Dispatch R71 about four letters. If, however, they are For this to occur we need to have, in 4. Carrasco, M., Ling, S., and Read, S. (2004). Attention alters appearance. Nat. Neurosci. 7, instructed to report as many letters as Block’s own words ([13] p. 573), 308–313. possible from one particular row then, ‘‘unconscious representations that 5. Motter, B.C. (1993). Focal attention produces even if the instruction is given just after are specific enough to do the task with spatially selective processing in visual cortical areas V1, V2, and V4 in the presence of the letters were presented, observers the observed accuracy. the cue is competing stimuli. J. Neurophysiol. 70, usually manage to report the complete supposed to promote attentional 909–919. 6. Offen, S., Schluppeck, D., and Heeger, D.J. row of four letters. It seems that all of amplification of the cued unconscious (2009). The role of early visual cortex in visual the letters are potentially reportable, specific representation, which, when short-term memory and visual attention. Vision but only four can actually be reported. combined with the conscious generic Res. 49, 1352–1362. 7. Lamme, V.A.F. (2006). Towards a true neural The cue instructs the observer which representation, results in a conscious stance on consciousness. Trends Cogn. Sci. four to select. specific representation of the cued 10, 494–501. 8. Dehaene, S., Changeux, J.-P., Naccache, L., Block [10] emphasises that item.’’ That is, of course, exactly what Sackur, J., and Sergent, C. (2006). Conscious, observers have the impression they see Sergent et al. [3] have found (except preconscious, and subliminal processing: all of the letters even though they that their subjects do not even appear a testable taxonomy. Trends Cogn. Sci. 10, 204–211. cannot report all their identities. He to report a generic representation of 9. Kentridge, R.W., Nijboer, T.C.W., and claims that the experience of the the unseen stimulus). Heywood, C.A. (2008). Attended but unseen: Visual attention is not sufficient for visual unreported items is complete — it is not Sergent et al.’s [3] result does not awareness. Neuropsychologia 46, 864–869. a matter of seeing ‘blurs’ or generic necessarily invalidate the distinction 10. Block, N. (2007). Consciousness, accessibility, impressions of letters, but rather between access and phenomenal and the mesh between psychology and neuroscience. Behav. Brain Sci. 30, 481–548. seeing all of the letters in the array with consciousness, but it does lend weight 11. Sperling, G. (1960). The information available in equal levels of phenomenal detail to the alternative, and perhaps simpler, brief visual presentation. Psychol. Monogr. Gen. Appl. 74, 1–29. despite only able to access the identity position that consciousness is just 12. Cohen, M.A., and Dennett, D. (2011). of the reported subset. Items can exist consciousness. Consciousness cannot be separated from that are seen phenomenally but whose function. Trends Cogn. Sci. 15, 358–364. 13. Block, N. (2011). Perceptual consciousness identity cannot be reported because overflows cognitive access. Trends Cogn. Sci. References 15, 567–575. the capacities of phenomenal and 1. Posner, M.I. (1980). Orienting of attention. Q. J. access consciousness differ. Exp. Psychol. 32, 3–25. The contrary position, for example 2. Carrasco, M. (2011). Visual attention: the past Department of Psychology, Durham 25 years. Vision Res. 51, 1484–1525. [12], is that experience of the 3. Sergent, C., Wyart, V., Babo-Rebelo, M., University, Durham DH1 3LE, UK. unreported items is incomplete and so Cohen, L., Naccache, L., and Tallon-Baudry, C. E-mail: [email protected] (2012). Cueing attention after the stimulus is there is no dissociation between gone can retrospectively trigger conscious experience and cognitive access. perception. Curr. Biol. 23, 150–155. http://dx.doi.org/10.1016/j.cub.2012.11.056

Adaptive Radiation: Convergence Insights into these long-standing questions, as often in evolutionary and Non-equilibrium biology, have come from insular systems, habitats isolated by surroundings that are inhospitable The spectacular adaptive radiation of cichlid fish in Lake Tanganyika to the respective organisms, encompasses extensive morphological convergence and co-occurrence as these provide discrete settings, of ecologically similar species, forcing a reevaluation of non-equilibrium often replicated over space and dynamics in community assembly. time. Moreover, with the advent of sophisticated genomic, isotopic, Rosemary G. Gillespie constrained such that the appearance and visualization tools, it has of certain forms at a given time and become possible to understand the The diversity of life is bewildering, but place becomes ‘‘very probable, if not detailed history of lineages, and the two age-old questions remain: first, is inevitable’’ [2]. With regards to extent to which patterns of species origination dictated by chance patterns of species composition, the differentiation are linked to shifts in evolutionary events or constrained to debate concerns the ‘balance of ecology and associated morphology. follow fairly predictable trajectories? nature’ — the idea that the overall In a recent issue of Current Biology, Second, does the observed diversity diversity at a site tends toward Muschick et al. [3] summarize and composition of species reflect an a relatively steady state. This the results of an extraordinarily equilibrium, and if so, over what time supposition was questioned with the comprehensive study of the period? In terms of species origin, recognition of the importance of adaptive radiation of cichlid fish in one argument is that evolutionary the dynamic nature of biodiversity, the African Great Lakes, in which outcomes are shaped by the whims and that patterns may be governed the ecological identity of species, of immediate events: ‘‘The divine tape more commonly by non-equilibrium and their occurrence within a given player holds a million scenarios . [and] processes in which species diversity community, is frequently predictable. the end results are so different’’ [1]. is inherently unstable and changing The study represents the most The alternative is that outcomes are over time. extensive quantitative analysis to date Current Biology Vol 23 No 2 R72

change in response to different diets, Algae scraper Shrimp eater Picker (invertebrates) placing the animal under a different selective regime; this plastic response may then serve as the basis for subsequent adaptive radiation [14]. Other fish can show similar flexibility. In particular, individuals of anadromous sticklebacks are limnetic EretmodusEretmodus cyanostictuscyanostictus NeolamprologusNeolamprologus prochiluprochiluss GGnathochromisnathochromis ppfefferifefferi when young, becoming more benthic with age: it appears that selection on the timing of this developmentally plastic response has served as the basis for repeated evolution of pairs of benthic and limnetic species as the fish have moved into freshwater lakes [13]. Telmatochromis temporalis Ctenochromis benthicola Tylochromis polylepis The intriguing point is that actual changes in gene frequency can be Current Biology achieved through ecological or developmental plasticity, Figure 1. Tanganyika cichlid ecomorphs. a phenomenon known as ‘genetic Set of three of about a dozen primary ecomorphological types of cichlid fish; each pair accommodation’, and that co-occurs within Lake Tanganyika [3]. Photo credits: Moritz Muschick, Adrian Indermaur, this flexibility may facilitate rapid Walter Salzburger. adaptation while constraining it to specific trajectories. of the ecological underpinnings of of similar genetic changes to allow The second major point made by adaptive radiation in cichlids. rapid and repeated adaptive change, Muschick et al. [3] is that similar The authors [3] make two major including the colonization of freshwater ecomorphs (though not closely points: the first relates to how diversity glacial lakes by marine sticklebacks related species) often co-exist in originated, the second to the dynamics with the repeated evolution of similar Lake Tanganyika, which might be of the communities thus generated. benthic and limnetic forms [9], and the surprising given that theory predicts In the context of the ecological establishment of lizards and mice in competitive exclusion should prevent predictability of species origination, desert environments of North America co-occurrence of taxa that might the authors show that morphological with repeated evolution of traits occupy the same niche. The authors characters, including body and jaw associated with adaptation to the light suggest that the relatively advanced shape, are correlated with the trophic and dry habitats [10]. Likewise, small age of the adaptive radiation in Lake niche (as indicated by stable isotopes changes in a single gene appear to be Tanganyika allows similar ecomorphs and gut content). The important point responsible for the repeated evolution from distant lineages to coexist simply here is that convergence to similar form of similar coloration in the mimicry because they have accumulated is strongly associated with the trophic complexes of Heliconius butterflies differences in other attributes, and niche of the organisms (Figure 1). This [11]. This kind of recurrent evolution of so may occupy slightly different has long been suspected, and has similar forms controlled by the same niches. This pattern is reminiscent served as the basis for the idea of genetic pathways can span many of the Anolis radiation in which ‘ecomorphs’, or sets of species that are taxonomic levels: adaptation to cave co-occurrence of ecomorphs is similar in ecology, morphology, and environments has been found to possible when they differentiate along behavior, but are not necessarily involve a similar mutation at the first another (physiological) axis [5]. closely related [4]. The repeated step of melanin synthesis, in both However, the significance of this evolution of similar functional planthoppers (from Hawaii and Croatia) finding becomes apparent when morphologies has now been illustrated and Mexican cavefish [12]. While it is considered in the context of the in many other adaptive radiations, clear that use of the same genetic growing number of studies showing including Hawaiian finches, Caribbean pathways can explain some of the that co-occurrence of ecologically Anolis lizards [5], Mandarina snails of remarkable examples of convergent equivalent species may be quite the Bonin Islands [6], Hawaiian spiders evolution during adaptive radiation, common in nature [15]. For example, [7], and Hawaiian creepers [8], among there are other factors at play. Perhaps among select groups of treefrogs others (Figure 2). most intriguingly, plasticity has been and lizards, lineages of an ecological The detailed ecomorphological work highlighted as having a major role in form can readily colonize areas in by Muschick et al. [3] in cichlids is adaptive radiation: It appears that which a similar form already resides particularly important in the light of flexibility in ecology, behavior, or [16]. The corollary is that particular recent advances in genomics which are morphology allows organisms to environments may allow many showing that, when similar traits evolve explore the adaptive landscape while evolutionary outcomes, rather than in an adaptive radiation, the same being buffered from the effects of a fixed equilibrium of defined niches. genetic pathways can be deployed, novel genetic variants [13]. Here Indeed, it is not clear as to whether though often in concert with other again, cichlids have provided species composition can achieve genetic changes [9]. There are now a superb illustration: the jaw shape steady state when speciation, as many examples showing deployment of neotropical Midas cichlids can opposed to immigration, is the Dispatch R73

Figure 2. Sets of ecomorphological equiva- A Trunk-crown Trunk-ground Twig lents for different adaptive radiations. The examples illustrate first, the taxonomic Cuba Cuba Cuba diversity across which the repeated evolution of ecomorphological similarity is found; second, the same ecomorph in different islands/lakes is not identical, and conver- gence along one morphological/ecological axis might differ in another; third, while the A. allisoni A. sagrei A. angusticeps occurrence of similar ecomorphs on different islands/lakes is frequently due to conver- Hispaniola Hispaniola Hispaniola gence, as in Anolis lizards and Mandarina snails, it can involve a mixture of both coloni- zation of multiple islands by a single species as well as convergence to the same ecologies between islands, as in the Hawaiian honey- creepers. (A) Anolis lizards — three of six A. chlorocyanus A. cybotes A. insolitus known ecomorphs, from two islands of the Greater Antilles; in each case, the different B Ground Semi-arboreal Arboreal ecomorphs within islands are more closely related to each other than they are to the Chichijima Is. Chichijima Is. Chichijima Is. same ecomorph on the other island [20]. (B) Mandarina land snails — three of four known ecotypes from two of the Bonin Islands in the west Pacific; taxa belonging to lineages within each island are monophyletic [6]. (C) Three of four known ecomorphs of the spiny leg clade M. mandrina M. hirasei M. suenoae of Hawaiian Tetragnatha spiders on older (Kauai, Oahu) and younger (Maui) islands [7]; N Hajajima N Hajajima N Hajajima the taxa shown from different ecomorphs on the same island are more closely related to each other than to the same ecomorph on different islands. (D) Hawaiian honeycreepers showing that similar ecomorphs occur on different islands, though it has involved M. ponderosa M. exoptata M. hahajimana (N type) a mixture of colonization of multiple islands by a single species (the two nectarivores) as C Green Maroon Large brown well as convergence to different ecologies within islands (the insectivore creepers Kauai Oahu Kauai which have evolved independently [8]). Photo credits: A: Jonathan Losos (except A. insolitus – Kevin de Queiroz); B: Satoshi Chi- ba; C: R. Gillespie except T. kamakou, Darko Cotoras; D: Jack Jeffrey. T. kauaiensis T. perreirai T. pilosa principal contributor to species Maui Maui Maui richness: the protracted rate of speciation may prevent diversity reaching a steady state, with species richness dictated simply by diversification rates and time. The finding of co-occurrence of T. waikamoi T. kamakou T. quasimodo ecologically equivalent species is particularly fascinating given recent D Nectarivore (long) Insectivore Nectarivore (short) work on Anolis lizards showing All islands Hawaii All islands that species richness is primarily determined by island-specific limits on total diversification, thus arguing for some form of equilibrium diversity [17]. Meanwhile, studies that have used Vestiaria coccinea Oreomystis mana Himatione sanguinea island chronologies to look at changes in diversity over the course of adaptive Current Biology radiation have revealed a peak of diversity on islands of intermediate age in the archipelagoes of Hawaii [18] and In the cichlid study [3], the authors find if it does, in the context of adaptive Macaronesia [19], though only in more no indication of equilibrium having radiation. The stage is now set for diverse lineages [18]. This pattern been reached in the lineage. Further understanding how convergence suggests that there may be some form research is clearly required to identify might facilitate rapid saturation of of steady state, but the rate at which it the timeframe over which lineage communities, and potentially allow might be attained differs between taxa. diversity might reach equilibrium, ‘super-saturation’ such that multiple Current Biology Vol 23 No 2 R74 species can come together within 9. Elmer, K.R., and Meyer, A. (2011). Adaptation in 16. Wiens, J.J. (2011). The niche, biogeography the age of ecological genomics: insights from and species interactions. Philos. Trans. Roy. a broadly defined niche. parallelism and convergence. Trends Ecol. Soc. B 366, 2336–2350. Evol. 26, 298–306. 17. Rabosky, D.L., and Glor, R.E. (2010). 10. Manceau, M., Domingues, V.S., Linnen, C.R., Equilibrium speciation dynamics in a model References Rosenblum, E.B., and Hoekstra, H.E. (2010). adaptive radiation of island lizards. Proc. 1. Gould, S.J. (1989). Wonderful Life (Cambridge, Convergence in pigmentation at multiple levels: Nat. Acad. Sci. 107, 22178–22183. MA: Harvard University Press). mutations, genes and function. Philos. Trans. 18. Gillespie, R.G., and Baldwin, B.G. (2009). 2. Conway Morris, S. (2003). Life’s Solution: Roy. Soc. B 365, 2439–2450. Island biogeography of remote archipelagos: Inevitable Humans in a Lonely Universe 11. Martin, A., Papa, R., Nadeaud, N.J., Hill, R.I., Interplay between ecological and evolutionary (Cambridge, U.K: Cambridge University Press). Counterman, B.A., Halder, G., Jiggins, C.D., processes. In The Theory of Island 3. Muschick, M., Indermaur, A., and Kronforst, M.R., Long, A.D., McMillan, W.O., Biogeography Revisited, J.B. Losos and Salzburger, W. (2012). Convergent evolution et al. (2012). Diversification of complex butterfly R.E. Ricklefs, eds. (Princeton, NJ: Princeton within an adaptive radiation of cichlid fishes. wing patterns by repeated regulatory evolution University Press), pp. 358–387. Curr. Biol. 22, 2362–2368. of a Wnt ligand. Proc. Nat. Acad. Sci. USA 109, 19. Macı´as-Herna´ ndez, N., Oromı´, P., and 4. Ruber, L., Verheyen, E., and Meyer, A. (1999). 12632–12637. Arnedo, M.A. (2008). Patterns of diversification Replicated evolution of trophic specializations 12. Bilandzija, H., Cetkovic, H., and Jeffery, W.R. on old volcanic islands as revealed by the in an endemic cichlid fish lineage from Lake (2012). Evolution of albinism in cave woodlouse-hunter spider genus Dysdera Tanganyika. Proc. Nat. Acad. Sci. USA 96, planthoppers by a convergent defect in the first (Araneae, Dysderidae) in the eastern Canary 10230–10235. step of melanin biosynthesis. Evol. Dev. 14, Islands. Biol. J. Linn. Soc. 94, 589–615. 5. Losos, J.B. (2009). Lizards in an Evolutionary 196–203. 20. 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Quality Control: Putting Protein It then used quantitative particle Aggregates in a Bind tracking analysis of hundreds of protein aggregates to show that aggregates move in a stochastic but Asymmetric inheritance of protein aggregates in budding yeast is a fascinating confined manner that does not yet controversial area of aging research. A recent study demonstrates that contain any statistically significantly unfolded protein aggregates are confined to the mother by tethering to transport component throughout organelles rather than retrograde transport. the cell cycle [2] (Figure 1A, middle). This finding led to a mathematical model to explain asymmetric Jay R. Unruh1, Brian D. Slaughter1, motility as a result of accumulation in aggregate inheritance based on the and Rong Li1,2,* juxtanuclear quality control study’s phenomenological compartments (JUNQ) or insoluble measurements. The model predicted One of the most intriguing aspects protein deposit compartments (IPOD). that the observed properties of the of aging is the ability of cells to An earlier study suggested that an confined diffusion of the aggregates asymmetrically distribute potentially active transport mechanism involving combined with the geometry of harmful protein aggregates during the actin cables is responsible for the budding yeast cells were sufficient to process of cell division and therefore clearance of heat-shock-induced yield a very low probability of allow half of the progeny of each protein aggregates, decorated with aggregates entering the bud from the division to begin life with a clean slate. the Hsp104 chaperone, from the bud to mother during the time span of a cell Recent studies have investigated the the mother prior to cytokinesis cycle. Parameters of this model that mechanism for this phenomenon in (Figure 1A, top) [1]. This hypothesis impact this probability include the budding yeast [1,2], which undergoes was supported by data showing that cell-cycle duration, the width of the asymmetric mitotic cell division disruption of the actin network led to opening between the bud and the and segregation of aging related defects in asymmetric inheritance of mother, the presence or absence of aggregates between the mother (aged) aggregates and that some aggregates confinement, and the diffusion and bud (newborn) [3,4]. A debate in the bud moved across the bud coefficient of the aggregates. has centered over the role of the neck into the mother side. A later The above model (referred to herein motility of protein aggregates and the study from our laboratory [2] as ‘the stochastic model’), however, contribution of actin in generating questioned this hypothesis, firstly on was based simply on the asymmetric inheritance. A new study by the grounds that cell polarity and well experimentally measured diffusion Spokoini et al. [5] now reveals that oriented actin cables only exist in parameters and made no assumptions certain aggregates are asymmetrically a limited time window prior to entry about the mechanism underlying the inherited due to confinement of their into mitosis, well before cell division [6]. observed confined diffusion of the