Constraints on the Ecomorphological Convergence of Zooplanktivorous Butterflyfishes.

Whether distantly related organisms evolve similar strategies to meet the demands of a shared ecological niche depends on their evolutionary history and the nature of form-function relationships. In fishes, the visual identification and consumption of microscopic zooplankters, selective zooplanktivory, is a distinct type of foraging often associated with a suite of morphological specializations. Previous work has identified inconsistencies in the trajectory and magnitude of morphological change following transitions to selective zooplanktivory, alluding to the diversity and importance of ancestral effects. Here we investigate whether transitions to selective zooplanktivory have influenced the morphological evolution of marine butterflyfishes (family Chaetodontidae), a group of small-prey specialists well known for several types of high-precision benthivory. Using Bayesian ancestral state estimation, we inferred the recent evolution of zooplanktivory among benthivorous ancestors that hunted small invertebrates and browsed by picking or scraping coral polyps. Traits related to the capture of prey appear to be functionally versatile, with little morphological distinction between species with benthivorous and planktivorous foraging modes. In contrast, multiple traits related to prey detection or swimming performance are evolving toward novel, zooplanktivore-specific optima. Despite a relatively short evolutionary history, general morphological indistinctiveness, and evidence of constraint on the evolution of body size, convergent evolution has closed a near significant amount of the morphological distance between zooplanktivorous species. Overall, our findings describe the extent to which the functional demands associated with selective zooplanktivory have led to generalizable morphological features among butterflyfishes and highlight the importance of ancestral effects in shaping patterns of morphological convergence.

A evolução de estratégias similares para suprir as demandas de nichos ecológicos compartilhados em organismos pouco relacionados, depende da sua história evolutiva e da natureza das relações entre forma e função. Em peixes, a identificação visual e o consumo de zooplanctôn microscópico, a zooplanctivoria seletiva, é um tipo distinto de forrageamento frequentemente associado a um conjunto de especializações morfológicas. Estudos anteriores identificaram inconsistências na trajetória e magnitude das mudanças morfológicas que surgem a partir das transições para a zooplanctivoria seletiva, fazendo alusão à diversidade e importância dos efeitos ancestrais. Aqui investigamos se transições para a zooplanctivoria seletiva influenciaram a evolução morfológica dos peixes-borboleta marinhos (família Chaetodontidae), um grupo especialista em presas pequenas conhecido pelos muitos tipos de bentivoria de alta precisão. Utilizando uma estimativa ancestral bayesiana, inferimos a evolução recente da zooplanctivoria dentre os ancestrais bentívoros que caçavam pequenos invertebrados e alimentavam-se de pólipos de coral. Características relacionadas a captura de presa parecem ser funcionalmente versáteis com pouca distinção entre as espécies com modo de forrageamento bentívoro e planctívoro. Em contraste, várias características relacionadas a detecção da presa ou capacidade natatória estão evoluindo em direção a um novo ótimo, específico para a zooplanctivoria. Apesar da história evolutiva relativamente recente, uma morfologia geral comum, e evidência de uma restrição na evolução do tamanho corporal, a evolução convergente reduziu significativamente a distância morfológica entre as espécies zooplanctívoras. No geral, nossos resultados descrevem até que ponto as demandas funcionais associadas à zooplanctivoria seletiva levaram a características morfológicas generalizadas nos peixes-borboleta e destacam a importância dos efeitos ancestrais em moldar os padrões de convergência morfológica.

El hecho de que organismos con parentesco lejano evolucionen estrategias similares para satisfacer las demandas de un nicho ecológico compartido depende de su historia evolutiva y de la naturaleza de la relación forma-función. En peces, la identificación visual y el consumo de plancton microscópico, la zooplanctivoría selectiva, es un tipo específico de alimentación usualmente asociado a un conjunto de especializaciones morfológicas. Estudios previos han identificado inconsistencias en la trayectoria y magnitud de cambios morfológicos tras transiciones hacia zooplanctivoría selectiva, aludiendo a la diversidad e importancia de efectos ancestrales. Aquí investigamos si las transiciones a zooplanctivoría selectiva han influido en la evolución morfológica de los peces mariposa marinos (familia Chaetodontidae), un grupo especializado en presas pequeñas conocido por varios tipos de alimentación de alta precisión en el bentos. Usando una estimación de estado ancestral Bayesiana, inferimos la evolución reciente de la zooplanctivoría entre ancestros bentívoros que cazaron pequeños invertebrados y se alimentaron de pólipos de coral. Los rasgos relacionados con la captura de presas parecen ser versátiles funcionalmente con escasa distinción morfológica entre especies con modos de alimentación bentívoros y planctívoros. En cambio, múltiples rasgos relacionados con la detección de presas o con la capacidad natatoria están evolucionando hacia un nuevo óptimo específico para zooplanctivoría. A pesar de una historia evolutiva relativamente corta, una morfología general común, y evidencia de restricción en la evolución del tamaño de los peces, una evolución convergente ha reducido la distancia morfológica entre especies zooplanctívoras de forma casi significativa. En conclusión, nuestros hallazgos describen hasta qué punto las demandas funcionales asociadas con la zooplanctivoría selectiva han desembocado en rasgos morfológicos generalizados en peces mariposa y destacan la importancia de los efectos ancestrales en la creación de patrones de morfología convergente.

Colour dimorphism in labrid fishes as an adaptation to life on coral reefs.

Conspicuous coloration displayed by animals that express sexual colour dimorphism is generally explained as an adaptation to sexual selection, yet the interactions and relative effects of selective forces influencing colour dimorphism are largely unknown. Qualitatively, colour dimorphism appears more pronounced in marine fishes that live on coral reefs where traits associated with strong sexual selection are purportedly more common. Using phylogenetic comparative analysis, we show that wrasses and parrotfishes exclusive to coral reefs are the most colour dimorphic, but surprisingly, the effect of habitat is not influenced by traits associated with strong sexual selection. Rather, habitat-specific selective forces, including clear water and structural refuge, promote the evolution of pronounced colour dimorphism that manifests colours less likely to be displayed in other habitats. Our results demonstrate that environmental context ultimately determines the evolution of conspicuous coloration in colour-dimorphic labrid fishes, despite other influential selective forces.

Discrimination, reversal, and shift learning in Huntington's disease: mechanisms of impaired response selection.

In a series of three experiments, we investigated different aspects of response selection in early-stage clinically symptomatic Huntington's disease (HD) patients in the context of discrimination learning. A series of structurally related response selection tasks involving discrimination, reversal, and shift learning were employed. In Experiment 1, the mechanisms of our previously reported [37] finding of impaired extra-dimensional shift learning were explored. The results suggested that impaired shift learning in HD is a result of perseverative responding. In Experiment 2, performance on a concurrent-pair (CP) discrimination and reversal task was examined. HD patients showed no deficits in CP discrimination learning or reversal. In Experiment 3, the performance of HD patients on a probabilistic discrimination and reversal task was examined. HD patients were impaired in the learning of a probabilistic discrimination, and also its reversal. This reversal deficit was again the result of perseverative responding. In addition, there was a strong correlation between HD patients' activities of daily living scores and reversal errors. The result are consistent with current theories of the role of the basal ganglia in cognition, and suggest specific impairments in response selection mechanisms in HD, in particular, in overcoming selection biases based on prior reinforcement.