Plant Sciences Group
A completely unknown lifecycle in mushrooms: cyclical inbreeding and haplo-diploidy
Author(s): Aanen, DK
Mycena galericulata (Basidiomycota, Agaricales) occurs in two forms, a clampless with two-spored basidia and a clamped with four-spored basidia. It is generally accepted that the two-spored form is haploid asexual (apomictic), and the four-spored form sexual (dikaryotic and heterothallic). In order to study the interrelationship between both forms, we performed mating tests and phylogenetic and genetic analyses of a sample of both forms. Surprisingly, our results are inconsistent with any currently known life-cycle. While the four-spored form is heterothallic indeed, we show that the two-spored form is diploid, and produces diploid spores via intra-tetrad selfing. However, the absence of genetic differentiation between both forms, and the high degree of heterozygosity in the two-spored form, indicate that the two-spored form frequently arises from the four-spored. We hypothesise that the two-spored form can again give rise to four-spored forms. Consistent with this, we discovered that a small percentage of fruiting bodies has both two-spored and four-spored basidia.
A genetic approach of reef colonization by a surgeon fish (Acanthurus triostegus) in La Réunion Island
Author(s): Gelin, P, Riou, A, Collet, A, Magalon, H
Resilience of coral reefs is highly dependent on the ability of reef organisms to colonize and survive, and thus to maintain these reefs connected. The aim of this study was to better understand, through population genetics, the fine-scale spatio-temporal colonization pattern of the surgeon fish A. triostegus. This species is well distributed all over the Indo-Pacific reefs and presents a good model to study the variability of reproductive success in marine organisms. The recruits, arriving in two locations 20 km apart, were collected from March 2011 to February 2013 using light traps. A total of 520 post-larvae were caught. Sampling was divided into several nested groups for each location: 4 reproduction seasons (mean duration: 3 months), 17 fishing campaign (6 days around the new moon), 64 days (whenever catches number was higher than 25 individuals). The genetic structure of these juveniles’ populations was assessed using 14 microsatellites loci. For a given location, we found no significant genetic differentiation (1) between days among a fishing campaign, (2) between fishing campaign among a reproduction season, and (3) between reproduction season (maximum FST = 0.0043, NS). On the 34 comparisons performed between locations over fishing campaign, only 4 were differentiated from the others (maximum FST = 0.012 ; P=0.042). Assignment tests did not allow identifying any genetic cluster over the overall sampling. These results showed the absence of temporal or spatial genetic heterogeneity between the post-larvae samples (no chaotic genetic patchiness): the pool of reproductive adults was stable through time. Moreover, the heterozygote deficiency (mean FIS = 0.153±0.006) can be linked to related fishes within samples. So, we performed sib-ship and half-ship reconstruction and found brothers and sisters among samples, showing that post-larvae migration is concerted. Key-words: colonization, A. triostegus, fish, population structure, microsatellites.
A newly discovered role of evolution in published consumer-resource dynamics
Author(s): Hiltunen, T, Hairston, NG, Hooker, G, Jones, LE, Ellner, SP
The consumer-resource relationship is central to population biology and evolutionary ecology. While the interaction is conceptually simple, the mechanisms behind the persistence of any given consumer-resource relationship vary and can be extremely complex. The interaction is generic: a majority of species participate as either consumer or resource, diner or dinner. Traditionally when population biologists interpret results, evolution is not considered to affect the population dynamics because ecological and evolutionary dynamics are assumed to occur on different time scales. Yet recent research has demonstrated that evolutionary change can happen rapidly and on the same time scale as ecological processes affecting population dynamics qualitatively.
In here we present a reanalysis of 21 consumer-resource data published over the last 80 years, approximately. Of the 21 published studies of consumer-resource dynamics we analyzed, evolution played a significant and substantial role in ten and a marginally significant role in another three, even though the original authors did not recognize its effect. In addition to a reanalysis of previously published data, we demonstrate via mathematical modeling how rapid prey evolution results in a transition from predator-prey dynamics with classical quarter-lag cycles, to anti-phase oscillations typical of eco-evolutionary dynamics and at the extreme, to cryptic cycling. We then show that this mechanism very likely explains dynamics observed in historical data, where possibility of rapid evolution was originally ignored. In general, our reanalysis suggests that evolutionary dynamics occurred in many of these, but the significance of qualitative features in the dynamics went unrecognized at the time. Furthermore, with more prey generations and larger population sizes the likelihood of evolutionary dynamics was higher.
University of Southern Denmark, Insitute of Biology
Aging and imperfect asymmetric division in bacteria
Author(s): Steiner, U, Ni, M
The process of aging is assumed to result from accumulating damage over the lifespan, and such damage finally leads to death. Evolutionary theory predicts that dividing organisms such as bacteria flee from that process at the population level by asymmetric division, that is one cell (presumably the mother cell) takes over more of the damage and the other cell (daughter) is perfectly rejuvenated. To test these arguments and to see whether asymmetric division remains perfect throughout life we conducted experiments on a single cell microfluidic bacteria system to compare demographic parameters of daughter cells that came from young mothers with daughter cells coming from old mothers. Results show that daughters from young mothers have long lifespan and divide more often compared to daughters coming from old mothers. There seem to be no differences in cell growth. Our results suggest that asymmetric division is only perfect early in life of cells but not late in life. Our findings can explain the maintenance of the cell line by perfect rejuvenation of daughter cells produced early in life, and at the same time see substantial aging processes. The results therefore combine previously contrasting theories of aging and show how life-histories have to be considered across generations.
Chemical anthropogenic pollution interferes in prey recognition systems
Author(s): Polo-Cavia, N, Burraco, P, Gomez-Mestre, I
Chemical detection of predator cues is crucial for aquatic prey, because it allows predator avoidance and activation of plastic antipredatory defenses. This is the case of many larval amphibians that respond to water-borne cues from potential predators by strongly reducing activity levels. However, as a consequence of increasing anthropogenic activity, a variety of harmful contaminants are dumped in freshwater ecosystems, where they can create interferences in the cue recognition system of tadpoles. Here we analyze the potential effects of two contaminants (i. e., humic acid and ammonium nitrate) on the ability of tadpoles of the western spadefoot toad (Pelobates cultripes) to recognize chemical cues from a common predator, nymphs of the dragonfly Anax imperator. We compared swimming activity of tadpoles in presence and absence of water-borne chemical cues from dragonflies, at different concentrations of humic acid and ammonium nitrate. Changes in tadpole activity associated to toxicity were non-significant. In contrast, the interaction between predator cues and presence of contaminants was significant: tadpoles effectively responded to predator cues in the absence of pollutants by reducing their swimming activity, but remained unresponsive to predator cues when either humic acid or ammonium nitrate were added, even at low concentrations. These interferences due to chemical anthropogenic pollution may pose a threat to the cue recognition systems of prey-predator interactions evolved in amphibian populations.
Density-dependent dispersal in Sable Island horses: rate and direction varies with sex and age but also scale at which density is assessed
Author(s): McLoughlin, PD, Marjamäki, PH, Contasti, AL, Coulson, T
Density-dependent dispersal is known for most species; why it evolves is of fundamental interest to ecology and evolution. In this context, we have yet to fully appreciate how individuals of varying conditions might differently perceive quorum in their decision whether to disperse, which may be scale-dependent. Using an individual-based field study, we demonstrate how dispersal rate in an island population of feral horses (Equus ferus caballus, Sable Island, Canada, 2008–2010) is positively density-dependent for all age and sex categories with respect to local density (breeding adults within 8000 m of a horse’s centroid location), but negatively density-dependent for males and positively density-dependent for females in relation to group (band) size. Dispersal was generally female-biased, with the exception of foals which moved with their mothers (no sex effect), and for yearlings and subadults when band sizes were smaller than average, in which case males dispersed at higher rates than females. Dispersal distance was positively related to local density. We conclude that dispersal rate can be both positively and negatively density-dependent for feral horses, contingent on the state of individuals and the scale at which quorum is assessed. Scale effects and interactions of density-dependent and sex- and age-biased dispersal may have both ecological and evolutionary consequences through effects on resource and mate competition.
Evolutionary Ecology of Marine Fishes
Dispersal and evolution of the European eel shaped by variations of North Atlantic drift currents
Author(s): Baltazar-Soares, MA, Biastoch, A, Harrod, C, Hanel, R, Marohn, L, Prigge, E, Evans, D, Bodles, K, Behrens, E, Böning, CW, Eizaguirre, C
For open ocean broadcast spawners, environment-dependent dispersal is a crucial but critical life phase. The yearly recruitment fluctuations and cryptic adult population structure commonly observed in these species are assumed to reflect both the temporal and the spatial environmental conditions that early stages are exposed to. With a long-lasting ocean-dependent dispersal, the European eel (Anguilla anguilla) poses as perfect model organism to study the role of the environment in the evolutionary ecology of a broadcast spawner. To this end, we compared predictions made on dispersal, recruitment and population genetics by 45 years of high-resolution North Atlantic drift modeling with natural recruitment and population genetics at European coasts. We identify atmospherically-driven current variations in the Sargasso Sea as a key factor for a successful dispersal. We also demonstrate how unexpected findings of population structuring are consistent with contemporary recruitment levels, and with cryptic female philopatric behaviors within the Sargasso Sea. We suggest this strategy to be an evolutionary consequence of the unpredictable oceanic environment in the Sargasso Sea.
Department of Biosciences
Dispersal, flight metabolism and flight-induced gene expression in the Glanville fritillary butterfly
Author(s): Mattila, ALK, Somervuo, P, Kvist, J, Frilander, M, Lehtonen, R, Hanski, I
Flight is essential for reproduction and dispersal in butterflies and other flying insects. Studies on the Glanville fritillary butterfly have shown that the higher the rate of flight metabolism an individual can achieve, the higher is its capacity for dispersal in the field. However, thoracic muscles of flying insects exhibit the highest mass-specific rates of oxygen consumption known for any locomotor tissue, making insect flight an energetically demanding activity. Flight that is based on aerobic metabolism may become quickly limited by oxygen conductance to the flight muscles, leading to hypoxia. In this study, we investigate genome-wide gene expression induced by controlled active flight in the Glanville fritillary. We aim to identify genes and pathways that are up- or down-regulated in flight, and we study how allelic variation in annotated genes, gene expression, and flight metabolism phenotypes covary. We compare females and males, which exhibit significant differences in their flight metabolism and movement behaviors, reflecting different functions of flight in the two sexes. Second, we contrast individuals from two natural populations with very different genetic compositions, a large metapopulation in the Åland Islands and a small, completely isolated island population with low genetic variability, high genetic load as well as greatly reduced flight metabolic rate.
Department of Life Sciences
Do native and invasive populations of Oxalis pes-caprae differ in reproductive traits?
Author(s): Castro, M, Ferrero, V, Costa, J, Roiloa, S, Loureiro, J, Navarro, L, Castro, S
Biological invasions offer the opportunity to study evolutionary transitions in current timescales. Because reproductive strategies determine demographic and genetic characters of invasive populations, variations on reproductive characters have the potential to influence evolutionary processes during invasion, and the invasion process itself. Thus, comparative studies of reproductive systems between native and invaded ranges are crucial for understanding the mechanisms of plant invasion and for predicting microevolutionary changes in anthropogenic environments. Oxalis pes-caprae is a tristylous species native from South Africa and an invasive weed in Mediterranean climate regions worldwide. In its native habitat, the species presents three floral morphs, reproduces sexually and asexually, and has different cytotypes (2x, 4x, 5x). In most invaded areas, strong founder events lead to the introduction of the 5x short-styled morph only, leading to an exclusively asexual mode of reproduction. However, in the Mediterranean basin, new floral morphs and cytotypes with the ability to reproduce sexually were recently found. The aim of the present study was to assess evolutionary shifts in asexual and sexual reproduction traits between floral morphs and cytotypes, and between native and invasive populations of O. pes-caprae. For this, phenotypic characters directly linked with reproduction were assessed in plants from native and invasive populations growing in a common garden. The results of the sexual and asexual reproductive traits among floral morphs, cytotypes and invaded vs. native range are presented. The information gathered adds significant background information on the evolutionary biology and ecology of biological invasions. The knowledge of the probability and speed at which local adaptation evolves in invasive plants is particularly important for management practices, especially when evolutionary changes enhance ecological opportunities and invasive spread.
Department of Biological Science
Do prey respond appropriately to evolutionarily novel predators?
Author(s): Bleicher, SS, Brown, JS, Kotler, BP
Deserts provide a model system for studying convergent evolution. Sand dunes in the Mojave (USA) and Negev (Israel) deserts are home to distinct yet convergent community of species with granivorous rodents and sidewinding vipers, red foxes and barn owls as predators. By virtue of heat sensing pits(vipers) and external cheek pouches (hetromyid rodents) the Mojave possess constraint breaking adaptations over the counterpart species in the Negev.
In a semi-natural arena, we exposed Merriam’s kangaroo rat (Dipodomys merriami) and desert pocket mice (Chaetodipus penicillatus) of the Mojave, and Allenby’s gerbil (Gerbillus andersoni allenbyi) of the Negev to sidewinder rattlesnakes (Crotalus cereastes), a pit viper, and to the Saharan horned viper (Cerastes cerastes). We quantified the response of each rodent species to the snakes and in combination with owls. We monitored activity over all moon phases and asked whether the rodents responded differently to the novel, compared to the familiar, snake species. Specifically, we test the recognition of gerbils of a novel predator with heat sensing pits, and heteromyids’ assessment of a snake with limited tools.
Analysis shows that the gerbiline rodents, at first, risk encounters with the novel viper before rapidly learning to avoid both vipers. Lengthy exposure allowed gerbils to adjust and optimize their balancing of food and safety. This caused a 25% increase in foraging for both species of vipers. Pocket mice reduced their foraging equally regardless of viper species. Interestingly Kangaroo rats found both species equally frightening following exposure they ceased to be aversive of the novel predator.