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Evolution; International Journal of Organic Evolution

Hanna Nyborg Støstad, Arild Johnsen, Jan Terje Lifjeld, Melissah Rowe
Sperm exhibit extraordinary levels of morphological diversification across the animal kingdom. In songbirds, sperm have a helically shaped head incorporating a distinct acrosomal membrane or 'helical keel', the form and extent of which varies across species. The functional significance of this helical shape, however, remains unknown. Using scanning electron microscopy, we quantified inter- and intra-specific variation in sperm head morphology across 36 songbird species (Passeriformes: Passerida). Using phylogenetic comparative methods, we investigated the relationship between sperm head morphology and both sperm swimming speed and the frequency of extra-pair young (EPY)...
July 17, 2018: Evolution; International Journal of Organic Evolution
Jonathan M Henshaw, Michael D Jennions, Loeske E B Kruuk
Natural selection operates via fitness components like mating success, fecundity and longevity, which can be understood as intermediaries in the causal process linking traits to fitness. Sexual selection occurs when traits influence mating or fertilisation success, which, in turn, influences fitness. We show how to quantify both these steps in a single path analysis, leading to better estimates of the strength of sexual selection. Our model controls for confounding variables, such as body size or condition, when estimating the relationship between mating and reproductive success...
July 13, 2018: Evolution; International Journal of Organic Evolution
Eddie K H Ho, Aneil F Agrawal
Selfing species are prone to extinction, possibly because highly selfing populations can suffer from a continuous accumulation of deleterious mutations, a process analogous to Muller's ratchet in asexual populations. However, current theory provides little insight into which types of genes are most likely to accumulate deleterious alleles and what environmental circumstances may accelerate genomic degradation. Here we investigate temporal changes in the environment that cause fluctuations in the strength of purifying selection...
July 13, 2018: Evolution; International Journal of Organic Evolution
Fabian Cahenzli, Christophe Bonetti, Andreas Erhardt
Quantifying the relative contribution of multiple isolation barriers to gene flow between recently diverged species is essential for understanding speciation processes. In parapatric populations, local adaptation is thought to be a major contributor to the evolution of reproductive isolation. However, extrinsic postzygotic barriers assessed in reciprocal transplant experiments are often neglected in empirical assessments of multiple isolation barriers. We analyzed multiple isolation barriers between two closely related species of the plant genus Dianthus, a genus characterized by the most rapid species diversification in plants reported so far...
July 12, 2018: Evolution; International Journal of Organic Evolution
Caroline Parins-Fukuchi
Jointly developing a comprehensive tree of life from living and fossil taxa has long been a fundamental goal in evolutionary biology. One major challenge has stemmed from difficulties in merging evidence from extant and extinct organisms. While these efforts have resulted in varying stages of synthesis, they have been hindered by their dependence on qualitative descriptions of morphology. Though rarely applied to phylogenetic inference, traditional and geometric morphometric data can improve these issues by generating more rigorous ways to quantify variation in morphological structures...
July 11, 2018: Evolution; International Journal of Organic Evolution
Eloïse Vanhoenacker, Linnéa Sandell, Denis Roze
Stabilizing selection around a fixed phenotypic optimum is expected to disfavor sexual reproduction, since asexually reproducing organisms can maintain a higher fitness at equilibrium, while sex disrupts combinations of compensatory mutations. This conclusion rests on the assumption that mutational effects on phenotypic traits are unbiased, that is, mutation does not tend to push phenotypes in any particular direction. In this paper, we consider a model of stabilizing selection acting on an arbitrary number of polygenic traits coded by bialellic loci, and show that mutational bias may greatly reduce the mean fitness of asexual populations compared with sexual ones in regimes where mutations have weak to moderate fitness effects...
July 11, 2018: Evolution; International Journal of Organic Evolution
Babu Ram Paudel, Martin Burd, Mani Shrestha, Adrian G Dyer, Qing-Jun Li
Multiple barriers may contribute to reproductive isolation between closely related species. Understanding the relative strength of these barriers can illuminate the ecological factors that currently maintain species integrity and how these factors originally promoted speciation. Two Himalayan alpine gingers, Roscoea purpurea and R. tumjensis, occur sympatrically in central Nepal and have such similar morphology that it is not clear whether or how they maintain a distinct identity. Our quantitative measurements of the components of reproductive isolation show that they are, in fact, completely isolated by a combination of phenological displacement of flowering, earlier for R...
July 10, 2018: Evolution; International Journal of Organic Evolution
Benjamin R Groth, Yuheng Huang, Matthew J Monette, John E Pool
Natural selection may enhance or weaken the robustness of phenotypes against genetic or environmental perturbations. However, important aspects of the relationship between adaptive evolution and canalization remain unclear. Recent work showed that the evolution of larger wing size in a high altitude natural population of Drosophila melanogaster was accompanied by decanalized wing development - specifically a loss of robustness to genetic perturbation. But this study did not address environmental robustness, and it compared populations that may have numerous biological differences...
July 9, 2018: Evolution; International Journal of Organic Evolution
Adrian Indermaur, Anya Theis, Bernd Egger, Walter Salzburger
Random asymmetry, that is the co-existence of left- and right-sided (or -handed) individuals within a population, is a particular case of natural variation; what triggers and maintains such dimorphisms remains unknown in most cases. Here, we report a field-based cage experiment in the scale-eating Tanganyikan cichlid Perissodus microlepis (Boulenger, 1898), which occurs in two morphs in nature: left-skewed and right-skewed individuals with respect to mouth orientation. Using underwater cages stocked with scale-eaters and natural prey fish, we first confirm that, under semi-natural conditions, left-skewed scale-eaters preferentially attack the right flank of their prey, whereas right-skewed individuals feed predominantly from the left side...
July 9, 2018: Evolution; International Journal of Organic Evolution
Hannes Becher
We now have a flood of genomic sequencing data available to study reproductive isolation and selection in action, but how are these data best analyzed? Usually, genetic differentiation is compared between two groups, scanning along genomes. This approach has several drawbacks, and has been criticized repeatedly. An alternative, truly genetic approach, based on blocks of common ancestry in a hybrid zone setting, is presented by Hvala et al. (2018) in this issue. This article is protected by copyright. All rights reserved...
July 9, 2018: Evolution; International Journal of Organic Evolution
Belén Jiménez-Mena, Romina Henriques
Gallet et al. (2018) studied the effect of two selection regimes on the maintenance of polymorphism in experimental populations. They took two strains of Escherichia coli, each resistant to a different antibiotic, evolved them in culture conditions representing "soft" or "hard" selective regimes, and measured polymorphism levels for three to five transfers. Their results supported theoretical predictions that only "soft" selection maintains polymorphism, highlighting the importance of experimental studies to understand maintenance of variation in nature...
July 9, 2018: Evolution; International Journal of Organic Evolution
Anna Maria Skwierzyńska, Jacek Radwan, Agata Plesnar-Bielak
Selection for secondary sexual trait (SST) elaboration may increase intralocus sexual conflict over the optimal values of traits expressed from shared genomes. This conflict can reduce female fitness, and the resulting gender load can be exacerbated by environmental stress, with consequences for a population's ability to adapt to novel environments. However, how the evolution of SSTs interacts with environment in determining female fitness is not well understood. Here, we investigated this question using replicate lines of bulb mites selected for increased or decreased prevalence of a male SST-thickened legs used as weapons...
July 9, 2018: Evolution; International Journal of Organic Evolution
Holly English
The way an animal moves reveals key aspects of its ecology. Carnivore forelimbs are adapted to their predation style, and the structure of the elbow joint can indicate hunting strategy. In this issue, Figueirido (2018) investigates phenotypic disparity, or morphological variation, in domestic dog breeds, the canid family, and the carnivore order using the elbow joint as an indicator of movement and predatory behavior. This article is protected by copyright. All rights reserved.
July 4, 2018: Evolution; International Journal of Organic Evolution
Barbora Augstenová, Martina Johnson Pokorná, Marie Altmanová, Daniel Frynta, Michail Rovatsos, Lukáš Kratochvíl
Snakes are historically important in the formulation of several central concepts on the evolution of sex chromosomes. For over 50 years, it was believed that all snakes shared the same ZZ/ZW sex chromosomes, which are homomorphic and poorly differentiated in "basal" snakes such as pythons and boas, while heteromorphic and well differentiated in "advanced" (caenophidian) snakes. Recent molecular studies revealed that differentiated sex chromosomes are indeed shared among all families of caenophidian snakes, but that boas and pythons evolved likely independently male heterogamety (XX/XY sex chromosomes)...
July 4, 2018: Evolution; International Journal of Organic Evolution
Denon Start, Colin Bonner, Arthur E Weis, Benjamin Gilbert
Urbanization is an important component of global change. Urbanization affects species interactions, but the evolutionary implications are rarely studied. We investigate the evolutionary consequences of a common pattern: the loss of high trophic-level species in urban areas. Using a gall-forming fly, Eurosta solidaginis, and its natural enemies that select for opposite gall sizes, we test for patterns of enemy loss, selection, and local adaptation along five urbanization gradients. Eurosta declined in urban areas, as did predation by birds, which preferentially consume gallmakers that induce large galls...
July 4, 2018: Evolution; International Journal of Organic Evolution
L G Ashman, J G Bragg, P Doughty, M N Hutchinson, S Bank, N J Matzke, P Oliver, C Moritz
Ecological opportunity is a powerful driver of evolutionary diversification, and predicts rapid lineage and phenotypic diversification following colonisation of competitor-free habitats. Alternatively, topographic or environmental heterogeneity could be key to generating and sustaining diversity. We explore these hypotheses in a widespread lineage of Australian lizards: the Gehyra variegata group. This clade occurs across two biomes: the Australian monsoonal tropics (AMT), where it overlaps a separate, larger bodied clade of Gehyra and is largely restricted to rocks; and in the larger Australian arid zone (AAZ) where it has no congeners and occupies trees and rocks...
July 4, 2018: Evolution; International Journal of Organic Evolution
Moises Exposito-Alonso, Adrian C Brennan, Carlos Alonso-Blanco, F Xavier Picó
The evolutionary response of organisms to global climate change is expected to be strongly conditioned by preexisting standing genetic variation. In addition, natural selection imposed by global climate change on fitness-related traits can be heterogeneous over time. We estimated selection of life-history traits of an entire genetic lineage of the plant Arabidopsis thaliana occurring in north-western Iberian Peninsula that were transplanted over multiple years into two environmentally contrasting field sites in southern Spain, as southern environments are expected to move progressively northwards with climate change in the Iberian Peninsula...
June 27, 2018: Evolution; International Journal of Organic Evolution
Robert D Denton, Ariadna E Morales, H Lisle Gibbs
Quantifying introgression between sexual species and polyploid lineages traditionally thought to be asexual is an important step in understanding what drives the longevity of putatively asexual groups. Here, we capitalize on three recent innovations-ultraconserved element (UCE) sequencing, bioinformatic techniques for identifying genome-specific variation in polyploids, and model-based methods for evaluating historical gene flow-to measure the extent and tempo of introgression over the evolutionary history of an allopolyploid lineage of all-female salamanders and two ancestral sexual species...
June 21, 2018: Evolution; International Journal of Organic Evolution
Christopher M Martinez, Matthew D McGee, Samuel R Borstein, Peter C Wainwright
The fish feeding apparatus is among the most diverse functional systems in vertebrates. While morphological and mechanical variation of feeding systems are well studied, we know far less about the diversity of the motions that they produce. We explored patterns of feeding movements in African cichlids from Lakes Malawi and Tanganyika, asking whether the degree of kinesis is associated with dietary habits of species. We used geometric morphometrics to measure feeding kinesis as trajectories of shape change, based on 326 high-speed videos in 56 species...
June 19, 2018: Evolution; International Journal of Organic Evolution
Alexandrea M Kranz, Leonard G Forgan, Gemma L Cole, John A Endler
Light environments critically impact species that rely on vision to survive and reproduce. Animal visual systems must accommodate changes in light that occur from minutes to years, yet the mechanistic basis of their response to spectral (color) changes is largely unknown. Here we used a laboratory experiment where replicate guppy populations were kept under three different light environments for up to 8-12 generations to explore possible differences in the expression levels of nine guppy opsin genes. Previous evidence for opsin expression-light environment 'tuning' has been either correlative or focused exclusively on the relationship between the light environment and opsin expression over one or two generations...
June 19, 2018: Evolution; International Journal of Organic Evolution
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