Walls Susan C, Belanger Secret S, Blaustein Andrew R
Department of Zoology, Oregon State University, Cordley Hall 3029, 97331-2914, Corvallis, OR, USA.
Oecologia. 1993 Nov;96(2):162-168. doi: 10.1007/BF00317728.
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.
我们研究了哥伦比亚东部长趾蝾螈（Ambystoma macrodactylum columbianum）幼体头部形状的饮食依赖性可塑性。该物种某些种群的幼体表现出营养多态性，一些个体具有夸张的营养特征，这是蝾螈幼体食同类形态的特征；例如，头部异常宽阔，犁骨齿肥大。我们假设：1）头部形状的变化是由于以不同类型的猎物为食所致，以及2）食同类形态是由同类相食引发产生的。为了诱导变化，我们给三组幼体投喂不同的食物：1）仅卤虫无节幼体；2）无节幼体加蛙类蝌蚪；3）无节幼体、蝌蚪和同种幼体蝾螈。对大小（质量）调整后的均值进行比较发现，这种饮食处理在六种头部形状测量指标上诱导出了显著变化，但犁骨齿斑区域没有变化。在六种头部特征中的五种上，食用蝌蚪和卤虫无节幼体的幼体比仅食用卤虫无节幼体的幼体发育出更宽、更长且更深的头部。与仅投喂卤虫无节幼体和蝌蚪的幼体相比，除了无节幼体和蝌蚪之外还摄入同种个体，显著改变了两种头部特征（眼间距和头部深度）。典型判别函数分析检测到两个具有统计学可靠性的典型变量：头部深度与第一个典型变量的相关性最高，而三种头部宽度测量指标（颌部、鳃部和眼部宽度）以及眼间距与第二个典型变量的相关性最高。尽管这种饮食增强了形态变化，但没有迹象表明这三种饮食类型中的任何一种（包括同种猎物）能诱导该物种“食同类者”形态那种夸张的营养特征。这些结果表明，摄入不同类型的猎物有助于头部形状的可塑性，但某些其他直接线索，单独或与饮食变化相结合，对于诱导该物种营养多态性的极端情况至关重要。
