Phillips , who turned to two of his students in the UO Center for Ecology and Evolutionary Biology to help determine what good could possibly come of worms having partners. This article has been cited by other articles in PMC. Given that sexual reproduction is costly from an evolutionary point of view, one could wonder why not all animals and plants reproduce asexually. The major theme of this book is: Hawkmoths are not uncommon in Eurasia, raising the question of why no Eurasian species have evolved hawkmoth pollination. The trend from generalization to specialization characterizes most transitions, although reversals are possible. Molecular studies of genetic changes to floral pigments, particularly loss-of-function mutations, provide insight on why the shift from bee to bird pollination is hard to reverse [ 17 ]. Homomorphic and heteromorphic self-incompatibility systems have multiple origins but breakdown to self-compatibility occurs much more frequently with little evidence for subsequent gains, at least over short time-spans. The traits initially appear within populations and, if adaptive, can spread to survive numerous speciation events and ultimately characterize entire lineages, e.
Here, I review examples of transitions in pollination syndromes that are characterized by a strong directional tendency and consider why these patterns occur. But, evolutionary transitions in reproductive form and function are never entirely unconstrained and many changes exhibit strong directionality. Long-distance dispersal has clearly played a key role in this transition to generalized pollination. Pollinator-mediated selection on reproductive traits is the primary mechanism of floral diversification and can involve different structural adaptations among related species driven by the same type of pollinator, for example, Pedicularis and Bombus [ 12 ], to more specialized floral changes that result from shifts between different functional groups of pollinators [ 13 ]. The offspring of "outcrossing" the sexy science term for mating males and females, on the other hand, share 50 percent of each parent's genes. This article has been cited by other articles in PMC. By contrast, sexual dimorphism in plants is of the much less widely appreciated. Among pollination systems, shifts from bee to hummingbird pollination are rarely reversible, whereas transitions from animal to wind pollination are occasionally reversed. The longevity of reproductive traits and their influence on diversification rates are currently major topics in evolutionary biology [ 7 ]. These include selective mechanisms associated with differences between these pollinator groups in pollen-transfer efficiency, and the nature of genetic mutations in floral pigments associated with the two syndromes [ 15 ]. Cases studies in many animals focusing on both invertebrates and vertebrates and plants reveal parallel, but also singularly novel adaptations to the absence of meiosis and syngamy. But how flexible are angiosperm reproductive traits and are some evolutionary transitions more likely to occur than others? Parallel changes in reproductive characters among unrelated lineages are of special interest as they can provide insights into selective mechanisms and the genetic and developmental basis of trait convergence. We hope that this book not only provides an update to Lloyd and Webb's seminal work but also dispels doubts about the widespread nature of sexual dimorphism in plants. Gender dimorphism in plants has been an active topic of research from theoretical and empirical perspectives, and has been the focus of several re cent reviews and book chapters. Although the lability of floral traits has been considered a hallmark of angiosperm evolution, lineage diversification is never entirely unconstrained. The hummingbird syndrome has originated on numerous occasions, particularly in western North America where it may have occurred more than times [ 15 ]. While males are clearly problematic for several reasons, their evolutionarily benefits do outweigh their costs, Phillips concludes. Here, I consider why this occurs by examining transitions in pollination, mating and sexual systems, some of which have been considered irreversible. Similarly, numerous examples of the shift from outcrossing to predominant self-fertilization are known, but cases of reversal are very limited supporting the view that autogamy usually represents an evolutionary dead-end. For example, in the clade comprising Penstemon and segregate genera, a minimum estimate of 21 separate transitions are reported [ 16 ]. And last but not least, are asexuals really doomed to early extinction or do genuine ancient asexuals exist? It has recently been shown, however, that a single lineage on Madagascar has rapidly evolved secondary specialization involving buzz pollination by carpenter bees Xylocopa spp. Some offspring, naturally, are males that cannot bear offspring. While selfing females don't have to put up with "pesky males" to reproduce, a problem known as the evolutionary "cost" of males, and they can, in fact, populate twice as quickly when going it alone, the genetic benefits of outcrossing explain why the phenomenon exists at all, the researchers explained. The traits initially appear within populations and, if adaptive, can spread to survive numerous speciation events and ultimately characterize entire lineages, e.
Video about selfing sex:
Dolphin self masturbates with beheaded fish
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