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PubMed1990

How to measure inclusive fitness.

Although inclusive fitness (Hamilton 1964) is regarded as the basic currency of natural selection, difficulty in applying inclusive fitness theory to field studies persists, a quarter-century after its introduction (Grafen 1982, 1984; Brown 1987). For instance, strict application of the original (and currently accepted) definition of inclusive fitness predicts that no one should ever attempt to breed among obligately cooperative breeders. Much of this confusion may have arisen because Hamilton's (1964) original verbal definition of inclusive fitness was not in complete accord with his justifying model. By re-examining Hamilton's original model, a modified verbal definition of inclusive fitness can be justified.

Animals↗

PubMed2000

Non-random fitness variation in two populations of Darwin's finches.

Darwinian fitness of an individual is measured by the number of recruits it contributes to the next generation. We studied variation in fitness among members of three cohorts of two species of Darwin's finches living on the Galipagos island of Daphne Major: the medium ground finch (Geospiza fortis) and cactus finch (Geospiza scandens). Individuals of both species live for up to 16 years. Variation in fitness was neither random nor heritable. Non-randomness arises as a result of a few individuals living for an exceptionally long time and breeding many times. For each cohort, the number of recruits per breeder is strongly predicted by the number of fledglings per breeder. In turn, the number of fledglings is strongly predicted by longevity of the breeder. These results suggest that the most important determinant of fitness is the ability of an individual to survive to breed in many years. Morphological traits affect this ability. Although morphological traits are heritable they do not change unidirectionally because they are selected in opposite directions, and in different combinations, under fluctuating environmental conditions. Non-random fitness variation in fluctuating populations implies much smaller genetically effective sizes than breeding population sizes.

Age Factors↗

PubMed2004

Post-copulatory sexual selection and female fitness in Scathophaga stercoraria.

Whether sexual selection increases or decreases female fitness is determined by the occurrence and relative importance of sexual-conflict processes and the ability of females to choose high-quality males. Experimentally enforced polyandry and monogamy have previously been shown to cause rapid evolution in the yellow dung fly Scathophaga stercoraria. Flies from polyandrous lines invested more in reproductive tissue, and this investment influenced paternity in sperm competition, but came at a cost to immune function. While some fitness consequences of enforced polyandry or monogamy have been examined when flies mate multiply, the consequences for female fitness when singly copulated remain unexplored. Under a good-genes scenario females from polyandrous lines should be of higher general quality and should outperform females from monogamous lines even with a single copulation. Under sexual conflict, costly adaptations will afford no advantages when females are allowed to mate only once. We investigate the lifetime reproductive success and longevity of females evolving under enforced monogamy or polyandry when mating once with males from these selection regimes. Females from polyandrous lines were found to have lower fitness than their monogamous counterparts when mating once. They died earlier and produced significantly fewer eggs and offspring. These results suggest that sexual conflict probably drove evolution under enforced polyandry as female fitness did not increase overall as expected with purely good-genes effects.

Animals↗

PubMed2006

A Wolbachia-associated fitness benefit depends on genetic background in Drosophila simulans.

The alpha-proteobacteria Wolbachia infect a number of insect species and influence host reproduction to favour the spread of infected females through a population. The fitness effect of this infection is important in understanding the spread and maintenance of Wolbachia within and among host populations. However, a full elucidation of fitness effect requires careful control of host genetic background. Here, I transferred a single clone of Wolbachia (the wHa strain) into three genetically distinct isofemale lines of the fly Drosophila simulans using microinjection methodology. These lines carried one of the three described mitochondrial haplogroups (siI, siII or siIII) and differ in nuclear genome as well. Population cage assays showed that wHa-infected siIII flies enjoyed a dramatic fitness benefit compared to uninfected siIII. In contrast, wHa did not affect the fitness of siI or siII flies. This study points to the importance of host-by-symbiont interaction terms that may play an important role in organismal-fitness.

Animals↗

PubMed2006

Fitness cost of incubation in great tits (Parus major) is related to clutch size.

Life-history theory predicts that parents produce the number of offspring that maximizes their fitness. In birds, natural selection on parental decisions regarding clutch size may act during egg laying, incubation or nestling phase. To study the fitness consequences of clutch size during the incubation phase, we manipulated the clutch sizes during this phase only in three breeding seasons and measured the fitness consequences on the short and the long term. Clutch enlargement did not affect the offspring fitness of the manipulated first clutches, but fledging probability of the subsequent clutch in the same season was reduced. Parents incubating enlarged first clutches provided adequate care for the offspring of their first clutches during the nestling phase, but paid the price when caring for the offspring of their second clutch. Parents that incubated enlarged first clutches had lower local survival in the 2 years when the population had a relatively high production of second clutches, but not in the third year when there was a very low production of second clutches. During these 2 years, the costs of incubation were strong enough to change positive selection, as established by brood size manipulations in this study population, into stabilizing selection through the negative effect of incubation on parental fitness.

Animals↗

PubMed1999

Adaptive walks on time-dependent fitness landscapes.

The idea of adaptive walks on fitness landscapes as a means of studying evolutionary processes on large time scales is extended to fitness landscapes that are slowly changing over time. The influence of ruggedness and of the amount of static fitness contributions is investigated for model landscapes derived from Kauffman's NK landscapes. Depending on the amount of static fitness contributions in the landscape, the evolutionary dynamics can be divided into a percolating and a nonpercolating phase. In the percolating phase, the walker performs a random walk over the regions of the landscape with high fitness.

Biological Evolution↗

PubMed2026

Comfort and Usability of Digital Versus Conventional Custom-Fit Mouthguards: A Randomized Clinical Trial.

BACKGROUND/OBJECTIVES: The use of mouthguards protects teeth and the supporting tissues against impacts. Digital impressions and 3D-printed models can reduce manufacturing steps and minimize discomfort. This study evaluated the fit, comfort, and usability of custom-made mouthguards, obtained by conventional and digital workflow, in amateur athletes. MATERIALS AND METHODS: Amateur athletes were recruited for this randomized, double-blind, crossover clinical study. Each participant received two 4-mm-thick custom-fit mouthguards made of ethylene vinyl acetate (EVA) sheets using two protocols: conventional impression using alginate to produce dental stone cast (CMP) and intraoral digital scanning to produce 3D-printed resin models (DMP). Each mouthguard was worn during all training and matches over 3 months. The order of mouthguard use was randomly assigned. Patient satisfaction with the impression protocol and mouthguard use, model accuracy, and mouthguard fit were assessed. RESULTS: Overall, 46 participants completed the study. The DMP protocol required less execution time (p = 0.023), caused less discomfort (p = 0.018), anxiety (p = 0.008), nausea (p = 0.027), difficulty breathing (p < 0.001), and unpleasant taste (p = 0.006) compared to the CMP protocol. The pain (p = 0.971) perceived by the participants was similar in both impression protocols. The CMP-mouthguards were considered to be better fitting by the majority of participants (p = 0.027). Between-group comparisons revealed that DMP-mouthguard caused less discomfort immediately postadaptation (p = 0.034), with no significant differences observed at 30 or 90 days. CONCLUSIONS: The digital workflow demonstrated to be efficient in the fabrication of mouthguards. Digital impression was more comfortable, requiring less execution time, with more accurate printed models and produced mouthguards with reported comfort and fit levels similar to those manufactured conventionally.

Humans↗

PubMed2000

Fitness differences among diploids, tetraploids, and their triploid progeny in Chamerion angustifolium: mechanisms of inviability and implications for polyploid evolution.

Theoretical models indicate that the evolution of tetraploids in diploid populations will depend on both the relative fitness of the tetraploid and that of the diploid-tetraploid hybrids. Hybrids are believed to have lower fitness due to imbalances in either the ploidy (endosperm imbalance) or the ratio of maternal to paternal genomes in their endosperm (genomic imprinting). In this study we created diploids, tetraploids, and hybrid triploids of Chamerion angustifolium from crosses between field-collected diploid and tetraploid plants and evaluated them at six life stages in a greenhouse comparison. Diploid offspring (from 2x x 2x crosses) had significantly higher seed production and lower biomass than tetraploid offspring (from 4x x 4x crosses). Relative to the diploid, the cumulative fitness of tetraploids was 0.67. In general, triploids (from 2x x 4x, 4x x 2x crosses) had significantly lower seed production, lower pollen viability, and higher biomass than diploid individuals. Triploid offspring derived from diploid maternal parents had lower germination rates, but higher pollen production than those with tetraploid mothers. Relative to diploids, the cumulative fitness of 2x x 4x triploids and 4x x 2x triploids was 0.12 and 0.06, respectively, providing some support for effect of differing maternal:paternal ratios and endosperm development as a mechanism of hybrid inviability. Collectively, the data show that tetraploids exhibit an inherent fitness disadvantage, although the partial viability and fertility of triploids may help to reduce the barrier to tetraploid establishment in sympatric populations.

Biological Evolution↗

PubMed2000

The fitness effects of spontaneous mutations in Caenorhabditis elegans.

Spontaneous mutation to mildly deleterious alleles has emerged as a potentially unifying component of a variety of observations in evolutionary genetics and molecular evolution. However, the biological significance of hypotheses based on mildly deleterious mutation depends critically on the rate at which new mutations arise and on their average effects. A long-term mutation-accumulation experiment with replicate lines of the nematode Caenorhabditis elegans maintained by single-progeny descent indicates that recurrent spontaneous mutation causes approximately 0.1% decline in fitness per generation, which is about an order of magnitude less than that suggested by previous studies with Drosophila. Two rather different approaches, Bateman-Mukai and maximum likelihood, suggest that this observation, along with the observed rate of increase in the variance of fitness among lines, is consistent with a genomic deleterious mutation rate for fitness of approximately 0.03 per generation and with an average homozygous effect of approximately 12%. The distribution of mutational effects for fitness appears to have a relatively low coefficient of variation, being no more extreme than expected for a negative exponential, and for one composite fitness measure (total progeny production) approaches constancy of effects. These results are derived from assays in a benign environment. At stressful temperatures, estimates of the genomic deleterious mutation rate (for genes expressed at such temperatures) is sixfold lower, whereas those for the average homozygous effect is approximately eightfold higher. Our results are reasonably compatible with existing estimates for flies, when one considers the differences between these species in the number of germ-line cell divisions per generation and the magnitude of transposable element activity.

Animals↗

PubMed2000

Factors affecting the genetic load in Drosophila: synergistic epistasis and correlations among fitness components.

Two factors that can affect genetic load, synergistic epistasis and sexual selection, were investigated in Drosophila melanogaster. A set of five chromosomal regions containing visible recessive mutations were put together in all combinations to create a full set of 32 homozygous lines fixed for different numbers of known mutations. Two measures of fitness were made for each line: productivity (a combined measure of fecundity and egg-to-adult survivorship) and competitive male mating success. Productivity, but not male mating success, showed a pattern of strong average synergistic epistasis, such that the log fitness declined nonlinearly with increasing numbers of mutations. Synergistic epistasis is known to reduce the mutation load. Both fitness components show some positive and some negative interactions between specific sets of mutations. Furthermore, alleles with deleterious effects on productivity tend to also diminish male mating success. Given that male mating success can affect relative fitness without changing the mean productivity of a population, these additional effects would lead to lower frequencies and lower fixation rates of deleterious alleles without higher costs to the mean fitness of the population.

Animals↗

PubMed2001

Is survivorship a better fitness surrogate than fecundity?

Although fitness depends on both survivorship and fecundity, we tend to assume fecundity relates to fitness more directly than survivorship. In fact, several recent ecological studies suggest fitness depends more heavily on annual survivorship than annual fecundity for most taxa with lifespans longer than one year. These studies review elasticities of transition matrices for a broad range of taxa. Elasticities covary monotonically with selection gradients for demographic rates and are identical to selection gradients for traits rescaled to have mean values of zero and variance of one. For all taxa except semelparous perennial plants, adult survivorship has consistently higher elasticity than other suites of demographic rates. Fecundity only rarely has the highest elasticity. Thus, differences in yearly survival affect fitness disproportionately more than differences in yearly fecundity, even in many exponentially growing populations. This pattern reinforces the importance of interpreting the contribution of vital rates to fitness in the context of life history and population dynamics.

Animals↗

PubMed2001

Parental and developmental temperature effects on the thermal dependence of fitness in Drosophila melanogaster.

Cross-generational effects refer to nongenetic influences of the parental phenotype or environment on offspring phenotypes. Such effects are commonly observed, but their adaptive significance is largely unresolved. We examined cross-generational effects of parental temperature on offspring fitness (estimated via a serial-transfer assay) at different temperatures in a laboratory population of Drosophila melanogaster. Parents were reared at 18 degrees C, 25 degrees C, or 29 degrees C (Tpar) and then their offspring were reared at 18 degrees C, 25 degrees C, or 29 degrees C (Toff) to evaluate several competing hypotheses (including an adaptive one) involving interaction effects of parental and offspring temperature on offspring fitness. The results clearly show that hotter parents are better; in other words, the higher the temperature of the parents, the higher the fitness of their offspring, independent of offspring thermal environment. These data contradict the adaptive cross-generational hypothesis, which proposes that offspring fitness is maximal when the offspring thermal regime matches the parental one. Flies with hot parents have high fitness seemingly because their own offspring develop relatively quickly, not because they have higher fecundity early in life.

Acclimatization↗

PubMed2002

The ecology and genetics of fitness in Chlamydomonas. VIII. The dynamics of adaptation to novel environments after a single episode of sex.

According to classical evolutionary theory, sexual recombination can generate the variation necessary to adapt to changing environments and thereby confer an evolutionary advantage of sexual over asexual reproduction. Using the green alga, Chlamydomonas reinhardtii, we investigated the effect of a single sexual episode on adaptation of heterotrophic growth on different carbon sources. In an initial mixture of isolates, sex was induced and the resulting offspring constituted the sexual populations, along with any unmated vegetative cells; the unmated mixture of isolates represented the asexual populations. Mean and variance in division rates (i.e., fitness) were measured four times during approximately 50 generations of vegetative growth in the dark on all possible combinations of four carbon sources. Consistent with effects of recombination of epistatic genes in linkage disequilibrium, sexual populations initially had a higher variance in fitness, but their mean fitness was lower than that of asexual populations, possibly due to recombinational load. Subsequently, fitness of sexual populations exceeded that of asexual ones, but finally they regained parity in both mean and variance of fitness. Although recombination was not more effective on more complex substrates, these results generally support the idea that sex can accelerate adaptation to novel environments.

Adaptation, Physiological↗

PubMed2004

Person-Environment Fit and its implications for personality development: a longitudinal study.

Continuity and change in Person-Environment Fit (PE Fit) and its relation to personality development was studied in a 4-year longitudinal study of college students (N=305). PE Fit demonstrated moderate rank-order stability and small increases in mean-levels over time. Antecedents to PE Fit included gender (being male), high academic ability, low agreeableness, and low neuroticism. Outcomes associated with PE Fit included greater personality consistency and changes in personality in the direction of higher self-esteem and lower agreeableness and neuroticism. The implications of the findings for personality development are discussed.

Achievement↗

PubMed2005

Consequence of herbivory for the fitness cost of herbicide resistance: photosynthetic variation in the context of plant-herbivore interactions.

The cost of adaptations may depend on environmental conditions. We consider how the fitness cost of resistance to the herbicide triazine in Amaranthus hybridus interacts with folivory from the beetle Disonycha glabrata. Triazine-resistant (TR) genotypes suffer a fitness cost because of a pleiotropic reduction in the light reaction of photosynthesis, which in turn often leads to a reduction in photosynthetic rate. We found that the fitness cost of triazine resistance was 360% greater in the presence than absence of D. glabrata. This resulted from multiple phenotypic trade-offs, with TR plants suffering greater herbivory and displaying a diminished tolerance of damage. Our work highlights the importance of incorporating appropriate ecological variation into the assessment of fitness trade-offs. The results of this study also illustrate the potential for herbivores to impose selection on photosynthetic variation, and for variation in resource acquisition to obscure fitness costs.

Adaptation, Physiological↗

PubMedDate not supplied

The effect of die spacer on retention and fitting of complete cast crowns.

PURPOSE: This study evaluated the effect of die spacer on the fit and retention of complete cast crowns by using three different cements. MATERIALS AND METHODS: Standardized full crown restoration preparations were completed on 99 extracted molar teeth, impressions were made with poly(vinyl siloxane), and stone dies were made. Dies were covered with four layers of die spacer using three techniques: (1) covering the occlusal and 1/3 of the axial surfaces, (2) covering the occlusal and 2/3 of the axial surfaces, and (3) covering the entire preparation except the apical 0.5 mm of the preparation. Complete metal crowns were cast using Pors-on 4 alloy. Crowns were then assigned to one of three luting agent groups: resin modified glass ionomer cement, resin cement, or zinc phosphate cement. The castings were placed on their respective teeth and the marginal opening was recorded by two methods: 72 specimens were examined before and after cementation using optical microscopy with 0.001 mm resolution, and 27 specimens were examined after cementation with scanning electron microscopy. After cementation, the teeth were thermocycled for 700 cycles between 5 degrees C and 55 degrees C. The tensile retentive strength was measured on a universal testing machine with a crosshead speed of 0.5 mm/min. The data obtained for the fitting were recorded in millimeters and the data for the tensile retentive strength were recorded in KgF. The statistical analysis was performed by analysis of variance and post hoc Tukey's test (p< 0.05). RESULTS: Before cementation, better marginal fit was obtained when the die spacer covered all but the area 0.5 mm short of the margin of the preparation; however, after cementation, the resin modified glass ionomer cement group had the best fit with the same application of die spacer. Castings luted with resin cement required the greatest tensile force to produce cement failure. CONCLUSIONS: Increasing the area of the die surface covered with spacer improved the fit of the cast restoration. After cementation, the resin modified glass ionomer showed better adaptation; however, the optical microscopy and scanning microscopy correlate well. Resin cement had the highest resistance to tensile forces.

Analysis of Variance↗

PubMed1988

Relative importance of eight oral conditions for a fit dentition according to Dutch general practitioners.

Almost 5 million Dutch National Health Service members visit the dentist half-yearly in order to keep their so-called "dental fitness certificate" valid. The methods of paired comparisons and direct ranking were used to study the relative importance of eight oral conditions for a fit dentition: plaque, calculus, gingivitis, a pocket, a cavity, a root/radicle, a fistula and an extraction diastema. The assessments were made by a sample of Dutch general practitioners under contract to the National Health Service (n = 49). Each dentist was consistent in his comparative pairwise choices. Although agreement between the dentists was statistically significant, the low coefficient indicated individual differences between the dentists. The average rank orders of the eight oral conditions obtained from the dentists as a group by means of the two methods were highly comparable. To obtain dental fitness the dentists judged the treatment of a fistula and gingivitis more important than the treatment of plaque, calculus and cavities, and least important, the three conditions: root/radicles, pockets and extraction diastema. This average rank order indicates a shift in the concept of "dentally fit" as stated in the requirements, dating back to 1960, for granting a dental fitness certificate.

Decision Making↗

PubMed2000

Interaction of force-fitting and surface roughness of implants.

BACKGROUND: Increased surface roughness may increase installation torque and thus appear to increase the initial stability of an implant. However, it is not immediately clear if the increased torque is attributable to an increase in the effective diameter of the implant or to increased resistance of the bone because of the greater roughness. PURPOSE: Force-fitting stresses arise when an implant is placed into a predrilled hole of smaller-diameter in bone. The purpose of this report is to discuss the interaction of force-fitting stresses and surface roughness effects and to develop some general guidelines as to clinical procedures based on this theory. MATERIALS AND METHODS: Solutions for the force-fitting stresses are derived from well-known equations of elasticity. RESULTS: Substantial force-fitting stresses on the order of several tens of MPa can be generated when a titanium cylinder is placed into a hole in bone, the diameter of which is only 100 microns smaller. CONCLUSION: When a hole slightly smaller than the implant diameter is prepared for implant placement, force-fitting stress increases installation torque and stability can be induced. Thus, large surface roughness of implants should not be viewed as an exclusive mechanism for providing a desirable level of initial fixity. Smaller roughness with the same mean diameter is equally effective.

Bone and Bones↗