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Genital Evolution: Cock-A-Doodle-Don't Dispatch R523 prototype is significantly larger than the brain flexibly shifts the reference 9. Leopold, D.A., Bondar, I.V., and Giese, M.A. (2006). Norm-based face encoding by single the one based on voice adaptation. point as we become familiar with neurons in the monkey inferotemporal cortex. Moreover, this relationship was other people’s voices. Also, what is Nature 442, 572–575. stronger than the relationship between the fidelity with which prototypes 10. Andics, A., McQueen, J.M., Petersson, K.M., Gal, V., Rudas, G., and Vidnyanszky, Z. (2010). TVA response and the distance to the represent certain features, and which Neural mechanisms for voice recognition. androgynous prototype. These features, or life experiences, have a Neuroimage 52, 1528–1540. 11. Bruckert, L., Bestelmeyer, P., Latinus, M., additional results strengthen the case greater influence on the formation of Rouger, J., Charest, I., Rousselet, G.A., for the norm-based coding of voice prototypes? Kawahara, H., and Belin, P. (2010). Vocal identity in the TVA. No doubt, studying these issues will attractiveness increases by averaging. Curr. Biol. 20, 116–120. Nonetheless, it is unlikely that continue to provide insights into how 12. Kanwisher, N., McDermott, J., and Chun, M.M. norm-based coding and we so effortlessly identity others and (1997). The fusiform face area: a module in human extrastriate cortex specialized exemplar-based coding accounts are how this process comes to a grinding for face perception. J. Neurosci. 17, mutually exclusive. For instance, halt for people with face or voice 4302–4311. exemplar-based coding might recognition deficits. We will possibly 13. Kayaert, G., Biederman, I., Op de Beeck, H.P., and Vogels, R. (2005). Tuning for shape predominate in certain brain regions, or also better understand how judges like dimensions in macaque inferior temporal when a prototype has not been formed Simon Cowell evaluate exceptional cortex. Eur. J. Neurosci. 22, 212–224. or is difficult to form. Also if many voices/faces, in relation to those that 14. Rhodes, G., Jeffery, L., Boeing, A., and ‘prototypes’ exist, norm-based coding we as a society might not find as Calder, A.J. (2013). Visual coding of human is difficult to distinguish from mesmerizing as the neurons in our bodies: Perceptual aftereffects reveal norm-based, opponent coding of body identity. exemplar-based coding. brains. J. Exp. Psychol. Hum. Percept. Perform 39, 313–317. Glimpse ahead and the ‘Mysterious’ References 15. Nosofsky, R.M. (1992). Exemplar-based 1. Latinus, M., McAleer, P., Bestelmeyer, P.E.G., approach to relating categorization, Prototype and Belin, P. (2013). Norm-based coding of identification, and recognition. In A psychological curiosity is that the voice identity in human auditory cortex. Curr. Multidimensional Models of Perception and Cognition, F.G. Ashby, ed. (Hillsdale, NJ: brain apparently can form a prototype Biol. 23, 1075–1080. 2. Belin, P., Zatorre, R.J., Lafaille, P., Ahad, P., Erlbaum), pp. 363–393. without ever experiencing it. In a and Pike, B. (2000). Voice-selective 16. Palmeri, T.J., and Gauthier, I. (2004). Visual classic study, Posner and Keele [19] areas in human auditory cortex. Nature 403, object understanding. Nat. Rev. Neurosci. 5, 309–312. 291–303. presented participants with many dot 3. Perrodin, C., Kayser, C., Logothetis, N.K., and 17. Grill-Spector, K., and Malach, R. (2001). patterns, which were synthesized by Petkov, C.I. (2011). Voice cells in the primate fMR-adaptation: a tool for studying the functional properties of human cortical distorting a prototype pattern. temporal lobe. Curr. Biol. 21, 1408–1415. 4. Quiroga, R.Q., Fried, I., and Koch, C. (2013). neurons. Acta. Psychol. 107, Although participants never saw the Brain cells for grandmother. Sci. Am. 308, 293–321. prototype during an exposure phase, 30–35. 18. Kahn, D.A., and Aguirre, G.K. (2012). 5. Quiroga, R.Q., Reddy, L., Kreiman, G., Koch, C., Confounding of norm-based and adaptation their responses to it afterwards and Fried, I. (2005). Invariant visual effects in brain responses. Neuroimage 60, suggested that they had abstracted it, representation by single neurons in the human 2294–2299. 19. Posner, M.I., and Keele, S.W. (1968). merely by being exposed to the brain. Nature 435, 1102–1107. 6. Quiroga, R.Q., Kreiman, G., Koch, C., and On the genesis of abstract ideas. J. Exp. distorted dot patterns. Fried, I. (2008). Sparse but not Psychol. 77, 353–363. If the brain does rely on prototypical ‘grandmother-cell’ coding in the medial face or voice representations, even if it temporal lobe. Trends Cogn. Sci. 12, 87–91. 7. Cutzu, F., and Edelman, S. (1996). Faithful Institute of Neuroscience, Newcastle has never experienced them, a number representation of similarities among University, Newcastle upon Tyne, UK. of questions arise: How does the brain three-dimensional shapes in human vision. Proc. Natl. Acad. Sci. USA 93, E-mail: [email protected], form and maintain prototypes? In this 12046–12050. [email protected] regard it is important to consider the 8. Loffler, G., Yourganov, G., Wilkinson, F., and Wilson, H.R. (2005). fMRI evidence for the form of learning; for instance, Andics neural representation of faces. Nat. Neurosci. 8, and colleagues [10] suggest that 1386–1390. http://dx.doi.org/10.1016/j.cub.2013.04.077 Genital Evolution: Cock-a- Biology, we get an answer to the Doodle-Don’t second question in a paper by Herrera et al. [4] that describes a developmental mechanism Losing the penis in species with internal fertilization may seem paradoxical, responsible for the loss of intromittent but birds have managed to do it multiple times. A new study addresses one function in the avian penis. developmental mechanism responsible for penis reduction in birds, and opens Only three percent of avian species the door to further examination of this little understood evolutionary belonging to two main clades have phenomenon. retained the ancestral copulatory organ: the Paleognathes (e.g., Patricia L.R. Brennan the loss of an organ that seems crucial ostriches, kiwis and tinamous), and the to internal fertilization, and how exactly Galloanseridae (e.g., chickens, turkeys, Most amniotes with internal fertilization can a penis be lost? The answer to the megapodes, cracids and ducks) [1]. All have a penis, with the exception of first question is still largely unresolved other birds have completely lost the most birds [1]. What could have driven [2,3]. However, in this issue of Current penis. Avian penis evolution is complex Current Biology Vol 23 No 12 R524 elegantly demonstrating that Bmp4 expression is both necessary and sufficient to regress growth of the penis. Bmps are involved in the development of several other organs [12], so their role in genital reduction suggests the possibility that the loss of the intromittent function of the avian penis may have resulted from pleiotropic selection on another organ system, rather than selection for Figure 1. Avian penis diversity. reduced genitalia per se. If true, Avian penises can be intromittent (A; Rhynchotus, a tinamou), non-intromittent (B; Crypturel- this could explain the seemingly lus), or completely absent (C; Leipoa). paradoxical loss and regression of genitalia in birds. However, the five (see Figure 1Ain[4]). In addition to the regulation of genital growth and independent evolutionary reductions loss of the penis in the ancestor of patterning that are already known and losses of intromittent penis all Neoaves, birds have experienced in mammals would explain the function have occurred in avian multiple reductions of the penis’ differences in morphology of the groups that differ greatly in ecology, intromittent function (at least once in avian penis. morphology and behavior. While most tinamous and twice in galliformes) One possible developmental route tinamous have an intromittent penis and another complete penis loss (in a for the chicken penis to become (Figure 1A), those in the genus megapode) [5]. Herrera et al. provide a non-intromittent would be for it to Crypturellus have a non-intromittent developmental picture of how birds can simply stop growing. Expression of Shh one that is very different from the transition from a fully intromittent to a (a morphogenic protein) and Hoxa13 non-intromittent chicken penis non-intromittent penis by examining and Hoxd13 (transcription factors), is (Figure 1B) [5]. Crypturellus are small genital development of chicken and known to be involved in promoting ground-dwelling forest birds with duck embryos. The chicken penis is genital growth in mammals [9,10]; exclusive male incubation and parental non-intromittent; and although it swells however, their expression was no care, and mating systems ranging during copulation and may help to different between chicken and duck. In from monogamy to promiscuity [13]. direct the ejaculate inside the female addition, cell proliferation response Megapodes are large mound [1], it extends no further than the of genital tissues to these signals was incubators from Australasia; they also proximate portion of the vagina. In similar in both groups. An alternative have a range of mating systems, but in contrast, the duck penis is a fully mechanism is for differential all species males build and defend the intromittent copulatory organ with cell-death/apoptosis to occur in the mound [14]. Some megapodes have a many remarkable features: it can developing chicken penis. Bone non-intromittent penis, while in at achieve prodigious lengths [6], morphogenic proteins (Bmps) are least one species (Leipoa ocellata)it sometimes longer than the known to be involved in apoptosis in is completely lost (Figure 1C) [5]. male himself [7], spirals in a mice genitalia [11]. Herrera et al. report The Phasianoidea superfamily (e.g., counterclockwise direction [1], and that indeed a derived pattern of Bmp chicken, quail and turkey) have features a unique explosive eversion expression results in reduction of non-intromittent penises [1], variable and insemination mechanism [8].
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