Variation In Individual Traits Research Articles

Consequences of individual size variation for survival of an insect herbivore: an analytical model and experimental field testing using the red-legged grasshopper

Variation in body size exists within any natural population. Moreover, variation in this fundamental physiologically based trait often translates into variation in demographic rates. Here we explore the effects of variation in the initial body size of individuals on the mean survival trajectory of a generalist herbivore living in a seasonal environment. We first present the results from an individual-based model, which provided expectations for the form of the relationship between mean survival and standard deviation in initial size. We then develop a heuristic analytical model that captures the essentials of the influence of initial-size variation on mean survival to end of season. Both theoretical formulations demonstrate that as initial body size variation increases, mean survival might initially increase; however, this initial positive effect is eventually reversed, causing mean survival to fall steeply as size variation becomes high. We then test these qualitative predictions in the field by manipulating the magnitude of initial size variation in experimental populations of the generalist grasshopper, Melanoplus femurrubrum. We show good qualitative congruence between model predictions and experimental results. Because herbivore survival is strongly linked to the strength of food-web interactions, we suggest that adopting such a combined theoretical and empirical approach can provide a profitable avenue toward a full understanding of the interplay between individual trait variation and higher-level dynamics.

Breeding potential of durum wheat landraces from Jordan

A Jordanian durum wheat collection consisting of 132 landraces was evaluated in an arid and a semiarid location for 21 morphological and developmental traits. Phenotypic diversity indices (H') were calculated for traits, districts, and regions of collection. Average diversity for Jordan was 0.675 ± 0.05. The pattern of variation of individual traits varied among districts and among regions. Polymorphism was high for waxiness (H' = 0.95), lodging resistance (0.91), stem solidness (0.86), glume color (0.80), and fertility of the basal floret (0.80). However, H' estimates were relatively low for early growth vigor (0.49), seed color (0.44) and juvenile growth habit (0.19). A clinal pattern was observed for resistance to common bunt, Tillelia foetiila (H' = 0.73), stripe rust, Puccinia striiformis (H' = 0.74), and powdery mildew, Erysiphe graminis f.sp. tritici (H' = 0.63). The frequency of resistant entries increased from the xeric south to the mesic north. Average diversity for developmental traits (i.e., days to heading, days to maturity, and filling period) was significantly higher in the semiarid (H'= 0.847 ± 0.05) than in the arid (H'= 0.658 ± 0.12) location. A hierarchical analysis of variance indicated that significant differences for H' estimates existed among regions and among districts within regions of collection. Landraces and districts with high frequency of agronom-ically desirable traits have been identified.

Breeding potential of durum wheat landraces from Jordan I. Phenotypic diversity

A Jordanian durum wheat collection consisting of 132 landraces was evaluated in an arid and a semiarid location for 21 morphological and developmental traits. Phenotypic diversity indices (H) were calculated for traits, districts, and regions of collection. Average diversity for Jordan was 0.675 ± 0.05. The pattern of variation of individual traits varied among districts and among regions. Polymorphism was high for waxiness (H’= 0.95), lodging resistance (0.91), stem solidness (0.86), glume color (0.80), and fertility of the basal floret (0.80). However, H’ estimates were relatively low for early growth vigor (0.49), seed color (0.44) and juvenile growth habit (0.19). A clinal pattern was observed for resistance to common bunt, Tillelia foetiila (H’= 0.73), stripe rust, Puccinia striiformis (H’= 0.74), and powdery mildew, Erysiphe graminis f.sp. tritici (H’= 0.63). The frequency of resistant entries increased from the xeric south to the mesic north. Average diversity for developmental traits (i.e., days to heading, days to maturity, and filling period) was significantly higher in the semiarid (H= 0.847 ± 0.05) than in the arid (H= 0.658 ± 0.12) location. A hierarchical analysis of variance indicated that significant differences for H’ estimates existed among regions and among districts within regions of collection. Landraces and districts with high frequency of agronomically desirable traits have been identified.

An overview of life-history variation in female threespine stickleback

[The threespine stickleback superspecies has become a model for evolutionary studies of morphology, behaviour, early-life development and host–parasite relationships. Its potential value for studying life-history evolution is also great. Fourteen years ago, a review of female stickleback life-history illustrated both the potential of the system to inform life-history evolution, and the limitations of the data at the time. In the succeeding years much more information has become available, especially from northwestern North America. Additionally, much more information is now available for the ancestral marine stickleback, a deficiency that was highlighted in the first stickleback book. One purpose of this review was to update information on female life history in the species. To this end, variation in the major life-history correlates (reproductive effort, clutch size, egg size and age/size at reproduction) is described, and a description of geographical structuring of this variation is provided. A second goal was to go beyond variation in individual traits to explore variation in trait correlations. The review ends with an exploration of allometric relationships between life-history traits and female size., The threespine stickleback superspecies has become a model for evolutionary studies of morphology, behaviour, early-life development and host–parasite relationships. Its potential value for studying life-history evolution is also great. Fourteen years ago, a review of female stickleback life-history illustrated both the potential of the system to inform life-history evolution, and the limitations of the data at the time. In the succeeding years much more information has become available, especially from northwestern North America. Additionally, much more information is now available for the ancestral marine stickleback, a deficiency that was highlighted in the first stickleback book. One purpose of this review was to update information on female life history in the species. To this end, variation in the major life-history correlates (reproductive effort, clutch size, egg size and age/size at reproduction) is described, and a description of geographical structuring of this variation is provided. A second goal was to go beyond variation in individual traits to explore variation in trait correlations. The review ends with an exploration of allometric relationships between life-history traits and female size.]

Coevolution of slow–fast populations: evolutionary sliding, evolutionary pseudo-equilibria and complex Red Queen dynamics

We study the interplay of ecological and evolutionary dynamics in communities composed of populations with contrasting time-scales. In such communities, genetic variation of individual traits can cause population transitions between stationary and cyclic ecological regimes, hence abrupt variations in fitness. Such abrupt variations raise ridges in the adaptive landscape, where the populations are poised between equilibrium and cyclic coexistence and along which evolutionary trajectories can remain sliding for long times or halt at special points called evolutionary pseudo-equilibria. These novel phenomena should be generic to all systems in which ecological interactions cause fitness to vary discontinuously. They are demonstrated by the analysis of a predator-prey community, with one adaptive trait for each population. The eco-evolutionary dynamics of the system show a number of other distinctive features, including evolutionary extinction and two forms of Red Queen dynamics. One of them is characterized by intermittent bouts of cyclic oscillations of the two populations.

Female mate attraction in ornate tree lizards, Urosaurus ornatus: a multivariate analysis

Recent reviews of mate choice have concluded that this phenomenon is rare or nonexistent in lizards. However, direct tests of lizard mate choice are few and generally limited in scope. We present results of a mate choice experiment with Urosaurus ornatus in which two male lizards differing in morphology, colour and behaviour were given the opportunity to attract a female lizard. Pairwise comparisons of selected and unselected males revealed that variation in individual traits failed to account for much of the variation in mate attraction success. However, a multivariate analysis revealed that mate attraction was related to multiple cues from a male's phenotype: body mass and head size as well as body and tail coloration all contributed to mate attraction. We argue that the additive and interactive effects of several traits combined may be more important than single traits in mate choice. We suggest that mate choice studies should account for multivariate effects of male traits, and also allow mate attraction to occur over variable spatial and temporal scales, paralleling mate choice under natural conditions.

Unstructured Individual Variation and Demographic Stochasticity

Author(s): Kendall, Bruce E; Fox, Gordon A | Abstract: Demographic stochasticity increases the variance in the growth rate of small populations, and is an important factor to consider when predicting the fates of such populations. Unfortunately, the concept has been treated inconsistently. It is often defined verbally as representing chance variation among individuals in both traits (such as survival probability) and fates (such as whether the individual survived or not). In practice it is modeled as variation in fates only, with all individuals having identical underlying traits. In previous work we demonstrated that structured (but unmodeled) individual variability in survival traits can reduce the variance in population survivorship associated with demographic stochasticity, but that unstructured random variability in survival traits has no such effect. We implicitly generalized the latter result to fecundity, without offering proof. Robert et al. (2003) have demonstrated, using simulations, that unstructured individual variability in fecundity traits can increase the extinction risk of a small population when demographic stochasticity in fecundity is modeled as following a Poisson distribution. In this paper we extend our earlier theory to correct our mistaken speculations and analytically show the source of Robert et al.’s results. We also provide general predictions about the circumstances under which both structured and unstructured individual trait variation should either increase or decrease the magnitude of demographic stochasticity in the population.

Body size and sex allocation in simultaneously hermaphroditic animals

Sex allocation theory predicts that hermaphrodites optimally divide resources between male and female function, and this strategy may vary with a wide range of individual and population traits. We present a model of reproductive strategies for simultaneously hermaphroditic animals that incorporates multiple sex allocation tactics depending on the traits of an individual, its current mate, and the population at large. We examined the effect of resource variation on sex allocation in a sperm-storing population with two body-size classes. We found that an individual's sex allocation depends on its own size relative to its mate; when stored sperm is displaced exponentially, small animals (with fewer resources) invest a greater proportion of resources in male function than do large animals, and animals of either size invest more in male function when mating with a large mate than with a small mate. Optimal sex allocation depends on the size distribution in the population, the disparity of resources between size classes, the cost of filling a sperm storage organ, and the shape of the sperm displacement function. A function with S-shaped returns to sperm transfer results in a contrary finding: large animals invest more resources in male function than small animals when the cost of filling a sperm storage organ is high. Under many conditions, pronounced sex allocation differences between individuals result in similar proportions of sperm displaced and paternity gained. Thus, variation in individual traits within a population leads to multiple sex-allocation strategies that can produce equal outcomes in the game of sperm competition.

Morphological Uniformity Among Widely Disjunct Populations of the Rare "Copper Moss," Scopelophila cataractae (Pottiaceae)

Eight morphological characters of the gametophyte generation and three of the sporophyte generation were measured in 15 plants from each of 76 populations of the rare and geographically disjunctive moss, Scopelophila cataractae, in order to assess whether subtle differences exist between plants from widely separated populations. Plants were variable in all morphological traits, but most of the variation occurred among individual stems within populations and among populations within broad geographic regions. In spite of statistically significant differences between plants from widely disjunct regions (including different continents) for eight of the 11 morphological traits, the percentage of the total variation attributable to regional differences was minimal. Little regional variation in individual traits was corroborated by multivariate analyses including UPGMA clustering and principal component analysis. Furthermore, the degree and pattern of correlations among morphological traits were remarkably similar in populations of plants separated by thousands of miles. The general rarity and habitat specificity of S. cataractae throughout its range suggest that widely disjunct populations have been continuously separated. This, combined with the present analysis of morphology, suggests that morphological diversification may occur slowly in this moss. Relative to seed plants, most species of have broad geographic ranges. Less than 25% of the of the eastern United States, for example, are endemic even in the broad regional sense, with most taxa occupying remarkably broad ranges that include Europe and/ or Asia (Crum and Anderson 1981; Schuster 1983). Even in floristically rich areas such as the Ozarks, 90% of the are widespread elsewhere in the eastern United States and 70% occur also in the Old World (Crum and Anderson 1981). Indeed, on a worldwide basis, endemism at the specific level is low in mosses. It is common knowledge among moss monographers that many species occur disjunctively on several continents and that there is often little or no morphological differentiation between widely disjunct populations. These systematic and biogeographic observations have led some bryologists to hypothesize that many species of are geologically old and that presently disjunct populations of such species have undergone little or no morphological evolution over vast amounts of time (Crum 1972; Crum and Anderson 1981; Schuster 1983). Arguments in this regard often cite the observation that many intraspecific disjunctions in correspond to the same patterns that occur at the generic level in seed plants. Such patterns (e.g., eastern Asia-eastern North America) have been widely accepted as having derived from fragmentation of the Arctotertiary flora (Herzog 1926; Crum 1972). The likelihood of more recent long-range dispersal has also been discussed for some species (e.g., van Zanten 1984; van Zanten and Pocs 1981). In spite of the common perception of monographers that little morphological differentiation exists between widely disjunct populations of many mosses, there have been few quantitative studies to determine whether subtle patterns of regional variation do in fact occur. The ecologically unique mosses provide an especially good opportunity to address this issue. The copper include about ten species of and liverworts that exhibit an ecological association with substrates with higher than average concentrations of copper or other metals (Persson 1948, 1956; Shacklette 1967). In addition to the unusual habitat of the copper mosses, these species share the characteristic of having remarkably broad and highly disjunctive geographic distributions. Furthermore, most of the copper do not reproduce sexually (as evidenced by sporophyte formation) over large portions of their ranges. One such copper moss, Scopelophila cataractae (Mitt.) Broth., occurs disjunctively in central America and Mexico, the United States, Europe, the Himalayan Mountains, and southeast Asia including the Philippine Islands northward to Japan (Zander 1967). The species is extremely rare throughout its range. In the United States, for example, it occurs at one locality each in

Physiology of yield expression in sunflower

Abstract This paper evaluates currently available information on the physiology of sunflower (Helianthus annuus L.) in the context of field growth responses and the determination of crop yield. It deals with phenology, water economy, mineral nutrition, carbon fixation and partitioning, yield formation, and seed quality. Attention is drawn to information on intraspecific variation of individual traits to highlight the possibilities that exist for cultivar adaptation and improvement. Properties commonly attributed to this crop such as high photosynthetic capacity, profligate use of water and low water-use efficiency are evaluated.

Independence of Life History Parameters in Populations of Vaccinium angustifolium (Ericaceae)

PRITTS, M. P. AND J. F. HANCOCK (Department of Pomology, Cornell University, Ithaca, NY 14853 and Department of Horticulture, Michigan State University, East Lansing, MI 48824). Independence of life history parameters in populations of Vaccinium angustifolium (Ericaceae). Bull. Torrey Bot. Club. 111: 451-461. 1984.-Many predictions concerning optimal patterns of resource partitioning imply that limiting resources are shared among several life history components, and this results in trade-offs (negative correlations) among the competing components. This implication was examined by measuring covariation among several life history traits and yield components in 13 diverse populations of Vaccinium angustifolium Ait. A principal component analysis revealed little covariation among life history parameters even though there was substantial variation in individual traits. Yield components also exhibited independent or slightly additive interactions and only one negative relationship was observed. Environmental factors were also strongly associated with life history and demographic variables. These results suggested that resource sharing does not always occur among life history parameters possibly because 1) components of growth and reproduction often are regulated by different limiting resources, 2) shared resources may not be limiting, and 3) natural selection may favor those individuals which minimize resource sharing through asynchronous periods of component development.