La Croix Suzanne, Holekamp Kay E, Shivik John A, Lundrigan Barbara L, Zelditch Miriam Leah
Department of Zoology, Michigan State University, East Lansing, Michigan, USA.
J Morphol. 2011 Jun;272(6):662-74. doi: 10.1002/jmor.10934. Epub 2011 Apr 11.
Developing animals must resolve the conflicting demands of survival and growth, ensuring that they can function as infants or juveniles while developing toward their adult form. In the case of the mammalian skull, the cranium and mandible must maintain functional integrity to meet the feeding needs of a juvenile even as the relationship between parts must change to meet the demands imposed on adults. We examine growth and development of the cranium and mandible, using a unique ontogenetic series of known-age coyotes (Canis latrans), analyzing ontogenetic changes in the shapes of each part, and the relationship between them, relative to key life-history events. Both cranial and mandibular development conform to general mammalian patterns, but each also exhibits temporally and spatially localized maturational transformations, yielding a complex relationship between growth and development of each part as well as complex patterns of synchronous growth and asynchronous development between parts. One major difference between cranium and mandible is that the cranium changes dramatically in both size and shape over ontogeny, whereas the mandible undergoes only modest shape change. Cranium and mandible are synchronous in growth, reaching adult size at the same life-history stage; growth and development are synchronous for the cranium but not for the mandible. This synchrony of growth between cranium and mandible, and asynchrony of mandibular development, is also characteristic of a highly specialized carnivore, the spotted hyena (Crocuta crocuta), but coyotes have a much less protracted development, being handicapped relative to adults for a much shorter time. Morphological development does not predict life-history events in these two carnivores, which is contrary to what has been reported for two rodent species. The changes seen in skull shape in successive life-history stages suggest that adult functional demands cannot be satisfied by the morphology characterizing earlier life-history stages.
发育中的动物必须解决生存和生长之间相互冲突的需求，确保它们在向成年形态发育的同时能够以幼崽或幼年的状态正常运作。就哺乳动物的头骨而言，即使颅骨和下颌骨各部分之间的关系必须改变以满足成年动物的需求，但它们仍必须保持功能完整性，以满足幼年动物的进食需求。我们利用一系列已知年龄的郊狼（犬属草原狼）独特的个体发育序列，研究颅骨和下颌骨的生长与发育，分析各部分形状的个体发育变化以及它们之间相对于关键生命史事件的关系。颅骨和下颌骨的发育都符合一般哺乳动物的模式，但每一个也都表现出时间和空间上局部化的成熟转变，从而在各部分的生长和发育之间产生复杂的关系，以及各部分之间同步生长和异步发育的复杂模式。颅骨和下颌骨之间的一个主要区别在于，颅骨在个体发育过程中大小和形状都会发生巨大变化，而下颌骨仅经历适度的形状变化。颅骨和下颌骨在生长上是同步的，在相同的生命史阶段达到成年大小；颅骨的生长和发育是同步的，但下颌骨不是。颅骨和下颌骨之间的这种生长同步性以及下颌骨发育的异步性，也是高度特化的食肉动物斑鬣狗（斑点鬣狗）的特征，但郊狼的发育过程没有那么漫长，相对于成年动物而言，其发育受限的时间要短得多。形态发育并不能预测这两种食肉动物的生命史事件，这与对两种啮齿动物物种的报道相反。在连续的生命史阶段中颅骨形状的变化表明，成年动物的功能需求无法通过早期生命史阶段所特有的形态来满足。
