Womack Molly C, Bell Rayna C
Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA.
Department of Biology, Utah State University, Logan, Utah, USA.
J Evol Biol. 2020 Oct;33(10):1417-1432. doi: 10.1111/jeb.13679. Epub 2020 Aug 2.
Surprisingly, little is known about body-size evolution within the most diverse amphibian order, anurans (frogs and toads), despite known effects of body size on the physiological, ecological and life-history traits of animals more generally. Here, we examined anuran body-size evolution among 2,434 species with over 200 million years of shared evolutionary history. We found clade-specific evolutionary shifts to new body-size optima along with numerous independent transitions to gigantic and miniature body sizes, despite the upper limits of anuran body size remaining quite consistent throughout the fossil record. We found a weak, positive correlation between a species' body size and maximum latitude and elevation, including a dearth of small species at higher elevations and broader latitudinal and elevational ranges in larger anurans. Although we found modest differences in mean anuran body size among microhabitats, there was extensive overlap in the range of body sizes across microhabitats. Finally, we found that larger anurans are more likely to consume vertebrate prey than smaller anurans are and that species with a free-swimming larval phase during development are larger on average than those in which development into a froglet occurs within the egg. Overall, anuran body size does not conform to geographic and ecological patterns observed in other tetrapods but is perhaps more notable for variation in body size within geographic regions, ecologies and life histories. Here, we document this variation and propose target clades for detailed studies aimed at disentangling how and why variation in body size was generated and is maintained in anurans.
令人惊讶的是，尽管体型对动物的生理、生态和生活史特征具有普遍影响，但对于最多样化的两栖动物目——无尾目（青蛙和蟾蜍）内的体型进化，我们却知之甚少。在此，我们研究了2434个物种的无尾目体型进化，这些物种拥有超过2亿年的共同进化历史。我们发现，尽管在整个化石记录中无尾目体型的上限相当一致，但仍存在特定分支向新的体型最优值的进化转变，以及众多向巨大体型和微小体型的独立转变。我们发现一个物种的体型与最大纬度和海拔之间存在微弱的正相关，包括高海拔地区小物种的缺乏，以及大型无尾目动物更广泛的纬度和海拔范围。尽管我们发现不同微生境中的无尾目平均体型存在适度差异，但各微生境的体型范围有广泛重叠。最后，我们发现大型无尾目动物比小型无尾目动物更有可能捕食脊椎动物猎物，并且在发育过程中有自由游动幼体阶段的物种平均比那些在卵内发育成幼蛙的物种体型更大。总体而言，无尾目体型并不符合在其他四足动物中观察到的地理和生态模式，但其在地理区域、生态和生活史内的体型变化可能更为显著。在此，我们记录了这种变化，并提出了目标分支，以便进行详细研究，旨在弄清楚无尾目体型变化是如何产生以及为何得以维持的。
