Relationships between egg size and maternal size, life-history forms, and habitats of Greenlandic Arctic charr (Salvelinus alpinus)

Arctic charr (Salvelinus alpinus [L.] complex) has been widely used as a model system for studies in evolutionary ecology because of its diversity in feeding ecology, habitat use, life-history forms, and associated morphologies observed in matured individuals. However, we still know relatively little about traits exhibited early in life of the species, although the trait diversity of matured individuals may largely be shaped during development. Egg size is a key determinant ofvarious traits exhibited early in life. Therefore, describing egg size variation within- and between-individuals as well as the link between egg size and adult traits will be a useful step in understanding the early life trait diversity of Arctic charr. Here, using Greenlandic Arctic charr, which includes alternative life-history forms (i.e., anadromous and resident) and spawning habitat use (i.e., lake- and river- spawner), we described egg size variation (i.e., clutch-mean egg diameter and within-clutch variation) and explored the link between egg size variation and female body length, life-history form, and spawning habitats. As in many other fishes, clutch-mean egg diameter increased with female body length. No significant effect of other female traits on clutch mean-egg diameter was detected, suggesting that female body size variation could be a direct cause of early life history trait variation. On the other hand, we found that the degree of within-clutch variation of the anadromous life-history form was higher than that of the resident life-history form. The pattern could be interpreted in an adaptive context. For instance, given that the anadromous life-history form tends to be semelparous, anadromous females could decrease the likelihood of complete reproductive failure by producing variable-sized offspring within a clutch since at least some offspring are expected to be matched to the prevailing environment.

北极红点鲑（Arctic charr，*Salvelinus alpinus* [L.]复合类群）因成熟个体在摄食生态、栖息地利用、生活史类型及相关形态特征上表现出丰富多样性，已被广泛用作进化生态学研究的模式系统。然而，尽管成熟个体的性状多样性大概率在发育阶段便已塑造，但我们对该物种早期生命阶段所呈现的性状仍知之甚少。卵大小是早期生命诸多关键性状的核心决定因子。因此，刻画个体内与个体间的卵大小变异，以及卵大小与成体性状之间的关联，将是理解北极红点鲑早期生命性状多样性的重要一步。
本研究以格陵兰北极红点鲑为研究对象，该类群包含两种不同的生活史类型：溯河洄游型（anadromous）与定居型（resident），以及两种产卵栖息地利用模式：湖泊产卵与河流产卵。我们量化了卵大小变异，即单窝平均卵径（clutch-mean egg diameter）与窝内卵径变异（within-clutch variation），并探讨了卵大小变异与雌性体长、生活史类型及产卵栖息地之间的关联。
研究结果显示，与多数其他鱼类一致，单窝平均卵径随雌性体长增加而增大。未检测到其他雌性性状对单窝平均卵径存在显著影响，这表明雌性体型变异可能是早期生命性状变异的直接诱因。另一方面，我们发现溯河洄游型生活史类群的窝内卵径变异程度显著高于定居型类群。该模式可从适应性视角进行解读：例如，鉴于溯河洄游型个体多为单次生殖（semelparous），溯河洄游雌性可通过产出窝内卵径存在差异的后代，降低完全生殖失败的概率，因为至少有部分后代能够匹配所处的环境条件。