Browsing by Subject "LINEAGES"

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Open Access
Complexity by Subtraction
(Evolutionary Biology, 2013) McShea, DW; Hordijk, W
The eye and brain: standard thinking is that these devices are both complex and functional. They are complex in the sense of having many different types of parts, and functional in the sense of having capacities that promote survival and reproduction. Standard thinking says that the evolution of complex functionality proceeds by the addition of new parts, and that this build-up of complexity is driven by selection, by the functional advantages of complex design. The standard thinking could be right, even in general. But alternatives have not been much discussed or investigated, and the possibility remains open that other routes may not only exist but may be the norm. Our purpose here is to introduce a new route to functional complexity, a route in which complexity starts high, rising perhaps on account of the spontaneous tendency for parts to differentiate. Then, driven by selection for effective and efficient function, complexity decreases over time. Eventually, the result is a system that is highly functional and retains considerable residual complexity, enough to impress us. We try to raise this alternative route to the level of plausibility as a general mechanism in evolution by describing two cases, one from a computational model and one from the history of life. © 2013 Springer Science+Business Media New York.
Open Access
Maidenhair ferns, adiantum, are indeed monophyletic and sister to shoestring ferns, vittarioids (Pteridaceae)
(Systematic Botany, 2016-01-01) Pryer, KM; Huiet, L; Li, F; Rothfels, CJ; Schuettpelz, E
© 2016 by the American Society of Plant Taxonomists. Across the tree of life, molecular phylogenetic studies often reveal surprising relationships between taxa with radically different morphologies that have long obscured their close affiliations. A spectacular botanical example is Rafflesia, a holoparasite that produces the largest flowers in the world, but that evolved from tiny-flowered ancestors within the Euphorbiaceae. Outside of parasitic lineages, such abrupt transformations are rarely seen. One exception involves the "maidenhair ferns" (Adiantum), which are quintessential ferns: beautifully dissected, terrestrial, and shade loving. The closely related "shoestring ferns" (vittarioids), in contrast, have an extremely simplified morphology, are canopy-dwelling epiphytes, and exhibit greatly accelerated rates of molecular evolution. While Adiantum and the vittarioids together have been shown to form a robust monophyletic group (adiantoids), there remain unanswered questions regarding the monophyly of Adiantum and the evolutionary history of the vittarioids. Here we review recent phylogenetic evidence suggesting support for the monophyly of Adiantum, and analyze new plastid data to confirm this result. We find that Adiantum is monophyletic and sister to the vittarioids. With this robust phylogenetic framework established for the broadest relationships in the adiantoid clade, we can now focus on understanding the evolutionary processes associated with the extreme morphological, ecological, and genetic transitions that took place within this lineage.