Sankar Murugesan, Fraser Thomas W K, Kryvi Harald, Hvas Malthe, Hansen Tom J, Fjelldal Per Gunnar
Reproduction and Developmental Biology Group, Institute of Marine Research (IMR), Matre Aquaculture Research station, Matredal, Norway.
Department of Biological Sciences, University of Bergen, Bergen, Norway.
J Fish Biol. 2025 Aug;107(2):441-453. doi: 10.1111/jfb.70032. Epub 2025 Apr 9.
The teleostean post-cranial axial skeleton is a highly specialized structure for an aquatic mode of life. However, there is limited knowledge regarding parental contributions, early-life environmental impacts on its meristic variation and if reduced heterozygosity challenges its development. To address this, the present study used isogenic homozygous and heterozygous lines of Atlantic salmon (Salmo salar) combined with ploidy manipulation (triploidization) to manipulate parental contributions, and incubation temperature (4 vs. 8°C) as an early-life variable, and reared the fish to ~150 g for a detailed radiological examination. Genetically identical fish incubated at 4°C, but not 8°C, segregated into two size modes (upper/lower), which differed in dorsal and tail fin lepidotrich counts as well as anal-fin pterygiophore counts. Incubation temperature did not impact on vertebrae counts, whereas 8°C incubation produced more supraneurals than 4°C incubation. After 8°C incubation, homozygous diploids (100% maternal chromosomes) and heterozygous triploids (67% maternal chromosomes) developed lower total vertebrae and dorsal- and anal-fin pterygiophore counts than heterozygous diploids (50% maternal chromosomes). For tail fin lepidotrichs, the same groups showed the following pattern: diploid heterozygous > triploid heterozygous > diploid homozygous. Homozygous diploids developed a high level of complete fusions in the vertebral column. The result of the present study indicates that the ability to enter different growth modes is dependent on embryo incubation temperature and may be controlled by epigenetic mechanisms. Further, the results show a strong maternal dosage effect on tail fin lepidotrich counts, whereas for other post-cranial skeletal parts, the presence of extra maternal chromosomes seems to overrule the paternal contribution. The findings may reflect evolutionary adaptations for the shaping of offspring phenotypes. Such mechanisms would impact on important fitness-related traits, such as swimming ability and fecundity, which are relevant for conservation and evolutionary biology and ecological and aquaculture sciences. Vertebral deformities developing in homozygous fish seem to be supported by active repair mechanisms, which may reflect an organism's ability to reduce the cost of inbreeding.
硬骨鱼的颅后轴骨骼是一种高度特化的结构，以适应水生生活方式。然而，关于亲代贡献、早期生活环境对其可数性状变异的影响，以及杂合性降低是否会对其发育构成挑战，我们所知有限。为了解决这个问题，本研究使用了大西洋鲑（Salmo salar）的同基因纯合和杂合品系，并结合倍性操作（三倍体化）来控制亲代贡献，同时将孵化温度（4℃与8℃）作为早期生活变量，将鱼饲养至约150克进行详细的放射学检查。在4℃而非8℃下孵化的基因相同的鱼分为两种大小模式（上/下），它们在背鳍和尾鳍鳍条数量以及臀鳍鳍担骨数量上存在差异。孵化温度对椎骨数量没有影响，而8℃孵化产生的上神经骨比4℃孵化更多。在8℃孵化后，纯合二倍体（100%母本染色体）和杂合三倍体（67%母本染色体）发育出的总椎骨数量以及背鳍和臀鳍鳍担骨数量均低于杂合二倍体（50%母本染色体）。对于尾鳍鳍条，相同的组呈现出以下模式：二倍体杂合>三倍体杂合>二倍体纯合。纯合二倍体在脊柱中出现了高水平的完全融合。本研究结果表明，进入不同生长模式的能力取决于胚胎孵化温度，可能受表观遗传机制控制。此外，结果显示母本剂量对尾鳍鳍条数量有强烈影响，而对于其他颅后骨骼部分，额外母本染色体的存在似乎压倒了父本贡献。这些发现可能反映了塑造后代表型的进化适应性。这种机制将影响重要的与适应性相关的性状，如游泳能力和繁殖力，这与保护生物学、进化生物学以及生态和水产科学相关。纯合鱼中出现的椎骨畸形似乎得到了活跃修复机制的支持，这可能反映了生物体降低近亲繁殖成本的能力。
