Insights into adaptive behavioural plasticity from the guppy model system.

Behavioural plasticity allows organisms to respond to environmental challenges on short time scales. But what are the ecological and evolutionary processes that underlie behavioural plasticity? The answer to this question is complex and requires experimental dissection of the physiological, neural and molecular mechanisms contributing to behavioural plasticity as well as an understanding of the ecological and evolutionary contexts under which behavioural plasticity is adaptive. Here, we discuss key insights that research with Trinidadian guppies has provided on the underpinnings of adaptive behavioural plasticity. First, we present evidence that guppies exhibit contextual, developmental and transgenerational behavioural plasticity. Next, we review work on behavioural plasticity in guppies spanning three ecological contexts (predation, parasitism and turbidity) and three underlying mechanisms (endocrinological, neurobiological and genetic). Finally, we provide three outstanding questions that could leverage guppies further as a study system and give suggestions for how this research could be done. Research on behavioural plasticity in guppies has provided, and will continue to provide, a valuable opportunity to improve understanding of the ecological and evolutionary causes and consequences of behavioural plasticity.

Compiling forty years of guppy research to investigate the factors contributing to (non)parallel evolution.

Examples of parallel evolution have been crucial for our understanding of adaptation via natural selection. However, strong parallelism is not always observed even in seemingly similar environments where natural selection is expected to favour similar phenotypes. Leveraging this variation in parallelism within well-researched study systems can provide insight into the factors that contribute to variation in adaptive responses. Here we analyse the results of 36 studies reporting 446 average trait values in Trinidadian guppies, Poecilia reticulata, from different predation regimes. We examine how the extent of predator-driven phenotypic parallelism is influenced by six factors: sex, trait type, rearing environment, ecological complexity, evolutionary history, and time since colonization. Analyses show that parallel evolution in guppies is highly variable and weak on average, with only 24.7% of the variation among populations being explained by predation regime. Levels of parallelism appeared to be especially weak for colour traits, and parallelism decreased with increasing complexity of evolutionary history (i.e., when estimates of parallelism from populations within a single drainage were compared to estimates of parallelism from populations pooled between two major drainages). Suggestive - but not significant - trends that warrant further research include interactions between the sexes and different trait categories. Quantifying and accounting for these and other sources of variation among evolutionary 'replicates' can be leveraged to better understand the extent to which seemingly similar environments drive parallel and nonparallel aspects of phenotypic divergence.

The effect of group size on sleep in a neotropical bat, Artibeus jamaicensis.

Sleep is associated with many costs, but is also important to survival, with a lack of sleep impairing cognitive function and increasing mortality. Sleeping in groups could alleviate sleep-associated costs, or could introduce new costs if social sleeping disrupts sleep. Working with the Jamaican fruit bat (Artibeus jamaicensis), we aimed to: (1) describe sleep architecture, (2) assess how sleeping in groups affects sleep, and (3) quantify total sleep time and identify rapid eye movement (REM) sleep using behavioral indicators that complement physiological evidence of sleep. Twenty-five adult bats were captured in Panama and recorded sleeping in an artificial roost enclosure. Three bats were fitted with an electromyograph and accelerometer and video recorded sleeping alone in controlled laboratory settings. The remaining 22 bats were assigned to differing social configurations (alone, dyad, triad, and tetrad) and video recorded sleeping in an outdoor flight cage. We found that sleep was highly variable among individuals (ranging from 2 h 53 min to 9 h 39 min over a 12-h period). Although we did not detect statistically significant effects and our sample size was limited, preliminary trends suggest that male bats may sleep longer than females, and individuals sleeping in groups may sleep longer than individuals sleeping alone. We also found a high correspondence between total sleep time quantified visually and quantified using actigraphy (with a 2-min immobility threshold) and identified physiological correlates of behaviorally-defined REM. These results serve as a starting point for future work on the ecology and evolution of sleep in bats and other wild mammals.

Dormir está asociado con muchos costos, pero también es importante para la supervivencia, ya que la falta de sueño perjudica la función cognitiva y aumenta la mortalidad. Dormir en grupos podría disminuir los costos asociados con el sueño o podría introducir nuevos costos si este descanso grupal interrumpe el sueño. Trabajando con el murciélago frugívoro jamaicano (A. jamaicensis), nos propusimos: (1) describir la arquitectura del sueño, (2) evaluar cómo dormir en grupos afecta el sueño y (3) cuantificar el tiempo total de sueño e identificar el sueño REM empleando indicadores de comportamiento que complementen la evidencia fisiológica del sueño. Se capturaron 25 murciélagos adultos en Panamá y se les grabó durmiendo en un recinto artificial de descanso. A tres murciélagos se les equipó con un electromiógrafo y un acelerómetro y se les grabó en video durmiendo solos en entornos de laboratorio controlados. Los 22 murciélagos restantes fueron asignados a diferentes configuraciones sociales (solo, díada, tríada, tétrada) y se grabaron en video durmiendo en una jaula de vuelo al aire libre. El sueño fue muy variable entre individuos (desde 2 h 53 min hasta 9 h 39 min durante un período de 12 h). Aunque no detectamos efectos estadísticamente significativos, y nuestro tamaño muestral fue limitado, las tendencias preliminares sugieren que los murciélagos macho pueden dormir más que las hembras, y que los individuos que duermen en grupos pueden dormir más que los individuos que duermen solos. Encontramos una alta correspondencia entre el tiempo total de sueño cuantificado visualmente y cuantificado mediante actigrafía (con un umbral de inmovilidad de 2 minutos) e identificamos correlaciones fisiológicas de lo que definimos como REM en términos de comportamiento. Estos resultados sirven como punto de partida para futuros estudios sobre la ecología y la evolución del sueño en murciélagos y otros mamíferos salvajes.

Tropical bat ectoparasitism in continuous versus fragmented forests: A gap analysis and preliminary meta-analysis.

Tropical regions are experiencing rapid rates of forest fragmentation, which can have several effects on wildlife, including altered parasite dynamics. Bats are a useful host group to consider the effects of fragmentation, because they are abundant in the tropics, serve important ecological roles, and harbor many parasites. Nevertheless, research on the effects of fragmentation on bat ectoparasites is still limited. To help guide ongoing and future research efforts, this study had two objectives: (1) conduct a gap analysis to characterize the state of currently available research on fragmentation effects on bat ectoparasites and (2) conduct a preliminary meta-analysis to identify current trends. We systematically highlighted several research gaps: Studies comparing the effects of fragmented versus continuous forests on ectoparasites are limited and have primarily been conducted in the Neotropics, with a focus on bats in the superfamily Noctilionidea (especially frugivorous phyllostomids). Our preliminary meta-analysis suggested that ectoparasite prevalence (but not the mean or variance in intensity) was higher in fragments than in continuous forests. Moreover, prevalence increased with increasing roost duration, and mean intensity was higher for bats with higher wing aspect ratios. Intensity variance was affected by an interaction between forest type and wing aspect ratio, such that variance increased for bats with high-wing aspect ratios in continuous forests but decreased in fragments. These results suggest that fragmentation can shape aspects of bat ectoparasitism and could have implications for the ecology, health, and conservation of bats in fragmented landscapes. However, existing research gaps could bias our current understanding of habitat change and bat health, and future research should thus investigate these effects in the Paleotropics and with other bat families.

How might Gyrodactylus parasitism modify trade-offs between female preference and susceptibility of males to predation in Trinidadian guppies?

A number of examples exist of trade-offs between mating success and survival; that is, success in one fitness component comes at the cost of success in the other fitness component. However, these expected trade-offs are - perhaps even more commonly - not observed. One explanation for this apparent paradox of missing trade-offs could be that the other factors generating fitness variation across individuals confound or obscure the expected trade-off. These confounding effects could arise in two general ways: (i) the additional source of variation could positively (or negatively) influence both fitness components ("shared confounder" hypothesis), or (ii) the additional source of variation could influence only one fitness component ("non-shared confounder" hypothesis). We tested whether parasitism by Gyrodactylus spp. could be a confounder of trade-offs between female preference and susceptibility to predation for male Trinidadian guppies (Poecilia reticulata). As in previous work, we did not find the expected trade-off; that is, the males preferred by females were not more likely to be eaten by predators. Because half of the experimental males were infected by Gyrodactylus in a paired design, we were able to show that females discriminated against infected males, but that infected males were not more susceptible to predation. Our results thus provide support for the non-shared confounder hypothesis. That is, by negatively affecting one fitness component (female choice) but not the other (susceptibility to predation), parasitism by Gyrodactylus could obscure the expected trade-off between female preference and susceptibility to predation.