Department of Biology and Environmental Sciences
A common garden test of local adaptation in barnacle populations along a salinity gradient
Author(s): Wrange, A, André, C, Jonsson, P, Havenhand, J
Environmental gradients may select for locally adapted populations. The barnacle Balanus (Amphibalanus) improvisus is found across a broad range of salinities and has during the past 150 years invaded the Baltic Sea with its gradient from fresh water to near marine salinity. This system may serve as a model of how marine organisms may respond to rapid environmental changes, e.g. climate change which is expected to reduce salinity in many coastal areas. We tested the hypothesis that local adaptations to low salinity have evolved during the past 150 years along the stable salinity gradient in the Baltic Sea. Common-garden experiments were performed to characterize physiological plasticity and possible local adaptations. Newly settled barnacles from each of three different geographical areas along the North Sea-Baltic Sea salinity gradient were exposed to different salinities (6 psu, 15 psu, 30 psu), and phenotypic traits including survival, growth, shell strength, condition index and reproductive maturity were recorded. The study showed that B. improvisus is a plastic and highly euryhaline species performing best at intermediate salinities, both in terms of maximum shell size and reproductive maturity. However, the results also indicate that low salinity has sub-lethal effects on fitness-related traits including slower initial growth and weaker shells. Overall, there were weak differences between populations in most measured traits, indicating little local adaptation to specific salinity conditions. However, some traits showed population-specific responses, e.g. that populations from high salinities obtained stronger shells in their native salinity compared to the other populations, possibly indicating local adaptation to different predation pressures. These results show that B. improvisus may be a rare example of a true brackish-water species, and that plastic responses are more likely than evolutionary tracking in coping with future changes in coastal salinity.
Department of Evolutionary Biology
A developmental switch gene for a feeding dimorphism in Pristionchus nematodes is coupled to micro- and macroevolution of plasticity
Author(s): Ragsdale, EJ, Müller, MR, Sommer, RJ
The mechanistic study of ecologically relevant traits is essential for understanding how ecology and development interact in the evolution of novel phenotypes. The nematode model Pristionchus pacificus shows plasticity in its teeth-like feeding structures, which are a novelty that enable predation of other nematodes. The plasticity consists of two discrete forms, stenostomatous (St) and eurystomatous (Eu), the latter bearing a claw-like dorsal tooth and an opposing subventral tooth. To study the genetic basis of the dimorphism, we used forward genetics to isolate Eu-form-defective (eud) mutants. A mutant with dominant alleles, eud-1, is haploinsufficient and was rescued by genetic transformation with a wild-type allele. Extra copies of this X-linked gene also drive highly St males to be Eu, indicating a role for EUD-1 in sexual dimorphism. Overexpression of eud-1 results in saturation of the Eu form and therefore acts as a dose-dependent master switch for the dimorphism. Further experiments revealed that EUD-1 is not only necessary and sufficient for the mouth-form decision in mutants but also represents a key determinant of micro- and macroevolutionary diversification. A survey of over 100 wild populations of P. pacificus gave a population genetics context, revealing natural variation in mouth-form phenotypes. Variation correlated with eud-1 expression, and genetic transformation of highly St strains confirmed the role of EUD-1 as a dimorphism switch. Thus, a gene identified by laboratory genetics can be a key player in natural history. Recent discovery of a sister species to P. pacificus, P. exspectatus, allows tests across species boundaries by the success of hybrid crosses, and transformation by this technique showed maintenance of the EUD-1 switch in macroevolution. By integrating genetics analysis, phylogenetics, and natural history, studies in this system ultimately aim to test the role of phenotypic plasticity in the evolution of novelty.
Dept of Ecological Sciences
A new perspective on phenotypic plasticity: taking into account physiological mechanisms challenges classic plasticity theory
Author(s): Ellers, J
Phenotypic plasticity is ubiquitous but we have poor knowledge about the underlying mechanisms. The reason for this is that classical studies of phenotypic plasticity developed and tested theory only for organismal traits, such as morphology or life history. However, a new and upcoming perspective on plasticity encompasses also transcriptional and physiological flexibility in an effort to study the underlying mechanisms of phenotypic plasticity. This raises the question how plasticity at different organisational levels interacts to produce the optimal phenotype in different environments. Here, I will focus on the evolution of temperature-induced plasticity as a case study to show that greater phenotypic plasticity at one organisational level is associated with environmental canalization (lack of plasticity) at the other level. More specifically, my work shows that strong physiological flexibility in response to temperature correlates with low sensitivity to temperature for fitness traits. In this context, I will discuss costs of plasticity and the evolution of plasticity as a means of adaptation to changing thermal conditions. I will also identify candidate physiological pathways underlying variation in thermal response. Ultimately, taking into account the mechanism underlying plasticity will challenge the classical dichotomy between phenotypic plasticity and environmental canalization. Instead, the key question is at what level of biological organization phenotypic plasticity will evolve.
Deparment of Biology
Adaptive phenotypic plasticity in an ecologically relevant foraging trait
Author(s): Machado-Schiaffino, G, Henning, F, Meyer, A
The spectacular species richness of cichlid fishes and their famous diversity in morphology, coloration, and behaviour have made them a well-known textbook model for the study of speciation and adaptive evolution. In their natural environment, hypertrophic lip cichlids forage predominantly in rocky crevices. It has been hypothesized that this foraging behaviour associated with mechanical stress caused by friction could result in larger lips through phenotypic plasticity. In order to test how strongly phenotypic plasticity can influence the size and development of lips, we conducted a split design experiment in Nicaraguan cichlids and a series of breeding experiments on both Nicaraguan and African cichlids. Two months old full-sibs of A. labiatus (thick-lipped) and A. citrinellus (thin-lipped) were randomly assigned into two feeding groups, a control group (C) where food was released into the water column and a treatment group (T) fed with the same amount and type of food, but fixed to substrates in order to induce mechanical stress on lips. Treatment fish in the thick-lipped species had highly significant larger lips. Interestingly, no differentiation was found between treatment and control groups for the thin-lipped species. The thick-lipped species developed hypertrophic lips in both groups and these were significantly larger in both groups when compared to the thin-lipped species demonstrating a genetic component. The genetic component was further investigated by analyzing the phenotypic segregation in F1 and F2 fish obtained from a cross of thick- and thin-lipped species. F1 of both African and Nicaraguan crosses had intermediate lips and F2s exhibited large phenotypic variance, consistent with a polygenic basis. These results show that not only a genetic, but also a plastic component is involved in the development of hypertrophic lips in cichlids and opens the exciting possibility that plasticity is selected for in recent thick-lipped species.
Centre for Marine Biology
Adult conspecific cues affect molting rate, survival and claw morphology of early recruits of the shore crab Carcinus maenas
Author(s): Duarte, RC, Ré, A, Flores, AAV, Queiroga, H
Besides signaling adequate benthic habitat, conspecific cues often shorten development time to metamorphosis and affect both survival and growth of early juvenile stages. However, aggregation of juvenile cohorts in preferred habitat, usually biogenic substrates holding intricate physical structure and high food supply, may lead to strong intraspecific competition and cannibalistic interactions. Using a simple laboratory experiment and the crab species Carcinus maenas as a biological model, we investigated the effects of cues released by adults on intermolt time, growth, and survival of conspecific megalop larvae and juveniles. Using geometric morphometric analyses, we also compared the size and shape of the carapace and claw of stimulated (St) and control (C) juveniles at both the 1st (J1) and 5th (J5) benthic stages. Results obtained showed that conspecific cues can reduce significantly intermoult time and survival, but these differences are restricted to some specific stages. Neither the size nor the increment at molt differed between treatments. There were no differences of carapace characteristics, but conspecific cues affected claw size and shape of J1 and J5 individuals, respectively. For J1 crabs, claws of St individuals were larger than those of C ones, showing an initial size effect. In the case of J5 juveniles, there were no size differences but evident morphological differences suggest that St crabs bear stronger chelae. By the J5 stage, both St and C juveniles exhibit initial heterochely which precedes the prevailing adult pattern. In spite of reducing survival rate, we conclude that overall effects of conspecific cues are positive. Stimulated juveniles may attain a size-refuge from cannibalism earlier than C individuals, and are likely to more efficiently use valuable feeding resources demanding crushing power, such as mollusk prey, in habitat patches characterized by high density of benthic consumers where competitive interactions are very likely.
Between-host phylogenetic distance and performance of haematophagous ectoparasites
Author(s): Krasnov, B, Khokhlova, I, Fileden, L
Parasites vary in their abundance among host species. The host used by the majority of parasite individuals is considered the principal host, while the remaining host species are referred to as auxiliary hosts. Variation in parasite abundance among auxiliary hosts reflects the degree of phylogenetic proximity between the principal host and the auxiliary hosts it used. The mechanism underlying this pattern is expected to be related to differential performance (feeding and reproductive) of parasites in auxiliary hosts that differ in their phylogenetic distance from the principal host. We tested this hypothesis using fleas parasitic on small mammals. Although feeding performance (blood meal size, energy expenditure for digestion and time of digestion) of parasites differed among different hosts, (1) they did not always perform better on a principal host than on an auxiliary host; and (2) their performance on an auxiliary host was not negatively correlated with phylogenetic distance of this host from the principal host. In accordance with our hypothesis, reproductive performance of parasites (egg and/or new imago production) in an auxiliary host decreased significantly with an increase in phylogenetic distance between an auxiliary and the principal host. However, this was true only for auxiliary hosts belonging to the same family as the principal host. One of the proximate causes for lower reproductive performance and subsequent lower abundance of parasites on auxiliary hosts appeared to be the higher energy cost of egg production in the latter. However, in some parasite species, lower offspring number in an auxiliary host was compensated to some extent by offspring size, although this compensation might also compromise parasites’ future reproduction via decreased survival. In other words, reproductive strategy implied during exploitation of low profitable (i.e., auxiliary) hosts may differ between parasite species.
Institute of Plant Sciences
Biodiversity affects phenotypic plasticity in subtropical trees
Author(s): Blum, JA, Allan, E, Durka, W, Fischer, M
Plasticity allows plants to respond to environmental changes through changing phenotypes during their lifetime and this may be especially important for long lived species such as trees. Biodiversity loss could affect the expression of phenotypic plasticity of growth related traits and this could in turn affect the ability of species to respond to environmental changes. It is therefore important to understand what effects biodiversity has on phenotypic plasticity and we might expect two possible outcomes: firstly, more species rich communities might be more structurally diverse forcing plants to also express higher trait variation in diverse communities. Alternatively in low diversity communities niche space for individual species might be larger allowing niche expansion through an increased variation in growth traits between individuals. To test these ideas we studied plasticity of trees in a large biodiversity experiment in China "BEF China". In this experiment large scale experimental communities were established on an area of 24ha. A total of 60, 000 seed family replicates of thirteen subtropical tree species were grown in plots comprising 1, 2, 4, 8, 16 and 24 species. We measured total height, crown height, crown volume, stem diameter and herbivore damage in twelve species, across the diversity gradient. We calculated plasticity as the variance in growth traits between individuals of the same seed family within a plot. Our results show a significant and consistent decrease of growth trait variation with increasing species diversity. They indicate that biodiversity can influence the expression of phenotypic plasticity and they support the hypothesis that reduced interspecific competition causes increased trait variation. Trees in low diversity communities therefore seem to expand their niches by increasing trait variation.
Earth & Life Institute
Can we predict the effect of thermal fluctuations on specialist and generalist reaction norms?
Author(s): Foray, V, Desouhant, E, Gibert, P
Reaction norms depict the environmental effects on phenotypic traits and are used to predict the global change consequences on organisms. However, studies performed at constant temperatures have limited ecological significance because expressed phenotypes depend on the range and frequency of environmental states. By using the Jensen’s Inequality (a mathematical property of nonlinear functions), we predict that the effect of thermal fluctuations on the phenotype depends on the shape of the reaction norm: a negative effect of the thermal fluctuations when the reaction norm is convex and a positive effect when the reaction norm is concave. This study measures the impact of diel fluctuations in developmental temperature on phenotypic expression of traits related to fitness and energetic resources in two strains of the parasitoid wasp Venturia canescens differing in their thermal sensitivity. In a first experiment, we compare the effect of a constant versus a fluctuating thermal regime having the same means (20, 25 and 30 °C) on reaction norms of life history traits and of energetic reserves. In a second experiment, we examine the effects of a natural thermoperiod in field on these traits. As predicted, our results show that the shape of the reaction norm defines the phenotypic changes induced by the development under fluctuating thermal conditions. Moreover, our results emphasize the significance of taking into account several phenotypic life history traits to study the adaptive value of phenotypic plasticity. We also show that the level of energetic resources depends on the mean developmental temperature and not on the thermal regime. Finally, the field experiment confirms that the phenotype of these parasitoids depends on the temperature variation. This is the first experimental study demonstrating that Jensen’s Inequality can quantitatively predict the effect of thermal fluctuations on life-history traits of an ectotherm species.
Laboratoire des Sciences de l’Environnement Marin
Causes and consequences of developmental plasticity in Daphnia maturation
Author(s): Harney, ED, Van Dooren, TJM, Paterson, S, Plaistow, SJ
Maturation is a key life history transition, due to the importance of age and size at maturity in determining fitness. Understanding how maturation phenotypes evolve requires an appreciation of the underlying ontogenetic mechanisms, including the maturation threshold, which determines when an individual ‘decides’ to mature. Maturation thresholds are poorly understood, and little is known about how phenotypically plastic or genetically variable they are, but the parthenogenetic crustacean Daphnia is the ideal organism in which to study their evolution. Statistically modelling the maturation process shows that the maturation threshold is a developmentally plastic trait in response to variable resource availability, and more closely resembles a process with a rate than a discrete switch. The idea that the threshold is better thought of as a rate than a switch is further supported by gene expression changes during maturation. The maturation threshold also differs between genotypes and species of Daphnia, and clone-specific maternal effects in the development and growth rate interact to produce phenotypically plastic adult phenotypes. Furthermore, experiments studying the fitness consequences of maturation variation showed that Daphnia magna genotypes initiating maturation at smaller sizes had a higher intrinsic rate of population increase, but this size did not correlate well with competitive success when five clones were directly competed with each other, suggesting that interactions with other factors were influencing fitness. Maturation thresholds in Daphnia do not appear to be based on a single fixed state, but are responsive to environmental variation. The presence of heritable variation and transgenerational effects in these developmentally plastic traits suggests that they have an important role in the evolution of age and size at maturity.
Functional and Evolutionary Ecology Lab
Circadian fluctuation of gene expression along a bathymetrical cline in the marine angiosperm Posidonia oceanica
Author(s): Dattolo, E, D'Esposito, D, Lauritano, C, Ruocco, M, Procaccini, G
Plants develop mechanisms of adaptations at multiple levels to track and cope with fluctuations in the light environment. At molecular level, the correct matching of circadian variation of gene expression with environmental rhythms allows plants to optimize the utilization of environmental light and to prevent damages due to light excess. Several studies highlighted that a correct matching of endogenous rhythms and external rhythms increases organismal fitness over a board geographic range. Indeed, latitudinal clines in circadian clock gene expression levels (and polymorphism in clock genes) were found in plants, suggesting that natural variation in clock parameters are required to synchronize organisms with their specific environment. Understanding the genetic and physiological mechanisms that plants develop for the seasonal and daily response to environmental conditions, could allow to predict their response to unexpected changes in environmental conditions that could happen in the future due to anthropogenic and climatic changes. Here we explore variations existing, in the daily phase, along a bathymetrical cline in the marine angiosperm Posidonia oceanica (L.) Delile, a key species in costal Mediterranean ecosystems. To do that, we measured modulation of genes expression, by RT-qPCR, at six time points during the day, in several genes related to photosynthesis and circadian rhythms regulation in plants growing at three target depths during the daily cycle along a bathymetrical cline (5 to 30 meter depth). Sampling was performed in a continuous meadow located in the Bay of Calvi, Corsica (thanks to the ESF Cost Action 0906). We analyze the effects of the distinct environmental light conditions on the circadian fluctuation of gene expression. Further, we assess the phenotypic variation among and between genotypes and we discuss its potential adaptive relevance on P. oceanica fitness and survival.