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.
Ecology, Evolution, and Organismal Biology
A fluctuating environment drives coexistence in five non-pollinating fig wasps
Author(s): Duthie, AB, Abbott, KC, Nason, JD
The principle of competitive exclusion states that species competing for identical resources cannot coexist, but this appears paradoxical given myriad ecologically similar competitors. Theory shows coexistence is possible if a fluctuating environment changes the competitive dominance of species, but only when environmental variation leads to non-linear or non-additive population growth. Non-additivity facilitates coexistence when competition and environment covary in their effects on growth such that competition is weaker in poor environments. The variation required to facilitate coexistence is typically interpreted as a physical aspect of environment. We investigate a system that might be considered constant under such interpretations, but show a hidden source of temporal variability relying on fluctuating dispersal distances between resource patches. We model populations that use resources in discrete, ephemeral, patches. Such ephemeral patch systems often support many competing species. We frame our model with respect to the highly diverse non-pollinating fig wasp communities that oviposit and develop within fig fruit. Using numerical and individual-based models, we show that temporal storage of larval wasps leads to long-term community coexistence under a wide range of biologically realistic parameter values when wasps face a trade-off between dispersal ability and fecundity. We empirically test whether or not such a trade-off exists in a community of five competitor species of non-pollinators associated with Ficus petiolaris. We find strong evidence of a negative correlation between species dispersal abilities and fecundities, which we present as an extreme case in which a single fluctuating environmental variable appears to mediate coexistence in a community of competitors. We suggest that fluctuating environmental conditions may drive coexistence more generally, especially among competitors regularly dispersing between ephemerally available habitat patches.
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.
Department of Biodiversity and Evolutionary Biology
Cichlid evolution in crater lakes and ecological opportunity
Author(s): Barluenga, M, Magalhaes, IS
Ecological opportunity fuels the generation of biodiversity. When empty habitats are colonized ecological release favors species niche expansion and eventually the divergence of taxa via intraspecific resource competition and character release. The very young cichlid fish radiations from the Nicaraguan lakes in Central America are a powerful model for the study of very rapid diversification. Multiple recently formed crater lakes exist in this area, and all of them have been independently colonized by a subset of the fish fauna from the larger and older close by Nicaraguan Great Lakes. This setting is excellent to test the idea of ecological and character release following ecological opportunity. To this end we have studied the entire fish fauna of several crater lakes and characterized the ecological role of each of the species. We investigate the consequence of the absence of some of these species in the community for the remaining species, and the ability of the latter to expand their niche, release their morphological design and ultimately speciate.
Departement of Ecology and Evolution
Co-evolutionary branching of dispersal and sociality in structured populations
Author(s): Mullon, CDL, Keller, L, Lehmann, L
Dispersal has antagonistic effects for the evolution of altruism, cooperation and social behavior. On one hand, dispersal of individuals from their native patches decreases relatedness between locally interacting individuals, and thus disfavors the evolution of social traits. On the other hand, dispersal reduces local competition among kin, thereby favoring cooperation. It is traditionally thought that these two antagonistic effects balance, and as a consequence, an intermediate level of dispersion and sociality evolves. However, recent numerical experiments have suggested that when social traits and dispersal evolve together, evolutionary branching may take place, leading to the stable coexistence of social and asocial individuals with different dispersal strategies. In order to clarify the effects of dispersal on the evolution of cooperation, we developed analytical tools to study the evolution of multiple phenotypic traits in structured populations. By tracking changes in the phenotypic distribution in a population over time, we are able to explicitly predict the conditions that lead to evolutionary branching, and thus the coexistence of different dispersal and cooperating strategies. More generally, our method can be applied to study the emergence of highly differentiated life histories in structured 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.
Department of Zoology
Disentangling the social, parental and genetic influences on natal dispersal in great tits
Author(s): Garroway, CJ, Hinde, C, Verhelst, B, Sheldon, BC
Natal dispersal is a key process underpinning the structure and dynamics of populations. Individual variation in dispersal behaviour is substantial, but we know very little about the causes of individual variation in dispersal, and the extent to which this variation is influenced by social processes. Here, we integrate longitudinal data collected over five decades from a wild great tit (Parus major) population with two cross-fostering experiments to disentangle the influence of social processes, parental effects and genetics on dispersal behaviour. We show first that parental dispersal phenotype, whether they are themselves locally hatched or immigrants, has scale-independent effects on dispersal by offspring. Birds with immigrant parents dispersed further within patches and were more likely to disperse outside patches. Using an index of the composition of early social environments, with reference to the immigrant and locally hatched status of neighbours, we then show that dispersal is independent of the local social environment in which birds are raised. We used two large-scale cross-fostering experiments to demonstrate that parental effects on dispersal are primarily intrinsic to offspring, and therefore independent of parental behaviour. Finally, we show that parental dispersal phenotypes show similar fledging success but differing rates of local recruitment of offspring, implying that dispersal phenotypes will be genetically structured across landscapes. Our findings suggest that understanding the underpinning genetics of dispersal will be important for understanding the behaviour of populations in fragmented landscapes. Non-random dispersal of particular types of individuals suggests scope for the emergence of fine-scale population structure and has important consequences for interpretations of selection studies and dispersal theory.