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.
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.
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.
Laboratoire Evolution Génome et Spéciation
Contributions of a novel population to the understanding of the role of male hydrocarbon polymorphism in Drosophila melanogaster
Author(s): Bontonou, G, Denis, B, Wicker-Thomas, C
In Drosophila, female hydrocarbons are known to be involved in premating isolation between different species and pheromonal races. However, the role of male-specific hydrocarbon polymorphism is not as well documented. The dominant cuticular hydrocarbon (CHC) in male D. melanogaster is usually 7-tricosene (7-T; C23:1), with the exception of central African populations, in which 7-pentacosene (7-P; C25:1) is dominant. Here, we describe a novel population from Comoro Island (Com) that includes males with sex pheromone profiles ranging from high 7-T to high 7-P. We maintained Com flies at different temperatures, without selection. After 18 months, flies reared at 21°C had a 7-T hydrocarbon profile and flies reared at 25°C had an intermediary to 7-P profile. We specifically selected for high 7-T, high 7-P, or intermediate hydrocarbon profiles. We showed that the 7-P/7-T ratio depended on temperature in Com with generally more 7-P at higher temperatures. There was partial reproductive isolation between flies with clear-cut phenotypes (7-T and 7-P). These results show that the dominant male pheromones are under environmental selection due to heat/desiccation stress.
School of Animal Biology
Correlated evolution of sexual dimorphism and male dimorphism in a lineage of Neotropical harvestmen
Author(s): Buzatto, BA, Tomkins, JL, Simmons, LW, Machado, G
Secondary sexual traits (ornaments and weapons) increase male fitness, but are generally maladaptive when expressed in females, generating intralocus sexual conflict that is ameliorated through the evolution of sexual dimorphism. Intense sexual selection on males can also favor the evolution of male dimorphism, where alternative phenotypes that avoid expenditure in secondary sexual traits achieve copulations using ‘alternative mating tactics’ (AMTs). Secondary sexual traits can thus increase or decrease fitness in males, depending on which AMT they employ, generating a conflict within males that can be ameliorated by the evolution of male dimorphism. Thus, the phenotypic optima of females and small males are similar in terms of including the suppression of such secondary sexual traits. Male dimorphism could hence coevolve with sexual dimorphism, due to the evolutionary forces acting against both intralocus sexual conflict and conflict between males employing different AMTs. Here we tested this hypothesis by investigating the evolution of sexual and male dimorphism for two secondary sexual traits in 48 species of Neotropical harvestmen (Arachnida: Opiliones). Using a Bayesian approach with reversible-jump Markov chain Monte Carlo, we demonstrate that the two types of dimorphism present strongly correlated evolution, and that sexual dimorphism consistently precedes male dimorphism in this major arachnid group. Our findings were consistent for two different traits, and are robust to phylogenetic uncertainty. We propose that sexual dimorphism evolves earlier than male dimorphism because the genetic architecture for sex specific expression is already present even in sexually monomorphic species, due to sex chromosomes. The same is not true in the case for male dimorphism. We suggest that if a sexual trait arises first in an autosome and is expressed in all individuals, its suppression in females evolves more readily than its suppression in small males that adopt AMTs.
Department of Ecology & Evolution
Deciphering the importance of genetics and environment in shaping the phenotype of low and high altitude vole populations: countergradient effect and cryptic evolution
Author(s): Bize, P, Lehto, M, Figeat, L
Phenotypic variance along altitudinal gradients is determined by the influenced of both genetic and environment, and counter-gradient selection occurs when genetic and environment influences on phenotype oppose one another. Although we have previously found that high-altitude common voles (Microtus arvalis) are growing at slower rates and are lighter than low-altitude voles under standardized ‘common garden’ conditions (25°C), field based observations report no difference in body mass between high- and low-altitude populations. The heat dissipation theory has recently pointed out that cold ambient temperatures allow endotherms to increase their metabolic ceiling, and in turn favour for instance female lactation and offspring growth rates. Hence, one hypothesis is that genetically based differences in growth and body mass at adulthood between high- and low-altitude vole populations are masked in the wild by the cooler environments encounter by high-altitude voles, which might increase their metabolic ceiling and growth rates. To address this issue, Wild derived offspring (F1) of low and high altitude parents (F0) were reproduced at 10°C and 25°C in order to examine the influence of genetic (high vs. low altitude) and temperature on the growth of their pups (F2). We found that voles from high-altitude populations were growing at slower rates than those from low-altitude populations, but cool ambient temperatures allowed high-altitude voles to catch-up in size with low-altitude voles. Our study highlights the occurrence of coutergradient effect, and in turn cryptic evolution, on the phenotype of an endotherm in response to temperature change.
School of Biology and Environmental Science
Demographic and behavioural landscape of damselfish reproductive success
Author(s): Mascolino, S, Sacchi, C, Boufana, B, Gubili, C, Woodward, S, Mariani, S
Alternative reproductive strategies are common features in sexually reproducing organisms. For instance, in territorial species dominant males (having primary access to females) can be observed alongside other males adopting different strategies, such as parasitic fertilisation. In order for the alternative strategy to persist in a population, it has to hold some degree of reproductive success. In the case of the Mediterranean damselfish (Chromis chromis), during the reproductive season, only territorial males colonise nest on the bottom of rocky reefs, and compete for females in order to receive egg deposition. Sneaker males float above the nesting area waiting for the right moment to parasitically spawn in the nests of territorial males. In this context, the success of sneakers is expected to be negatively affected by the ability of territorial males to recognise the rivals and chase them away. Variance in individual behavioural traits of nesting males as well as population-level factors, such as density can both affect the contribution of parasitic spawners to the next generation. Here we combine behavioural observation in the field with molecular analyses, using bi-parentally and maternally inherited markers to investigate the contribution of both individual chasing behaviour and population density on the relative reproductive success of nest-guarding males and sneakers.