the “fatted male phenomenon”, which is commonly observed in large polygynous mammals with seasonal reproduction, but not in bats. This shows the importance of body reserves for reproduction in flying foxes, despite their severe constraints on body mass.