Control of brood male production in the Argentine ant Iridomyrmex humilis (Mayr)

The influence of various social factors on the production of males was investigated in the Argentine ant, Iridomyrmex humilis. In this polygynous species, the workers which are monomorphic are unable to lay reproductive eggs, so all the males are the progeny of the queens. Although male eggs appear to be laid by mated queens throughout the year, in large stock colonies males are reared periodically (every 3 or 4 months); males develop from brood taken from these colonies at any point in the cycle and given queenless or queenright (1 to 5 queens) units. This is in striking contrast to many other species of ants where it is generally assumed that male eggs are laid seasonnally. Comparative experiments suggest that several related factors influence the rearing of males as far as the pupal stage. Worker/larva ratio: The proportion of male larvae developing in standardized units in which the worker/larva ratio was varied from 0.25 to 25 demonstrated that low ratios inhibit male production. Queen influence: In standardized units where the worker/larva ratio was high the presence of queens did not inhibit the rearing of males suggesting that there is no queen inhibitory pheromone controlling male experimental production. Data suggest evidence that queens prevent male production by means of appropriation of food. Diet: Male larvae failed to pupate in experimental societies deprived of protein. Thus, the production of males appears to be controlled by the amount of food available to larvae. This depends on foraging activity, the quantity of brood in relation to the number of workers and the number of queens in the society.

Ecology and evolution of soil nematode chemotaxis.

Plants influence the behavior of and modify community composition of soil-dwelling organisms through the exudation of organic molecules. Given the chemical complexity of the soil matrix, soil-dwelling organisms have evolved the ability to detect and respond to these cues for successful foraging. A key question is how specific these responses are and how they may evolve. Here, we review and discuss the ecology and evolution of chemotaxis of soil nematodes. Soil nematodes are a group of diverse functional and taxonomic types, which may reveal a variety of responses. We predicted that nematodes of different feeding guilds use host-specific cues for chemotaxis. However, the examination of a comprehensive nematode phylogeny revealed that distantly related nematodes, and nematodes from different feeding guilds, can exploit the same signals for positive orientation. Carbon dioxide (CO(2)), which is ubiquitous in soil and indicates biological activity, is widely used as such a cue. The use of the same signals by a variety of species and species groups suggests that parts of the chemo-sensory machinery have remained highly conserved during the radiation of nematodes. However, besides CO(2), many other chemical compounds, belonging to different chemical classes, have been shown to induce chemotaxis in nematodes. Plants surrounded by a complex nematode community, including beneficial entomopathogenic nematodes, plant-parasitic nematodes, as well as microbial feeders, are thus under diffuse selection for producing specific molecules in the rhizosphere that maximize their fitness. However, it is largely unknown how selection may operate and how belowground signaling may evolve. Given the paucity of data for certain groups of nematodes, future work is needed to better understand the evolutionary mechanisms of communication between plant roots and soil biota.

Size-dependent predation by Dugesia lugubris (Turbellaria) on Physa acuta (Gastropoda): experiments and model

1. We investigated experimentally predation by the flatworm Dugesia lugubris on the snail Physa acuta in relation to predator body length and to prey morphology [shell length (SL) and aperture width (AW)]. 2. SL and AW correlate strongly in the field, but display significant and independent variance among populations. In the laboratory, predation by Dugesia resulted in large and significant selection differentials on both SL and AW. Analysis of partial effects suggests that selection on AW was indirect, and mediated through its strong correlation with SL. 3. The probability P(ij) for a snail of size category i (SL) to be preyed upon by a flatworm of size category j was fitted with a Poisson-probability distribution, the mean of which increased linearly with predator size (i). Despite the low number of parameters, the fit was excellent (r2 = 0.96). We offer brief biological interpretations of this relationship with reference to optimal foraging theory. 4. The largest size class of Dugesia (>2 cm) did not prey on snails larger than 7 mm shell length. This size threshold might offer Physa a refuge against flatworm predation and thereby allow coexistence in the field. 5. Our results are further discussed with respect to previous field and laboratory observations on P acuta life-history patterns, in particular its phenotypic variance in adult body size.

Introduced ants in Galápagos (Floreana Island) : importance of competition, coexistence and agressive behaviors

Abstract Invasive species represent with fragmentation of habitat the most serious threats to biodiversity in the world. Galápagos Archipelago, as most oceanic islands, suffers a high rate of introduced animals and plants that affect equilibrium and biodiversity of this unique biota. Ants rank among the most devastating invaders. Their social organization confer them a high ability to adapt and to spread in new environments forming rapidly populous communities. We studied the ant community of Floreana Island composed mainly of introduced species (at least 1 S). Introduction events occurred successively during last century. The last record is Monomorium destructor arrived in the eighties. Our aim is to investigate the modalities of interaction and coexistence of these introduced species. We highlighted the competition hierarchy of the coexisting species using attractive food baits. Two species behave as competitively dominant by monopolizing an important part of resources. They are M. destructor restricted to a small area and the fire ant Solenopsis geminata widely distributed on the island. Then we evaluated the relative importance of abiotic factors and interspecific competition in structuring the community. Ecological data were collected and presence and abundance of species were estimated using different methods in a wide range of habitats. Several species showed preferences either for arid or for humid areas. The little fire ant Wasmannia auropunctata, awell-known devastating species when introduced, was exclusively found in moist habitat in and around the agricultural area situated in the upper and central part of thé island. It coexists with other species in several parts but in a restricted perimeter it excludes all other ants and worker's density on the ground is nearly 70 times higher than ant's density in similar habitats occupied by several species. But most opportunist tramp species establish everywhere without particular ecological requirement. Analyses of species co-occurrences at various levels didn't reveal any marked effect of competition in structuring ant's assemblages. We supposed that the lack ofcompetition-derived structure has to be attributed to the dynamic of the system. Indeed, across the successive census of 1996, 2003, 2004 and 2005, species distributions and abundances appeared to be highly variables. In particular harsh conditions occurring in dry season in certain parts seem to be limiting to S. geminatai. We suggest that huge variations in the local distribution of the dominant S. geminata disrupt the community organization. Finally we conducted artificial ant confrontations to evaluate to what extend an aggressive behavior at the worker level maybe linked to the ecological success of a species on the island. S. geminata was rather indifferent when confronted to a submissive species on food sources, suggesting that its competitive dominance is largely due to a numerical superiority. On the other hand M. destructor exhibits a strong agonistic behavior in similar confrontations. As soon as the presence of a competitor is detected, most workers were observed to abandon foraging and to take part in physical aggressions. Since it is still restricted nearby its introduction spot two decades after its arrival, we suggest that the energetic cost of such an aggressive behavior prevent it to spread on that island already highly colonized. Dominant invasive species such as the fire ants S. geminata and W. auropunctata have negative impacts on Galápagos fauna, disturbing the hatching of land tortoises and birds. But very little is known about the impact of other exotic ants. Indeed, impact on arthropods and generally on ground-dwelling organisms is very diffcult to evaluate. As a consequence of the dynamic character of Floreana I. ant community it is difficult to build models or to málce predictions on evolution of introduced ant fauna. But Camponotus macilentus, an abundant endemic species seems today to be little affected by introduced ant species thanks to its strong interference competition ability and its preference for arid and harsh environments. Résumé Les espèces envahissantes représentent, avec la fragmentation du paysage, la plus grande menace pour la biodiversité. L'archipel des Galápagos, comme la plupart des îles du Pacifique, compte un grand nombre d'espèces introduites qui menacent la biodiversité de ce milieu unique.. Les fourmis sont parmi les envahisseurs les plus dévastateurs. Leur organisation sociale leur permet de s'adapter et de se propager pour devenir rapidement abondantes. Nous avons étudié la communauté de fourmis sur l'île de Floreana principalement composée d'espèces introduites (au moins 15). Les introductions se sont succédées au cours du siècle précédent. La dernière espèce recensée est Monomorium destructor introduite dans les années 80. Notre objectif est de mettre à jour les modalités des interactions et de la coexistence de ces espèces introduites. Nous avons mis en évidence la hiérarchie de compétition des différentes espèces à l'aide d'appâts de nourriture. Deux espèces se comportent de façon dominante en monopolisant une part importante des ressources. Ce sont M. destructor, restreintes à un petit périmètre, et la fourmi de feu Solenopsis geminata, largement distribuée sur l'île. Nous avons évalué l'importance relative des facteurs abiotiques et de la compétition interspécifique dans la structuration des peuplements. Des données écologiques ont été collectées et la présence et l'abondance des espèces ont été estimées à l'aide de trois méthodes au sein d'une grande diversité d'habitats. Plusieurs espèces .montrent des préférences soit pour les milieux humides, soit pour les milieux arides. La petite fourmi de feu Wasmannia auropunctata, une espèce connue pour être dévastatrice dans ses sites d'introduction, est présente exclusivement dans les habitats humides dans et à proximité de la zone agricole située dans la partie centrale de l'île. Elle coexiste en plusieurs points avec d'autres espèces mais au sein d'un périmètre restreint elle exclut toute autre fourmi et atteint des densités record au sol presque 70 fois supérieures aux densités de fourmis observées sur les sites voisins occupés par plusieurs espèces. Mais la plupart des espèces vagabondes opportunistes s'établissent partout sans exigences écologiques particulières. Des analyses de cooccurrence d'espèces à plusieurs niveaux n'ont pas révélé de rôle marqué de la compétition dans la structuration des communautés. Nous supposons que l'absence d'une telle structure doit être attribuée à la dynamique du système. En effet, au cours des différents recensements de 1996-1997, 2003, 2004 et 2005, la distribution et l'abondance des espèces était très variable. En particulier, les conditions rudes qui règnent dans la zone aride durant la saison sèche semblent affecter particulièrement S. geminata. Nous suggérons que de fortes variations dans la distribution de l'espèce dominante perturbent l'orgaiùsation des communautés. Finalement nous avons effectué des confrontations artificielles pour évaluer dans quelle mesure un comportement agressif au niveau de l'ouvrière peut être lié au succès écologique d'une espèce sur l'île. S. geminata montre très peu de réaction face à une espèce subordonnée sur une même source de nourriture, ce qui laisse supposer que sa dominance est largement due à sa supériorité numérique. Par contre, dans des conditions similaires, M. destructor est fortement agressive. En présence d'un compétiteur, la plupart des ouvrières renoncent très vite à leur activité de fourragement pour agresser les individus de l'autre espèce. Puisque deux décennies après son introduction elle est toujours confinée à son point d'arrivée, nous supposons que le coût en énergie et en ouvrières de ce comportement très agressif est un obstacle à son expansion sur cette île déjà fortement colonisée. Les espèces envahissantes dominantes comme les fourmis de feu S. geminata et W. auropunctata sont connues pour leur impact négatif sur la faune des Galápagos, entre autre sur les jeunes des tortues terrestres et des oiseaux. Mais nous savons très peu de choses sur l'impact des autres espèces de fourmis introduites. En effet, l'impact sur les arthropodes, et plus généralement sur la faune du sol, est très difficile à évaluer. En raison du caractère dynamique de la communauté de fourmi de Floreana, il est difficile de construire des modèles et de faire des prédictions sur l'évolution des peuplements de fourmis introduites. Mais Camponotus macilentus, une espèce endémique abondante, semble aujourd'hui peu affectée par les espèces introduites grâce à ses capacités de compétition par interférence et sa préférence pour les milieux arides. Resumen Las, especies invasoras representan, junto con la fragmentación del paisaje, la mayor amenaza para la biodiversidad. El archipiélago de Galápagos, como la mayoría de las islas del Pacífico, cuenta con un gran número de especies introducidas que amenazan la biodiversidad de este lugar único. Las hormigas son uno de los invasores más devastadores. Su organización social les permite adaptarse y propagarse para ser rápidamente abundante. Estudiamos la comunidad de hormigas de la isla Floreana principalmente compuesta de especies introducidas (al menos 15). Las introducciones se sucedieron durante el siglo anterior. La última especie contabilizada es Monomorium destructor introducida en los años 80. Nuestro objetivo es poner al día las modalidades de las interacciones y de la coexistencia de estas especies introducidas. Pusimos de relieve la jerarquía de competencia de las distintas especies con ayuda de cebos de comida. Dos especies se implican de manera dominante monopolizando una parte importante de los recursos. Son M. destructor, limitado a un pequeño perímetro, y la hormiga de fuego Solenopsis geminata; ampliamente distribuida por la isla. Evaluamos la importancia relativa de los factores abióticos y de la competencia interespecífica en la estructuración de la communidad. Se recogieron algunos datos ecológicos y se consideraron la presencia y la abundancia de las especies con ayuda de tres métodos en una gran diversidad de hábitats. Varias especies muestran preferencias o por los medios húmedos, o por los medios áridos. La pequeña hormiga de fuego Wasmannia auropunctata, una especie conocida por ser devastadora en sus lugares de introducción, está presente exclusivamente en los hábitats húmedos y cerca de la zona agrícola situada en la parte central de la isla. Coexiste en varios puntos con otras especies pero en un perímetro limitado excluye a cualquier otra hormiga y alcanza densidades en el suelo casi 70 veces superiores a las densidades de hormigas observadas en los lugares vecinos ocupados por varias especies. Pero la mayoría de las especies vagabundas oportunistas se establecen por todas partes sin exigencias ecológicas particulares. Análisis de cooccurrencía de las especies a varios niveles no revelaron una grande importancía de la competencia en la estructuración de las comunidades. Suponemos que la ausencia de tal estructura Bebé ser por la dinámica del sistema. Efectivamente, durante los distintos censos de 1996-1997, 2003,.2004 y 2005, la distribución ? la abundancia de las especies eran muy variables. En particular, las condiciones drásticas que reinan en la zona árida durante la temporada seca parecen afectar especialmente a S. geminata. Sugerimos que fuertes variaciones en la distribución de la especie dominante perturben la organización de las comunidades. Finalmente efectuamos confrontaciones artificiales para evaluar hastá que punto un comportamiento agresivo a nivel de la obrera puede explicar el éxito ecológico de una especie en la isla. S. geminata muestra muy poca reacción ante una especie subordinada mientras comparten la misma comida, lo que deja suponer que su dominancia se debe a su superioridad numérica. Por el contrario, en condiciones similares, M. destructor es muy agresivo. En presencia de otra especie, la mayóría de las obreras renuncian muy rápidamente a alimentarse para atacar a los individuos de la otra especie. Puesto que dos décadas después de su introducción todavía se confina en su punto de llegada, suponemos que el coste en energía y en obreras de este comportamiento muy agresivo es un obstáculo a su extensión en esta isla ya muy colonizada. Las especiés invasoras dominantes como las hormigas de fuego S. geminata y W. auropunctata son conocidas por su impacto negativo en la fauna de Galápagos, entre otras cosas sobre los juveniles de las tortugas terrestres y pájaros. Pero sabemos muy poco sobre el impacto de las otras especies de hormigas introducidas. Efectivamente es muy difïcil de evaluar el impacto en los artrópodos, y más generalmente en la fauna del suelo. Debido al carácter dinámico de la comunidad de hormiga de Floreana, es diEcil construir modelos y hacer predicciones sobre la evolución de las poblaciones de hormigas introducidas. Pero Camponotus macilentus, una especie endémica abundante, parece poco afectadá hoy por las especies introducidas gracias a sus capacidades de competencia por interferencia y su preferencia por los medios áridos.

Covariation between plumage colour polymorphism and diet in the Barn Owl Tyto alba

Several hypotheses might explain the evolution and maintenance of colour morphs within animal populations. The 'alternative foraging strategy' hypothesis states that alternative colour morphs exploit different ecological niches. This hypothesis predicts that morphs differ in diet, either because foraging success on alternative prey species is morph-dependent or because differently coloured individuals exploit alternative habitats. I examined this prediction in the Barn Owl Tyto alba, a bird that varies in plumage coloration continuously from dark reddish-brown to white. On the European continent, Owls are light-coloured (subspecies T. a. alba) in the south and reddish-brown (T. a. guttata) in the north; in central Europe the two subspecies interbreed, generating many colour variants. If plumage coloration indicates alternative foraging strategies, in sympatry dark- and light-coloured owls should consume prey species that are typical of the diets of T. a. guttata and T. a. alba in allopatry, respectively. In line with this prediction, both in allopatry and in sympatry in Switzerland T. a. guttata fed primarily upon Common Voles Microtus arvalis and T. a. alba upon Wood Mice Apodemus spp. Statistical analyses suggest that morph-dependent diet did not arise from a non-random habitat distribution of owls with respect to plumage coloration. This suggests that foraging success upon alternative prey is morph-dependent.

Relatedness influences signal reliability in evolving robots.

Communication is an indispensable component of animal societies, yet many open questions remain regarding the factors affecting the evolution and reliability of signalling systems. A potentially important factor is the level of genetic relatedness between signallers and receivers. To quantitatively explore the role of relatedness in the evolution of reliable signals, we conducted artificial evolution over 500 generations in a system of foraging robots that can emit and perceive light signals. By devising a quantitative measure of signal reliability, and comparing independently evolving populations differing in within-group relatedness, we show a strong positive correlation between relatedness and reliability. Unrelated robots produced unreliable signals, whereas highly related robots produced signals that reliably indicated the location of the food source and thereby increased performance. Comparisons across populations also revealed that the frequency for signal production-which is often used as a proxy of signal reliability in empirical studies on animal communication-is a poor predictor of signal reliability and, accordingly, is not consistently correlated with group performance. This has important implications for our understanding of signal evolution and the empirical tools that are used to investigate communication.

Pheomelanin-based colouration is correlated with indices of flying strategies in the barn owl

Resource polymorphism refers to individuals from the same population foraging in alternative habitats or on alternative food. Food specialization can be associated with adaptations such as colour polymorphism, with pale and dark colours conferring differential camouflage in different habitats. Pale and dark-reddish pheomelanic Barn Owls (Tyto alba) forage on different prey species in closed and open habitats, respectively. We show here that darker-reddish owls have heavier stomach content when found dead, and their 5th secondary wing feather is more deeply anchored inside the integument. These correlations suggest that their feathers bend less when flying, and that darker-reddish Barn Owls are able sustain more intense flying than their paler conspecifics.

Molecular basis for changes in behavioral state in ant social behaviors.

A hallmark of behavior is that animals respond to environmental change by switching from one behavioral state to another. However, information on the molecular underpinnings of these behavioral shifts and how they are mediated by the environment is lacking. The ant Pheidole pallidula with its morphologically and behaviorally distinct major and minor workers is an ideal system to investigate behavioral shifts. The physically larger majors are predisposed to defend the ant nest, whereas the smaller minors are the foragers. Despite this predisposition, majors are able to shift to foraging according to the needs of the colony. We show that the ant foraging (ppfor) gene, which encodes a cGMP-dependent protein kinase (PKG), mediates this shift. Majors have higher brain PKG activities than minors, and the spatial distribution of the PPFOR protein differs in these workers. Specifically, majors express the PPFOR protein in 5 cells in the anterior face of the ant brain, whereas minors do not. Environmental manipulations show that PKG is lower in the presence of a foraging stimulus and higher when defense is required. Finally, pharmacological activation of PKG increases defense and reduces foraging behavior. Thus, PKG signaling plays a critical role in P. pallidula behavioral shifts.

Genetic team composition and level of selection in the evolution of cooperation

In cooperative multiagent systems, agents interac to solve tasks. Global dynamics of multiagent teams result from local agent interactions, and are complex and difficult to predict. Evolutionary computation has proven a promising approach to the design of such teams. The majority of current studies use teams composed of agents with identical control rules ("geneti- cally homogeneous teams") and select behavior at the team level ("team-level selection"). Here we extend current approaches to include four combinations of genetic team composition and level of selection. We compare the performance of genetically homo- geneous teams evolved with individual-level selection, genetically homogeneous teams evolved with team-level selection, genetically heterogeneous teams evolved with individual-level selection, and genetically heterogeneous teams evolved with team-level selection. We use a simulated foraging task to show that the optimal combination depends on the amount of cooperation required by the task. Accordingly, we distinguish between three types of cooperative tasks and suggest guidelines for the optimal choice of genetic team composition and level of selection

Historical contingency affects signaling strategies and competitive abilities in evolving populations of simulated robots.

One of the key innovations during the evolution of life on earth has been the emergence of efficient communication systems, yet little is known about the causes and consequences of the great diversity within and between species. By conducting experimental evolution in 20 independently evolving populations of cooperatively foraging simulated robots, we found that historical contingency in the occurrence order of novel phenotypic traits resulted in the emergence of two distinct communication strategies. The more complex foraging strategy was less efficient than the simpler strategy. However, when the 20 populations were placed in competition with each other, the populations with the more complex strategy outperformed the populations with the less complex strategy. These results demonstrate a tradeoff between communication efficiency and robustness and suggest that stochastic events have important effects on signal evolution and the outcome of competition between distinct populations.

Effects of (p)ppGpp on the progression of the cell cycle of Caulobacter crescentus.

Bacteria must control the progression of their cell cycle in response to nutrient availability. This regulation can be mediated by guanosine tetra- or pentaphosphate [(p)ppGpp], which are synthesized by enzymes of the RelA/SpoT homologue (Rsh) family, particularly under starvation conditions. Here, we study the effects of (p)ppGpp on the cell cycle of Caulobacter crescentus, an oligotrophic bacterium with a dimorphic life cycle. C. crescentus divides asymmetrically, producing a motile swarmer cell that cannot replicate its chromosome and a sessile stalked cell that is replication competent. The swarmer cell rapidly differentiates into a stalked cell in appropriate conditions. An artificial increase in the levels of (p)ppGpp in nonstarved C. crescentus cells was achieved by expressing a truncated relA gene from Escherichia coli, encoding a constitutively active (p)ppGpp synthetase. By combining single-cell microscopy, flow cytometry approaches, and swarming assays, we show that an increase in the intracellular concentration of (p)ppGpp is sufficient to slow down the swarmer-to-stalked cell differentiation process and to delay the initiation of chromosome replication. We also present evidence that the intracellular levels of two master regulators of the cell cycle of C. crescentus, DnaA and CtrA, are modulated in response to (p)ppGpp accumulation, even in the absence of actual starvation. CtrA proteolysis and DnaA synthesis seem indirectly inhibited by (p)ppGpp accumulation. By extending the life span of the motile nonreproductive swarmer cell and thus promoting dispersal and foraging functions over multiplication under starvation conditions, (p)ppGpp may play a central role in the ecological adaptation of C. crescentus to nutritional stresses.

The activity of Crocidura russula (Insectivora, Soricidae) in the field and in captivity

Studied was the activity of the shrew Crocidura russula in the field (by radioactive tracking) and in laboratory (by continuous recording of nest temperature and by video). Under natural conditions, the total daily activity remained nearly constant throughout the year accounting for about 33 % of the total time. Activity was polyphasic and showed a daily rhythm; on an average, one activity phases occured every two hours and lasted 36 min. The activity periods of captive shrews were generally shorter, but always more frequent, and the total daily activity of captive shrews was much lower in winter. Two experiments carried out in the filed on shrews artificially fed, demonstrated that under natural conditions, foraging takes a major part of the winter activity. The activity patterns of Crocidura russula are compared with those of another European shrew, Sorex araneus.

Experimental manipulation of colony genetic diversity had no effect on short-term task efficiency in the Argentine ant Linepithema humile

Genetic diversity might increase the performance of social groups by improving task efficiency or disease resistance, but direct experimental tests of these hypotheses are rare. We manipulated the level of genetic diversity in colonies of the Argentine ant Linepithema humile, and then recorded the short-term task efficiency of these experimental colonies. The efficiency of low and high genetic diversity colonies did not differ significantly for any of the following tasks: exploring a new territory, foraging, moving to a new nest site, or removing corpses. The tests were powerful enough to detect large effects, but may have failed to detect small differences. Indeed, observed effect sizes were generally small, except for the time to create a trail during nest emigration. In addition, genetic diversity had no statistically significant impact on the number of workers, males and females produced by the colony, but these tests had low power. Higher genetic diversity also did not result in lower variance in task efficiency and productivity. In contrast to genetic diversity, colony size was positively correlated with the efficiency at performing most tasks and with colony productivity. Altogether, these results suggest that genetic diversity does not strongly improve short-term task efficiency in L. humile, but that worker number is a key factor determining the success of this invasive species.

Intrahippocampal cholinergic grafts in aged rats compensate impairments in a radial maze and in a place learning task

Age-related cognitive impairments were studied in rats kept in semi-enriched conditions during their whole life, and tested during ontogeny and adult life in various classical spatial tasks. In addition, the effect of intrahippocampal grafts of fetal septal-diagonal band tissue, rich in cholinergic neurons, was studied in some of these subjects. The rats received bilateral cell suspensions when aged 23-24 months. Starting 4 weeks after grafting, they were trained during 5 weeks in an 8-arm maze made of connected plexiglass tunnels. No age-related impairment was detected during the first eight trials, when the maze shape was that of a classical radial maze in which the rats had already been trained when young. The older rats were impaired when the task was made more difficult by rendering two arms parallel to each other. They developed an important neglect of one of the parallel tunnels resulting in a high amount of errors before completion of the task. In addition, the old rats developed a systematic response pattern of visits to adjacent arms in a sequence, which was not observed in the younger subjects. None of these behaviours were observed in the old rats with a septal transplant. Sixteen weeks after grafting, another experiment was conducted in a homing hole board task. Rats were allowed to escape from a large circular arena through one hole out of many, and to reach home via a flexible tube under the table. The escape hole was at a fixed position according to distant room cues, and olfactory cues were made irrelevant by rotating the table between the trials. An additional cue was placed on the escape position. No age-related difference in escape was observed during training. During a probe trial with no hole connected and no proximal cue present, the old untreated rats were less clearly focussed on the training sector than were either the younger or the grafted old subjects. Taken together, these experiments indicate that enriched housing conditions and spatial training during adult life do not protect against all age-related deterioration in spatial ability. However, it might be that the considerable improvement observed in the grafted subjects results from an interaction between the graft treatment and the housing conditions.

Iridophores and not carotenoids account for chromatic variation of carotenoid-basedcColoration in Common lizards (Lacerta vivipara).

Abstract Carotenoids typically need reflective background components to shine. Such components, iridophores, leucophores, and keratin- and collagen-derived structures, are generally assumed to show no or little environmental variability. Here, we investigate the origin of environmentally induced variation in the carotenoid-based ventral coloration of male common lizards (Lacerta vivipara) by investigating the effects of dietary carotenoids and corticosterone on both carotenoid- and background-related reflectance. We observed a general negative chromatic change that was prevented by β-carotene supplementation. However, chromatic changes did not result from changes in carotenoid-related reflectance or skin carotenoid content but from changes in background-related reflectance that may have been mediated by vitamin A. An in vitro experiment showed that the encountered chromatic changes most likely resulted from changes in iridophore reflectance. Our findings demonstrate that chromatic variation in carotenoid-based ornaments may not exclusively reflect differences in integumentary carotenoid content and, hence, in qualities linked to carotenoid deposition (e.g., foraging ability, immune response, or antioxidant capacity). Moreover, skin carotenoid content and carotenoid-related reflectance were related to male color polymorphism, suggesting that carotenoid-based coloration of male common lizards is a multicomponent signal, with iridophores reflecting environmental conditions and carotenoids reflecting genetically based color morphs.