| 1. |
- Andersson, Malte, 1941, et al.
(författare)
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Don't Put All Your Eggs in One Nest: Spread Them and Cut Time at Risk
- 2012
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 180:3, s. 354-363
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Tidskriftsartikel (refereegranskat)abstract
- In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa-for instance, polyandry with male parental care in some birds and fishes.
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| 2. |
- Andersson, Malte, 1941
(författare)
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Helping Relatives Survive and Reproduce: Inclusive Fitness and Reproductive Value in Brood Parasitism
- 2017
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 189:2, s. 138-152
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Tidskriftsartikel (refereegranskat)abstract
- Costly help can raise a relative's reproduction, survival, and reproductive value and increase the inclusive fitness of the donor of help. Donor fitness is explored here in conspecific brood parasitism. In this alternative reproductive tactic, some females, "parasites," lay eggs in nests of other females of the same species, "hosts," suppliers of help that alone take care of the offspring. Modeling shows that hosts can gain inclusive fitness if parasitized by relatives whose reproduction or survival is thereby increased. These predictions are explored in waterfowl with frequent brood parasitism, female-biased philopatry, and neighbor relatedness. Approximate estimates based on waterfowl reproductive and life-history data show that host inclusive-fitness gain is often possible with related parasites. The largest gains can be achieved through increased reproduction, but gain is also possible through higher survival of parasites that avoid increased predation and other risks of nesting. Inclusive fitness depends on parasite reproductive value and can be highest for a host parasitized by her mother and for old, senescent hosts with low fecundity, helping young related parasites. These results and observed levels of host-parasite relatedness suggest that being "parasitized" in waterfowl is sometimes neutral or even advantageous because of inclusive-fitness benefits, contributing to evolution of frequent conspecific brood parasitism in this group.
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| 3. |
- Andersson, Martin, et al.
(författare)
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Multiple-Strain Infections of Borrelia afzelii: A Role for Within-Host Interactions in the Maintenance of Antigenic Diversity?
- 2013
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 181:4, s. 545-554
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Tidskriftsartikel (refereegranskat)abstract
- Genetically diverse infections are common but little is known about what effects coinfecting strains have on each other in natural host-parasite systems. To explore the nature and consequences of interactions in the wild, we studied the tick-transmitted bacterium Borrelia afzelii in one of its main reservoir hosts, the bank vole Myodes glareolus. We measured overall infection intensity with quantitative polymerase chain reaction (PCR) and resolved the composition of multiple infections using strain-specific PCR assays targeting the ospC gene (which encodes an immunodominant surface protein). We found seven different strains, as defined by ospC genotype. There was little evidence for interactions affecting infection intensities, but strains were highly aggregated (i.e., there were more multiple infections than expected from random co-occurrence). Moreover, there was a positive correlation between the difference at the amino acid level between two OspC types and their degree of association. Overall, the observed patterns suggest that facilitation is more important than competition in this system and that more diverse infections have an advantage in establishing and/or maintaining infection. We propose that this advantage is one of the factors that favors antigenic diversity.
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| 4. |
- Andersson, Staffan, 1959, et al.
(författare)
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Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird.
- 2002
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Ingår i: The American naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 160:5, s. 683-91
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Tidskriftsartikel (refereegranskat)abstract
- Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Attwell, Joanna R., et al.
(författare)
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Fish avoid visually noisy environments where prey targeting is reduced
- 2021
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 198:3, s. 421-432
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Tidskriftsartikel (refereegranskat)abstract
- The environment contains different forms of ecological noise that can reduce the ability of animals to detect information. Here, we ask whether animals adapt their behavior to either exploit or avoid areas of their environment with increased dynamic visual noise. Threespined sticklebacks (Gasterosteus aculeatus) were immersed in environments with a simulated formof naturally occurring visual noise— moving light bands that formon underwater substrates caused by the refraction of light through surface waves. We tested whether this form of visual noise affected fish’s habitat selection, movements, and preytargeting behavior. Fish avoided areas of the environment with increased visual noise and achieved this by increasing their activity as a function of the locally perceived noise level. Fish were less likely to respond to virtual prey in environments with increased visual noise, highlighting a potential impact that visual noise has on their perceptual abilities. Fish did not increase or decrease their refuge use in environments with increased visual noise, providing no evidence that visual noise increased either exploratory or risk-aversive behavior. Our results indicate that animals can use simple behavioral strategies to avoid visually noisy environments, thereby mitigating the impacts that these environments appear to have on their perceptual abilities.
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| 9. |
- Aunapuu, Maano, et al.
(författare)
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Spatial patterns and dynamic responses of arctic food webs corroborate the exploitation ecosystems hypothesis (EEH)
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:2, s. 249-262
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Tidskriftsartikel (refereegranskat)abstract
- According to the exploitation ecosystems hypothesis (EEH), productive terrestrial ecosystems are characterized by community‐level trophic cascades, whereas unproductive ecosystems harbor food‐limited grazers, which regulate community‐level plant biomass. We tested this hypothesis along arctic‐alpine productivity gradients at the Joatka field base, Finnmark, Norway. In unproductive habitats, mammalian predators were absent and plant biomass was constant, whereas herbivore biomass varied, reflecting the productivity of the habitat. In productive habitats, predatory mammals were persistently present and plant biomass varied in space, but herbivore biomass did not. Plant biomass of productive tundra scrublands declined by 40% when vegetation blocks were transferred to predation‐free islands. Corresponding transfer to herbivore‐free islands triggered an increase in plant biomass. Fertilization of an unproductive tundra heath resulted in a fourfold increase in rodent density and a corresponding increase in winter grazing activity, whereas the total aboveground plant biomass remained unchanged. These results corroborate the predictions of the EEH, implying that the endotherm community and the vegetation of the North European tundra behaves dynamically as if each trophic level consisted of a single population, in spite of local co‐occurrence of >20 plant species representing different major taxonomic groups, growth forms, and defensive strategies.
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| 10. |
- Bachmann, Judith C., et al.
(författare)
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Gene Flow Limits Adaptation along Steep Environmental Gradients
- 2020
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Ingår i: American Naturalist. - : UNIV CHICAGO PRESS. - 0003-0147 .- 1537-5323. ; 195:3, s. E67-E86
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Tidskriftsartikel (refereegranskat)abstract
- When environmental variation is spatially continuous, dispersing individuals move among nearby sites with similar habitat conditions. But as an environmental gradient becomes steeper, gene flow may connect more divergent habitats, and this is predicted to reduce the slope of the adaptive dine that evolves. We compared quantitative genetic divergence of Rana temporaria frog populations along a 2,000-m elevational gradient in eastern Switzerland (new experimental results) with divergence along a 1,550-km latitudinal gradient in Fennoscandia (previously published results). Both studies found significant countergradient variation in larval development rate (i.e., animals from cold climates developed more rapidly). The dine was weaker with elevation than with latitude. Animals collected on both gradients were genotyped at similar to 2,000 singlenucleotide polymorphism markers, revealing that dispersal distance was 30% farther on the latitudinal gradient but 3.9 times greater with respect to environmental conditions on the elevational gradient. A meta-analysis of 19 experimental studies of anuran populations spanning temperature gradients revealed that countergradient variation in larval development, while significant overal I, was weaker when measured on steeper gradients. These findings support the prediction that adaptive population divergence is less pronounced, and maladaptation more pervasive, on steep environmental gradients.
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| 11. |
- Barabas, György
(författare)
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Parameter Sensitivity of Transient Community Dynamics
- 2024
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Ingår i: American Naturalist. - : UNIV CHICAGO PRESS. - 0003-0147 .- 1537-5323.
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Tidskriftsartikel (refereegranskat)abstract
- Transient dynamics have always intrigued ecologists, but current rapid environmental change (inducing transients even in previously undisturbed systems) has highlighted their importance more than ever. Here, I introduce a method for analyzing the sensitivity of transient ecological dynamics to parameter perturbations. The question the method answers is: how would the community dynamics have unfolded for some time horizon had the parameters been slightly different? I apply the method to three empirically parameterized models: competition between native forbs and exotic grasses in California, a host-parasitoid system, and an experimental chemostat predator-prey model. These applications showcase the ecological insights one can gain from models using transient sensitivity analysis. First, one can find parameters and their combinations whose perturbations disproportionately affect a system. Second, one can identify particular windows of time during which the predicted deviation from the unperturbed trajectories is especially large and utilize this information for management purposes. Third, there is an inverse relationship between transient and long-term sensitivities whenever the interacting populations are ecologically similar; paradoxically, the smaller the immediate response of the system, the more extreme its long-term response will be.
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| 12. |
- Berger, David, et al.
(författare)
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Ecological Constraints on Female Fitness in a Phytophagous Insect
- 2012
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 180:4, s. 464-480
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Tidskriftsartikel (refereegranskat)abstract
- Although understanding female reproduction is crucial for population demography, determining how and to what relative extent it is constrained by different ecological factors is complicated by difficulties in studying the links between individual behavior, life history, and fitness in nature. We present data on females in a natural population of the butterfly Leptidea sinapis. These data were combined with climate records and laboratory estimates of life-history parameters to predict the relative impact of different ecological constraints on female fitness in the wild. Using simulation models, we partitioned effects of male courtship, host plant availability, and temperature on female fitness. Results of these models indicate that temperature is the most constraining factor on female fitness, followed by host plant availability; the short-term negative effects of male courtship that were detected in the field study were less important in models predicting female reproductive success over the entire life span. In the simulations, females with more reproductive reserves were more limited by the ecological variables. Reproductive physiology and egg-laying behavior were therefore predicted to be co-optimized but reach different optima for females of different body sizes; this prediction is supported by the empirical data. This study thus highlights the need for studying behavioral and life-history variation in orchestration to achieve a more complete picture of both demographic and evolutionary processes in naturally variable and unpredictable environments.
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| 13. |
- Berger, David, et al.
(författare)
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Intralocus Sexual Conflict and the Tragedy of the Commons in Seed Beetles
- 2016
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 188:4, s. E98-E112
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of male traits that inflict direct harm on females during mating interactions can result in a so-called tragedy of the commons, where selfish male strategies depress population viability. This tragedy of the commons can be magnified by intralocus sexual conflict (IaSC) whenever alleles that reduce fecundity when expressed in females spread in the population because of their benefits in males. We evaluated this prediction by detailed phenotyping of 73 isofemale lines of the seed beetle Callosobruchus maculatus. We quantified genetic variation in life history andmorphology, as well as associated covariance in male and female adult reproductive success. In parallel, we created replicated artificial populations of each line and measured their productivity. Genetic constraints limited independent trait expression in the sexes, and we identified several instances of sexually antagonistic covariance between traits and fitness, signifying IaSC. Population productivity was strongly positively correlated to female adult reproductive success but uncorrelated with male reproductive success. Moreover, male (female) phenotypic optima for several traits under sexually antagonistic selection were exhibited by the genotypes with the lowest (highest) population productivity. Our study forms a direct link between individuallevel sex-specific selection and population demography and places lifehistory traits at the epicenter of these dynamics.
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| 14. |
- Berglund, Anders, et al.
(författare)
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Reproductive success of females limited by males in two pipefish species
- 1989
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Ingår i: American Naturalist. - 0003-0147 .- 1537-5323. ; 133:4, s. 506-516
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Tidskriftsartikel (refereegranskat)abstract
- We investigate whether males limit the reproductive success of females in the two pipefish species Syngnathus typhle and Nerophis ophidion. Syngnathus typhle is sexually monomorphic, and courtship behavior does not differ between the sexes. In N. ophidion, on the contrary, females are larger, more colorful, and more active during courtship, possessing appearance-enlarging skin folds. In both species, males brood the offspring on their bodies, one internally and one externally. Males do not invest more energy in reproduction than do females, and in the sexually dimorphic species, males invest even less than females do. Natural sex ratios are equal in both species. Experimentally, we provided each female with an excess of males (i.e., three), in order to measure a female's maximal reproductive rate, and found that females of both species produced more eggs, or produced them at a faster rate, than naturally available males could care for. Within the time span of one male pregnancy, S. typhle females filled an average of 1.9 males and N. ophidion an average of 1.8 males; both numbers are significantly more than one (which is the average mate availability in natural populations). Measured in another way, during one male pregnancy, S. typhle and N. ophidion females both produced 41% more eggs than needed to fill a male, significantly more than no egg surplus in both species. Therefore, brood space and the rate of embryonic development limit female reproduction in these species. There was no significant difference between the species, however. Syngnathus typhle males might be expected to be less limiting than N. ophidion males, but sexual size dimorphism may be absent in S. typhle because, by contrast with N. ophidion, larger males enjoy greater reproductive success. Directional selection for increased male size may decrease sexual size dimorphism in S. typhle. At any rate, the limitation of the reproductive success of one sex by the other seems to be a necessary but not sufficient prerequisite for the evolution of sexual dimorphism and "sex roles."
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| 15. |
- Berglund, Helena, et al.
(författare)
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Endemism Predicts Intrinsic Vulnerability to Nonindigenous Species on Islands.
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:1, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: While numerous efforts have been made to identify and quantify factors controlling invasibility of biological communities, less attention has been given to analyzing the expressions of vulnerability to nonindigenous species (NIS). Using the International Union for the Conservation of Nature and Natural Resources Red List database for birds, mammals, and amphibians and the Invasive Species Specialist Group global invasive species database as sources of information, we developed a new indicator for the relative intrinsic vulnerability of islands to NIS. It was calculated from the residuals to the global relationship between the impact of NIS and their exposure to the islands. The impact of NIS was expressed as the proportion of indigenous species threatened by NIS, and the exposure was the number of invasive NIS per number of native species. The residuals corresponded to the variability in impact, about 60%, that was not explained by exposure. The proportion of endemic species on the islands was positively correlated with the relative intrinsic vulnerability and explained about 60% of its variability. The robust relationship between endemism and intrinsic vulnerability reinforces the role of long-term isolation for the fate of island indigenous species to biological invasions and is useful in identifying vulnerable environments without having a specific invader in mind.
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| 16. |
- Brand, Jack
(författare)
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Sexual Selection Increases Male Behavioral Consistency in Drosophila melanogaster
- 2024
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Ingår i: American Naturalist. - 0003-0147 .- 1537-5323. ; 203, s. 713 - 725
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Tidskriftsartikel (refereegranskat)abstract
- Sexual selection has been suggested to influence the expression of male behavioral consistency. However, despite predictions, direct experimental support for this hypothesis has been lacking. Here, we investigated whether sexual selection altered male behavioral consistency in Drosophila melanogaster-a species with both pre- and postcopulatory sexual selection. We took 1,144 measures of locomotor activity (a fitness-related trait in D. melanogaster) from 286 flies derived from replicated populations that have experimentally evolved under either high or low levels of sexual selection for >320 generations. We found that high sexual selection males were more consistent (decreased within-individual variance) in their locomotor activity than male conspecifics from low sexual selection populations. There were no differences in behavioral consistency between females from the high and low sexual selection populations. Furthermore, while females were more behaviorally consistent than males in the low sexual selection populations, there were no sex differences in behavioral consistency in high sexual selection populations. Our results demonstrate that behavioral plasticity is reduced in males from populations exposed to high levels of sexual selection. Disentangling whether these effects represent an evolved response to changes in the intensity of selection or are manifested through nongenetic parental effects represents a challenge for future research.
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| 17. |
- Brengdahl, Martin, et al.
(författare)
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Genetic Quality Affects the Rate of Male and Female Reproductive Aging Differently in Drosophila melanogaster
- 2018
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 192:6, s. 761-772
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Tidskriftsartikel (refereegranskat)abstract
- Males and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive aging. Here we investigate whether reproductive aging and life span respond to condition differently in male and female Drosophila melanogaster, as predicted if sexual selection has shaped male and female resource-allocation patterns. We manipulate condition through genetic quality by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male reproductive output than on female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive aging between the sexes in low condition, but in high condition reproductive aging is relatively faster in males. No corresponding sex-specific change was found for life span. The sex difference in reproductive aging appearing in high condition was specifically due to a decreased aging rate in females rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more toward somatic maintenance than males.
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| 18. |
- Brice, Claire, et al.
(författare)
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Hybridization Outcomes Have Strong Genomic and Environmental Contingencies
- 2021
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 198:3
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Tidskriftsartikel (refereegranskat)abstract
- Extreme F2 phenotypes known as transgressive segregants can cause increased or decreased fitness in hybrids beyond the ranges seen in parental populations. Despite the usefulness of transgression for plant and animal breeding and its potential role in hybrid speciation, the genetic mechanisms and predictors of transgressive segregation remain largely untested. We generated seven hybrid crosses between five widely divergent Saccharomyces yeast species and measured the fitness of the parents and their viable F1 and F2 hybrids in seven stressful environments. We found that on average 16.6% of all replicate F2 hybrids had higher fitness than both parents. Against our predictions, transgression frequency was not a function of parental genetic and phenotypic distances across test environments. Within environments, some relationships were significant, but not in the predicted direction; for example, genetic distance was negatively related to transgression in ethanol and hydrogen peroxide. Significant effects of hybrid cross, test environment, and cross × environment interactions suggest that the amount of transgression produced in a hybrid cross is highly context specific and that outcomes of hybridization differ even among crosses made from the same two parents. If the goal is to reliably predict hybrid fitness and forecast the evolutionary potential of admixed populations, we need more efforts to identify patterns beyond the idiosyncrasies caused by specific genomic or environmental contexts.
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| 19. |
- Brodin, Anders, et al.
(författare)
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The effect of dominance on food hoarding: A game theoretical model
- 2001
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Ingår i: American Naturalist. - 0003-0147. ; 157:1, s. 66-75
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Tidskriftsartikel (refereegranskat)abstract
- Many food hoarding animals live in small groups structured by rank. The presence of conspecifics in the hoarding area increases the risk of losing stored supplies. The possibility of stealing from others depends on a forager's rank in the group. Highly ranked individuals can steal from subordinates and also protect their own caches. Since storing incurs both costs and benefits, the optimal hoarding investment will differ between individuals of different rank. In a game theoretical model, we investigate how dominant and subordinate individuals should optimize their hoarding effort. Our model imagines animals that are large-scale hoarders in autumn and dependent on stored supplies for winter survival. Many examples can be found in the bird families Paridae and Corvidae, but the model can be used for any hoarding species that forage in groups. Predictions from the model are as follows: First, subordinates should store more than dominants, but in a predictable environment, this difference will decrease as the environment gets harsher. Under harsh conditions, dominants should store almost as much as subordinates and, later, spend almost as much time retrieving their own caches as subordinates. Second, if on the other hand, bad winter conditions were not expected when storing, dominants should spend more time pilfering caches from subordinates. Third, in populations that are highly dependent on stored supplies, dominants should store relatively more than in populations that are less dependent on stored supplies. Fourth, harsher environments will favor hoarding. And finally, if dominant individuals store, it implies that hoarders have a selfish recovery advantage over conspecific pilferers.
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| 20. |
- Brommer, J.E., et al.
(författare)
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Exploring the genetics of aging in a wild passerine bird
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170:4, s. 643-650
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Tidskriftsartikel (refereegranskat)abstract
- Senescence is the decline in survival and reproduction as an organism ages and is known to occur in collared flycatchers Ficedula albicollis. We consider annual fitness (the estimated genetic contribution that an individual makes to next year’s gene pool) as a measure of age‐specific fitness. We apply a restricted maximum likelihood linear mixed‐model approach on 25 years of data on 3,844 male and 4,992 female collared flycatchers. Annual fitness had a significant additive genetic component (h2 of about 4%). Annual fitness declined at later ages in both sexes. Using a random regression animal model, we show that the observed age‐related phenotypic changes in annual fitness were not present on the additive genetic level, contrary to predictions of genetic hypotheses of senescence. Our study suggests that patterns of aging in the wild need to be interpreted with caution in terms of underlying genetics because they may be largely determined by environmental processes.
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| 21. |
- Brommer, Jon E., et al.
(författare)
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Passerine Extrapair Mating Dynamics : A Bayesian Modeling Approach Comparing Four Species
- 2010
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 176:2, s. 178-187
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Tidskriftsartikel (refereegranskat)abstract
- In many socially monogamous animals, females engage in extrapair copulation (EPC), causing some broods to contain both within-pair and extrapair young (EPY). The proportion of all young that are EPY varies across populations and species. Because an EPC that does not result in EPY leaves no forensic trace, this variation in the proportion of EPY reflects both variation in the tendency to engage in EPC and variation in the extrapair fertilization (EPF) process across populations and species. We analyzed data on the distribution of EPY in broods of four passerines (blue tit, great tit, collared flycatcher, and pied flycatcher), with 18,564 genotyped nestlings from 2,346 broods in two to nine populations per species. Our Bayesian modeling approach estimated the underlying probability function of EPC (assumed to be a Poisson function) and conditional binomial EPF probability. We used an information theoretical approach to show that the expected distribution of EPC per female varies across populations but that EPF probabilities vary on the above-species level (tits vs. flycatchers). Hence, for these four passerines, our model suggests that the probability of an EPC mainly is determined by ecological (population-specific) conditions, whereas EPF probabilities reflect processes that are fixed above the species level.
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| 22. |
- Butlin, Roger, 1955, et al.
(författare)
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Coupling, reinforcement, and speciation
- 2018
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 191, s. 155-172
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 by The University of Chicago. During the process of speciation, populations may diverge for traits and at their underlying loci that contribute barriers to gene flow. These barrier traits and barrier loci underlie individual barrier effects, by which we mean the contribution that a barrier locus or trait—or some combination of barrier loci or traits—makes to overall isolation. The evolution of strong reproductive isolation typically requires the origin of multiple barrier effects. Critically, it also requires the coincidence of barrier effects; for example, two barrier effects, one due to assortative mating and the other due to hybrid inviability, create a stronger overall barrier to gene flow if they coincide than if they distinguish independent pairs of populations. Here, we define “coupling” as any process that generates coincidence of barrier effects, resulting in a stronger overall barrier to gene flow. We argue that speciation research, both empirical and theoretical, needs to consider both the origin of barrier effects and the ways in which they are coupled. Coincidence of barrier effects can occur either as a by-product of selection on individual barrier effects or of population processes, or as an adaptive response to indirect selection. Adaptive coupling may be accompanied by further evolution that enhances individual barrier effects. Reinforcement, classically viewed as the evolution of prezygotic barriers to gene flow in response to costs of hybridization, is an example of this type of process. However, we argue for an extended view of reinforcement that includes coupling processes involving enhancement of any type of additional barrier effect as a result of an existing barrier. This view of coupling and reinforcement may help to guide development of both theoretical and empirical research on the process of speciation.
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| 23. |
- Caruso, Christina M., et al.
(författare)
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What Are the Environmental Determinants of Phenotypic Selection? : A Meta-analysis of Experimental Studies
- 2017
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 190:3, s. 363-376
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Tidskriftsartikel (refereegranskat)abstract
- Although many selection estimates have been published, the environmental factors that cause selection to vary in space and time have rarely been identified. One way to identify these factors is by experimentally manipulating the environment and measuring selection in each treatment. We compiled and analyzed selection estimates from experimental studies. First, we tested whether the effect of manipulating the environment on selection gradients depends on taxon, trait type, or fitness component. We found that the effect of manipulating the environment was larger when selection was measured on life-history traits or via survival. Second, we tested two predictions about the environmental factors that cause variation in selection. We found support for the prediction that variation in selection is more likely to be caused by environmental factors that have a large effect on mean fitness but not for the prediction that variation is more likely to be caused by biotic factors. Third, we compared selection gradients from experimental and observational studies. We found that selection varied more among treatments in experimental studies than among spatial and temporal replicates in observational studies, suggesting that experimental studies can detect relationships between environmental factors and selection that would not be apparent in observational studies.
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| 24. |
- Cherif, Mehdi, et al.
(författare)
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Stoichiometric constraints on resource use, competitive interactions, and elemental cycling in microbial decomposers
- 2007
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Ingår i: American Naturalist. - McGill Univ, Dept Biol, Montreal, PQ H3A 1B1, Canada. Ecole Normale Super, Biogeochim & Ecol Milieux Continentaux Lab, UMR 7618, F-75230 Paris 05, France. : UNIV CHICAGO PRESS. - 0003-0147 .- 1537-5323. ; 169:6, s. 709-724
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Tidskriftsartikel (refereegranskat)abstract
- Heterotrophic microbial decomposers, such as bacteria and fungi, immobilize or mineralize inorganic elements, depending on their elemental composition and that of their organic resource. This fact has major implications for their interactions with other consumers of inorganic elements. We combine the stoichiometric and resource-ratio approaches in a model describing the use by decomposers of an organic and an inorganic resource containing the same essential element, to study its consequences on decomposer interactions and their role in elemental cycling. Our model considers the elemental composition of organic matter and the principle of its homeostasis explicitly. New predictions emerge, in particular, ( 1) stoichiometric constraints generate a trade-off between the R* values of decomposers for the two resources; ( 2) they create favorable conditions for the coexistence of decomposers limited by different resources and with different elemental demands; ( 3) however, combined with conditions on species-specific equilibrium limitation, they draw decomposers toward colimitation by the organic and inorganic resources on an evolutionary time scale. Moreover, we derive the conditions under which decomposers switch from consumption to excretion of the inorganic resource. We expect our predictions to be useful in explaining the community structure of decomposers and their interactions with other consumers of inorganic resources, particularly primary producers.
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| 25. |
- Claessen, David, et al.
(författare)
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The effect of population size and recombination on delayed evolution of polymorphism and speciation in sexual populations
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 172:1, s. E18-34
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Tidskriftsartikel (refereegranskat)abstract
- Recent theory suggests that absolute population size may qualitatively influence the outcome of evolution under disruptive selection in asexual populations. Large populations are predicted to undergo rapid evolutionary branching; however, in small populations, the waiting time to branching increases steeply with decreasing abundance, and below a critical size, the population remains monomorphic indefinitely. Here, we (1) extend the theory to sexual populations and (2) confront its predictions with empirical data, testing statistically whether lake size affects the level of resource polymorphism in arctic char (Salvelinus alpinus) in 22 lakes of different sizes. For a given level of recombination, our model predicts qualitatively similar relations between population size and time to evolutionary branching (either speciation or evolution of genetic polymorphism) as the asexual model, while recombination further increases the delay to branching. The loss of polymorphism at certain loci, an inherent aspect of multilocus-trait evolution, may increase the delay to speciation, resulting in stable genetic polymorphism without speciation. The empirical analysis demonstrates that the occurrence of resource polymorphism depends on both lake size and the number of coexisting fish species. For a given number of coexisting species, the level of polymorphism increases significantly with lake size, thus confirming our model prediction.
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