Rawlings Timothy A
Department of Zoology, University of Alberta, Edmonton, Alberta, T6G 2E9.
Bamfield Marine Station, Bamfield, B.C., V0R 1B0, Canada.
Evolution. 1994 Aug;48(4):1301-1313. doi: 10.1111/j.1558-5646.1994.tb05314.x.
Representatives of many plant and animal taxa enclose their embryos within some form of protective structure. Inter- and intraspecific differences in the morphology of these egg coverings may have profound effects on the development and survival of encapsulated embryos, yet in many taxa little is known about the causes or potential consequences of this variation. Comparisons of capsule morphology among populations of the rocky shore gastropod, Nucella emarginata, revealed significant variation in the thickness of capsule walls, the only barrier separating developing embryos from the external environment. Laboratory experiments demonstrated that thicker-walled capsules were more resistant to predation by a co-occurring isopod, Gnorimosphaeroma oregonense, than were thinner-walled capsules. Control experiments confirmed that these differences in vulnerability were not caused by differences in the palatability of the capsule wall or attractiveness of the capsule contents. The actual mechanism by which thick-walled capsules differentially protect developing embryos remains unclear, although decreased vulnerability of thick-walled capsules to these isopods may simply result from increased handling time by predators. Subtle differences in capsule morphology thus appear to have substantial effects on the survival of encapsulated embryos. Hence, predators may have played an important role in selecting for the production of thick-walled capsules among populations of N. emarginata.
许多动植物类群的代表会将其胚胎包裹在某种形式的保护结构内。这些卵覆盖物形态上的种间和种内差异可能对被包裹胚胎的发育和存活产生深远影响，然而在许多类群中，对于这种变异的原因或潜在后果却知之甚少。对岩石海岸腹足动物——凹缘核螺（Nucella emarginata）不同种群的卵囊形态进行比较后发现，卵囊壁的厚度存在显著差异，而卵囊壁是将发育中的胚胎与外部环境分隔开的唯一屏障。实验室实验表明，与薄壁卵囊相比，厚壁卵囊更能抵抗同时存在的一种等足目动物——俄勒冈瘤背蜾蠃蜚（Gnorimosphaeroma oregonense）的捕食。对照实验证实，这些易感性差异并非由卵囊壁的适口性或卵囊内容物的吸引力差异所致。尽管厚壁卵囊对这些等足目动物的易感性降低可能仅仅是因为捕食者的处理时间增加，但厚壁卵囊以何种实际机制来差异保护发育中的胚胎仍不清楚。因此，卵囊形态的细微差异似乎对被包裹胚胎的存活有重大影响。所以，捕食者可能在凹缘核螺不同种群中选择产生厚壁卵囊的过程中起到了重要作用。
