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1.  Continental variation in relative hippocampal volume in birds: the phylogenetic extent of the effect and the potential role of winter temperatures 
Biology letters  2005;1(3):330-333.
Hippocampal (HC) volume has been hypothesized to increase with an increase in food-hoarding specialization in corvids and parids. Recent studies revealed that (i) the HC/hoarding relationship is significant when a difference in HC volume between Eurasian and North American species is controlled for and (ii) the evolutionary association has been acting on a broader phylogenetic context involving avian families outside the Corvidae and Paridae. However, the phylogenetic extent of the continent effect has not been previously addressed. Using data representing 48 avian species, we performed a phylogenetic analysis to test if continental effects are important in a wider evolutionary spectrum. Our results support the observation that Eurasian species have generally larger HC than North American species if variation in food hoarding, which also varied between continents, was held constant. Surprisingly, the relationship between continental distribution and relative HC volume was significant when we included only non-hoarding families in our analysis, indicating that the extent of the continent effect is much broader than originally described. We investigated the potential role of minimal winter temperatures at the northernmost distribution borders in mediating continent effects. The effect of winter temperatures on HC volume was weak and it did not vary consistently along continents. We suggest that the general continental differences in relative HC size are independent of food hoarding and that its determinants should be sought among other ecological factors and life-history traits.
doi:10.1098/rsbl.2005.0328
PMCID: PMC1523380  PMID: 16878181
Corvidae; food caching; hippocampus; Paridae; phylogeny
2.  Pregnancy weight gain: marmoset and tamarin dads show it too 
Biology letters  2006;2(2):181-183.
Paternal behaviour is critical for the survival of offspring in many monogamous species. Common marmoset (Callithrix jacchus) and cotton-top tamarin (Saguinus oedipus) fathers spend as much or more time caring for infants than mothers. Expectant males of both species showed significant increases in weight across the pregnancy whereas control males did not (five consecutive months for marmoset males and six months for cotton-top tamarin males). Expectant fathers might be preparing for the energetic cost of fatherhood by gaining weight during their mate’s pregnancy.
doi:10.1098/rsbl.2005.0426
PMCID: PMC1483903  PMID: 16810338
weight gain; paternal care; couvades; primates
3.  Pregnancy weight gain: marmoset and tamarin dads show it too 
Biology Letters  2006;2(2):181-183.
Paternal behaviour is critical for the survival of offspring in many monogamous species. Common marmoset (Callithrix jacchus) and cotton-top tamarin (Saguinus oedipus) fathers spend as much or more time caring for infants than mothers. Expectant males of both species showed significant increases in weight across the pregnancy whereas control males did not (five consecutive months for marmoset males and six months for cotton-top tamarin males). Expectant fathers might be preparing for the energetic cost of fatherhood by gaining weight during their mate's pregnancy.
doi:10.1098/rsbl.2005.0426
PMCID: PMC1483903  PMID: 16810338
weight gain; paternal care; couvade; primates
4.  Continental variation in relative hippocampal volume in birds: the phylogenetic extent of the effect and the potential role of winter temperatures 
Biology Letters  2005;1(3):330-333.
Hippocampal (HC) volume has been hypothesized to increase with an increase in food-hoarding specialization in corvids and parids. Recent studies revealed that (i) the HC/hoarding relationship is significant when a difference in HC volume between Eurasian and North American species is controlled for and (ii) the evolutionary association has been acting on a broader phylogenetic context involving avian families outside the Corvidae and Paridae. However, the phylogenetic extent of the continent effect has not been previously addressed. Using data representing 48 avian species, we performed a phylogenetic analysis to test if continental effects are important in a wider evolutionary spectrum. Our results support the observation that Eurasian species have generally larger HC than North American species if variation in food hoarding, which also varied between continents, was held constant. Surprisingly, the relationship between continental distribution and relative HC volume was significant when we included only non-hoarding families in our analysis, indicating that the extent of the continent effect is much broader than originally described. We investigated the potential role of minimal winter temperatures at the northernmost distribution borders in mediating continent effects. The effect of winter temperatures on HC volume was weak and it did not vary consistently along continents. We suggest that the general continental differences in relative HC size are independent of food hoarding and that its determinants should be sought among other ecological factors and life-history traits.
doi:10.1098/rsbl.2005.0328
PMCID: PMC1523380  PMID: 16878181
Corvidae; food caching; hippocampus; Paridae; phylogeny
5.  Chimpanzees predict that a competitor's preference will match their own 
Biology Letters  2013;9(1):20120829.
The ability to predict how another individual will behave is useful in social competition. Chimpanzees can predict the behaviour of another based on what they observe her to see, hear, know and infer. Here we show that chimpanzees act on the assumption that others have preferences that match their own. All subjects began with a preference for a box with a picture of food over one with a picture of nothing, even though the pictures had no causal relation to the contents. In a back-and-forth food competition, chimpanzees then avoided the box with the picture of food when their competitor had chosen one of the boxes before them—presumably on the assumption that the competitor shared their own preference for it and had already chosen it. Chimpanzees predicted that their competitor's preference would match their own and adjusted their behavioural strategies accordingly.
doi:10.1098/rsbl.2012.0829
PMCID: PMC3565493  PMID: 23193044
theory of mind; competition; preference; social cognition; chimpanzee
6.  Model and test in a fungus of the probability that beneficial mutations survive drift 
Biology Letters  2013;9(1):20120310.
Determining the probability of fixation of beneficial mutations is critically important for building predictive models of adaptive evolution. Despite considerable theoretical work, models of fixation probability have stood untested for nearly a century. However, recent advances in experimental and theoretical techniques permit the development of models with testable predictions. We developed a new model for the probability of surviving genetic drift, a major component of fixation probability, for novel beneficial mutations in the fungus Aspergillus nidulans, based on the life-history characteristics of its colony growth on a solid surface. We tested the model by measuring the probability of surviving drift in 11 adapted strains introduced into wild-type populations of different densities. We found that the probability of surviving drift increased with mutant invasion fitness, and decreased with wild-type density, as expected. The model accurately predicted the survival probability for the majority of mutants, yielding one of the first direct tests of the extinction probability of beneficial mutations.
doi:10.1098/rsbl.2012.0310
PMCID: PMC3565475  PMID: 22740642
probability of fixation; adaptive evolution; selection; beneficial mutations
7.  Genetic background affects epistatic interactions between two beneficial mutations 
Biology Letters  2013;9(1):20120328.
The phenotypic effect of mutations can depend on their genetic background, a phenomenon known as epistasis. Many experimental studies have found that epistasis is pervasive, and some indicate that it may follow a general pattern dependent on the fitness effect of the interacting mutations. These studies have, however, typically examined the effect of interactions between a small number of focal mutations in a single genetic background. Here, we extend this approach by considering how the interaction between two beneficial mutations that were isolated from a population of laboratory evolved Escherichia coli changes when they are added to divergent natural isolate strains of E. coli. We find that interactions between the focal mutations and the different genetic backgrounds are common. Moreover, the pair-wise interaction between the focal mutations also depended on their genetic background, being more negative in backgrounds with higher absolute fitness. Together, our results indicate the presence of interactions between focal mutations, but also caution that these interactions depend quantitatively on the wider genetic background.
doi:10.1098/rsbl.2012.0328
PMCID: PMC3565476  PMID: 22896270
beneficial mutations; epistasis; genetic background; experimental evolution
8.  Temperature, stress and spontaneous mutation in Caenorhabditis briggsae and Caenorhabditis elegans 
Biology Letters  2013;9(1):20120334.
Mutation rate often increases with environmental temperature, but establishing causality is complicated. Asymmetry between physiological stress and deviation from the optimal temperature means that temperature and stress are often confounded. We allowed mutations to accumulate in two species of Caenorhabditis for approximately 100 generations at 18°C and for approximately 165 generations at 26°C; 26°C is stressful for Caenorhabditis elegans but not for Caenorhabditis briggsae. We report mutation rates at a set of microsatellite loci and estimates of the per-generation decay of fitness (ΔMw), the genomic mutation rate for fitness (U) and the average effect of a new mutation (E[a]), assayed at both temperatures. In C. elegans, the microsatellite mutation rate is significantly greater at 26°C than at 18°C whereas in C. briggsae there is only a slight, non-significant increase in mutation rate at 26°C, consistent with stress-dependent mutation in C. elegans. The fitness data from both species qualitatively reinforce the microsatellite results. The fitness results of C. elegans are potentially complicated by selection but also suggest temperature-dependent mutation; the difference between the two species suggests that physiological stress plays a significant role in the mutational process.
doi:10.1098/rsbl.2012.0334
PMCID: PMC3565477  PMID: 22875817
mutation accumulation; fitness; microsatellite; metabolic rate
9.  Epistasis between mutations is host-dependent for an RNA virus 
Biology Letters  2013;9(1):20120396.
How, and to what extent, does the environment influence the way mutations interact? Do environmental changes affect both the sign and the magnitude of epistasis? Are there any correlations between environments in the variability, sign or magnitude of epistasis? Very few studies have tackled these questions. Here, we addressed them in the context of viral emergence. Most emerging viruses are RNA viruses with small genomes, overlapping reading frames and multifunctional proteins for which epistasis is abundant. Understanding the effect of host species in the sign and magnitude of epistasis will provide insights into the evolutionary ecology of infectious diseases and the predictability of viral emergence.
doi:10.1098/rsbl.2012.0396
PMCID: PMC3565478  PMID: 22809724
emerging viruses; deleterious mutations; epistasis; genotype-by-environment; virus evolution
10.  The role of ‘soaking’ in spiteful toxin production in Pseudomonas aeruginosa 
Biology Letters  2013;9(1):20120569.
The ubiquitous production of antibacterial toxins, such as bacteriocins, is an ecologically significant class of interbacterial interactions that have primarily evolved through their indirect fitness benefits to the producer. Bacteria release bacteriocins into the environment at a cost to individual cell, but individual bacteriocin-producing cells are unlikely to gain any direct benefit from their own toxin; indeed, cell lysis is required in many species. There is a growing body of research describing the ecological conditions that can favour the evolution of bacteriocin production. However, an important aspect of many bacteriocins has yet to be investigated: the ability of bacteriocin-producing cells to neutralize toxin (‘soaking’) produced by other clonemates. By competing Pseudomonas aeruginosa bacteriocin-producing wild-type and ‘non-soaking’ strains against a bacteriocin-susceptible strain, we find that soaking markedly reduces the fitness of a bacteriocin-producing strain at both high and low frequencies.
doi:10.1098/rsbl.2012.0569
PMCID: PMC3565479  PMID: 22933037
bacteriocin; microbial ecology; pyocin
12.  Mutational effects depend on ploidy level: all else is not equal 
Biology Letters  2013;9(1):20120614.
Ploidy is predicted to influence adaptation directly, yet whether single mutations behave the same in different ploidy backgrounds has not been well studied. It has often been assumed theoretically that aside from dominance, selective parameters do not differ between cells of varying ploidy. Using the budding yeast Saccharomyces cerevisiae, I compared the effect size of 20 adaptive mutations in haploids and homozygous diploids and found, surprisingly, that the same mutations often had a much larger effect in haploids than homozygous diploids. This empirical result demonstrates that it cannot be assumed that mutations will have the same effect in haploids and homozygous diploids.
doi:10.1098/rsbl.2012.0614
PMCID: PMC3565481  PMID: 23054913
effect size; fitness; growth rate; dose–response; IC50
13.  Competition and the origins of novelty: experimental evolution of niche-width expansion in a virus 
Biology Letters  2013;9(1):20120616.
Competition for resources has long been viewed as a key agent of divergent selection. Theory holds that populations facing severe intraspecific competition will tend to use a wider range of resources, possibly even using entirely novel resources that are less in demand. Yet, there have been few experimental tests of these ideas. Using the bacterial virus (bacteriophage) ϕ6 as a model system, we examined whether competition for host resources promotes the evolution of novel resource use. In the laboratory, ϕ6 exhibits a narrow host range but readily produces mutants capable of infecting novel bacterial hosts. Here, we show that when ϕ6 populations were subjected to intense intraspecific competition for their standard laboratory host, they rapidly evolved new generalist morphs that infect novel hosts. Our results therefore suggest that competition for host resources may drive the evolution of host range expansion in viruses. More generally, our findings demonstrate that intraspecific resource competition can indeed promote the evolution of novel resource-use phenotypes.
doi:10.1098/rsbl.2012.0616
PMCID: PMC3565482  PMID: 23075527
bacteriophage; intraspecific competition; resource polymorphism; host range expansion
14.  Experimental evolution of multicellularity using microbial pseudo-organisms 
Biology Letters  2013;9(1):20120636.
In a major evolutionary transition to a new level of organization, internal conflicts must be controlled before the transition can truly be successful. One such transition is that from single cells to multicellularity. Conflicts among cells in multicellular organisms can be greatly reduced if they consist of genetically identical clones. However, mutations to cheaters that experience one round of within-individual selection could still be a problem, particularly for certain life cycles. We propose an experimental evolution method to investigate this issue, using micro-organisms to construct multicellular pseudo-organisms, which can be evolved under different artificial life cycles. These experiments can be used to test the importance of various life cycle features in maintaining cooperation. They include structured reproduction, in which small propagule size reduces within-individual genetic variation. They also include structured growth, which increases local relatedness within individual bodies. Our method provides a novel way to test how different life cycles favour cooperation, even for life cycles that do not exist.
doi:10.1098/rsbl.2012.0636
PMCID: PMC3565483  PMID: 23015456
multicellularity; experimental evolution; relatedness; cooperation; cell-lineage conflict; structured growth
15.  Ecological niche structure and rangewide abundance patterns of species 
Biology Letters  2013;9(1):20120637.
Spatial abundance patterns across species' ranges have attracted intense attention in macroecology and biogeography. One key hypothesis has been that abundance declines with geographical distance from the range centre, but tests of this idea have shown that the effect may occur indeed only in a minority of cases. We explore an alternative hypothesis: that species' abundances decline with distance from the centroid of the species' habitable conditions in environmental space (the ecological niche). We demonstrate consistent negative abundance–ecological distance relationships across all 11 species analysed (turtles to wolves), and that relationships in environmental space are consistently stronger than relationships in geographical space.
doi:10.1098/rsbl.2012.0637
PMCID: PMC3565484  PMID: 23134784
abundance; geographical range; environmental space; abundant-centre hypothesis
16.  Leaf morphology shift is not linked to climate change 
Biology Letters  2013;9(1):20120659.
doi:10.1098/rsbl.2012.0659
PMCID: PMC3565485  PMID: 23118433
17.  Experimentally increased noise levels change spatial and singing behaviour 
Biology Letters  2013;9(1):20120771.
The reasons why animal populations decline in response to anthropogenic noise are still poorly understood. To understand how populations are affected by noise, we must understand how individuals are affected by noise. By modifying the acoustic environment experimentally, we studied the potential relationship between noise levels and both spatial and singing behaviour in the European robin (Erithacus rubecula). We found that with increasing noise levels, males were more likely to move away from the noise source and changed their singing behaviour. Our results provide the first experimental evidence in a free ranging species, that not merely the presence of noise causes changes in behaviour and distribution, but that the level of noise pollution plays a crucial role as well. Our results have important implications for estimating the impact of infrastructure which differs in the level of noise produced. Thus, governmental planning bodies should not only consider the physical effect on the landscape when assessing the impact of new infrastructure, but also the noise levels emitted, which may reduce the loss of suitable habitats available for animals.
doi:10.1098/rsbl.2012.0771
PMCID: PMC3565486  PMID: 23173189
animal communication; environmental change; noise pollution; urbanization
18.  Saccharide-mediated antagonistic effects of bark beetle fungal associates on larvae 
Biology Letters  2013;9(1):20120787.
Bark beetles are among the most destructive of pine forest pests and they form close symbiotic relationships with ophiostomatoid fungi. Although some fungi are considered to be mutualistic symbionts of bark beetles with respect to the supply of nutrients, detrimental effects of fungal symbionts on larval growth have also been frequently reported. The mechanisms of such antagonistic effects are hypothesized to be a decrease in nutritional resources caused by competition for saccharides by the fungi. Here, we provide experimental evidence that three beetle-associated fungi modify the nutritional content of an artificial phloem diet, leading to a detrimental effect on the growth of Dendroctonus valens larvae. When larvae were fed a diet of pine phloem in agar medium colonized with any of these fungi, feeding activity was not affected but weight significantly decreased. Additional analysis showed that fungi depleted the fructose and glucose concentrations in the phloem media. Furthermore, these detrimental effects were neutralized by supplementing the media with fructose or glucose, suggesting that fungi may affect larval growth by modifying diet saccharide contents. These data indicate that fungus-induced nutritional changes in bark beetle diet can affect larval growth, and that the mechanism involves fungus-induced saccharide depletion from the larval diet.
doi:10.1098/rsbl.2012.0787
PMCID: PMC3565487  PMID: 23193043
bark beetle; symbiosis; ophiostomatoid; antagonism; saccharide; nutrition
19.  Climate change and elevational diversity capacity: do weedy species take up the slack? 
Biology Letters  2013;9(1):20120806.
Climate change leads to species range shifts and consequently to changes in diversity. For many systems, increases in diversity capacity have been forecast, with spare capacity to be taken up by a pool of weedy species moved around by humans. Few tests of this hypothesis have been undertaken, and in many temperate systems, climate change impacts may be confounded by simultaneous increases in human-related disturbance, which also promote weedy species. Areas to which weedy species are being introduced, but with little human disturbance, are therefore ideal for testing the idea. We make predictions about how such diversity capacity increases play out across elevational gradients in non-water-limited systems. Then, using modern and historical data on the elevational range of indigenous and naturalized alien vascular plant species from the relatively undisturbed sub-Antarctic Marion Island, we show that alien species have contributed significantly to filling available diversity capacity and that increases in energy availability rather than disturbance are the probable underlying cause.
doi:10.1098/rsbl.2012.0806
PMCID: PMC3565488  PMID: 23097460
climate change; elevational gradients; species-energy theory; species richness
20.  Passive rafting is a powerful driver of transoceanic gene flow 
Biology Letters  2013;9(1):20120821.
Dispersal by passive oceanic rafting is considered important for the assembly of biotic communities on islands. However, not much is known about levels of population genetic connectivity maintained by rafting over transoceanic distances. We assess the evolutionary impact of kelp-rafting by estimating population genetic differentiation in three kelp-associated invertebrate species across a system of islands isolated by oceanic gaps for over 5 million years, using mtDNA and AFLP markers. The species occur throughout New Zealand's subantarctic islands, but lack pelagic stages and any opportunity for anthropogenic transportation, and hence must rely on passive rafting for long-distance dispersal. They all have been directly observed to survive transoceanic kelp-rafting journeys in this region. Our analyses indicate that regular gene flow occurs among populations of all three species between all of the islands, especially those on either side of the subtropical front oceanographic boundary. Notwithstanding its perceived sporadic nature, long-distance kelp-rafting appears to enable significant gene flow among island populations separated by hundreds of kilometres of open ocean.
doi:10.1098/rsbl.2012.0821
PMCID: PMC3565489  PMID: 23134782
AFLP; gene flow; island; migration; rafting; mtDNA
21.  Evolutionary rescue of a green alga kept in the dark 
Biology Letters  2013;9(1):20120823.
Chlamydomonas (Chlorophyta) can grow as a heterotroph on medium supplemented with acetate in the dark. A long-term experiment to investigate adaptation to dark conditions was set up with hundreds of replicate lines. Growth was initially slow, and most lines became extinct when transferred every few weeks. Some lines survived through the expansion of lineages derived from cells with extreme phenotypes and exhibited a U-shaped curve of collapse and recovery. Two short-term experiments were set up to evaluate the effect of sex on the frequency of ‘evolutionary rescue’ by deriving replicate lines from ancestral populations with contrasting sexual histories that had been cultured in the light for hundreds of generations. When transferred to dark conditions of growth, lines derived from obligately sexual populations survived more often than lines derived from facultatively sexual or asexual populations. This reflected the higher initial frequency of cells able to grow in the dark, due to greater genetic diversity supported by sexual fusion and recombination. The greater probability of evolutionary rescue suggests a general reason for the prevalence of sexual species.
doi:10.1098/rsbl.2012.0823
PMCID: PMC3565490  PMID: 23097464
autotrophic; heterotrophic; evolutionary rescue; sex; recombination; Chlamydomonas
22.  Marine trophic diversity in an anadromous fish is linked to its life-history variation in fresh water 
Biology Letters  2013;9(1):20120824.
We used carbon and nitrogen stable isotopes from muscle tissues accrued in the ocean to examine whether marine foraging tactics in anadromous sockeye salmon (Oncorhynchus nerka) are linked to their ultimate freshwater life history as adults. Adults from large-bodied populations spawning in deep freshwater habitats had more enriched δ15N than individuals from small-bodied populations from shallow streams. Within populations, earlier maturing individuals had higher δ15N than older fish. These differences in δ15N suggest that the fish with different life histories or spawning habitats in freshwater either fed at different trophic positions or in different habitats in the ocean. We propose that, nested within interspecific diversity in the ecological attributes of salmon, population and life-history diversity in spawning adults is associated with variation in marine foraging tactics. These results further indicate that the trophic diversity of sockeye salmon in the ocean may be linked to trade-offs in ecological and evolutionary constraints they eventually experience as adults in freshwater ecosystems.
doi:10.1098/rsbl.2012.0824
PMCID: PMC3565491  PMID: 23173190
stable isotopes; sockeye salmon; nitrogen; geomorphology
23.  A low trophic position of Japanese eel larvae indicates feeding on marine snow 
Biology Letters  2013;9(1):20120826.
What eel larvae feed on in the surface layer of the ocean has remained mysterious. Gut contents and bulk nitrogen stable isotope studies suggested that these unusual larvae, called leptocephali, feed at a low level in the oceanic food web, whereas other types of evidence have suggested that small zooplankton are eaten. In this study, we determined the nitrogen isotopic composition of amino acids of both natural larvae and laboratory-reared larvae of the Japanese eel to estimate the trophic position (TP) of leptocephali. We observed a mean TP of 2.4 for natural leptocephali, which is consistent with feeding on particulate organic matter (POM) such as marine snow and discarded appendicularian houses containing bacteria, protozoans and other biological materials. The nitrogen isotope enrichment values of the reared larvae confirm that the primary food source of natural larvae is consistent only with POM. This shows that leptocephali feed on readily available particulate material originating from various sources closely linked to ocean primary production and that leptocephali are a previously unrecognized part of oceanic POM cycling.
doi:10.1098/rsbl.2012.0826
PMCID: PMC3565492  PMID: 23134783
trophic ecology; leptocephali; amino acid nitrogen isotopes; Japanese eel; particulate organic matter
24.  Opposite differential allocation by males and females of the same species 
Biology Letters  2013;9(1):20120835.
Differential allocation (DA)—the adjustment of an individual's parental investment in relation to its mate's attractiveness—is increasingly recognized as an important component of sexual selection. However, although DA is expected by both sexes of parents in species with biparental care, DA by males has rarely been investigated. We have previously demonstrated a decrease in the feeding rates of female blue tits Cyanistes caeruleus when their mate's UV coloration was experimentally reduced (i.e. positive DA). In this study, we used the same experimental protocol in the same population to investigate DA by male blue tits in relation to their female's UV coloration. Males mated to UV-reduced females had higher feeding rates than those mated to control females (i.e. negative DA). Thus, male and female blue tits display opposite DA for the same component of parental effort (chick provisioning), the first time that this has been reported for any species.
doi:10.1098/rsbl.2012.0835
PMCID: PMC3565494  PMID: 23193045
differential allocation; reproductive compensation; parental effort; UV coloration; blue tits; mate attractiveness
25.  Parturition date for a given female is highly repeatable within five roe deer populations 
Biology Letters  2013;9(1):20120841.
Births are highly synchronized among females in many mammal populations in temperate areas. Although laying date for a given female is also repeatable within populations of birds, limited evidence suggests low repeatability of parturition date for individual females in mammals, and between-population variability in repeatability has never, to our knowledge, been assessed. We quantified the repeatability of parturition date for individual females in five populations of roe deer, which we found to vary between 0.54 and 0.93. Each year, some females gave birth consistently earlier in the year, whereas others gave birth consistently later. In addition, all females followed the same lifetime trajectory for parturition date, giving birth progressively earlier as they aged. Giving birth early should allow mothers to increase offspring survival, although few females managed to do so. The marked repeatability of parturition date in roe deer females is the highest ever reported for a mammal, suggesting low phenotypic plasticity in this trait.
doi:10.1098/rsbl.2012.0841
PMCID: PMC3565495  PMID: 23234861
repeatability; Capreolus capreolus; trajectory; birth date

Résultats 1-25 (1852)