Department of Biology, University of Louisville, Louisville, KY 40292, USA.
Auburn University Museum of Natural History, Auburn, AL 36849, USA.
Integr Comp Biol. 2024 Nov 21;64(5):1454-1466. doi: 10.1093/icb/icae067.
Strong selective pressure on phenotype can arise when habitat transitions fundamentally alter the physical media in which animals live, such as the invasion of land by lobe-finned fishes and insects. When environmental gradients differ drastically among habitats and multiple lineages transition between these habitats, we expect phenotypic convergence to be prevalent. One transition where widespread convergence has been observed is the shift from aboveground to subterranean environments in fossorial animals. Subterranean environments are low-light, confined spaces and tend to be hypoxic or anoxic, not to mention that the act of burrowing itself demands morphological specializations for excavation. Research suggests burrowing promotes morphological convergence in crayfish, with non-burrowing forms having a dorsoventrally compressed carapace and long, slender claws (chelae), while primary burrowing forms have a dorsolaterally compressed carapace and shorter, more powerful claws. However, earlier ecomorphological comparisons relied on qualitative rather than quantitative assessments of phenotypic differences. This study tested for convergence in North American crayfishes using a geometric morphometric approach. We photographed the carapace and claw for representative species across 13 North American genera. We hypothesized that crayfishes that occur in similar habitats and exhibit similar burrowing behaviors, would converge in their carapace and claw shapes. We found evidence for convergence in carapace and claw morphologies in burrowing crayfishes. However, claw phenotypes did not converge as strongly as carapace shape, an example of "imperfect" or "incomplete" convergence we attribute to the multiple competing demands on claw form and function. We argue that nuances in habitat characteristics, like soil type or compaction, make complete convergence unlikely for range- and dispersal-limited fossorial crayfishes.
当栖息地的转变从根本上改变了动物生活的物理介质时，例如肉鳍鱼类和昆虫对陆地的入侵，就会对表型产生强烈的选择性压力。当环境梯度在栖息地之间有很大差异，并且多个谱系在这些栖息地之间转换时，我们预计表型趋同会很普遍。一个观察到广泛趋同的转变是在穴居动物中从地上到地下环境的转变。地下环境光照低，空间狭窄，往往缺氧或无氧，更不用说挖掘本身就需要形态上的特殊化来进行挖掘。研究表明，挖掘促进了小龙虾的形态趋同，非挖掘形式的甲壳呈背腹压缩状，爪子（螯）长而细，而主要挖掘形式的甲壳呈背侧压缩状，爪子更短、更有力。然而，早期的生态形态比较依赖于对表型差异的定性而不是定量评估。本研究采用几何形态测量方法对北美的小龙虾进行了趋同检验。我们为 13 个北美的属的代表性物种拍摄了甲壳和爪子的照片。我们假设，生活在相似栖息地并表现出相似挖掘行为的小龙虾，其甲壳和爪子形状会趋同。我们发现，在挖掘的小龙虾中，甲壳和爪子形态存在趋同的证据。然而，爪子的表型并没有像甲壳形状那样趋同，这是我们归因于爪子形态和功能的多种竞争需求的“不完美”或“不完全”趋同的一个例子。我们认为，像土壤类型或压实度这样的栖息地特征的细微差别，使得范围和扩散受限的穴居小龙虾不太可能完全趋同。
