Relative Reproductive Success Research Articles

Unbiased estimation of relative reproductive success of different groups: evaluation and correction of bias caused by parentage assignment errors

Parentage assignment is widely applied to studies on mating systems, population dynamics and natural selection. However, little is known about the consequence of assignment errors, especially when some parents are not sampled. We investigated the effects of two types of error in parentage assignment, failing to assign a true parent (type A) and assigning an untrue parent (type B), on an estimate of the relative reproductive success (RRS) of two groups of parents. Employing a mathematical approach, we found that (i) when all parents are sampled, minimizing either type A or type B error insures the minimum bias on RRS, and (ii) when a large number of parents is not sampled, type B error substantially biases the estimated RRS towards one. Interestingly, however, (iii) when all parents were sampled and both error rates were moderately high, type A error biased the estimated RRS even more than type B error. We propose new methods to obtain an unbiased estimate of RRS and the number of offspring whose parents are not sampled (zW(z)), by correcting the error effects. Applying them to genotypic data from steelhead trout (Oncorhynchus mykiss), we illustrated how to estimate and control the assignment errors. In the data, we observed up to a 30% assignment error and a strong trade-off between the two types of error, depending on the stringency of the assignment decision criterion. We show that our methods can efficiently estimate an unbiased RRS and zW(z) regardless of assignment method, and how to maximize the statistical power to detect a difference in reproductive success between groups.

Decision-making in variable environments — a case of group selection and inter-generational conflict?

Suppose organisms need to engage in a particular action exactly once during some fixed period of time. Further suppose they can time this action to optimise their fitness based on the expected current payoff and the probability distribution of later payoffs. For an example we consider the timing of the annual nuptial flight in eusocial insects. Using two population genetics models, we ask whether stochasticity leads to evolutionary conflict between the queen and her offspring. We find that the winning phenotype is independent of who controls the timing. The best response to any non-equilibrium population strategy is the same in both control scenarios, a result that carries over to the diploid case. Although inter-generational conflict is therefore ruled out, the models support a previous observation that at equilibrium some of the offspring have a lower expected payoff than others. By measuring fitness in terms of relative reproductive success, we show that all individuals are in fact equally well off making group-selectionist arguments unnecessary. As such, the models should improve our understanding of the difficult conceptual problem of the unit of natural selection in stochastic environments.

Sexual reproduction of the high mountain plant Saxifraga moschata Wulfen at varying lengths of the growing season

Flowering phenology, dynamics of seed development and reproductive success of Saxifraga moschata Wulfen, occurring from the alpine to the nival zone, was investigated in three climatically varying years on early- and late-thawing sites at 2340 m a.s.l. in the Austrian Alps. The growing season was particularly short in 2001, about normal in 2002 and exceptionally long and warm in 2003. S. moschata is a mid-season flowering species, which started to bloom about 1 month after snowmelt. From onset of anthesis until seed maturity an individual flower required 6–7 weeks, and all individuals of a site 9–11 weeks. In 2001, late flowering individuals lost about 40% of the seed crop because of too early snowfalls in autumn. No clear relationship could be found between thermal time and the length of different reproductive phases, which indicates that temperature was not a limiting factor for reproductive development in the growing seasons 2001–2003. Plants from the earliest-thawing site produced about double the reproductive structures (reproductive shoots per individual, number of flowers per inflorescence, number of ovules per ovary), and had a significantly higher reproductive output (number of fruits and mature seeds per inflorescence) compared with individuals from the late-thawing site. Reproductive success was additionally affected by the seasonal climate and was lowest in the warm and dry summer of 2003. Fruit/flower ratio ranged between 0.6 and 0.8, seed/ovule ratio between 0.4 and 0.5 and relative reproductive success (RRS) between 0.3 and 0.4, depending on the site and year. Different from our expectations, it took S. moschata relatively long to undergo reproductive development; however, its phenological plasticity and ability to continue seed maturation even under snow are most advantageous for a life at higher altitudes.

Effects of local density and flower colour polymorphism on pollination and reproduction in the rewardless orchid Dactylorhiza sambucina (L.) So�

The rewardless orchid Dactylorhiza sambucina shows a stable flower colour polymorphism, with both yellow- and red-flowered morphs growing sympatrically. Pollination biology and breeding system were investigated to examine the effects of density of plants, colour polymorphism, inflorescence dimension, and flower position within inflorescence on male and female reproductive success in three natural populations of D. sambucina. There were significant differences among sites in the number of pollinia removed and in fruit set per inflorescence. Number of removed pollinia and capsule production in D. sambucina were independent from flower and inflorescence size or flower position. As a whole, the red morphs showed the highest number of capsules produced, while the yellow morphs had the greatest male success. The relative male and female reproductive success were independent from plant density but were significantly correlated with the yellow morph frequency at the population level. Overall, our findings show that the contribution to the total reproductive success deriving from the two colour morphs does not conform with the predictions of negative frequency-dependent selection.

Adaptive mutation: how growth under selection stimulates Lac(+) reversion by increasing target copy number.

From the time of Darwin until about 1950, a controversy continued over whether selective stress induces mutations or only affects the relative reproductive success of organisms with different genotypes (30). The controversy was resolved by the classic experiments of Luria and Delbruck (27) and of Leder- berg and Lederberg (25), who showed that some bacterial mutants arise prior to application of the selection that allows their detection and thus could not have been caused by selec- tive conditions. However, these experiments used lethal selec- tions and therefore did not eliminate the possibility that an- other fraction of total mutations might be formed in response to stress and be detected only by nonlethal selection. Shapiro and Cairns et al. reopened the controversy by pointing out this caveat and presenting data that seemed to support stress-in- duced mutation (7, 45). Because very few genetic systems behave in ways that sug- gest stress-induced mutation, the rare cases that seem to ex- hibit such behavior have attracted close attention. In one case, mutants were later shown to preexist selection (14, 28, 29, 44). For the system devised by Cairns and Foster (5), we suggest that reversion occurs by a multistep process initiated prior to selection and the appearance of stress-induced mutagenesis results from growth under strong selection.

Lifetime reproductive success in relation to morphology in the house sparrowPasser domesticus

SummaryIn this study we relate variation in lifetime reproductive success (LRS) of male and female house sparrowsPasser domesticusto morphological characteristics.Our analyses demonstrated no sex‐specific difference in the distribution ofLRS. The variance inLRSwas influenced mainly by variation in individual annual reproductive success, and to a lesser extent by variation in individual lifespan.Phenotypic traits explained a significant proportion of the variation inLRSin males, but not in females. The effect of male morphology onLRSoperated mainly through an effect on the number of recruiting daughters.The size of the patch of black feathers on the chest of males (badge size) and male bill length were both positively associated withLRS. Lifespan and bill length were positively related and reproductive success increased with badge size. In females, number of recruiting daughters was positively related to bill length, body mass and body condition index due to the positive effect of these traits on annual production of daughters.These results indicate that identifying factors causing the large individual variation inLRS, which is likely to be closely related to fitness, will be important to understand microevolutionary processes in this metapopulation, and hence their demographic feedbacks.

Reproductive success of hatchery‐produced and wild‐born brown trout in an experimental stream

Summary Although releases of hatchery‐produced salmonids to support conspecific wild populations have increased dramatically during recent decades, little information is available about the performance in the wild of hatchery fish and their offspring. Important factors determining the success and genetic outcomes of supportive breeding programmes include (i) the relative reproductive success of released hatchery fish in the wild, and (ii) the extent to which the propagation affects the variance in reproductive success in the population as a whole. We performed two field experiments on brown trout Salmo trutta from the River Dalälven in Sweden, where we examined reproductive success in an experimental stream. In experiment 1 we compared reproductive success between trout from a seventh‐generation hatchery stock of native origin and wild‐born trout from the river. In experiment 2, we compared reproductive success between seventh‐generation hatchery trout and hatchery‐reared trout derived from wild‐born parents. Individual reproductive success, based on the number of offspring assigned using microsatellite markers, was assessed on three occasions after reproduction: immediately after hatching and after the first and second growth seasons. In experiment 1 there were no significant differences in reproductive success between seventh‐generation hatchery trout and wild‐born trout. In experiment 2, males from wild‐born parents were more successful than males from the seventh‐generation hatchery stock, but this difference was not observed among females. There was some evidence for a positive association between body size and reproductive success among females but not males. For males, the number of mates was significantly associated with reproductive success, but this relationship was not evident among females. The variance in reproductive success was pronounced in both experiments, yielding estimates of the ratio between the genetically effective size and the census size of our experimental populations ranging from 0·12 to 0·59. Synthesis and applications. Our results suggest that the reproductive success in the wild of hatchery‐produced and wild‐born trout with a common genetic background may be rather similar. These findings, in combination with the pronounced variance in reproductive success observed among breeders, indicate that supportive breeding can be managed to increase not only the census but also the genetically effective size of small, endangered salmonid populations. However, to minimize negative effects of hatchery selection, it is important to give priority to the restoration of natural habitats and thereby increase the reproductive output from individuals in the wild.

The Matthew Effect: Evolutionary Implications

This article suggests that, in prehistoric man, the results of competition magnified the effect of small genetic differences between competing individuals, thereby increasing the differential in their relative reproductive success (difference amplification). This had the effect of accelerating the evolution of early man. The differential effect of success and failure on competing individuals led to “difference amplification”. These mechanisms can still be observed today. This model is relevant to psychotherapy with depressed clients.

Lizard Distributions and Reproductive Success in a Ponderosa Pine Forest

We assessed relative abundance, demographic, and reproductive success data for two lizard species in a Northern Arizona ponderosa pine forest, a fire-dependent system unnaturally modified by fire suppression over the past century. During May to October 1997-1999, we employed up to 70 pitfall arrays to sample lizards over 6990 array-days. At each array, we described macro-vegetative cover, stand, and microhabitat characteristics. Sceloporus graciosus responded to habitat variation at all three spatial scales. Adult S. graciosus were widely distributed among cover and stand types. However, reproductive success and hatchling abundance were highest in the most open cover (meadow) and stand (savannah) types, and lowest in pure ponderosa cover and dense ponderosa stands. Adult females replaced themselves annually only in meadows, savannahs, and forest with a deciduous component. Eumeces skiltonianus adults and juveniles were least abundant in meadows, but females replaced themselves each year in meadow and ponderosa-pinyon- juniper vegetative cover and in savannahs. Hatchlings were least abundant in intermediate- and high-density ponderosa stands, whereas juveniles of both species were most abundant in areas containing a deciduous tree component. Both species were present in plots having lower percent duff groundcover than at plots containing no lizards. Increased tree densities, canopy closure, and litter accumulation influenced distributions of both lizards. Furthermore, abundance and reproduction in these lizards were generally optimized in habitat with features most similar to that present prior to fire suppression activities and in areas containing a deciduous tree component.

The power of experiments for estimating relative reproductive success of hatchery-born spawners

An a priori power analysis was conducted to aid the design of experiments aimed at estimating the reproductive success of hatchery-born spawners relative to wild-born spawners using parentage assignment. Power was defined as the probability of rejecting the null hypothesis of equal reproductive contributions of hatchery- and wild-born spawners. A maximum likelihood estimator of relative reproductive success and its variance were derived. The estimator allowed multiple brood years of data, which was an extension of current approaches. Power increased with stock productivity, initial spawner abundance, fraction of recruits and spawners sampled, and the number of brood years examined. Power decreased with error variance used in the production function. Assuming a fixed total number of spawners, power was a concave-down function of the fraction of hatchery-born spawners. Using nominal values of productivity, error variance, and fraction of hatchery-born spawners, an experiment could achieve 0.8 power if it was run for at least 5 years or if it was applied to a stock with high initial female spawners (>200) and run for at least 2 years.

Alternative male life‐history tactics as potential vehicles for speeding introgression of farm salmon traits into wild populations

AbstractReleases of cultured organisms, such as farm Atlantic salmon (Salmo salar L.), threaten native biodiversity and the integrity of natural communities. Salmon escaping from sea farms, however, have relatively poor reproductive success, suggesting that the rate of spread of domesticated traits may be reduced. We now compare the relative reproductive success of males that mature precociously in freshwater (parr) and find that those of farm origin have higher breeding and fertilization success than wild and hybrid individuals. Specifically, hybrid parr had 57% and wild parr 25% the success of farm parr. Early maturing males could thus be important vehicles promoting introgression of domesticated and/or non‐native traits into wild populations and ultimately have long‐term impact on the genetic integrity of native populations.

The influence of slope aspect and soil type on immigration and emergence of some northern temperate dung beetles

Summary Soil type is a habitat factor that influences both adult habitat choice and reproductive success in tropical dung beetles. However, soil type habitat preferences of northern temperate dung beetles have not been studied, nor has their reproductive success in relation to habitat heterogeneity been investigated. The aim of this study was, firstly, to study the impact of slope aspect (southern vs. northern) and soil type (sand vs. clay) on immigration and subsequent emergence of dung beetle offspring. A second aim was to evaluate whether the soil type selection was reflected in reproductive success. The study was performed with cow dung during early summer in central Sweden. Beetle immigration was estimated using dung-baited pitfall traps and numbers of emerging beetles were assessed using specially designed emergence traps. Immigrating beetles collected represented 11 Aphodius species (Scarabaeidae), three Sphaeridium species (Hydrophilidae), and one Geotrupes species (Geotrupidae). Seven emerging species were caught, all from the genus Aphodius. Immigration was influenced by soil type, i.e. more individuals of A. ater, were caught on clay while more individuals of A. haemorrhoidalis were caught on sand. Slope aspect had no significant influence on immigration. Four species (A. ater, A. fimetarius, A. fossor and A. pusillus) dominated amongst the emerging beetles at both sites. Emergence was earlier on the south-facing slope for A. fimetarius and on both the south-facing slope and on sand for A. fossor. Emergence patterns were dependent on soil type. More individuals of A. ater emerged on clay while more individuals of A. fossor and A. pusillus emerged on sand. Slope aspect did not significantly influence the number of emerging beetles. We conclude that soil type influenced both adult habitat selection and reproduction, while slope aspect had less effect. Patterns of immigration and emigration corresponded for some species but not for others, hence selection of soil type may not directly correspond to reproductive success. Our results also indicate that Aphodius reproduction may be risky in wet clay soils because of mortality in over-wintering individuals.

Dominance Relationships Between Male Territorial Neighbors in the Beaugregory Damselfish (Stegastes leucostictus)

Using the permanently territorial beaugregory damselfish ( Stegastes leucostictus ), we examined behavioral differences between neighbors and how they relate to territory quality, male size, and social interactions. We manipulated territory quality by replacing some male's poor quality natural breeding sites with artificial sites. These artificial sites were known to rapidly increase a male's reproductive success. Three types of paired neighbors were tested: both males with high quality artificial sites (Group I); both neighbors with low quality natural sites (Group II); one male with a low quality natural site and his neighbor with a high quality artificial site (Group III). Because neighbors rarely interact, we stimulated interactions by placing a bottled male or a bottled female midway between the two breeding sites. The area between the 2 sites was rarely patrolled by either neighbor and we judged them to be outside of either male's territory. Although we found that both neighbors were in close proximity to each other while they simultaneously attacked a bottled male or courted a bottled female, the neighbors rarely interacted. Without one neighbor aggressively dominating the other neighbor, the neighbor that attacked or courted the bottled animal most intensively was termed 'dominant.' For pairs where both neighbors defended sites of similar quality (Group I and II), dominance was not related to male size. Reproductive success was only measured for Group I (both males with artificial sites) and relative reproductive success was not related to dominance. For heterogeneous pairs (Group III), dominance was related to territory quality (the male given the artificial site was always dominant when compared to his neighbor) but not male size. Irrespective of pair type (Groups I, II, or III), there was no inter-group differences in behavior among the dominants or among the subordinates. With the removal of the dominant individual, the remaining subordinates increased their aggressiveness toward bottled males and resembled the dominant individuals that were removed. Removing subordinate individuals caused no change in the behavior of remaining dominant individuals. Thus, the dominant males of all group types appeared to suppress the behavior of subordinates. We speculate that when neighbors have similar sites (Groups I and II), their past social interactions may be responsible for the development of the initial dominant-subordinate relationship. However, this dominant-subordinate relationship can be reversed by giving the subordinate male a higher quality breeding site ( i.e . Group III). We found no evidence that a subordinate's reproductive success was influenced by his more dominant neighbor and we speculate that it may influence his ability to secure a breeding site.

Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.

North Atlantic Oscillation (NAO) effects of climate on the relative importance of first and second clutches in a migratory passerine bird

summary Climatic variables are known to affect reproduction and survival in birds. Barn swallows Hirundo rustica L. are long‐distance migratory passerines that produce two broods in much of the European range. The relative importance of first and second broods for annual reproductive success in relation to a measure of general climatic conditions – the North Atlantic Oscillation (NAO) – was assessed during a long‐term study from 1970 to 2000. The size of first clutches increased with increasing NAO values, and clutch size increased during the study period. Brood size and hatching, fledging or breeding success did not show a significant temporal change, nor were they related significantly to NAO. However, in years with high NAO index values first broods were relatively larger than second broods compared to years with low NAO values. Similarly, the breeding success of first relative to second broods was larger in years with high NAO index values compared to years with low NAO values. The quality of offspring measured in terms of T cell‐mediated immune response at age 12 days was related to NAO, with offspring of first broods having stronger immune responses than offspring from second broods during years with high NAO values. Individual females showed patterns of change in brood size in response to change in NAO that paralleled the patterns observed at the population level. This provides evidence of phenotypic plasticity. Immigration to the study population increased following a year when annual productivity was caused mainly by fledglings from the first brood. This implies that increases in NAO increases the size of the barn swallow population through effects on the relative productivity of first broods.

To sea or not to sea: a brief review on salmon migration evolution

Since many salmonid species have the alternative life history strategies, they provide us a good opportunity to solve such a riddle. In a model, the anadromous life history of salmon may not be an evolutionarily stable state. If the gain in fitness from staying in a river exceeds the fitness from the sea, the fluvial life history can occur or vice versa. Some data may support these predictions. The relative reproductive success of migratory and fluvial females has latitudinal variation (so called geocline); the latter will be higher at the southern limits of the ranges, and conversely, the former will have higher fitness at the northern part, probably supporting the food availability hypothesis.

Developing Baltic cod recruitment models. I. Resolving spatial and temporal dynamics of spawning stock and recruitment for cod, herring, and sprat

The Baltic Sea comprises a heterogeneous oceanographic environment influencing the spatial and temporal potential for reproductive success of cod (Gadus morhua) and sprat (Sprattus sprattus) in the different spawning basins. Hence, to quantify stock and recruitment dynamics, it is necessary to resolve species-specific regional reproductive success in relation to size, structure, and distribution of the spawning stock. Furthermore, as species and fisheries interactions vary between areas, it is necessary to include these interactions on an area-specific basis. Therefore, area-disaggregated multispecies virtual population analyses (MSVPA) were performed for interacting species cod, herring (Clupea harengus), and sprat in the different subdivisions of the Central Baltic. The MSVPA runs revealed distinct spatial trends in population abundance, spawning biomass, recruitment, and predation-induced mortality. Results, when evaluated with respect to trends in population sizes from research surveys, were similar for the cod and sprat stocks but different for herring. Horizontal distributions from MSVPA runs and research surveys indicate that cod and sprat undergo migrations between basins during different life stages. This is an observation potentially influencing estimates for the different stock components but not affecting the overall stock sizes.

Statistical approaches to paternity analysis in natural populations and applications to the North Atlantic humpback whale.

We present a new method for paternity analysis in natural populations that is based on genotypic data that can take the sampling fraction of putative parents into account. The method allows paternity assignment to be performed in a decision theoretic framework. Simulations are performed to evaluate the utility and robustness of the method and to assess how many loci are necessary for reliable paternity inference. In addition we present a method for testing hypotheses regarding relative reproductive success of different ecologically or behaviorally defined groups as well as a new method for estimating the current population size of males from genotypic data. This method is an extension of the fractional paternity method to the case where only a proportion of all putative fathers have been sampled. It can also be applied to provide abundance estimates of the number of breeding males from genetic data. Throughout, the methods were applied to genotypic data collected from North Atlantic humpback whales (Megaptera novaeangliae) to test if the males that appear dominant during the mating season have a higher reproductive success than the subdominant males.

Developing Baltic cod recruitment models. I. Resolving spatial and temporal dynamics of spawning stock and recruitment for cod, herring, and sprat

The Baltic Sea comprises a heterogeneous oceanographic environment influencing the spatial and temporal potential for reproductive success of cod (Gadus morhua) and sprat (Sprattus sprattus) in the different spawning basins. Hence, to quantify stock and recruitment dynamics, it is necessary to resolve species-specific regional reproductive success in relation to size, structure, and distribution of the spawning stock. Furthermore, as species and fisheries interactions vary between areas, it is necessary to include these interactions on an area-specific basis. Therefore, areadisaggregated multispecies virtual population analyses (MSVPA) were performed for interacting species cod, herring (Clupea harengus), and sprat in the different subdivisions of the Central Baltic. The MSVPA runs revealed distinct spatial trends in population abundance, spawning biomass, recruitment, and predation-induced mortality. Results, when evaluated with respect to trends in population sizes from research surveys, were similar for the cod and sprat stocks but different for herring. Horizontal distributions from MSVPA runs and research surveys indicate that cod and sprat undergo migrations between basins during different life stages. This is an observation potentially influencing estimates for the different stock components but not affecting the overall stock sizes.

Parentage analysis in Chamaelirium luteum (L.) Gray (Liliaceae): why do some males have higher reproductive contributions?

Abstract Much of the contemporary study of adaptation in natural populations involves the regression of some component of fitness, usually survivorship or viability, on one or more characters of interest. It is difficult to apply this approach to measures of paternal reproduction, however, because paternity is typically estimated indirectly from genetic markers, rather than being measured directly from progeny counts. Here, we present maximum likelihood methods for modelling relative male reproductive success as a log-linear function of one or more potentially predictive features, as well as providing a framework for the assessment of pairwise (male:female) effects, as they affect male reproductive performance. We also provide nonparametric statistical tests for alternative models. Using this formulation, we examine the impact of inflorescence morphology on male reproductive success in Chamaelirium luteum L., and we also assess the importance of intermate distances between males and particular females. While male reproductive success and male inflorescence morphology are both quite variable, reproductive morphology does not appear to predict male reproductive success in this study. Intermate distance is an extremely effective predictor of pairwise success, however; but averaged over females, there is almost no net effect for different males.