Evolutionary divergence of developmental plasticity and learning of mating tactics in Trinidadian guppies.

Behavioural plasticity is a major driver in the early stages of adaptation, but its effects in mediating evolution remain elusive because behavioural plasticity itself can evolve. In this study, we investigated how male Trinidadian guppies (Poecilia reticulata) adapted to different predation regimes diverged in behavioural plasticity of their mating tactic. We reared F2 juveniles of high- or low-predation population origins with different combinations of social and predator cues and assayed their mating behaviour upon sexual maturity. High-predation males learned their mating tactic from conspecific adults as juveniles, while low-predation males did not. High-predation males increased courtship when exposed to chemical predator cues during development; low-predation males decreased courtship in response to immediate chemical predator cues, but only when they were not exposed to such cues during development. Behavioural changes induced by predator cues were associated with developmental plasticity in brain morphology, but changes acquired through social learning were not. We thus show that guppy populations diverged in their response to social and ecological cues during development, and correlational evidence suggests that different cues can shape the same behaviour via different neural mechanisms. Our study demonstrates that behavioural plasticity, both environmentally induced and socially learnt, evolves rapidly and shapes adaptation when organisms colonize ecologically divergent habitats.

La plasticidad conductual es un factor importante en las primeras fases de adaptación, pero se conocen poco sus efectos sobre la evolución porque la plasticidad conductual en sí puede evolucionar. En este estudio, investigamos cómo los machos del guppy de Trinidad (Poecilia reticulata) adaptados a regímenes de depredación diferentes, han divergido en la plasticidad de su táctica de apareamiento. Criamos juveniles provenientes de poblaciones de alta y baja depredación hasta segunda generación (F2) bajo diferentes combinaciones de señales sociales y de depredación, y evaluamos su comportamiento de apareamiento al llegar a la madurez sexual. Los machos de alta depredación aprendieron su táctica de apareamiento de sus conespecíficos adultos, mientras que los machos de baja depredación no. Los machos de alta depredación aumentaron su cortejo al ser expuestos a señales de depredadores durante su desarrollo; mientras que los machos de baja depredación redujeron su cortejo en respuesta a señales inmediatas de depredadores, pero tan solo cuando no fueron expuestos a tales señales durante el desarrollo. Los cambios conductuales observados inducidos por las señales de depredación están asociados con una plasticidad en el desarrollo de la morfología cerebral, pero los cambios adquiridos por aprendizaje social no. En conclusión, demostramos que las poblaciones de guppy han divergido en su respuesta a señales sociales y ecológicas durante su desarrollo, y mostramos evidencia correlativa que sugiere que diferentes tipos de señales pueden influenciar el mismo comportamiento via mecanismos neuronales diferentes. Nuestro estudio muestra que la plasticidad conductual, tanto inducida por el medio ambiente combo aprendida socialmente, evoluciona rápidamente e influencia la adaptación durante la colonización de hábitats ecológicamente divergentes.

Obligately silent males sire more offspring than singers in a rapidly evolving cricket population.

How sexual traits are gained and lost in the wild remains an important question in evolutionary biology. Pacific field crickets (Teleogryllus oceanicus) in Hawaii provide an unprecedented opportunity to investigate the factors facilitating evolutionary loss of a sexual signal in real time. Natural selection from an acoustically orienting parasitoid fly drove rapid evolution of a novel, silent male morph. While silent (flatwing) males enjoy protection from the fly, they face difficulty attracting mates. We tested how offspring production varies in association with three male attributes affected by the spread of flatwing: wing morph (flatwing or normal-wing), age (flatwings should survive longer than singers) and exposure to calling song during rearing (wild populations with many flatwings lack ambient calling song). Per mating event, flatwings sired more offspring than singers and older males were mounted more quickly by females when presented with standard courtship song. Despite prior work showing that male age and acoustic experience influence sperm characteristics associated with fertilization, age and song exposure had no influence on male offspring production per mating. This represents the first evidence that the silent male morph possesses a reproductive advantage that may help compensate for precopulatory barriers to mate attraction.

Diversity of Intraspecific Patterns of Brain Region Size Covariation in Fish.

Traits often do not evolve in isolation or vary independently of other traits. Instead, they can be affected by covariation, both within and across species. However, the importance of within-species trait covariation and, critically, the degree to which it varies between species has yet to be thoroughly studied. Brain morphology is a trait of great ecological and behavioral importance, with regions that are hypothesized to vary in size based on behavioral and cognitive demands. Sizes of brain regions have also been shown to covary with each other across various taxa. Here, we test the degree to which covariation in brain region sizes within species has been conserved across 10 teleost fish species. These 10 species span five orders, allowing us to examine how phylogenetic proximity influences similarities in intraspecific trait covariation. Our results showed a trend that similar patterns of brain region size covariation occur in more closely related species. Interestingly, there were certain brain region pairs that showed similar levels of covariation across all species regardless of phylogenetic distance, such as the telencephalon and optic tectum, while others, such as the olfactory bulb and the hypothalamus, varied more independently. Ultimately, the patterns of brain region covariation shown here suggest that evolutionary mechanisms or constraints can act on specific brain regions independently, and that these constraints can change over evolutionary time.