Data from: Trophy hunting mediates sex-specific associations between early-life environmental conditions and adult mortality in bighorn sheep

1. Environmental conditions during early development, from conception to
sexual maturity, can have lasting consequences on fitness components.
Although adult lifespan often accounts for much of the variation in
fitness in long-lived animals, we know little about how early environment
affects adult lifespan in the wild, and even less about whether these
effects differ between the sexes. 2. Using data collected over 45 years
from wild bighorn sheep (Ovis canadensis), we investigated the effects of
early environment on adult mortality in both sexes, distinguishing between
natural and anthropogenic sources of mortality. 3. We used the average
body mass of yearlings (at about 15 months of age) as a yearly index of
environmental quality. We first examined sex differences in natural
mortality responses to early environment by censoring harvested males in
the year they were shot. We then investigated sex differences in the
effects of early environment on overall mortality (natural and hunting
mortality combined). Finally, we used path analysis to separate the direct
influence of early environment from indirect influences, mediated by age
at first reproduction, adult mass and horn length. 4. As early
environmental conditions improved, natural adult mortality decreased in
both sexes, although for males the effect was not statistically supported.
Sex differences in the effects of early environment on adult mortality
were detected only when natural and hunting mortality were pooled. Males
that experienced favorable early environment had longer horns as adults
and died earlier because of trophy hunting, which does not mimic natural
mortality. Females that experienced favorable early environment started to
reproduce earlier and early primiparity was associated with reduced
mortality, suggesting a silver-spoon effect. 5. Our results show that
early conditions affect males and females differently because of trophy
hunting. These findings highlight the importance of considering natural
and anthropogenic environmental factors across different life stages to
understand sex differences in mortality.

1. 从受孕至性成熟的早期发育阶段，环境条件会对适合度（fitness）相关组分产生持久影响。尽管在长寿动物中，成体寿命往往解释了适合度变异的大部分来源，但我们对野生环境中早期环境如何影响成体寿命仍知之甚少，而对于这些影响是否存在性别差异则更是所知有限。
2. 本研究依托45余年采集的野生大角羊（Ovis canadensis）观测数据，探究了早期环境对雌雄成体死亡率的影响，并区分了死亡率的自然来源与人为来源。
3. 我们以约15月龄的一岁龄个体（yearlings）的平均体重作为年度环境质量的评价指标。首先，我们通过对当年被猎杀的雄性个体进行截尾处理，检验了早期环境对自然死亡率影响的性别差异；随后，我们探究了早期环境对总死亡率（自然死亡与狩猎死亡合并）影响的性别差异；最后，我们采用路径分析（path analysis）将早期环境的直接影响与通过首次繁殖年龄、成体体重以及角长介导的间接影响相分离。
4. 随着早期环境条件改善，雌雄成体的自然死亡率均有所下降，但该效应在雄性个体中未达到统计学显著性水平。仅当合并自然死亡与战利品狩猎（trophy hunting）死亡数据时，才能检测到早期环境对成体死亡率影响的性别差异。经历优渥早期环境的雄性个体，成体阶段的角更长，但因战利品狩猎的影响而更早死亡，这一死亡模式与自然死亡模式并不一致。而经历优渥早期环境的雌性个体首次繁殖的时间更早，早期初产（primiparity）与死亡率降低相关，这印证了银匙效应（silver-spoon effect）。
5. 本研究结果表明，由于战利品狩猎的存在，早期环境对雌雄个体的影响存在显著差异。这些发现凸显了在解析死亡率的性别差异时，综合考虑不同生命阶段的自然与人为环境因素的重要性。