The influence of relatedness on parental reproductive success and offspring fitness in Eastern chipmunks breeding in fluctuating environments

Mate choice and multiple paternity have been widely studied in natural
populations, especially in research assessing inbreeding avoidance
mechanisms. Ecological factors are expected to affect the costs and
benefits of mate choice and multiple paternity, for instance, through
their effects on the availability of partners. However, the relative
importance and variation of those costs/benefits across fluctuating
environmental contexts remain to be established. Here, we used
reproduction data collected over 18 years on a wild population of Eastern
chipmunks (Tamias striatus) to assess the influence of relatedness among
mating partners on their reproductive success and on their
offspring's fitness in different breeding contexts. In southern
Québec, chipmunks live in a pulse resource system where they anticipate
masting events of the American beech (Fagus grandifolia) and breed during
the summer preceding and/or the spring following a mast. We found that,
within a litter, less genetically related sires were assigned more
offspring than more closely related ones. This relationship was
significant during the summer breeding seasons only, which is
characterized by high availability of food and mating partners in the
environment. Multiple paternity was also more frequent during summer
breeding than during spring breeding. We found no additional effect of
parental relatedness on the juvenile survival, longevity, or reproductive
success of their offspring. Our results could suggest the presence of
context-specific inbreeding avoidance mechanisms by females or
differential mortality of offspring at early stages linked to inbreeding
depression. Altogether, our findings provide a better understanding of the
influence of fluctuating environments on reproduction in small mammals.

自然种群中的配偶选择与多父本现象已得到广泛研究，尤其是在探究近交回避机制的相关领域。生态因子被认为可通过影响配偶可获得性等途径，改变配偶选择与多父本现象的成本与收益。然而，这些成本与收益在动态环境背景下的相对重要性及其变化规律仍有待阐明。本研究依托18年间采集的东部花栗鼠（Eastern chipmunk, *Tamias striatus*）野生种群繁殖数据，旨在探究不同繁殖背景下，交配伙伴间的亲缘关系对其繁殖成功率以及后代适合度的影响。在魁北克南部地区，花栗鼠栖息于脉冲资源系统中：它们会预判美洲山毛榉（American beech, *Fagus grandifolia*）的大年结实事件，并在结实事件前的夏季以及/或结实后的春季进行繁殖。研究发现，在同一窝幼崽中，与母本遗传亲缘关系较远的父本，其所育幼崽数量显著多于亲缘关系较近的父本。该相关性仅在夏季繁殖季显著——此时环境中食物与配偶的可获得性均较高。夏季繁殖季的多父本现象发生频率也显著高于春季繁殖季。未发现亲本亲缘关系对子代的幼体存活率、寿命或繁殖成功率存在额外影响。本研究结果提示，雌性可能存在背景特异性的近交回避机制，或是存在与近交衰退相关的子代早期差异化死亡现象。综上，本研究结果有助于更深入地理解动态环境对小型哺乳动物繁殖行为的影响。