Nagle R D, Burke V J, Congdon J D
University of Georgia, Savannah River Ecology Laboratory, Aiken, SC 29802, USA.
Comp Biochem Physiol B Biochem Mol Biol. 1998 May;120(1):145-52. doi: 10.1016/s0305-0491(98)10003-2.
We measured egg components and pre-ovulatory parental investment in kinosternid turtles (Kinosternon baurii, Kinosternon subrubrum, Sternotherus minor, and Sternotherus odoratus) from the southeastern USA. Allocation patterns were determined by comparing lipid content of eggs and hatchlings, to determine whether females of species with hatchlings that exhibit a delayed nest-emergence strategy: (1) allocate higher proportions of energy storage lipids to eggs, (2) produce hatchlings with higher levels of storage lipids, and (3) have higher levels of pre-ovulatory parental investment in comparison to species whose hatchlings exhibit immediate emergence. Whereas total non-polar lipid (NPL) proportions by dry mass of eggs varied significantly among species, NPL proportions of hatchlings were not significantly different. Pre-ovulatory parental investment in care (proportion of hatchling NPL to egg NPL) was 40, 50, and 55% for K. subrubrum, S. minor, and S. odoratus, respectively. Lipid class composition of eggs and hatchlings was studied to distinguish lipids allocated for energy storage from those allocated to other functions. For both eggs and hatchlings, individual lipid classes (triacylglycerol, triacylglycerol fatty acid, cholesterol, cholesterol ester, and phospholipid) as proportions of total lipid, were similar among species. The major lipid class component of eggs and hatchlings of all species was triacylglycerol (> 83%), an energy storage lipid. Substantial changes in lipid classes during embryogenesis were similar among species and included: (1) depletion of triacylglycerol, (2) increase in cholesterol esters, and (3) changes in phospholipid composition. Incubation time varied significantly among species, and appeared to be responsible for differential energy utilization during embryogenesis. Our results are inconsistent with the previously observed pattern that hatchlings exhibiting a delayed nest-emergence strategy are allocated higher proportions of energy storage lipids than those that exhibit immediate emergence. However, because the species that overwinters in the nest (K. subrubrum) hatches approximately 40 days later than the species that typically does not (S. odoratus), hatchling K. subrubrum may contain higher non-polar lipid proportions than hatchling S. odoratus during similar winter time periods. Kinosternid hatchlings contain enough stored lipids to support basal maintenance costs for substantial time periods. We suggest that such reserves may be critical to hatchling survival during a period of negative energy balance, regardless of nest emergence strategy.
我们测量了来自美国东南部的动胸龟（巴氏动胸龟、红腹动胸龟、细纹动胸龟和麝香动胸龟）的卵成分和排卵前亲代投资。通过比较卵和幼体的脂质含量来确定分配模式，以确定具有幼体延迟出巢策略的物种的雌性是否：（1）将更高比例的能量储存脂质分配到卵中；（2）产出具有更高水平储存脂质的幼体；（3）与幼体立即出巢的物种相比，具有更高水平的排卵前亲代投资。尽管按干重计算的卵的总非极性脂质（NPL）比例在物种间有显著差异，但幼体的NPL比例并无显著差异。红腹动胸龟、细纹动胸龟和麝香动胸龟的排卵前亲代照顾投资（幼体NPL与卵NPL的比例）分别为40%、50%和55%。研究了卵和幼体的脂质类别组成，以区分分配用于能量储存的脂质和分配用于其他功能的脂质。对于卵和幼体，各物种间作为总脂质比例的单个脂质类别（三酰甘油、三酰甘油脂肪酸、胆固醇、胆固醇酯和磷脂）相似。所有物种的卵和幼体的主要脂质类别成分都是三酰甘油（>83%），一种能量储存脂质。胚胎发育过程中脂质类别的显著变化在物种间相似，包括：（1）三酰甘油的消耗；（2）胆固醇酯的增加；（3）磷脂组成变化。孵化时间在物种间有显著差异，似乎是胚胎发育过程中能量利用差异的原因。我们的结果与之前观察到的模式不一致，即表现出延迟出巢策略的幼体比表现出立即出巢的幼体分配到更高比例的能量储存脂质。然而，由于在巢中越冬的物种（红腹动胸龟）比通常不越冬的物种（麝香动胸龟）孵化时间晚约40天，在相似的冬季时间段内，红腹动胸龟幼体可能比麝香动胸龟幼体含有更高比例的非极性脂质。动胸龟幼体含有足够的储存脂质，可在相当长的时间内维持基础维持成本。我们认为，无论出巢策略如何，这些储备对于能量负平衡期间幼体的生存可能至关重要。
