STRATOCLADISTICS AND EVALUATION OF EVOLUTIONARY MODES IN THE FOSSIL RECORD: AN EXAMPLE FROM THE AMMONITE GENUS SEMIFORMICERAS

Abstract:  At least two predominating modes of evolution have been proposed for the Early Tithonian oppeliid ammonite genus Semiformiceras , including phyletic transformation of a single lineage ( S. darwini – S. semiforme – S. fallauxi ) and, most recently, a bifurcating or cladogenetic model of speciation. We discuss methodological obstacles in past studies that have focused on specific modes of evolution, and offer a reanalysis of the morphological data first presented by Cecca and Rouget [ Palaeontology , 49 , 1069–1080] using the stratocladistic software StrataPhy. The present analysis utilizes 11 ammonite taxa and 15 characters (14 morphological and one stratigraphic) and assesses all previous phylogenetic hypotheses, including those that recruit OTUs in ancestral or 'nodal' positions, without excluding evolutionary modes. The results cast doubt on the monophyly of S. darwini , S. semiforme and S. fallauxi , but do not follow completely the direct anagenetic progression proposed by stratophenetic hypotheses. We conclude that stratocladistics is a helpful tool for elucidating the extent of anagenesis and cladogenesis in extinct lineages owing to its capacity to reconstruct phylograms in their temporal framework, and to assess the distinctness and monophyly, not just of clades but of the OTUs themselves. Ultimately, this study addresses the novel utility of computer-assisted stratocladistic analysis in assessing evolutionary modes beyond the reach of traditional cladistic-based methodologies.     

Diet and a developmental time constraint alter life‐history trade‐offs in a caddis fly (Trichoptera: Limnephilidae)

Environmental factors influence variation in life histories by affecting growth, development, and reproduction. We conducted an experiment in outdoor mesocosms to examine how diet and a time constraint on juvenile development (pond‐drying) influence life‐history trade‐offs (growth, development, adult body mass) in the caddis fly Limnephilus externus (Trichoptera: Limnephilidae). We predicted that: (1) diet supplementation would accelerate larval growth and development, and enhance survival to adulthood; (2) pond‐drying would accelerate development and increase larval mortality; and (3) the relationship between adult mass and age at maturity would be negative. Diet supplementation did lead to larger adult mass under nondrying conditions, but did not significantly alter growth or development rates. Contrary to predictions, pond‐drying reduced growth rates and delayed development. The slope (positive or negative) of the female mass–age at maturity relationship depended on interactions with diet or pond‐drying, but the male mass–age relationship was negative and independent of treatment. Our results suggest that pond‐drying can have negative effects on the future fitness of individuals by increasing the risk of desiccation‐induced, pre‐reproductive mortality and decreasing adult body size at maturity. These negative effects on life history cannot be overcome with additional nutritional resources in this species. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 495–504.     

下呼吸道重开的生物流体力学研究:实验模拟

实验模拟了受阻塞肺下呼吸道重开的生物力学问题。呼吸是玻璃直圆管,以具有生物流体性质的机油作为阻塞液。实验给同了在压强差作用下阻塞液柱前陈面以及主粘液柱气泡前阵面的位置和速度曲线。结果表明,它们受外加压强,管直径,阻塞液以及初始阻塞液长度的影响。较高的外加中、阻塞液粘度较你攻管径较粗有利于呼吸道的重开。