When two trees go to war

Rooted phylogenetic networks are used to model non-treelike evolutionary histories. Such networks are often constructed by combining trees, clusters, triplets or characters into a single network that in some well-defined sense simultaneously represents them all. We review these four models and investigate how they are related. Motivated by the parsimony principle, one often aims to construct a network that contains as few reticulations (non-treelike evolutionary events) as possible. In general, the model chosen influences the minimum number of reticulation events required. However, when one obtains the input data from two binary (i.e. fully resolved) trees, we show that the minimum number of reticulations is independent of the model. The number of reticulations necessary to represent the trees, triplets, clusters (in the softwired sense) and characters (with unrestricted multiple crossover recombination) are all equal. Furthermore, we show that these results also hold when not the number of reticulations but the level of the constructed network is minimised. We use these unification results to settle several computational complexity questions that have been open in the field for some time. We also give explicit examples to show that already for data obtained from three binary trees the models begin to diverge.     

When cilia go bad: cilia defects and ciliopathies

Defects in the function of cellular organelles such as peroxisomes, lysosomes and mitochondria are well-known causes of human diseases. Recently, another organelle has also been added to this list. Cilia--tiny hair-like organelles attached to the cell surface--are located on almost all polarized cell types of the human body and have been adapted as versatile tools for various cellular functions, explaining why cilia-related disorders can affect many organ systems. Several molecular mechanisms involved in cilia-related disorders have been identified that affect the structure and function of distinct cilia types.     

When Earth started blooming: insights from the fossil record

Recent palaeobotanical studies have greatly increased the quantity and quality of information available about the structure and relationships of Cretaceous angiosperms. Discoveries of extremely well preserved Cretaceous flowers have been especially informative and, combined with results from phylogenetic analyses of extant angiosperms (based mainly on molecular sequence data), have greatly clarified important aspects of early angiosperm diversification. Nevertheless, many questions still persist. The phylogenetic origin of the group itself remains as enigmatic as ever and, in some cases, newly introduced techniques from molecular biology have given confusing results. In particular, relationships between the five groups of extant seed plants remain uncertain, and it has sometimes proved difficult to reconcile estimates of the time of divergence between extant lineages made using a 'molecular clock' with the fossil record. One result, however, is becoming increasingly clear: a great deal of angiosperm diversity is extinct. Some groups of angiosperms were evidently more diverse in the past than they are today. In other cases, fossils defy assignment to extant groups at the family level or below. This raises the possibility that evolutionary conclusions based solely upon extant taxa that are merely relics of groups that were once much more diverse might be misled by the effects of extinction. It also introduces the possibility that some early enigmatic fossils might represent lineages that diverged from the main line of angiosperm evolution below the most recent common ancestor of all extant taxa. These, and other questions, are among those that need to be addressed by future palaeobotanical research.     

When the lights go down in Cairo: Cinema as secular ritual

Can habits of spectatorship contribute to social transformation? This essay looks at moviegoing in downtown Cairo as a secular ritual that can potentially enable kinds of social change not necessarily envisioned by the state, approved by normative society, or engineered through films themselves. Although filmwatching in Cairene cinemas does, in some cases, verge on the carnivalesque, spectatorship in this context is important primarily as a zone of ambiguity in which middle‐class identity is defined by a tension between establishment visions of order and youthful experimentation.