Institute of Evolution and Ecology
A potential role for ecologically mediated sexual selection in the divergence of Tropical Pacific honeyeaters (Myzomela)
Author(s): Thomassen, HA, Waider, C, Dekker, RWRJ, Smith, TB
The relative roles of neutral and selective processes in divergence are of key interest in evolutionary biology. Due to the many large and small islands, the Indopacific area constitutes an ideal natural laboratory to study the different modes of diversification. It is a biotically extremely rich region, and as a result is designated as several distinct biodiversity hotspots. It was suggested that the islands of the Pacific are a likely source of biodiversity, rather than a sink of species that originated on the mainland, as has long been the established hypothesis. We use landscape genetic approaches to study the potential roles of drift, natural selection, and sexual selection to study the divergence among island and mainland species of sexually dimorphic honeyeaters, Myzomela sp. Sequence and microsatellite data indicate that these populations either very recently diverged or experience ongoing gene flow, and planned coalescence-based analyses will be useful in distinguishing these two hypotheses. We found that males exhibit distinct differences between islands in plumage coloration and song, but not in other, fitness-related morphological traits. Females did not show divergence in any morphological traits between islands. Environmental heterogeneity explained the observed divergence in song frequency characteristics, whereas oceanic barriers better explained divergence in temporal traits. These results suggest that sexual selection is a potential factor in maintaining and deepening population differentiation, and that environmental conditions pose selection pressures on some but not all sexual traits. The role of sexual selection in population divergence will be further evaluated using mate choice experiments.
Adaptive TE insertions in Drosophila: NATs, miRNAs, and piRNAs
Author(s): Gonzalez, J, Ullastres, A, Mateo, L
Recent Transposable Element (TE) insertions in Drosophila melanogaster are a useful tool to identify adaptive mutations. The objective of this study is moving from the identification of a putatively adaptive TE insertion to the molecular mechanisms and associated fitness effects. We have focused on a TE insertion located in the 3'UTR region of Kmn1 gene. The 3´UTR of Kmn1 overlaps with the 3´UTR of its nearby gene, CG11699, giving rise to a cis-natural antisense pair of transcripts (cis-NATs). We found that besides being incorporated into the 3’UTR of Kmn1, the TE insertion also affects the transcript length of CG11699. Specifically, the TE disrupts the GU-rich downstream element of the distal polyA signal of CG11699 and as a consequence a shorter transcript is produced. These structural changes are very likely to have functional consequences since the presence of the TE adds (Kmn1) and eliminates (CG11699) miRNA binding sites, introduces piRNA binding sites (Kmn1) and affects the length of the overlapping region between these two genes. Indeed, we detected that this TE insertion is associated with an under-expression of Kmn1 and an over-expression of CG11699. In order to identify the phenotypic effect of this insertion, we first focused on CG11699 since this gene is involved in the activation of Aldh-III, an enzyme involved in xenobiotic metabolism. We found that the TE insertion is associated with an increased survival rate after an acute exposure to benzaldehyde, a prototypical drug classically used to assess Aldh-III activity, strongly suggesting that this TE confers resistance to xenobiotic stress. Our results show that a single mutational event has broad molecular consequences that can be translated into ecologically relevant phenotypic effects. This example reinforces the idea that TEs are a powerful natural tool for genome evolution.
Department of Biology
Adaptive divergence in two coexisting stickleback species
Author(s): Raeymaekers, JAM, Chaturvedi, A, Konijnendijk, N, Maes, G, Volckaert, F
Natural populations are at least partially adapted to local environmental conditions. The level of adaptation is promoted by divergent selection on ecologically relevant traits, but hampered by gene flow. The relative strength of both forces depends on genomic architecture as well as dispersal abilities, both of which might differ between species. In this study, we tested for divergent selection and gene flow in two coexisting and phylogenetically related species, the three- and nine-spined stickleback. Populations occur across very similar environmental clines in biotic and abiotic conditions (salinity, oxygen concentration, predation, parasites and prey), and were sampled within exactly the same spatial matrix. In each species we assessed gene flow between populations from contrasting environments and determined divergence in ecologically relevant traits (body shape, armour, spleen size, and trophic morphology). An analyses of genome-wide differentiation was used to identify the genomic basis of adaptation. Based on these data we compared the relative strength of divergent selection and gene flow in both species, as well as the biological functions of the genes under selection. We discuss how these relationships explain how both stickleback species maintain partially overlapping habitats.
School of Biosciences
Age related changes in fitness traits in a wild field cricket population
Author(s): Rodríguez-Muñoz, R, Tregenza, T
Evidence for senescence in nature has been found in a growing number of vertebrate species, particularly birds and mammals, and more recently in a few invertebrates. Insects have proved very suitable for the study of senescence in laboratory studies but their mobility and small size make them very difficult to follow in their natural environment. We have extended the study of insect ageing into the wild, by using up to 90 video cameras to continuously monitor a natural field cricket population. We tagged individuals immediately after they became adult and followed them until their death was either inferred or directly observed. We recorded mating and fighting success, singing activity and movement over the entire adult life of individual crickets for five consecutive generations. We examine changes in behaviour over the adult lifespan and relationships with reproductive success. This allows us to determine whether crickets senesce in our population in terms of both survival probability and changes in behavioural measures such as activity, and to ask questions about interactions between ageing and sexual selection. Our model system provides an excellent opportunity for the study of the selective pressures acting on life history and ageing in wild insects.
Department of Biological evolution
Ant preadaptation to the urbanized territories: case study
Author(s): Lysenkov, S, Oparina, N
Urbanization is now one of the greatest threat caused on wildlife by human activity. Its negative impact consists of habitat and community destruction, high level of chemical, thermal and light pollution etc. Urban entomofauna is greatly depleted, but extinction is not random. Recently it has been shown that black garden ant Lasius niger (Hymenoptera: Formicidae) is the most robust to the urbanization pressure. It becomes even more abundant in the most disturbed areas in Moscow city. This species is also very interesting for ecological and evolutionary researches because it is widespread, in contrast to the genetically most studied ant species. We sequenced L. niger genome using NGS technology to search for possible adaptation to the urbanization pressure. Several results which can be treated as preadaptation were revealed. For example, detoxification system is often involved in the urban adaptation. We found that this species has an expansion of cytochrome P450 gene subfamily 9 which is unusual to hymenopterans – this subfamily is expanded in humans. This feature could possibly play a role in preadaptation to the urbanized environments. The next stage of the study is the search for the possible selective sweeps in urban populations.
Environmental Life Sciences
Assessing caribou ecotypes using functional genes
Author(s): Marques, AJ
Woodland caribou in Ontario use one of two distinct predator avoidance strategies during calving, commonly referred to as behavioural ecotypes. Migratory caribou undergo seasonal shifts in their range from boreal to tundra coasts while sedentary caribou disperse throughout the boreal forest. This project will assess the degree of genetic differentiation between caribou ecotypes within Ontario using functional gene markers. Range overlap and a mixture of caribou lineages in Ontario has made genetic differentiation challenging to detect with traditional neutral markers. Functional genes, however, are subject to selective pressure and may parallel differences between ecotypes. Six genes have been selected for analysis: Mc1R, DRD1, Cyt b, Opsin, IGF1, and PRKG1 several of which are known to vary among caribou subspecies. DNA will be extracted from multiple sources including blood, tissue, and feces. Functional genetic markers will be isolated using Reverse Transcription Polymerase Chain Reaction (RT-PCR) then sequenced using a next-generation sequencer to identify individual genotypes. Once sequenced, a statistical analysis will investigate whether a functional genotype can be ascribed more commonly to a particular ecotype. Determining the relationship between genotype and ecotype can provide insight into the adaptive potential of caribou in response to further northern development. Providing an alternative to mitochondrial classification may help to establish distinctions between caribou ecotypes for management purposes.
Assessing the effects of human selection through fishery on sea cucumber genetic structure and population dynamics
Author(s): Valente, SM, Sen, O, Ciftci, Y, Aydin, M, Serrão, E, González-Wangüemert, M
Increased fishing pressure has resulted in widespread overexploitation of populations, with declines in overall abundance of stocks and average size; adverse genetic selection leading to loss of potential fecundity; reduced average spawning size; change of sex-ratio and interspecific equilibrium; and loss of genetic diversity. After the failure of traditional management measures, marine protected areas have been strongly advocated as an ideal tool for the management of coastal fisheries protecting critical spawning stock biomass, intraspecific genetic diversity, population age structure, recruitment supply and ecosystem balance. The sea cucumber fisheries have increased world wide and several species (Holothuria polii, H. tubulosa and H. mammata) are now targeted in Turkish waters reaching a total production around 600,000 kg in the last year. In this work, we assess the fishery effects on the genetic structure and population dynamics of three sea cucumbers species. We found significant differences in H. tubulosa and H. polii among protected (Kusadasi) and non-protected (Ayvalik) localities considering their length and weight, showing Kusadasi the largest and heaviest individuals. H. mammata did not shown significant differences. Also, we found higher genetic diversity for the three target species (number of total and exclusive haplotypes, haplotype and nucleotide diversity, polimorphic sites) in Kusadasi (marine protected area) than Ayvalik.
Dept. of Biology
Assortative mating strength and selection of morphological characters in natural populations of two closely related damselfly species
Author(s): Nordén, AK, Svensson, EI, Waller, J
Assortative mating occurs when individuals in a population mate non-randomly and there is a correlation with respect to traits between individuals in mated pairs. It is important in evolutionary processes in that if selection acts on the same trait, assortative mating may lead to speciation and reproductive isolation. On the other hand, if assortative mating is free of selection, it will lead to stabilizing selection within a population. In this study, I examined assortative mating strength within and between two sympatric damselfly species (Calopteryx splendens and Calopteryx virgo) by correlating the male and female morphological characters in mated pairs. In addition, I investigated the relationship between assortative mating and sexual selection (linear, β and quadratic, γ) on the same traits for these damselfly species. In both species, positive assortative mating was more common than negative assortment (disassortative mating). Thorax width in both species had the greatest assortative mating strength. There was no relationship between assortative mating strength and linear selection or quadratic selection. This indicates that there is no strong connection between assortative mating and sexual selection on the same traits. Assortative mating strength for C. splendens and C. virgo were concordant, and positive, suggesting that there is no noticeable reproductive isolation between these two species and that stabilizing selection is probably operating. Rather, assortment in both species is based on quality, where high-quality males get high-quality females. This study contributes to the knowledge about evolution and selection in natural populations.
Chair of Genetics and Evolution
Boys and girls and plant-eaters: Is herbivory sex-biased in Mercurialis perennis?
Author(s): Rubinjoni, L, Vujić, V, Selaković, S, Cvetković, D
Sex-biased herbivory has been implicated as one of the driving forces in the evolution of dioecy. Different partitioning of resource sources and sinks in male and female plants allows different defense strategies. Along with constitutive and induced defences, plants can tolerate herbivore damage to a certain extent, and can ameliorate the pressure through changes in phenology and life history. Gender-dimorphic species of genus Mercurialis are informative model systems in addressing questions in plant evolutionary ecology, including interactions with herbivores. For Mercurialis annua, the most commonly studied species of the genus, herbivore prefference for male plants has been demonstrated in experimental conditions. The aim of our study was to explore the pattern of herbivore damage in natural populations of Mercurialis perennis, a dioecious perennial herb with wide geographic and altitudinal distribution. Plants were sampled from a range of habitats in Serbia. Damage to leaf area was scored and used as an estimate of herbivore load. Herbivore damage was examined in relation to plant gender, altitude, plant height and reproductive allocation. Our results do not confirm the pattern of male-biased herbivory in natural conditions. The variance of herbivore damage between the sexes among the habitats was large, with highly significant effect of site, and non significant effects of sex and sex-site interaction. In a montane population, herbivore damage was male-biased, but without statistical significance. Studied populations showed male-biased sexual size dimorphism. The study of Mercurialis perennis offers a promising approach to better understanding the effect of plant gender on general vigor, tolerance and resistance to herbivores.
Can a hybrid outcompete its parental species? - a story about a “super clone“ (Daphnia galeata × longispina hybrid)
Author(s): Griebel, J, Poxleitner, M, Navas Faria, A, Giessler, S, Wolinska, J
The role of hybridization in evolution has been underestimated for a long time. For example, hybrids were often considered less fit then their parental species, due to genetic incompatibility. However, hybridization occurs frequently in plants and in animals. Our recently collected field data showed that a Daphnia community of a small quarry lake in Munich, normally consisting of parental species and hybrids belonging to the D. longispina complex, has become dominated by a single hybrid clone - the “super clone”. By creating artificial communities consisting of the “super clone” and other clones of the D. longispina complex, we proved the competitive strength of the “super clone”. After ~6 generations the “super clone” had increased from 8% to 100% in some of the artificial communities. Additionally, we studied fitness parameters of these clones, kept under two different temperatures. Here, there was no special performance of the “super clone”. Therefore we are currently comparing the carrying capacity of “super clone” with the other clones, by measuring the change in numbers of Daphnia over time, in a certain volume of water. Additionally, we will study fitness parameters of the clones under crowding (and control) conditions. The crowded media will be obtained from crowded stock cultures. We expect the “super clone” to have higher carrying capacity as well as to be less affected by crowded media than the other clones, thereby preventing the other clones from reproducing and establishing within the population. Finding the pattern that makes the “super clone” so special will contribute to a general knowledge about hybrid-specific traits and their contribution to evolutionary processes.