Light, pattern geometry and colour vision in guppy mate choice

This PhD project aimed to combine information about colour discrimination with mate choice behavioural experiments, bringing new insights into the evolution of colour patterns in sexual selection

Selective disappearance of individuals with high levels of glycated haemoglobin in a free-living bird

This work was supported by the ANR (ANR-06-JCJC0082 to B.D.), the CNRS (PEPS INEE and PICS France–Switzerland to B.D.), the French Ministe`re de l’Enseignement Supe´rieur et de la Recherche (PhD fellowship to C.R.), the Re´gion Rhoˆne-Alpes (Explora’doc mobility grant to C.R.), the University of Aberdeen (stipend to C.R.), the L’Ore´al Foundation-UNESCO ‘For Women in Science’ program (fellowship to C.R.) and the Rectors’ Conference of the Swiss Universities (grant to C.R. and P.B.).Peer reviewedPostprin

An educated guess: how coral reef fish make decisions under uncertainty

For many animals, making informed decisions is crucial to survival. A critical problem is how to make optimal decisions in the face of incomplete, unreliable or conflicting information. In many aquatic environments, fish use visual information to guide key behaviours, but the environment itself can alter or mask the very signals they rely on. Here, we asked how a highly visual species, Rhinecanthus aculeatus, responds to a learned discrimination task as signal reliability decreases, and whether probabilistic information gained during previous experience can be incorporated into their decision strategy. Fish were first trained to select a target (dark grey circle) from three distractors (light grey circles). In the first experiment, the target was more likely to appear in one of four possible stimulus positions. In the second experiment, the target appeared in all positions equally. In a series of trials, the difference in brightness between the target and distractors was reduced until all four stimuli were identical. We found that target selection accuracy decreased with decreasing target and distractor disparity. In experiment 1 where the target was more likely to be in one position, fish increasingly selected stimuli in the biased position as target selection accuracy decreased, but not in experiment 2. These results demonstrate (1) that fish learned more than a simple select/avoid rule based on stimulus brightness; they also integrated information (stimulus position), which could be considered ancillary to the primary task. (2) Fish can learn probability distributions and apply this knowledge as uncertainty increases, ultimately increasing the overall frequency of correct choices. Our results reveal that probabilistic decision rules can be used by fish when visual information is unreliable, indicating a possible mechanism for decision making given the inherent noise in incoming sensory information

Taking a shortcut: what mechanisms do fish use?

Path integration is a powerful navigational mechanism whereby individuals continuously update their distance and angular vector of movement to calculate their position in relation to their departure location, allowing them to return along the most direct route even across unfamiliar terrain. While path integration has been investigated in several terrestrial animals, it has never been demonstrated in aquatic vertebrates, where movement occurs through volumetric space and sensory cues available for navigation are likely to differ substantially from those in terrestrial environments. By performing displacement experiments with Lamprologus ocellatus, we show evidence consistent with fish using path integration to navigate alongside other mechanisms (allothetic place cues and route recapitulation). These results indicate that the use of path integration is likely to be deeply rooted within the vertebrate phylogeny irrespective of the environment, and suggests that fish may possess a spatial encoding system that parallels that of mammals

Sex-specific ecophysiological responses to environmental fluctuations of free-ranging Hermann\u27s tortoises: implication for conservation

Physiological parameters provide indicators to evaluate how organisms respond to conservation actions. For example, individuals translocated during reinforcement programmes may not adapt to their novel host environment and may exhibit elevated chronic levels of stress hormones and/or decreasing body condition. Conversely, successful conservation actions should be associated with a lack of detrimental physiological perturbation. However, physiological references fluctuate over time and are influenced by various factors (e.g. sex, age, reproductive status). It is therefore necessary to determine the range of natural variations of the selected physiological metrics to establish useful baselines. This study focuses on endangered free-ranging Hermann\u27s tortoises (Testudo hermanni hermanni), where conservation actions have been preconized to prevent extinction of French mainland populations. The influence of sex and of environmental factors (site, year and season) on eight physiological parameters (e.g. body condition, corticosterone concentrations) was assessed in 82 individuals from two populations living in different habitats. Daily displacements were monitored by radio-tracking. Most parameters varied between years and seasons and exhibited contrasting sex patterns but with no or limited effect of site. By combining behavioural and physiological traits, this study provides sex-specific seasonal baselines that can be used to monitor the health status of Hermann\u27s tortoises facing environmental threats (e.g. habitat changes) or during conservation actions (e.g. translocation). These results might also assist in selection of the appropriate season for translocation

Success of the receptor noise model in predicting colour discrimination in guppies depends upon the colours tested.

Accurate knowledge of species colour discrimination is fundamental to explain colour based behaviours and the evolution of colour patterns. We tested how the receptor noise limited model, widely used in behavioural ecology, matched actual colour discrimination thresholds obtained using behavioural tests. Guppies (Poecilia reticulata) were first trained to push a target coloured disk placed among eight grey disks of various luminances on a grey plate. Guppies were then tested to find target disks, which varied in colour contrast from the plate. The target disks followed a gradient going from high contrast to inconspicuous against the grey background. We plotted the percentage of correct choices of each colour in the gradient against the model prediction and determined the discrimination thresholds using the inflection point of the fitted sigmoid curve. We performed the experiment on six colour gradients: red, orange, yellow, green, blue and purple. Four colour gradients: red, orange, green and blue, showed a discrimination threshold that matched the model predictions. However, deviations of the model for the yellow and purple gradients suggest that ecological relevance of some colours could affect decision-making in behavioural tests and that we can no longer assume that the rules for colour discrimination are independent of colours

The role of boundary length and adjacent patch contrast in guppy mate choice

The presence of various combinations of adjacent colors within polymorphic species’ color pattern could have a major impact on mate choice. We studied the role of pattern geometry in predicting mate choice in guppies using boundary strength analysis (BSA). BSA estimates the visual contrast intensity between two adjacent color patches (ΔS) weighted by the lengths of the boundaries between these adjacent color patches. We measured both the chromatic (hue and saturation) and achromatic (luminance) ΔS for each pair of adjacent patches. For each male’s color pattern, we measured BSA as both mean (mΔS) and coefficient of variation (cvΔS) of all ΔS weighted by their corresponding boundary lengths. We also determined if specific color patch boundaries had an impact on female preferences and whether these predicted overall male contrast (mΔS). We found that males with a higher mΔS were more attractive to females and that six boundaries containing either fuzzy black or black as one of the pair colors significantly affected female preferences, indicating that 1) females favored highly conspicuous males and 2) melanin-based patches could be used as a signal amplifier, not only for orange but for other colors