Young parents produce offspring with short telomeres: A study in a long-lived bird, the Black-browed Albatross (Thalassarche melanophrys)

In wild vertebrates, young parents are less likely to successfully rear offspring relative to older ones because of lower parental skills (‘the constraint hypothesis’), lower parental investment (‘the restraint hypothesis’) or because of a progressive disappearance of lower-quality individuals at young ages (‘the selection hypothesis’). Because it is practically difficult to follow an offspring during its entire life, most studies have only focused on the ability of individuals to breed or produce young, while neglecting the ability of such young to subsequently survive and reproduce. Several proxies of individual quality can be useful to assess the ability of young to survive and recruit into the population. Among them, telomere length measurement appears especially promising because telomere length has been linked to longevity and fitness in captive and wild animals. By sampling 51 chicks reared by known-aged parents, we specifically tested whether parental age was correlated to offspring telomere length and body condition in a long-lived bird species, the Black-browed Albatross (Thalassarche melanophrys). Young Black-browed albatrosses produced chicks with shorter telomere relative to those raised by older ones. Short offspring telomeres could result from poor developmental conditions or heritability of telomere length. Moreover, young parents also had chicks of lower body condition when compared with older parents, although this effect was significant in female offspring only. Overall, our study demonstrates that parental age is correlated to two proxies of offspring fitness (body condition and telomere length), suggesting therefore that older individuals provide better parental cares to their offspring because of increased parental investment (restraint hypothesis), better foraging/parental skills (constraint hypothesis) or because only high-quality individuals reach older ages (selection hypothesis).

在野生脊椎动物中，相较于老龄亲代，年轻亲代成功抚育后代的概率更低，这一现象可通过三种假说解释：亲代抚育技能不足（约束假说，constraint hypothesis）、亲代投入水平较低（投入限制假说，restraint hypothesis），或是低质量个体在年轻阶段逐渐被淘汰（选择假说，selection hypothesis）。由于实际追踪后代整个生命周期存在困难，绝大多数相关研究仅关注个体的繁殖产仔能力，却忽略了这些后代后续的存活与种群招募能力。有若干个体质量的替代指标可用于评估后代的存活及种群招募能力，其中端粒长度（telomere length）的检测方法尤其具有应用前景，因为已有研究证实，圈养及野生动物的端粒长度与其寿命及适合度密切相关。本研究以已知亲代年龄的51只雏鸟为研究样本，针对长寿命鸟类黑眉信天翁（Thalassarche melanophrys），专门检验了亲代年龄与后代端粒长度及身体状况的相关性。研究发现，相较于老龄亲代繁育的雏鸟，年轻亲代所育雏鸟的端粒长度更短。后代端粒较短可能源于发育条件不佳，或是端粒长度的遗传特性。此外，相较于老龄亲代，年轻亲代所育雏鸟的身体状况更差，但该效应仅在雌性后代中具有统计学显著性。综上，本研究证实亲代年龄与后代适合度的两项替代指标（身体状况与端粒长度）均存在相关性，这表明老龄亲代能够为后代提供更优质的抚育，这一结果可通过三种假说解释：亲代投入水平提升（投入限制假说，restraint hypothesis）、觅食与抚育技能更为娴熟（约束假说，constraint hypothesis），或是仅高质量个体才能存活至老龄阶段（选择假说，selection hypothesis）。