Morphological variation in a larval salamander: dietary induction of plasticity in head shape
Morphological variation in a larval salamander: dietary induction of plasticity in head shape
复制标题
蝾螈幼虫的形态变异：饮食诱导头部形状的可塑性
作者：
Susan C. Walls;S. Belanger;A. Blaustein
我们研究了东部长趾蝾螈，Ambystoma macrodactylum columbianum幼虫头部形状的饮食依赖性可塑性。该物种的某些种群中的幼虫表现出营养多态性，一些个体具有夸大的营养特征，这是Ambystoma幼虫的同类相食形态特征;例如，不成比例的宽头和肥大的犁骨齿。我们假设：1）头部形状的变化是由于进食不同类型的猎物，2）同类相食的变种是由消耗同种引起的。为了诱导变异，我们喂了三组幼虫不同的饲料：1）盐水虾无节幼体; 2）无节幼体加无尾类蝌蚪; 3）无节幼体，蝌蚪和同种幼蝾螈。大小（质量）调整的手段的比较显示，这种操纵的饮食引起显着的变化，在6个措施的头部形状，但不是在该地区的犁骨齿补丁。对于六个头部性状中的五个，吃蝌蚪和盐水虾无节幼体的幼虫比只吃盐水虾无节幼体的幼虫发育出更宽、更长和更深的头部。同类的摄入，除了无节幼体和蝌蚪，显着改变两个头部特征（interocular-width和头部深度），相比，幼虫只喂养无节幼体和蝌蚪。典型判别函数分析检测到两个统计上可靠的典型变量：头深与第一典型变量高度相关，而头宽（在下巴，鳃和眼睛）和眼间宽度的三个措施与第二典型变量高度相关。尽管这种饮食增强的形态变化，有没有迹象表明，任何三种类型的饮食（包括同种猎物）诱导夸张的营养功能的“食人族”在这个物种的形态。这些结果表明，不同类型的猎物的摄入有助于头部形状的可塑性，但其他一些接近的线索（S），无论是单独或与饮食变化相结合，是必不可少的，以诱导极端的营养多态性在这个物种。
We examined diet-dependent plasticity in head shape in larvae of the eastern long-toed salamander, Ambystoma macrodactylum columbianum. Larvae in some populations of this species exhibit trophic polymorphism, with some individuals possessing exaggerated trophic features characteristic of a cannibalistic morphology in larval Ambystoma; e.g. a disproportionately broad head and hypertrophied vomerine teeth. We hypothesized that 1) head shape variation results from feeding upon different types of prey and that 2) cannibal morphs are induced by consumption of conspecifics. To induce variation, we fed three groups of larvae different diets: 1) brine shrimp nauplii only; 2) nauplii plus anuran tadpoles; 3) nauplii, tadpoles and conspecific larval salamanders. Comparisons of size (mass)-adjusted means revealed that this manipulation of diet induced significant variation in six measures of head shape, but not in the area of the vomerine tooth patch. For five of the six head traits, larvae that ate tadpoles and brine shrimp nauplii developed significantly broader, longer and deeper heads than did larvae that only ate brine shrimp nauplii. The ingestion of conspecifics, in addition to nauplii and tadpoles, significantly altered two head traits (interocular-width and head depth), compared to larvae only fed nauplii and tadpoles. Canonical discriminant function analysis detected two statistically reliable canonical variables: head depth was most highly associated with the first canonical variable, whereas three measures of head width (at the jaws, gills and eyes) and interocular width were most highly associated with the second canonical variable. Despite this diet-enhanced morphological variation, there was no indication that any of the three types of diet (including conspecific prey) induced the exaggerated trophic features of the “cannibal” morph in this species. These results illustrate that ingestion of different types of prey contributes to plasticity in head shape, but that some other proximate cue(s), either alone or in combination with diet variation, is essential to induce the extremes of trophic polymorphism in this species.