Relative Reproductive Rate Research Articles

Kenyan Free-Tailed Bats Demonstrate Seasonal Birth Pulse Asynchrony with Implications for Virus Maintenance

Ecological information on wildlife reservoirs is fundamental for research targeting prevention of zoonotic infectious disease, yet basic information is lacking for many species in global hotspots of disease emergence. We provide the first estimates of synchronicity, magnitude, and timing of seasonal birthing in Mops condylurus, a putative ebolavirus host, and a co-roosting species, Mops pumilus (formerly Chaerephon pumilus). We show that population-level synchronicity of M. condylurus birthing is wide (~ 8.5 weeks) and even wider in M. pumilus (> 11 weeks). This is predicted to promote the likelihood of filovirus persistence under conditions of bi-annual birthing (two births per year). Ecological features underlying the magnitude of the birth pulse—relative female abundance (higher than expected for M. condylurus and lower for M. pumilus, based on literature) and reproductive rate (lower than expected)—will have countering effects on birthing magnitude. Species-specific models are needed to interpret how identified birth pulse attributes may interact with other features of molossid ebolavirus ecology to influence infection dynamics. As a common feature of wildlife species, and a key driver of infection dynamics, detailed information on seasonal birthing will be fundamental for future research on these species and will be informative for bat-borne zoonoses generally.

Effects of motion in structured populations.

In evolutionary processes, population structure has a substantial effect on natural selection. Here, we analyse how motion of individuals affects constant selection in structured populations. Motion is relevant because it leads to changes in the distribution of types as mutations march towards fixation or extinction. We describe motion as the swapping of individuals on graphs, and more generally as the shuffling of individuals between reproductive updates. Beginning with a one-dimensional graph, the cycle, we prove that motion suppresses natural selection for death-birth (DB) updating or for any process that combines birth-death (BD) and DB updating. If the rule is purely BD updating, no change in fixation probability appears in the presence of motion. We further investigate how motion affects evolution on the square lattice and weighted graphs. In the case of weighted graphs, we find that motion can be either an amplifier or a suppressor of natural selection. In some cases, whether it is one or the other can be a function of the relative reproductive rate, indicating that motion is a subtle and complex attribute of evolving populations. As a first step towards understanding less restricted types of motion in evolutionary graph theory, we consider a similar rule on dynamic graphs induced by a spatial flow and find qualitatively similar results, indicating that continuous motion also suppresses natural selection.

Relative live weight, fleece weight and reproductive rate of farmed feral sheep (Ovis aries L.)

ABSTRACTA sample of feral Hokonui, Campbell Island and Raglan sheep were captured after living feral > 40 years and managed on North and South Island farms alongside domesticated breeds for 28 years to understand relative performance in various traits. Fleece weight was significantly different (P < 0.001) between breeds (Hokonui, 1.48 kg; Campbell Island, 1.50 kg; and Raglan, 2.16 kg), lower than both domesticated Saxon Merino (3.26 kg) and Perendale (3.29 kg) in the North Island. Live weight was significantly different (P < 0.001) between flocks (Hokonui, 39.4 kg; Campbell Island, 38.6 kg; and Raglan, 43.0 kg), but intermediate between Saxon Merino (35.5 kg) and Perendale (51.6 kg). Reproductive rate depended on live weight and was also intermediate between the domesticated breeds, being significantly greater in the South Island (P < 0.001). Decreased fleece weight was common to farmed feral sheep from three different origins, suggesting this trait may have been an advantage during a feral existence.

Sex-specific incompatibility generates locus-specific rates of introgression between species.

Disruption of interactions among ensembles of epistatic loci has been shown to contribute to reproductive isolation among various animal and plant species. Under the Bateson–Dobzhansky–Muller model, such interspecific incompatibility arises as a by-product of genetic divergence in each species, and the Orr–Turelli model indicates that the number of loci involved in incompatible interactions may “snowball” over time. We address the combined effect of multiple incompatibility loci on the rate of introgression at neutral marker loci across the genome. Our analysis extends previous work by accommodating sex specificity: differences between the sexes in the expression of incompatibility, in rates of crossing over between neutral markers and incompatibility loci, and in transmission of markers or incompatibility factors. We show that the evolutionary process at neutral markers in a genome subject to incompatibility selection is well approximated by a purely neutral process with migration rates appropriately scaled to reflect the influence of selection targeted to incompatibility factors. We confirm that in the absence of sex specificity and functional epistasis among incompatibility factors, the barrier to introgression induced by multiple incompatibility factors corresponds to the product of the barriers induced by the factors individually. A new finding is that barriers to introgression due to sex-specific incompatibility depart in general from multiplicativity. Our partitioning of variation in relative reproductive rate suggests that such departures derive from associations between sex and incompatibility and between sex and neutral markers. Concordant sex-specific incompatibility (for example, greater impairment of male hybrids or longer map lengths in females) induces lower barriers (higher rates of introgression) than expected under multiplicativity, and discordant sex-specific incompatibility induces higher barriers.

More efficient mastication allows increasing intake without compromising digestibility or necessitating a larger gut: Comparative feeding trials in banteng ( Bos javanicus) and pygmy hippopotamus ( Hexaprotodon liberiensis)

The digestion of plant material in mammalian herbivores basically depends on the chemical and structural composition of the diet, the mean particle size to which the forage is processed, and the ingesta retention time. These different factors can be influenced by the animal, and they can presumably compensate for each other. The pygmy hippopotamus, a non-ruminating foregut fermenter, has longer mean retention times than ruminants; however hippos do not achieve higher (fibre) digestibilities on comparable diets, which could be due to ineffective mastication. We performed feeding trials with six pygmy hippos ( Hexaprotodon liberiensis) and six banteng cattle ( Bos javanicus) on a grass diet. As predicted, both species achieved similar dry matter, organic matter, crude protein and gross energy digestibilities. However, neutral and acid detergent fibre digestibility was lower in pygmy hippos. Apparently, in these species, fibre digestibility was more influenced by particle size, which was larger in pygmy hippos compared to banteng, than by retention time. In spite of their higher relative food intake, the banteng in this study did not have greater relative gut fills than the hippos. Ruminants traditionally appear intake-limited when compared to equids, because feed particles above a certain size cannot leave the rumen. But when compared to nonruminating foregut fermenters, rumination seems to free foregut fermenters from an intrinsic food intake limitation. The higher energy intakes and metabolic rates in wild cattle compared to hippos could have life-history consequences, such as a higher relative reproductive rate.

Rain, prey and predators: climatically driven shifts in frog abundance modify reproductive allometry in a tropical snake

To predict the impacts of climate change on animal populations, we need long-term data sets on the effects of annual climatic variation on the demographic traits (growth, survival, reproductive output) that determine population viability. One frequent complication is that fecundity also depends upon maternal body size, a trait that often spans a wide range within a single population. During an eight-year field study, we measured annual variation in weather conditions, frog abundance and snake reproduction on a floodplain in the Australian wet-dry tropics. Frog numbers varied considerably from year to year, and were highest in years with hotter wetter conditions during the monsoonal season ("wet season"). Mean maternal body sizes, egg sizes and post-partum maternal body conditions of frog-eating snakes (keelback, Tropidonophis mairii, Colubridae) showed no significant annual variation over this period, but mean clutch sizes were higher in years with higher prey abundance. Larger females were more sensitive to frog abundance in this respect than were smaller conspecifics, so that the rate at which fecundity increased with body size varied among years, and was highest when prey availability was greatest. Thus, the link between female body size and reproductive output varied among years, with climatic factors modifying the relative reproductive rates of larger (older) versus smaller (younger) animals within the keelback population.

Chance, Time Allocation, and The Evolution of Adaptively Flexible Sex Role Behavior

An alternative to classic sexual selection hypotheses for sex differentiated pre-mating behavior is that time available for mating-as individuals experience it-along with fitness differences among alternative potential mates, induces choosy versus indiscriminate mating behavior. This alternative hypothesis says that selection has acted so that all individuals flexibly express fitness-enhancing choosy, indiscriminate, and competitive mating behavior, induced by time-varying life histories, environmental and social cues. Key predictions of DYNAMATE, the formal model of adaptively flexible sex role behavior of individuals of both sexes within dynamically changing populations, include: (1) All individuals regardless of sex assess likely fitness outcomes from mating with alternative potential mates before expressing choosy or indiscriminate behavior. (2) Males and females express adaptively flexible, choosy and indiscriminate behavior so that individuals may change their behavior-from moment to moment-to fit dynamically changing circumstances. (3) Indiscriminate behavior of males and (4) choosy behavior of females would often be maladaptive even in species with greater female than male parental investment, when females have longer latencies to receptivity to re-mating than males, and when the relative reproductive rate of males is greater than in females. (5) Whether or not females show choosy behavior will not affect whether or not males exhibit choosy or indiscriminate behavior, and vice versa. (6) When other model parameters are equal, the proportion of individuals of a given sex expressing choosy or indiscriminate mating behavior is a function of the distribution of fitness ratios (a distribution of all fitness differences that would be conferred on an individual by mating with any two sequentially or simultaneously encountered alternative potential mates). (7) Whether same-sex individuals behaviorally compete is a function of the fitness that would be conferred if the strategist won access to a potential mate, but not a function of relative reproductive rate or its proxy, the operational sex ratio. We call for re-evaluation of sex differences in choosy, indiscriminate, and competitive behavior under strong experimental controls that level the ecological playing fields of males and females, i.e., under experimental conditions informing the mechanisms of phenotypic expression. We end with comments on the classic question of questions: why are the sexes as they are?

FOOD WEB CHAOS WITHOUT SUBCHAIN OSCILLATORS

A basic food web of four species is considered, of which there is a bottom prey X, two competing predators Y, Z on X, and a super predator W only on Y. The main finding is that population chaos does not require the existence of oscillators in any subsystem of the web. This minimum population chaos is demonstrated by increasing the relative reproductive rate of Z alone without alternating any other parameter nor any nullcline of the system. It occurs as the result of a period-doubling cascade from a Hopf bifurcation point. The method of singular perturbation is used to determine the Hopf bifurcation involved as well as the parameter values.

Estimation of Reproductive Rates of Burrowing Owls

Obtaining reliable estimates of absolute and relative reproductive rates is challenging for avian species whose nests are difficult to observe, such as the burrowing owl (Athene cunicularia). We compared methods for estimating reproductive rates of burrowing owls, defined as the number of 21- to 28-day-old young per successful nest. We compared observations using (1) the mean and (2) the maximum number of young observed during 5 30-min observation periods, and (3) the maximum number of young videotaped during 2-hr video surveillance. We evaluated the reliability of these methods with the known number of young present in nest boxes. All 3 methods performed poorly as estimators of absolute reproductive rates (absolute bias >23%, root mean square error [RMSE] >42%). Video surveillance performed most poorly of the 3, with a high incidence of failing to detect any young at successful nests. The maximum number of young observed from direct nest observations was correlated with the known number of young (r=0.82 ± 0.13, n = 21) and provided more reliable estimates of relative than absolute reproductive rates. The mean number of young observed from direct observations was correlated with the known number of young (r = 0.64 ± 0.18, n = 21), but had both higher bias and lower precision than the maximum number observed for estimation of relative reproductive rates. Our results suggest that using counts of young observed outside of the nest burrow may lead to incorrect conclusions on factors affecting reproductive rates. When counts are the basis of inference, the effort researchers use at each nest should be standardized and reported. Further work on field methods that allow estimation of detection probability, or ensuring that all young are observed, will be imperative in providing reliable estimates.

Testing hypotheses of aging in long-lived painted turtles ( Chrysemys picta)

For 38 of the past 50 years, Painted Turtles were studied on the University of Michigan's E.S. George Reserve in southeastern Michigan. We compared age specific body sizes, reproductive traits and survival of Painted Turtles ranging from 9 to 61 years of age to test contrasting predictions of the Relative Reproductive Rate and Senescence Hypotheses of aging. Indeterminate growth (i.e. continued body growth of adults) was important in increasing reproductive output of older turtles; however, growth rate of the oldest age-group was reduced compared to that of younger adults. Although clutch size and among year reproductive frequency did not increase with age, within year reproductive frequency (production of second clutches), egg size, and hatchling size did. Nest predation rates and the proportion of surviving nests that produced hatchlings were similar among age groups, and embryo mortality in nests was not related to age. Survivorship of males was less than that of females, and survivorship of the oldest group of females was not statistically different from that of a younger group of females. No decline in reproductive output or survivorship was detected in the oldest females as predicted by the Senescence Hypothesis. Thus, the majority of data on reproductive traits and survivorship support the Relative Reproductive Rate Hypothesis. We also compared Painted Turtles to Blanding's Turtles, another species studied on the E.S. George Reserve. That Painted Turtles exhibit indeterminate growth whereas Blanding's Turtles do not, appears to be a primary mechanism for some differences between species in the relationships between reproductive traits and age. An important mechanism for increasing reproductive output in both species was increased reproductive frequency in older females. Painted Turtles also increased offspring quality (egg and hatchling size) with age, whereas Blanding's Turtles did not. Compared to younger individuals, there was no reduction in survivorship in the oldest Painted Turtles and survivorship increased in the oldest Blanding's Turtles.

Hypotheses of aging in a long-lived vertebrate, Blanding's turtle (Emydoidea blandingii).

For 35 of the past 47 years, Blanding's turtles were studied on the University of Michigan's E.S. George Reserve in southeastern Michigan. Blanding's turtle is one of the longest-lived emydid turtles with individuals reaching ages greater than 75 years. We compared body sizes, reproductive traits and survival of Young, Middle, and Oldest age groups of Blanding's turtles to test predictions from two contrasting hypotheses of aging. The relative reproductive rate hypothesis predicts traits that increase the reproductive output or survival rates of older compared to younger individuals, whereas the senescence hypothesis predicts a reduction in reproductive output or survival in older versus younger individuals. Body size did not increase with age among groups; therefore, indeterminate growth was not a mechanism for increased reproductive output of the oldest individuals. Survivorship, reproductive frequency and size-adjusted mean clutch size were all higher in the Oldest age group compared to the younger age groups. Nest predation rate was highest in the Young age group compared to either group of older turtles. In nests that survived predation, the proportion of nests that failed entirely due to developmental problems was lowest in the Young, intermediate in the Middle, and highest in the Oldest age group. Successful nests produced similar numbers of hatchlings and similar sized hatchlings in all three age groups. Traits such as egg and offspring size, and offspring produced per nest did not support either the relative reproductive rate or the senescence hypothesis of aging. Increased embryo mortality in nests of older females compared to younger turtles supports predictions from the senescence hypothesis. Three traits; increased clutch size, reproductive frequency, and survivorship of individuals in the Oldest age group compared to younger turtles support the relative reproductive rate hypothesis for evolution of longevity.

Oak canopy effects on the distribution patterns of two annual grasses: the role of competition and soil nutrients

Within the oak woodlands of California there is often a distinct shift in the botanical composition between the open grassland and the herbaceous understory beneath oak canopy. Botanical sampling at two woodland sites indicated that the annual grass Bromus diandrus was dominant under deciduous blue oak canopy, while a congener, Bromus hordeaceus, was dominant in open grassland. We examined the relative importance of congeneric competition and edaphic factors in creating these differences in species distribution in two separate field experiments that manipulated both congeneric and intraspecific competition, as well as soil type. We used the demographic measure of relative reproductive rate as an index of population growth. In general, demographic performance correctly predicted the distribution of the two annual grasses in the field. Our results indicate that reduced abundance of B. hordeaceus under canopy reflects the negative effects of competition with B. diandrus. In contrast, B. diandrus is little affected by competition from B. hordeaceus. The reduced abundance of B. diandrus in open grassland may result, in part, from its inability to adapt as well as B. hordeaceus to lower nutrient availability in soils of the open grassland.

Fitness consequences of genetically engineered herbicide and antibiotic resistance in Arabidopsis thaliana.

Researchers have often invoked the concept of metabolic drain to explain the lower growth rates of bacteria containing plasmids that confer antibiotic resistance. This idea posits that the energetic input needed to produce detoxifying enzymes diverts resources from clonal reproduction. In this paper we examine whether the concept of metabolic drain can be applied successfully to plants that differ from bacteria in several key aspects including their relative genome size and reproductive rate. We have conducted a field experiment using mutant and transgenic Arabidopsis thaliana that allows the comparison of genotypes differing by a single gene conferring resistance to either the herbicide chlorsulfuron or the antibiotic kanamycin. In addition to testing whether these traits reduce fitness, this experiment was conducted at two levels of resource availability to examine whether costs of resistance are sensitive to environmental quality. We found that herbicide-resistant individuals produced 26% fewer seeds than susceptible counterparts. However, contrasting published results in bacterial systems, the fecundity of individuals was completely unaffected by the expression of an introduced antibiotic resistance gene. The fitness cost associated with chlorsulfuron resistance was greater in nutrient-poor conditions relative to nutrient-rich conditions for comparisons involving mutant, but not transgenic, genotypes.

Cytoplasmic Incompatibility and Population Structure

Wolbachiais a maternally inherited bacterial infection common in many insects. These bacteria cause cytoplasmic incompatibility, in which a cross between an infected male and an uninfected female is sterile. Infected females are always fertile, suggesting that an infected male produces a sterilizing product against which infected females are protected. This sterility trait is an evolutionary puzzle because it acts in males, but males never transmit the parasites. Previous work has suggested that the parasite gains by reducing the fecundity of uninfected females, thereby increasing the relative reproductive rate of infected females. This argument depends on kin selection effects: the parasite in the male does not reproduce, but can aid related parasites in neighbouring females. Formal population genetic models have failed to confirm the verbal kin selection models. Those models assumed pleiotropic gene action whereby incompatibility evolves as a correlated effect of other fitness components. A formal model presented here supports the original kin selection theories. This new model also suggests an explanation for observed variation in the degree of incompatibility among Wolbachiastrains isolated from Drosophila simulans.

RAPD assessment of California phylloxera diversity

AbstractGrape phylloxera, Daktulosphaira vitifoliae Fitch, is a parthenogenetic, aphid‐like pest which attacks the roots and leaves of many Vitis L. species. Feeding on the roots of V. vinifera L. cultivars leads to decreased plant productivity and eventual death. Isolates of phylloxera have been grouped into ‘biotypes’ based on the aggressiveness of their feeding behaviour, relative reproductive rates, and abilities to cause decline on V. vinifera and the grape rootstock AXR1. The goal of our research was to determine whether these bio‐type definitions were reflected in the genetic diversity among laboratory‐cultured colonies of Californian phylloxera. Thirteen phylloxera isolates, encompassing biotypes A, B and non‐A or ‐B types based on their feeding and reproduction, were analysed using the RAPD‐PCR method. Results indicate that there were genetic differences among isolates and that there was as much polymorphism within biotypes as among biotypes. This is surprising in a parthenogenetic organism and leads us to suggest that there have been multiple introductions of phylloxera into California, that phylloxera are not obligately parthenogenetic, or that there are other mechanisms whereby phylloxera may evolve relatively rapidly.

Temperature differentially affects male and female reproductive rates in the sand goby: consequences for operational sex ratio

The influence of temperature on the relative reproductive rates of male and female sand gobies (Pomatoschistus minutus) was measured in aquarium experiments, with naturally changing as well as constant temperatures over the entire reproductive season. In this fish species the male builds a nest and cares for the eggs until hatching. Reproductive rate increased with increasing water temperature in both sexes, but more strongly among males. This reflects a difference in developmental rates between eggs while still unfertilized in the female ovary and after fertilization in the care of the male, respectively. Under constant temperature, there was still a seasonal effect on male reproductive rate, with incubation time decreasing over the season. Calculations based on egg densities and sizes of natural nests showed that males were able to care for the clutches of two average females simultaneously. Combining information about the differential effects of temperature on the reproductive rates of males and females, and on the egg-receiving capacity of the nests provided by the males, a male bias in the operational sex ratio is predicted to arise and increase over the season.

Prospects for Sex Role Reversal in Teleost Fishes

Teleost fishes, by virtue of their diverse reproductive modes, offer an opportunity to address general questions about the evolution of sex differences. A comparison of the reproductive rates of males and females within a species or population provides an empirical basis for predicting which sex will compete more intensely for access to mates and thus be subject to stronger sexual selection: it will be the sex with the higher maximum reproductive rate. In order to assess relative reproductive rates in teleost fishes, and to test this principle, four reproductive measures are needed for each species or population: (1) maximum female clutch size, (2) minimum female interclutch interval, (3) maximum male brood size (relative to clutch size), and (4) minimum interbrood interval for males (relative to interclutch interval). This reproductive rates approach should reveal more examples of sex role reversal in teleosts and could contribute to the development of hitherto largely unformulated generalisations about sex differences in teleost fishes.

Group Selection, Population Growth Rate, and Competitive Ability in the Flour Beetles, Tribolium Spp.

This is a report of an empirical study of competition between a laboratory strain of Tribolium confusum and populations of T. castaneum selected for increased and decreased productivity by group and individual selection. A pronounced inverse relationship between productivity and competitive ability was observed: fast growing T. castaneum populations had the smallest effect on the ability of T. confusum to recruit adults and slow—growing populations had the largest effect. The average duration of fast—growing T. castaneum populations was prolonged by competition but slow—growing populations were not affected in this regard. Approximately half of the slow—growing populations were facilitated in the production of adults by the presence of a competitor. The data suggest that individual fitness, measured as relative reproductive rate, and population fitness, measured as persistence, may be in conflict. The relevance of these findings to group and individual selection in natural populations is discussed.

Comparative Dynamics of a Single-Host Aphid. I. The Evidence

SUMMARY (1) This paper compares the dynamics of thimbleberry aphid on its wild perennial host at different parts of its geographical range, and examines the external factors which restrict both the dynamics and the range. The insect occurs along the Pacific coast from British Columbia to California. (2) In any one region, different populations have sharply different densities, predation loads and lengths of season, but successive generations are well synchronized in all populations of the region. (3) Population dynamics in California are similar to those further north, but the insects' temperature requirements are adjusted to local conditions. (4) The edge of the range is determined by the time (three generations) needed to maintain existing populations in every season, plus the extra time (two generations) taken to cross gaps of 1 km or more in the distribution of host plants. Populations at the edge of the range are as dense and persistent as those at the centre. (5) Egg hatch is closely timed to bud break in the host plant. The relative survival and reproductive rates of early- and late-hatching fundatrices are compared. (6) Laboratory experiments show that fecundity and proportion of sexual males are determined by host plant quality and by non-genetical maternal effects. There is little or no genetical variation. (7) The density-dependent reduction in fecundity is due to competition between adult mothers, and is equally severe in different populations.

Associated growth of wheat and annual ryegrass. 2. Effect of varying the time of ryegrass germination in stands of wheat

In a field experiment, wheat cv. Gamenya and annual ryegrass cv. Wimmera were sown in four proportions, 80W : 20R, 60W : 40R, 40W : 60R, 20W : 80R, at a total density of 300 plants m-2 and in which a high level of nitrogen fertilizer application was maintained. Ryegrass was sown 17 days before, simultaneously with, and 17 days after wheat. At the simultaneous sowing there were also pure cultures of wheat and ryegrass; pure culture data for ryegrass corresponding to all the germination treatments were obtained in a supplementary experiment. All treatments were harvested on five occasions. Observations were made on tiller numbers, yield of dry matter, seed numbers and the yield components of wheat. There were marked effects of early and simultaneous sowing of ryegrass and of proportions; the results also showed interactions between the later sowings and proportions. In all treatments wheat tiller numbers rose to a maximum and declined to about half after about 100 days. A similar rise and fall was observed in the early and simultaneous germination of ryegrass, but not in the late one. In ryegrass, tiller numbers were much greater than in wheat, and the rate of decline was not as marked. In the late germination treatment ryegrass development and growth were seriously depressed. With respect to wheat, seed yield and ear numbers per unit area in the early and simultaneous sowings were less, while ears and grains per plant were greater in the presence of ryegrass than in pure culture. In ryegrass, seed production was highest in the early and least in the late treatments and was depressed as the proportion of wheat was increased; even in the treatment with the lowest proportion of ryegrass, seed numbers of ryegrass remained high. Relative reproductive rates showed a consistent pattern with time of sowing and with proportion, and the results suggest that control of ryegrass seed numbers cannot be achieved by manipulating planting treatments but requires positive intervention. Relative crowding coefficients (k) calculated from the data suggest that wheat was the stronger competitor. The results are discussed in terms of the competitive effects between species and the likelihood that wheat has the greater competitive ability. As in the previous study, it was noted that effects of competition were discernible at 28 days.