[论文解读] Evidence for a postreproductive phase in female false killer whales Pseudorca crassidens

Theoni Photopoulou, Ines M Ferreira+3 more|arXiv (Cornell University)|Jun 14, 2016

Marine animal studies overview参考文献 32被引用 5

一句话总结

本研究通过卵巢组织分析和非繁殖期比例（PrR）计算，提供了雌性伪虎鲸（Pseudorca crassidens）存在生殖后期寿命（PRLS）的形态学与统计学证据。研究证实了南非与日本两个种群均存在PRLS，其PrR值分别为0.37与0.12，使该物种成为继虎鲸与长鳍瓜头鲸之后第三种被确认具有PRLS的非人哺乳动物，其PRLS水平与虎鲸相近。

ABSTRACT

A substantial period of life after reproduction ends, known as postreproductive lifespan (PRLS), is at odds with classical life history theory. Prolonged PRLS has been confirmed in only two non-human mammals, both odontocete cetaceans. We investigate the evidence for PRLS in a third species, the false killer whale, Pseudorca crassidens, using a quantitative measure of PRLS and morphological evidence from reproductive tissue. We examined specimens from false killer whales from combined strandings (South Africa, 1981) and harvest (Japan 1979-80) and found morphological evidence of changes in the activity of the ovaries in relation to age. Ovulation had ceased in 50% of whales over 45 years, and all whales over 55 years old had ovaries classified as postreproductive. We also calculated a measure of PRLS, known as postreproductive representation (PrR) as an indication of the effect of inter-population demographic variability. PrR for the combined sample was 0.14, whereas the mean of the simulated distribution for PrR under the null hypothesis of no PRLS was 0.02. The 99th percentile of the simulated distribution was 0.08 and no simulated value exceeded 0.13. These results suggest that PrR was convincingly different from the measures simulated under the null hypothesis. We found morphological and statistical evidence for PRLS in South African and Japanese pods of false killer whales, suggesting that this species is the third non-human mammal in which this phenomenon has been demonstrated in wild populations. Our estimates for PrR in false killer whales (0.12-0.37) spanned the single values available for the short-finned pilot whale (0.28) and the killer whale (0.22) and are comparable to estimates for historical or hunter-gather human populations (0.3-0.47).

研究动机与目标

• 调查雌性伪虎鲸是否表现出延长的生殖后期寿命（PRLS），这一现象在非人哺乳动物中极为罕见。
• 利用搁浅与捕获个体的数据，评估野生种群中生殖衰老的生态学与形态学证据。
• 通过非繁殖期比例（PrR）量化PRLS，该指标为统计稳健的度量方法，可校正种群间人口统计学差异。
• 将伪虎鲸的PrR值与其他长寿社会性齿鲸及人类进行比较，以评估PRLS的进化意义。

提出的方法

• 从1981年南非搁浅个体与1979–1980年日本驱赶捕捞个体中，共收集了91只雌性伪虎鲸的卵巢组织样本。
• 通过黄体类型（CLO表示排卵，CLP表示妊娠）及卵巢萎缩程度评估卵巢形态，以判断生殖状态。
• 基于年龄特定生命表数据，计算非繁殖期比例（PrR），即成年寿命中处于非繁殖期的占比。
• 采用基于模拟的假设检验，将观测到的PrR与假设无PRLS的零分布进行比较，使用10,000组模拟数据集。
• 通过比较观测PrR与模拟零分布的第99百分位数（0.08）判断统计显著性，且所有模拟值均未超过0.13。
• 对南非与日本数据集分别进行分析，以评估PRLS证据在不同区域的一致性。

实验结果

研究问题

• RQ1 雌性伪虎鲸在野生种群中是否表现出生殖后期寿命（PRLS）？
• RQ2 所观测到的PRLS是否具有统计显著性，还是可由随机人口统计变异解释？
• RQ3 伪虎鲸的PRLS程度与其他长寿齿鲸（如虎鲸与瓜头鲸）相比如何？
• RQ4 卵巢形态与生殖后期雌性年龄之间存在何种关系？
• RQ5 当分别分析南非与日本种群时，PRLS的证据是否依然稳健？

主要发现

• 超过45岁的雌性伪虎鲸中，50%未显示任何排卵迹象，表明生殖功能已停止。
• 所有年龄超过55岁的雌性均根据卵巢组织组织学检查被归类为非繁殖期，表明其生殖功能已终止。
• 合并样本的非繁殖期比例（PrR）为0.14，显著高于模拟零分布的均值（0.02）与第99百分位数（0.08）。
• 南非样本的PrR为0.37，表明该种群存在强有力的PRLS证据。
• 日本样本的PrR为0.12，同样超过模拟零分布，具有统计显著性。
• 伪虎鲸的PrR值（0.12–0.37）与虎鲸（0.22）、短鳍瓜头鲸（0.28）以及历史/狩猎采集人类种群（0.3–0.47）相当。