Aquatic noise pollution: implications for individuals, populations, and ecosystems

Anthropogenically driven environmental changes affect our planet at an unprecedented scale, and are considered to be a key threat to biodiversity. According to the World Health Organisation, anthropogenic noise is one of the most hazardous forms of anthropogenically driven environmental change and is recognised as a major global pollutant. However, crucial advances in the rapidly emerging research on noise pollution focus exclusively on single aspects of noise pollution, e.g. on behaviour, physiology, terrestrial ecosystems or by focusing on certain taxa. Given that more than two thirds of our planet is covered with water, there is a pressing need to get a holistic understanding of the effects of anthropogenic noise in aquatic ecosystems. We found experimental evidence for negative effects of anthropogenic noise on an individual’s development, physiology, and/or behaviour in both invertebrates and vertebrates. We also found that species differ in their response to noise, and highlight the potential underlying mechanisms for these differences. Finally, we point out challenges in the study of aquatic noise pollution and provide directions for future research, which will enhance our understanding of this globally present pollutant.

Induction of apoptosis by UV in the flat oyster, Ostrea edulis

Apoptosis is a fundamental feature in the development of many organisms and tissue systems. It is also a mechanism of host defense against environmental stress factors or pathogens by contributing to the elimination of infected cells. Hemocytes play a key role in defense mechanisms in invertebrates and previous studies have shown that physical or chemical stress can increase apoptosis in hemocytes in mollusks. However this phenomenon has rarely been investigated in bivalves especially in the flat oyster Ostrea edulis. The apoptotic response of hemocytes from flat oysters, O. edulis, was investigated after exposure to UV and dexamethasone, two agents known to induce apoptosis in vertebrates. Flow cytometry and microscopy were combined to demonstrate that apoptosis occurs in flat oyster hemocytes. Investigated parameters like intracytoplasmic calcium activity, mitochondrial membrane potential and phosphatidyl-serine externalization were significantly modulated in cells exposed to UV whereas dexamethasone only induced an increase of DNA fragmentation. Morphological changes were also observed on UV-treated cells using fluorescence microscopy and transmission electron microscopy. Our results confirm the apoptotic effect of UV on hemocytes of O. edulis and suggest that apoptosis is an important mechanism developed by the flat oyster against stress factors.

Reorganisation ofHoxdregulatory landscapes during the evolution of a snake-like body plan

Within land vertebrate species, snakes display extreme variations in their body plan, characterized by the absence of limbs and an elongated morphology. Such a particular interpretation of the basic vertebrate body architecture has often been associated with changes in the function or regulation of Hox genes. Here, we use an interspecies comparative approach to investigate different regulatory aspects at the snake HoxD locus. We report that, unlike in other vertebrates, snake mesoderm-specific enhancers are mostly located within the HoxD cluster itself rather than outside. In addition, despite both the absence of limbs and an altered Hoxd gene regulation in external genitalia, the limb-associated bimodal HoxD chromatin structure is maintained at the snake locus. Finally, we show that snake and mouse orthologous enhancer sequences can display distinct expression specificities. These results show that vertebrate morphological evolution likely involved extensive reorganisation at Hox loci, yet within a generally conserved regulatory framework.

X-Linked Retinitis Pigmentosa 2 Is a Novel Maternal-Effect Gene Required for Left-Right Asymmetry in Zebrafish

Retinitis pigmentosa 2 (RP2) gene is responsible for up to 20% of X-linked retinitis pigmentosa, a severe heterogeneous genetic disorder resulting in progressive retinal degeneration in humans. In vertebrates, several bodies of evidence have clearly established the role of Rp2 protein in cilia genesis and/or function. Unexpectedly, some observations in zebrafish have suggested the oocyte-predominant expression of the rp2 gene, a typical feature of maternal-effect genes. In the present study, we investigate the maternal inheritance of rp2 gene products in zebrafish eggs in order to address whether rp2 could be a novel maternal-effect gene required for normal development. Although both rp2 mRNA and corresponding protein are expressed during oogenesis, rp2 mRNA is maternally inherited, in contrast to Rp2 protein. A knockdown of the protein transcribed from both rp2 maternal and zygotic mRNA results in delayed epiboly and severe developmental defects, including eye malformations, that were not observed when only the protein from zygotic origin was knocked down. Moreover, the knockdown of maternal and zygotic Rp2 revealed a high incidence of left-right asymmetry establishment defects compared to only zygotic knockdown. Here we show that rp2 is a novel maternal-effect gene exclusively expressed in oocytes within the zebrafish ovary and demonstrate that maternal rp2 mRNA is essential for successful embryonic development and thus contributes to egg developmental competence. Our observations also reveal that Rp2 protein translated from maternal mRNA is important to allow normal heart loop formation, thus providing evidence of a direct maternal contribution to left-right asymmetry establishment.

The RGBarrier assay: the parallel study of gene regulatory element performance at defined chromosomal locations

Vertebrate genomes are organised into a variety of nuclear environments and chromatin states that have profound effects on the regulation of gene transcription. This variation presents a major challenge to the expression of transgenes for experimental research, genetic therapies and the production of biopharmaceuticals. The majority of transgenes succumb to transcriptional silencing by their chromosomal environment when they are randomly integrated into the genome, a phenomenon known as chromosomal position effect (CPE). It is not always feasible to target transgene integration to transcriptionally permissive “safe harbour” loci that favour transgene expression, so there remains an unmet need to identify gene regulatory elements that can be added to transgenes which protect them against CPE. Dominant regulatory elements (DREs) with chromatin barrier (or boundary) activity have been shown to protect transgenes from CPE. The HS4 element from the chicken beta-globin locus and the A2UCOE element from a human housekeeping gene locus have been shown to function as DRE barriers in a wide variety of cell types and species. Despite rapid advances in the profiling of transcription factor binding, chromatin states and chromosomal looping interactions, progress towards functionally validating the many candidate barrier elements in vertebrates has been very slow. This is largely due to the lack of a tractable and efficient assay for chromatin barrier activity. In this study, I have developed the RGBarrier assay system to test the chromatin barrier activity of candidate DREs at pre-defined isogenic loci in human cells. The RGBarrier assay consists in a Flp-based RMCE reaction for the integration of an expression construct, carrying candidate DREs, in a pre-characterised chromosomal location. The RGBarrier system involves the tracking of red, green and blue fluorescent proteins by flow cytometry to monitor on-target versus off-target integration and transgene expression. The analysis of the reporter (GFP) expression for several weeks gives a measure of the protective ability of each candidate elements from chromosomal silencing. This assay can be scaled up to test tens of new putative barrier elements in the same chromosomal context in parallel. The defined chromosomal contexts of the RGBarrier assays will allow for detailed mechanistic studies of chromosomal silencing and DRE barrier element action. Understanding these mechanisms will be of paramount importance for the design of specific solutions for overcoming chromosomal silencing in specific transgenic applications.

Identificação e expressão de genes relacionados à via esteroidogênica e resposta antioxidante após a exposição à Atrazina em Poecilia vivipara (Poeciliidae, Cyprinodontiformes)

O herbicida Atrazina (ATR) é um agrotóxico utilizado há cerca de 50 anos, responsável pelo controle seletivo de plantas daninhas em cultivo de arroz, milho e cana-de-açúcar, principalmente. Estudos recentes apontam diversos efeitos desse herbicida em invertebrados e vertebrados, através da contaminação do solo, bem como da lixiviação para os ecossistemas aquáticos. Foi demonstrado que a ATR é um desregulador endócrino, além de causar efeitos como estresse oxidativo, imunotoxicidade e distúrbios no metabolismo energético. No presente estudo, a espécie nativa Poecilia vivipara foi utilizada como modelo experimental para identificar e analisar a expressão de genes atuantes na via esteroidogênica (StAR e Cyp19a1) e genes atuantes no sistema de defesa antioxidante enzimático (SOD-1 e CAT), frente a exposição à diferentes concentrações de ATR. Sequências parciais dos genes-alvo foram obtidas e comparadas com sequências disponíveis de espécies próximas. Foram analisadas a expressão órgãoespecífica para cada um dos genes isolados, bem como a expressão dos genes frente à exposição ao herbicida atrazina. Os animais foram expostos a ATR em concentrações de 2, 10 e 100 µg/L e a expressão dos genes em gônadas e fígado desses animais foram analisadas em 24 e 96 horas de exposição. As sequências obtidas dos genes StAR, Cyp19a1, SOD-1 e CAT apresentaram 821, 80, 954, 350 pares de bases respectivamente, com identidades que variam de 86 a 100% com espécies filogeneticamente próximas a P. vivipara. Os animais apresentaram uma maior expressão dos genes StAR e Cyp19a1 nas gônadas e no fígado, enquanto a menor expressão se mostrou em órgãos como intestino e baço. Já os genes SOD e CAT apresentaram uma maior expressão no fígado, e menor expressão no intestino. Em relação à expressão gênica frente à exposição à ATR, os resultados apontaram para uma indução dos genes StAR, SOD e CAT em 24 horas, nas gônadas e no fígado, enquanto 8 que a expressão do gene Cyp19a1 foi aumentada apenas após 96 horas de exposição. Foi demonstrado que o herbicida ATR, mesmo em baixas concentrações, é capaz de desregular a expressão de genes que codificam tanto para proteínas componentes da via de síntese de hormônios esteróides, quanto para enzimas atuantes na resposta antioxidante celular de P. vivipara. 

As rodovias e as aves de rapina nocturnas relação entre a densidade, o habitat e a mortalidade

As estradas e tráfego inerente surgem como a criação antrópica mais conspícua e penetrante na paisagem natural, sendo considerados os principais agentes causadores de fragmentação e destruição de habitats, assim como representam um obstáculo físico sem precedentes, limitando as relações directas entre os indivíduos, por diminuição da frequência de dispersão e aumento da mortalidade por atropelamento, impedindo o fluxo natural de genes e suscitando o aumento de fenómenos de inbreeding e perda de heterozigotia. Todos os impactes deletérios associados às rodovias são claramente perceptíveis em vertebrados, onde as aves de rapinas nocturnas não são excepção. Uma vez que estas rapaces beneficiam das suas bermas e orlas, como locais de poiso, nidificação ou como corredores de dispersão através da paisagem, são frequentemente vítimas de mortalidade por atropelamento em estradas, sendo esta problemática considerada actualmente uma das mais recentes e importantes formas de mortalidade não natural em rapinas nocturnas e vinculada como um dos maiores problemas de conservação que afecta este grupo. Não obstante, esse mútuo efeito de atracção/repulsa das estradas a estas rapaces, as rodovias criam uma barreira específica que limita a dinâmica, comportamento e densidade populacional das espécies residentes, reconhecendo-se que o isolamento daí resultante, pode comprometer a viabilidade populacional a longo prazo, podendo mesmo conduzir a altos riscos de extinção das populações locais devido a efeitos estocásticos. Mediante esta problemática, este trabalho debruçou-se sobre um único objectivo principal: a avaliação do impacte das rodovias e do tráfego, na densidade das aves de rapina nocturnas. Este estudo foi efectuado na região Alentejana, abrangendo uma área de cariz tipicamente mediterrânico, delimitada pelas localidades de Montemor-o-Novo, Arraiolos e Évora, sendo seccionada por 143 quilómetros de estradas, divididas em autoestrada, rodovias com elevada e reduzida densidade de tráfego. A monitorização das rapinas nocturnas foi conduzida em dois anos amostrais (2005 e 2007), tendo sido focalizada sobretudo em duas espécies de Strigiformes, a Coruja­ do-mato Strix aluco e o Mocho-galego Athene noctua, recorrendo ao uso de playbacks com reprodução de vocalizações de indivíduos conspecíficos. Foram usadas 32 variáveis explicativas integradas em três grandes grupos: variáveis de estrada, métricas da paisagem, uso do solo, tendo sido analiticamente testadas, recorrendo à aplicação de Modelos Lineares Generalizados. Os principais resultados obtidos demonstram que as variáveis de estrada, aliadas à densidade de tráfego e ruído inerente à sua circulação, são provavelmente, responsáveis por um comportamento de repulsa das espécies de aves de rapina nocturnas em estudo, apresentando estas densidades mais elevadas longe de áreas antropicamente perturbadas e, portanto, de menor qualidade que se encontram adjacentes às rodovias. Todavia a presença de habitat favorável a estas rapaces é provavelmente o descritor com maior poder estatístico no que concerne à sua distribuição e densidade, sendo os montados densos e a presença de zonas agrícolas de sequeiro, positivamente correlacionadas, respectivamente com a densidade de casais reprodutores de Coruja-do-mato e Mocho-galego. Mediante a observação dos resultados será veemente a aplicação de medidas de mitigação específicas, que fundamentalmente considerem o afastamento dos efectivos populacionais longe das estradas e tráfego, conservando e assegurando as características estruturais, requisitos e qualidade dos habitats, de modo a incrementar e garantir a viabilidade e densidade das populações, fidelizando a territorialidade e permanência destas aves nestas áreas. Adicionalmente deverá investir-se na conectividade das manchas de paisagem fragmentada pelas rodovias, criando opções de conservação estratégicas, em zonas ecologicamente mais sensíveis, que não somente minimizem o efeito de repulsa reconhecido nestas aves, mas também os níveis de mortalidade por atropelamento, tornando os ecossistemas mais funcionais para a sobrevivência destes rapaces. ABSTRACT; Roads and traffic are the most conspicuous and pervasive human creation, being the great responsible for fragmentation and habitats destruction, reducing animal movement through landscape, which implies decrease of gene flow and loss of variability that can fragmented populations, thus reducing their sizes and densities. All deleterious impacts associated with roads are clearly visible in vertebrates, where owls aren't exception, being frequent victims of road mortality, since they can use roadside habitats and edges for hunting, nesting or dispersal corridors through the landscape, being nowadays one of the most recent and important causes of non­natural mortality in owls and has been recognized as one of the largest conservation problems affecting this group. However, the attractive and avoidance effect of roads and his edges on owls creates a barrier effect that limits dynamics, behaviour and breeding density of resident species, recognizing that possible isolation, could compromise populations survival, make them more vulnerable to high risks of local extinction due to stochastic effects. Despite that, several authors suggest that owls use roads to hunt, as marginal habitats, or for navigation corridors through the landscape ln this context, the major aims of this study was to verify if there are negative effects of roads on the density of owls, considering traffic as an influencing factor. This study was conducted in Alentejo, covering a typical Mediterranean area, including three main localities Montemor-o-Novo, Évora and Arraiolos, being sectioned by 143 km of roads, including highway, roads with high traffic density, and the remaining with low traffic density. The owl census was conducted in two sampling years (2005 and 2007) and was focused mainly on Little owl Athene noctua and Tawny Owl Strix aluco species, using the playback technique, with conspecific calls. We used 32 explanatory variables, mainly included in three groups: road variables, landscape metrics and land use, having been analytically tested, with application of Generalised Linear Models. The main results show that noisy roads with high traffic density are probably the most responsible for the avoidance behaviour of owls, under the study area, showing density depression near high anthropogenic disturbed areas adjacent to roads. However, the presence of habitat quality to these birds is probably the descriptor with greater statistical power, considering its distribution and density, with the dense oak woodland and croplands and arable lands, positively correlated, respectively with Tawny owl and Little owl density. ln consequence, the great conservation effort should be done in order to keep breeding populations away from roads and traffic, ensuring the structural features, requirements and quality of its habitats in order to enhance and ensure the viability and density of owl's populations in these areas. ln addition, it is important to invest in connectivity between roadside fragmented patches, creating strategic conservation options, in sensitive areas, which minimize the avoidance effect, recognized in owls, but also road-kill levels, making ecosystems more functional to survival of these top predators.

Caractérisation des interactions établies par la région riche en prolines de la ligase de l’ubiquitine Itch

Itch est un membre de la famille des ligases de l’ubiquitine de type CWH (C2-WW- HECT) impliqué dans le contrôle de la signalisation inflammatoire, des facteurs de transcription et le tri des récepteurs membranaires. La fonction d’Itch implique généralement sa capacité à induire la dégradation de ses substrats. Pour accomplir cette fonction, Itch doit d’abord interagir avec ses cibles. Itch possède quatre domaines WW lui permettant d’accomplir la majorité de ses fonctions. En plus de ces domaines, Itch possède une PRR (région riche en prolines) unique parmi les ligases CWH. Cette région est bien conservée chez les vertébrés, ce qui suggère son importance. Cette région permet à Itch d’interagir avec des protéines contenant un domaine SH3 (Src homology 3). Plusieurs partenaires SH3 furent identifiés, cependant l’on connait peu de choses concernant la fonction et l’établissement de ces complexes. Dans ce projet, nous avons analysé les propriétés de liaison d’un sous-groupe de protéines à domaine SH3 impliquées dans l’endocytose et la signalisation cellulaire. Nos travaux ont permis d’identifier de nouveaux partenaires et aussi de déterminer que différents domaines SH3 ciblent la même région riche en prolines, mais impliquent des résidus distincts. Ces résultats démontrent la variété des propriétés de liaison démontrées par la PRR d’Itch et sa préférence marquée pour l’Endophiline. Parmi les partenaires identifiés, Grb2 (Growth factor receptor-bound protein 2) est particulièrement intéressant en raison de son rôle crucial dans la signalisation cellulaire. Nous avons démontré ici qu’Itch ubiquityle Grb2, mais ne cause pas sa dégradation, contrairement à l’Endophiline. Nos travaux démontrent que la PRR d’Itch est versatile quant à ses interactions et leurs conséquences.

Atividades antinociceptiva e anti-inflamatória de uma fração rica em heterogalactana sulfatada extraída da alga Codium isthmocladum (Vickers 1905)

Sulfated polysaccharides comprise a complex group of macromolecules with a range of several biological activities, including antiviral activity, anticoagulant, antiproliferative, antiherpética, antitumor, anti-inflammatory and antioxidant. These anionic polymers are widely distributed in tissues of vertebrates, invertebrates and algae. Seaweeds are the most abundant sources of sulfated polysaccharides in nature. The green algal sulfated polysaccharides are homo or heteropolysaccharides comprised of galactose, glucose, arabinose and/or glucuronic acid. They are described as anticoagulant, anti-inflammatory, antiviral, anti-angiogenic, antitumor compounds. However, there are few studies about elucidation and evaluation of biological/pharmacological effects of sulfated polysaccharides obtained from green algae, for example, there is only one paper reporting the antinociceptive activity of sulfated polysaccharides of these algae. Therefore this study aimed to obtain sulfated polysaccharides of green seaweed Codium isthmocladum and evaluates them as potential antinociceptive agents. Thus, in this study, the total extract of polysaccharides of green alga C. isthmocladum was obtained by proteolytic digestion, followed by fractionation resulting in five fractions (F0.3, F0.5, F0.7, F0.9 and F1.2) by sequential precipitation with acetone. Using the test of abdominal contractions we observed that the fraction F0.9 was the most potent antinociceptive aompound. F0.9 consists mainly of a sulfated heterogalactana. More specific tests showed that Fo.9 effect is dose and time dependent, reaching a maximum at 90 after administration (10 mg / kg of animal). F0.9 is associated with TRPV1 and TRPA1 receptors and inhibits painful sensation in animals. Furthermore, F0.9 inhibits the migration of lymphocytes induced peritonitis test. On the other hand, stimulates the release of NO and TNF-α. These results suggest that F0.9 has the potential to be used as a source of sulfated galactan antinociceptive and anti-inflammatory

Plantibodies in human and animal health: a review.

Background: Antibodies are essential part of vertebrates’ adaptive immune system; they can now be produced by transforming plants with antibody-coding genes from mammals/humans. Although plants do not naturally make antibodies, the plant-derived antibodies (plantibodies) have been shown to function in the same way as mammalian antibodies. Methods: PubMed and Google search engines were used to download relevant publications on plantibodies in medical and veterinary fields; the papers were reviewed and findings qualitatively described. Results: The process of bioproduction of plantibodies offers several advantages over the conventional method of antibody production in mammalian cells with the cost of antibody production in plants being substantially lesser. Contrary to what is possible with animal-derived antibodies, the process of making plantibodies almost exclusively precludes transfer of pathogens to the end product. Additionally, plants not only produce a relatively high yield of antibodies in a comparatively faster time, they also serve as cost-effective bioreactors to produce antibodies of diverse specificities. Conclusion: Plantibodies are safe, cost-effective and offer more advantages over animal-derived antibodies. Methods of producing them are described with a view to inspiring African scientists on the need to embrace and harness this rapidly evolving biotechnology in solving human and animal health challenges on the continent where the climate supports growth of diverse plants.

Asymmetrical processing of olfactory input in the piriform cortex mediates "activation" of the avian navigation circuitry

The role of odors in the long-distance navigation of birds has elicited intense debate for more than half a century. Failure to resolve many of the issues fueling this debate is due at least in part to the absence of controls for a variety of non-specific effects that odors have on the navigational process. The present experiments were carried out to investigate whether the olfactory inputs are involved only in “activation” of neuronal circuitry involved in navigation or are also playing a role in providing directional information. Experienced adult pigeons were exposed to controlled olfactory stimuli during different segments of the journey (release site vs. displacement + release site). Protein levels of IEGs (immediate early genes used to mark synaptic activity) were analyzed in areas within the olfactory/navigation avian circuitry. The results indicate that 1) exposure to natural odors at the release site (and not before) elicit greater activation across brain regions than exposure to filtered air, artificial odors, and natural odors along the entire outward journey (from home to the release site, inclusive); 2) activation of the piriform cortex in terms of odor discrimination is lateralized; 3) activation of the navigation circuitry is achieved by means of lateralized activation of piriform cortex neurons. Altogether, the findings provide the first direct evidence that activation of the avian navigation circuitry is mediated by asymmetrical processing of olfactory input occurring in the right piriform cortex.

Vocal differentiation parallels development of auditory saccular sensitivity in a highly soniferous fish

Vocal differentiation is widely documented in birds and mammals but has been poorly investigated in other vertebrates, including fish, which represent the oldest extant vertebrate group. Neural circuitry controlling vocal behaviour is thought to have evolved from conserved brain areas that originated in fish, making this taxon key to understanding the evolution and development of the vertebrate vocal-auditory systems. This study examines ontogenetic changes in the vocal repertoire and whether vocal differentiation parallels auditory development in the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae). This species exhibits a complex acoustic repertoire and is vocally active during early development. Vocalisations were recorded during social interactions for four size groups (fry: <2 cm; small juveniles: 2-4 cm; large juveniles: 5-7 cm; adults >25 cm, standard length). Auditory sensitivity of juveniles and adults was determined based on evoked potentials recorded from the inner ear saccule in response to pure tones of 75-945 Hz. We show an ontogenetic increment in the vocal repertoire from simple broadband-pulsed 'grunts' that later differentiate into four distinct vocalisations, including low-frequency amplitude-modulated 'boatwhistles'. Whereas fry emitted mostly single grunts, large juveniles exhibited vocalisations similar to the adult vocal repertoire. Saccular sensitivity revealed a three-fold enhancement at most frequencies tested from small to large juveniles; however, large juveniles were similar in sensitivity to adults. We provide the first clear evidence of ontogenetic vocal differentiation in fish, as previously described for higher vertebrates. Our results suggest a parallel development between the vocal motor pathway and the peripheral auditory system for acoustic social communication in fish.

Social buffering of fear in zebrafish

Tese de Doutoramento em Biologia Comportamental apresentada ao ISPA - Instituto Universitário

FREQUENCY DOMAIN CHARACTERIZATION OF OPTIC FLOW AND VISION-BASED OCELLAR SENSING FOR ROTATIONAL MOTION

The structure of an animal’s eye is determined by the tasks it must perform. While vertebrates rely on their two eyes for all visual functions, insects have evolved a wide range of specialized visual organs to support behaviors such as prey capture, predator evasion, mate pursuit, flight stabilization, and navigation. Compound eyes and ocelli constitute the vision forming and sensing mechanisms of some flying insects. They provide signals useful for flight stabilization and navigation. In contrast to the well-studied compound eye, the ocelli, seen as the second visual system, sense fast luminance changes and allows for fast visual processing. Using a luminance-based sensor that mimics the insect ocelli and a camera-based motion detection system, a frequency-domain characterization of an ocellar sensor and optic flow (due to rotational motion) are analyzed. Inspired by the insect neurons that make use of signals from both vision sensing mechanisms, advantages, disadvantages and complementary properties of ocellar and optic flow estimates are discussed.

Play behaviour in nonhuman animals and the animal welfare issue

The mission of defining animal welfare indicators is methodologically difficult, limited, and possibly impossible. A promising alternative, however, to evaluate suitable environmental conditions is the assessment of play behaviour. In the present review, we summarise the general aspects of play behaviour in nonhuman animals and propose its use as a potential indicator of animal welfare. Play behaviour probably occurs in most vertebrates and some invertebrates, but predominately in mammals. It is also more frequent in young males and is associated with the environmental context in which animals find themselves. Animals play if they are healthy and well-fed, but not if they are under stressful conditions or if they are in a stressful state. We can therefore use the prevalence of play behaviour as an indicator of suitable environmental conditions, considering the specificity associated with the above-mentioned modifying factors.