Manjarrez Javier, Macías Garcia Constantino, Drummond Hugh
Facultad de Ciencias Universidad Autónoma del Estado de México Toluca State of Mexico Mexico.
Instituto de Ecología Universidad Nacional Autónoma de México Mexico DF Mexico.
Ecol Evol. 2017 Aug 2;7(18):7178-7186. doi: 10.1002/ece3.3265. eCollection 2017 Sep.
Morphological convergence is expected when organisms which differ in phenotype experience similar functional demands, which lead to similar associations between resource utilization and performance. To consume prey with hard exoskeletons, snakes require either specialized head morphology, or to deal with them when they are vulnerable, for example, during molting. Such attributes may in turn reduce the efficiency with which they prey on soft-bodied, slippery animals such as fish. Snakes which consume a range of prey may present intermediate morphology, such as that of Thamnophiine (Natricinae), which may be classified morphometrically across the soft-hard prey dietary boundary. In this study, we compared the dentition and head structure of populations of that have entered the arthropod-crustacean (crayfish)-eating niche and those that have not, and tested for convergence between the former and two distantly related crayfish specialists of the genus (. and ). As a control, we included the congener . Multivariate analysis of jaw length, head length, head width, and number of maxillary teeth yielded three significant canonical variables that together explained 98.8% of the variance in the size-corrected morphological data. The first canonical variable significantly discriminated between the three species. The results show that head dimensions and number of teeth of the two species are more similar to those of crayfish-eating than to non-crayfish-eating snakes or of . It is unclear how particular head proportions or teeth number facilitates capture of crayfish, but our results and the rarity of soft crayfish ingestion by may reflect the novelty of this niche expansion, and are consistent with the hypothesis that some populations of have converged in their head morphology with the two soft crayfish-eating species, although we cannot rule out the possibility of a morphological pre-adaptation to ingest crayfish.
当表型不同的生物体经历相似的功能需求时，预计会出现形态趋同，这会导致资源利用与性能之间产生相似的关联。为了捕食具有坚硬外骨骼的猎物，蛇要么需要特殊的头部形态，要么在猎物脆弱时（例如在蜕皮期间）对付它们。这些特征反过来可能会降低它们捕食软体、滑溜动物（如鱼）的效率。捕食多种猎物的蛇可能呈现出中间形态，例如食鼠蛇属（水游蛇亚科）的形态，这种形态可以通过形态测量在软硬猎物饮食边界上进行分类。在本研究中，我们比较了已进入捕食节肢动物 - 甲壳类（小龙虾）生态位的种群和未进入该生态位的种群的齿列和头部结构，并测试了前者与该属两个远缘小龙虾专家物种（ 和 ）之间的趋同情况。作为对照，我们纳入了同属物种 。对颌长、头长、头宽和上颌齿数进行多变量分析，得出三个显著的典型变量，它们共同解释了大小校正形态数据中98.8%的方差。第一个典型变量显著区分了这三个物种。结果表明，这两个 物种的头部尺寸和齿数与捕食小龙虾的 更相似，而与不捕食小龙虾的蛇或 不同。尚不清楚特定的头部比例或齿数如何促进对小龙虾的捕获，但我们的结果以及 很少摄入软壳小龙虾的情况可能反映了这种生态位扩展的新颖性，并且与这样的假设一致，即 的一些种群在头部形态上与两个捕食软壳小龙虾的 物种趋同，尽管我们不能排除对摄取小龙虾存在形态预适应的可能性。
