Franz-Odendaal Tamara Anne, Adriaens Dominique
Mount Saint Vincent University, Halifax, Nova Scotia Canada.
University of Ghent, Ghent, Belgium.
Evodevo. 2014 Dec 22;5:45. doi: 10.1186/2041-9139-5-45. eCollection 2014.
Seahorses are well known for their highly derived head shape, prehensile tail and armoured body. They belong to the family of teleosts known as Syngnathidae, which also includes the pipefishes, pipehorses and seadragons. Very few studies have investigated the development of the skeleton of seahorses because larvae are extremely difficult to obtain in the wild and breeding in captivity is rarely successful. Here we compare the developmental osteology of Hippocampus reidi over an ontogenetic series spanning the first 93 days after release from the brood pouch to that of a smaller series of Hippocampus; namely H. subelongatus.
We compare the osteology in these two species over growth to the published description of the dwarf species, H. zosterae. We show that ossification onset in H. subelongatus is earlier than in H. reidi, despite similar sizes at parturition. Interestingly, the timing of development of the bony skeleton in H. zosterae is similar to that of the larger species, H. subelongatus. Furthermore, we show that the growth rate of all three species is similar up until about 30 days post pouch release. From this stage onwards in the life history, the size of the dwarf species H. zosterae remains relatively constant whilst the other two species continue growing with an accelerated growth phase.
This data together with a phylogenetic assessment suggests that there has been a heterochronic shift (a delay) in the timing of ossification in H. reidi and accelerated bonedevelopment in H. zosterae. That is, H. zosterae is not a developmentally truncated dwarf species but rather a smaller version of its larger ancestor, "a proportioned dwarf" species. Furthermore, we show that caudal fin loss is incomplete in Hippocampus seahorses. This study shows that these three species of Hippocampus seahorses have evolved (either directly or indirectly) different osteogenic strategies over the last 20-30 million years of seahorse evolution.
海马以其高度特化的头部形状、可抓握的尾巴和披甲的身体而闻名。它们属于硬骨鱼纲中被称为海龙科的家族，该家族还包括尖嘴鱼、管海马和叶形海龙。很少有研究调查海马骨骼的发育情况，因为在野外很难获得幼体，而且圈养繁殖很少成功。在这里，我们比较了雷氏海马从育儿袋中产出后的前93天内整个个体发育过程中的发育骨学，以及较小的海马系列；即长吻海马的发育骨学。
我们将这两个物种在生长过程中的骨学与已发表的矮海马物种的描述进行了比较。我们发现，尽管分娩时大小相似，但长吻海马的骨化开始时间比雷氏海马更早。有趣的是，矮海马的骨骼发育时间与较大的长吻海马相似。此外，我们表明，在育儿袋产出后约30天之前，所有这三个物种的生长速度相似。在生命史的这个阶段之后，矮海马物种的大小保持相对恒定，而其他两个物种则继续生长并进入加速生长阶段。
这些数据以及系统发育评估表明，雷氏海马的骨化时间发生了异时性转变（延迟），而矮海马的骨骼发育加速。也就是说，矮海马不是发育不全的侏儒物种，而是其较大祖先的较小版本，即“比例侏儒”物种。此外，我们表明海马的尾鳍缺失并不完全。这项研究表明，在过去2000万至3000万年的海马进化过程中，这三种海马已经（直接或间接地）进化出了不同的成骨策略。
