Journal of Evolutionary Biology

El Mouden, C.; André, J.‐B.; Morin, O.; Nettle, D.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12296pmid: 24329934

Transmitted culture can be viewed as an inheritance system somewhat independent of genes that is subject to processes of descent with modification in its own right. Although many authors have conceptualized cultural change as a Darwinian process, there is no generally agreed formal framework for defining key concepts such as natural selection, fitness, relatedness and altruism for the cultural case. Here, we present and explore such a framework using the Price equation. Assuming an isolated, independently measurable culturally transmitted trait, we show that cultural natural selection maximizes cultural fitness, a distinct quantity from genetic fitness, and also that cultural relatedness and cultural altruism are not reducible to or necessarily related to their genetic counterparts. We show that antagonistic coevolution will occur between genes and culture whenever cultural fitness is not perfectly aligned with genetic fitness, as genetic selection will shape psychological mechanisms to avoid susceptibility to cultural traits that bear a genetic fitness cost. We discuss the difficulties with conceptualizing cultural change using the framework of evolutionary theory, the degree to which cultural evolution is autonomous from genetic evolution, and the extent to which cultural change should be seen as a Darwinian process. We argue that the nonselection components of evolutionary change are much more important for culture than for genes, and that this and other important differences from the genetic case mean that different approaches and emphases are needed for cultural than genetic processes.

Price, S. L.; Powell, S.; Kronauer, D. J. C.; Tran, L. A. P.; Pierce, N. E.; Wayne, R. K.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12300pmid: 24417316

Ecological opportunity, defined as access to new resources free from competitors, is thought to be a catalyst for the process of adaptive radiation. Much of what we know about ecological opportunity, and the larger process of adaptive radiation, is derived from vertebrate diversification on islands. Here, we examine lineage diversification in the turtle ants (Cephalotes), a species‐rich group of ants that has diversified throughout the Neotropics. We show that crown group turtle ants originated during the Eocene (around 46 mya), coincident with global warming and the origin of many other clades. We also show a marked lineage‐wide slowdown in diversification rates in the Miocene. Contrasting this overall pattern, a species group associated with the young and seasonally harsh Chacoan biogeographic region underwent a recent burst of diversification. Subsequent analyses also indicated that there is significant phylogenetic clustering within the Chacoan region and that speciation rates are highest there. Together, these findings suggest that recent ecological opportunity, from successful colonization of novel habitat, may have facilitated renewed turtle ant diversification. Our findings highlight a central role of ecological opportunity within a successful continental radiation.

Patterson, S. H.; Hahn, T. P.; Cornelius, J. M.; Breuner, C. W.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12286pmid: 24341364

Glucocorticoid hormones are considered potent modulators of trade‐offs between reproduction and survival. As such, selection should affect glucocorticoid physiology, although relatively little is known about how selection may act on glucocorticoid profiles. In general, the evolution of physiology is less studied and less well understood than morphological or life history traits. Here, we used a long‐term data set from a population of mountain white‐crowned sparrows to estimate natural selection on glucocorticoid profiles. Our study suggests that survival selection favours higher hormone concentrations for multiple components of glucocorticoid physiology (both baseline and stress‐induced glucocorticoid levels). Fecundity selection varies depending on the component of hypothalamic–pituitary–adrenal physiology; greater reproductive output was associated with higher baseline glucocorticoid levels, but lower stress‐induced glucocorticoid levels. Additionally, the selection gradient was greater for glucocorticoids than for a morphological trait (wing length). These results support the hypothesis that stress‐induced glucocorticoids increase survival over reproduction within a wild population (the CORT‐trade‐off hypothesis). Taken together, these results add to our knowledge of how selection operates on physiological traits and also provide an evolutionary and ecological perspective on several key open issues in the field of glucocorticoid physiology.

Selz, O. M.; Thommen, R.; Maan, M. E.; Seehausen, O.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12287pmid: 24372872

Hybrid speciation is constrained by the homogenizing effects of gene flow from the parental species. In the absence of post‐mating isolation due to structural changes in the genome, or temporal or spatial premating isolation, another form of reproductive isolation would be needed for homoploid hybrid speciation to occur. Here, we investigate the potential of behavioural mate choice to generate assortative mating among hybrids and parental species. We made three‐first‐generation hybrid crosses between different species of African cichlid fish. In three‐way mate‐choice experiments, we allowed hybrid and nonhybrid females to mate with either hybrid or nonhybrid males. We found that hybrids generally mated nonrandomly and that hybridization can lead to the expression of new combinations of traits and preferences that behaviourally isolate hybrids from both parental species. Specifically, we find that the phenotypic distinctiveness of hybrids predicts the symmetry and extent of their reproductive isolation. Our data suggest that behavioural mate choice among hybrids may facilitate the establishment of isolated hybrid populations, even in proximity to one or both parental species.

DeFaveri, J.; Merilä, J.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12289pmid: 24330503

Different lines of evidence suggest that the occurrence and extent of local adaptation in high gene flow marine environments – even in mobile and long‐lived vertebrates with complex life cycles – may be more widespread than earlier thought. We conducted a common garden experiment to test for local adaptation to salinity in Baltic Sea sticklebacks (Gasterosteus aculeatus). Fish from three different native salinity regimes (high, mid and low) were subjected to three salinity treatments (high, mid and low) in a full‐factorial experimental design. Irrespective of their origin, fish subjected to low (and mid) salinity treatments exhibited higher juvenile survival, grew to largest sizes and were in better condition than fish subjected to the high salinity treatment. However, a significant interaction between native and treatment salinities – resulting mainly from the poor performance of fish native to low salinity in the high salinity treatment – provided clear cut evidence for adaptation to local variation in salinity. Additional support for this inference was provided by the fact that the results concur with an earlier demonstration of significant differentiation in a number of genes with osmoregulatory functions across the same populations and that the population‐specific responses to salinity treatments exceeded that to be expected by random genetic drift.

Gandon, S.; Vale, P. F.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12291pmid: 24329755

Opportunities for genetic exchange are abundant between bacteria and foreign genetic elements (FGEs) such as conjugative plasmids, transposable elements and bacteriophages. The genetic novelty that may arise from these forms of genetic exchange is potentially beneficial to bacterial hosts, but there are also potential costs, which may be considerable in the case of phage infection. Some bacterial resistance mechanisms target both beneficial and deleterious forms of genetic exchange. Using a general epidemiological model, we explored under which conditions such resistance mechanisms may evolve. We considered a population of hosts that may be infected by FGEs that either confer a benefit or are deleterious to host fitness, and we analysed the epidemiological and evolutionary outcomes of resistance evolving under different cost/benefit scenarios. We show that the degree of co‐infection between these two types of infection is particularly important in determining the evolutionarily stable level of host resistance. We explore these results using the example of CRISPR‐Cas, a form of bacterial immunity that targets a variety of FGEs, and we show the potential role of bacteriophage infection in selecting for resistance mechanisms that in turn limit the acquisition of plasmid‐borne antibiotic resistance. Finally, beyond microbes, we discuss how endosymbiotic associations may have shaped the evolution of host immune responses to pathogens.

Encinas‐Viso, F.; Revilla, T. A.; van Velzen, E.; Etienne, R. S.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12301pmid: 24456225

Animal seed dispersal provides an important ecosystem service by strongly benefiting plant communities. There are several theoretical studies on the ecology of plant–animal seed–disperser interactions, but few studies have explored the evolution of this mutualism. Moreover, these studies ignore plant life history and frugivore foraging behaviour. Thus, it remains an open question what the conditions for the diversification of fruit traits are, in spite of the multitude of empirical studies on fruit trait diversity. Here, we study the evolution of fruit traits using a spatially explicit individual‐based model, which considers the costs associated with adaptations inducing dispersal by frugivory, as well as frugivore foraging behaviour and abundance. Our model predicts that these costs are the main determinants of the evolution of fruit traits and that when the costs are not very high, the evolution of larger fruit traits (e.g. fleshy/colourful fruits) is controlled by the choosiness and response thresholds of the frugivores as well as their numerical abundance.

Campbell, D. R.; Forster, M.; Bischoff, M.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12295pmid: 24341383

Pollinators are known to exert natural selection on floral traits, but the extent to which combinations of floral traits are subject to correlational selection (nonadditive effects of two traits on fitness) is not well understood. Over two years, we used phenotypic manipulations of plant traits to test for effects of flower colour, flower shape and their interaction on rates of pollinator visitation to Polemonium foliosissimum. We also tested for correlational selection based on weighting visitation by the amount of conspecific pollen delivered per visit by each category of insect visitor. Although bumblebees were the presumed pollinators, solitary bees and flies contributed substantially (42%) to pollination. In manipulations of one trait at a time, insects visited flowers presenting the natural colour and shape over flowers manipulated to present artificial mutants with either paler colour or a more open or more tubular flower. When both colour and shape were manipulated in combination, selection on both traits arose, with bumblebees responding mainly to colour and flies responding mainly to shape. Despite selection on both floral traits, in a year with many bumblebees, we saw no evidence for correlational selection of these traits. In a year when flies predominated, fly visitation showed a pattern of correlational selection, but not favouring the natural phenotype, and correlational selection was still not detected for expected pollen receipt. These results show that flower colour and shape are subject to pollinator‐mediated selection and that correlational selection can be generated based on pollinator visitation alone, but provide no evidence for correlational selection specifically for the current phenotype.

Kleynhans, E.; Clusella‐Trullas, S.; Terblanche, J. S.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12297pmid: 24386875

Physiological responses to transient conditions may result in costly responses with little fitness benefits, and therefore, a trade‐off must exist between the speed of response and the duration of exposure to new conditions. Here, using the puparia of an important insect disease vector, Glossina pallidipes, we examine this potential trade‐off using a novel combination of an experimental approach and a population dynamics model. Specifically, we explore and dissect the interactions between plastic physiological responses, treatment‐duration and ‐intensity using an experimental approach. We then integrate these experimental results from organismal water‐balance data and their plastic responses into a population dynamics model to examine the potential relative fitness effects of simulated transient weather conditions on population growth rates. The results show evidence for the predicted trade‐off for plasticity of water loss rate (WLR) and the duration of new environmental conditions. When altered environmental conditions lasted for longer durations, physiological responses could match the new environmental conditions, and this resulted in a lower WLR and lower rates of population decline. At shorter time‐scales however, a mismatch between acclimation duration and physiological responses was reflected by reduced overall population growth rates. This may indicate a potential fitness cost due to insufficient time for physiological adjustments to take place. The outcomes of this work therefore suggest plastic water balance responses have both costs and benefits, and these depend on the time‐scale and magnitude of variation in environmental conditions. These results are significant for understanding the evolution of plastic physiological responses and changes in population abundance in the context of environmental variability.

Sathe, S.; Khetan, N.; Nanjundiah, V.

2014 Journal of Evolutionary Biology

doi: 10.1111/jeb.12298pmid: 24341405

The stable co‐existence of individuals of different genotypes and reproductive division of labour within heterogeneous groups are issues of fundamental interest from the viewpoint of evolution. Cellular slime moulds are convenient organisms in which to address both issues. Strains of a species co‐occur, as do different species; social groups are often genetically heterogeneous. Intra‐ and interspecies 1 : 1 mixes of wild isolates of Dictyostelium giganteum and D. purpureum form chimaeric aggregates, following which they segregate to varying extents. Intraspecies aggregates develop in concert and give rise to chimaeric fruiting bodies that usually contain more spores (reproductives) of one component than the other. Reproductive skew and variance in the proportion of reproductives are positively correlated. Interspecies aggregates exhibit almost complete sorting; most spores in a fruiting body come from a single species. Between strains, somatic compatibility correlates weakly with sexual compatibility. It is highest within clones, lower between strains of a species and lowest between strains of different species. Trade‐offs among fitness‐related traits (between compatible strains), sorting out (between incompatible strains) and avoidance (between species) appear to lie behind coexistence.