Savriama Yoland, Valtonen Mia, Kammonen Juhana I, Rastas Pasi, Smolander Olli-Pekka, Lyyski Annina, Häkkinen Teemu J, Corfe Ian J, Gerber Sylvain, Salazar-Ciudad Isaac, Paulin Lars, Holm Liisa, Löytynoja Ari, Auvinen Petri, Jernvall Jukka
Developmental Biology Program, Institute of Biotechnology, University of Helsinki, PO Box 56, 00014 Helsinki, Finland.
Department of Environmental and Biological Sciences, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland.
R Soc Open Sci. 2018 Nov 28;5(11):180903. doi: 10.1098/rsos.180903. eCollection 2018 Nov.
An increasing number of mammalian species have been shown to have a history of hybridization and introgression based on genetic analyses. Only relatively few fossils, however, preserve genetic material, and morphology must be used to identify the species and determine whether morphologically intermediate fossils could represent hybrids. Because dental and cranial fossils are typically the key body parts studied in mammalian palaeontology, here we bracket the potential for phenotypically extreme hybridizations by examining uniquely preserved cranio-dental material of a captive hybrid between grey and ringed seals. We analysed how distinct these species are genetically and morphologically, how easy it is to identify the hybrids using morphology and whether comparable hybridizations happen in the wild. We show that the genetic distance between these species is more than twice the modern human-Neanderthal distance, but still within that of morphologically similar species pairs known to hybridize. By contrast, morphological and developmental analyses show grey and ringed seals to be highly disparate, and that the hybrid is a predictable intermediate. Genetic analyses of the parent populations reveal introgression in the wild, suggesting that grey-ringed seal hybridization is not limited to captivity. Taken together, we postulate that there is considerable potential for mammalian hybridization between phenotypically disparate taxa.
基于基因分析，越来越多的哺乳动物物种被证明存在杂交和基因渗入的历史。然而，只有相对较少的化石保存了遗传物质，因此必须利用形态学来识别物种，并确定形态学上的中间型化石是否可能代表杂交种。由于牙齿和颅骨化石通常是哺乳动物古生物学研究的关键身体部位，因此我们通过研究一只圈养的灰海豹和环斑海豹杂交种独特保存的颅齿材料，来界定表型极端杂交的可能性。我们分析了这些物种在基因和形态上的差异程度，利用形态学识别杂交种的难易程度，以及在野外是否会发生类似的杂交。我们发现，这些物种之间的遗传距离是现代人类与尼安德特人之间距离的两倍多，但仍在已知会杂交的形态相似物种对的范围内。相比之下，形态学和发育分析表明，灰海豹和环斑海豹差异很大，而杂交种是可预测的中间型。对亲本种群的基因分析揭示了野外的基因渗入现象，这表明灰海豹与环斑海豹的杂交并不局限于圈养环境。综合来看，我们推测在表型差异较大的分类群之间，哺乳动物存在相当大的杂交潜力。
