Analyses Of Life History Evolution Research Articles

Integrating Causal and Evolutionary Analysis of Life-History Evolution: Arrival Date in a Long-Distant Migrant

In migratory species, the timing of arrival at the breeding grounds is a life-history trait with major fitness consequences. The optimal arrival date varies from year-to-year, and animals use cues to adjust their arrival dates to match this annual variation. However, which cues they use to time their arrival and whether these cues actually predict the annual optimal arrival date is largely unknown. Here, we integrate causal and evolutionary analysis by identifying the environmental variables used by a migratory songbird to time its arrival dates and testing whether these environmental variables also predicted the optimal time to arrive. We used 11 years of male arrival data of a pied flycatcher population. Specifically, we tested whether temperature and normalized difference vegetation index (NDVI) values from their breeding grounds in the Netherlands and from their wintering grounds in Ivory Coast explained the variation in arrival date, and whether these variables correlated with the position of the annual fitness peak at the breeding grounds. We found that temperature and NDVI, both from the wintering and the breeding grounds, explained the annual variation in arrival date, but did not correlate with the optimal arrival date. We explore three alternative explanations for this lack of correlation. Firstly, the date of the fitness peak may have been incorrectly estimated because a potentially important component of fitness (i.e., migration date dependent mortality en route or directly upon arrival) could not be measured. Secondly, we focused on male timing but the fitness landscape is also likely to be shaped by female timing. Finally, the correlation has recently disappeared because climate change disrupted the predictive value of the cues that the birds use to time their migration. In the latter case, birds may adapt by altering their sensitivity to temperature and NDVI.

Connecting species’ geographical distributions to environmental variables: range maps versus observed points of occurrence

Connecting the geographical occurrence of a species with underlying environmental variables is fundamental for many analyses of life history evolution and for modeling species distributions for both basic and practical ends. However, raw distributional information comes principally in two forms: points of occurrence (specific geographical coordinates where a species has been observed), and expert‐prepared range maps. Each form has potential short‐comings: range maps tend to overestimate the true occurrence of a species, whereas occurrence points (because of their frequent non‐random spatial distribution) tend to underestimate it. Whereas previous comparisons of the two forms have focused on how they may differ when estimating species richness, less attention has been paid to the extent to which the two forms actually differ in their representation of a species’ environmental associations. We assess such differences using the globally distributed avian order Galliformes (294 species). For each species we overlaid range maps obtained from IUCN and point‐of‐occurrence data obtained from GBIF on global maps of four climate variables and elevation. Over all species, the median difference in distribution centroids was 234 km, and median values of all five environmental variables were highly correlated, although there were a few species outliers for each variable. We also acquired species’ elevational distribution mid‐points (mid‐point between minimum and maximum elevational extent) from the literature; median elevations from point occurrences and ranges were consistently lower (median −420 m) than mid‐points. We concluded that in most cases occurrence points were likely to produce better estimates of underlying environmental variables than range maps, although differences were often slight. We also concluded that elevational range mid‐points were biased high, and that elevation distributions based on either points or range maps provided better estimates.

Population and colony structure of an ant with territorial males, Cardiocondyla venustula

BackgroundMany species of social insects have large-scale mating and dispersal flights and their populations are therefore often relatively homogenous. In contrast, dispersal on the wing appears to be uncommon in most species of the ant genus Cardiocondyla, because its males are wingless and the winged queens mate in their natal nests before dispersing on foot. Here we examine the population structure of C. venustula from South Africa. This species is of particular interest for the analysis of life history evolution in Cardiocondyla, as it occupies a phylogenetic position between tropical species with multi-queen (polygynous) colonies and fighting males and a Palearctic clade with single-queen colonies and mutually peaceful males. Males of C. venustula exhibit an intermediate strategy between lethal fighting and complete tolerance – they mostly engage in non-lethal fights and defend small territories inside their natal nests. We investigated how this reproductive behavior influences colony and population structure by analyzing samples on two geographic scales in South Africa: a small 40 × 40m2 plot and a larger area with distances up to 5 km between sampling sites in Rietvlei Nature Reserve near Pretoria.ResultsColonies were found to be facultatively polygynous and queens appear to mate only with a single male. The extraordinarily high inbreeding coefficient suggests regular sib-mating. Budding by workers and young queens is the predominant mode of colony-founding and leads to high population viscosity. In addition, some queens appear to found colonies independently or through adoption into foreign nests.ConclusionWhile C. venustula resembles tropical Cardiocondyla in queen number and mating frequency, it differs by the absence of winged disperser males. Dispersal by solitary, mated queens on foot or by short flights and their adoption by alien colonies might promote gene flow between colonies and counteract prolonged inbreeding. The abundance of suitable habitat and the high density of nests facilitate the spread of this species by budding and together with the apparent resistance against inbreeding make it a highly successful pioneer species and invader of degraded and man-made habitats.

EAT WELL TO LIVE LONG

![Figure][1] The theory that trade-offs exist between longevity and performance is a pervasive paradigm in analyses of life-history evolution. However, in the case of the naturally occurring indy mutant Drosophila , lifespan has been doubled without decreases in fitness; these flies are both

The effects of ecology on life history strategies and metabolic disturbances during development: an example from the African bovids

Life history theory predicts environmental factors to affect changes in life history strategies. However, owing to the interrelationships between body mass and life history variables, it is difficult to discern causal relationships, especially in large-bodied mammals and using a comparative approach. The situation is exacerbated in palaeobiological studies, where many of the variables cannot be observed directly. Specifically, mortality risk has been identified as one of the most important factors determining life history strategies, but its assessment is difficult. This hampers analyses of life history evolution. This study thus explored the possibility to extract previously untapped information from hard tissue, i.e. teeth, which may be useful for life history reconstruction. Histological sections of 25 molars of bovids, representing all subfamilies and spanning a wide range of body masses, were analysed with regard to: (i) molar crown formation times in relation to female body mass and gestation length, and (ii) metabolic disturbances from early to late forming teeth in relation to habitat type occupied, diet consumed and habitual walking style employed. It was found that molar crown formation times in bovids are highly correlated with gestation length once the effects of body mass have been removed. This differs from primates and indicates similarities in pre- and postnatal growth rates in these mammals. Closed-habitat species exhibit relatively fewer disturbances during development than open-country species, but the reverse holds for adult specimens. This accords with what is known about the ecological and behavioural adaptations of the species and is predicted by life history theory. It could thus be confirmed that teeth may provide vital information about life history variables. Exploitation of this information will allow hypotheses to be tested regarding the evolutionary changes in life history strategies of extinct species. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 271–279.

Life history consequences of fixed costs of reproduction

The distinction between fixed and variable factors of production and their corresponding costs has long played a fundamental role in economic theory. However, in analyses of life history evolution a distinction between fixed and variable costs of reproduction has not been made. In this paper, I discuss these concepts and analyze some effects of fixed costs of reproduction on reproductive decisions. While some fitness functions do not allow fixed costs of reproduction to affect optimal reproductive effort, others do. Increasing fixed costs reduces total fitness and increases the level of investment required to obtain a reproductive profit. Increased fixed costs may also narrow the parameter space of reproductive effort for positive profit. These results are discussed in the perspectives of age at maturity and the evolution of semelparity.

Life history evolution in heterogeneous environments: a review of theory

Analysis of life history evolution in spatially heterogeneous environments was revolutionized by the demonstration by Kawecki & Stearns (1993) and Houston & McNamara (1992) that earlier treatments had used incorrect fitness measures. The implications of this for the analysis of organisms with and without phenotypic plasticity are reviewed. It is shown that analyses ignoring age structure can give misleading results. The plausibility and implications of the assumptions are discussed, and suggestions are made for further work. The usefulness of reciprocal transplant and common garden experiments, in providing information relevant to the assumptions and predictions, is emphasized. Two simulation studies show that life history evolution in temporally heterogeneous environments in which trade-offs are fixed are well predicted by Schaffer’s (1974) model, with modification for asymmetric variations as necessary. Unfortunately the period of study needed to observe such effects is so long as to preclude experimental tests for most organsims.

In situ Rates of Fertilization Among Broadcast Spawning Gorgonian Corals.

Fertilization rates among marine benthic taxa have implicitly been assumed to be uniformly high in most analyses of life history evolution, but in situ fertilization rates during natural spawning events are rarely measured. Fertilization rates of the Caribbean gorgonians Plexaura kuna and Pseudoplexaura porosa were measured at a site in the San Blas Islands, Panama, by collecting eggs downstream of colonies during synchronous spawning events during the summer months in the years 1988-1994. Eggs collected by divers were incubated, and the proportion of eggs that developed was determined. Proportions of eggs developing suggest fertilization rates that vary from 0% to 100%. Monthly means ranged from 0% to 60.4%. Failure of gametes to develop can be attributed to sperm limitation, as eggs collected during spawning had higher fertilization rates if incubated with an excess of sperm. Plexaura kuna fertilization rates were highest during the July spawning events. Fertilization of Plexaura kuna eggs was usually lower during the first two nights of the 4-6 night spawning event. The proportion of eggs being fertilized when collected from a given place and time was highly variable, with one peak in the frequency distribution at or below 20% fertilization, and a second group of samples with greater fertilization rates. High variance in fertilization rates is evident at all levels of analysis: between replicate samples, times within nights, and among nights and months. This variance can be attributed to a combination of the effects of heterogeneity in the water column as gametes are diluted, spawning behavior of the gorgonians, and the current regime. Fertilization rates are often low and may represent a limiting step in recruitment during some years. Low fertilization rates may also be an important component of the life history evolution of these species.

An analysis of life history evolution in terms of the density-dependent Lefkovitch matrix model

The evolution of demographic characteristics is considered in terms of the density-dependent Lefkovitch matrix model, which describes a species' population dynamics with a stage-specific pattern of reproduction and mortality. We obtain the invadability condition of a mutant-type into the wild-type population at the equilibrium state. The condition depends on the left and right eigenvectors at the equilibrium state and the difference, between wild-type and mutant-type populations, of the values of elements in the Lefkovitch matrix at the equilibrium state. It is also shown that if elements of the density-dependent Lefkovitch matrix are decreasing functions of population density, then the equilibrium population density increases in the process of natural selection; that is, K-selection acts even on the stage-structured population. The evolution of life history in perennial plants is discussed through two models as an application of the above results. The evolution of perennial plants with no vegetative reproduction is analyzed in the first example. It is shown that whether monocarpic perennials (which reproduce once and die) or polycarpic perennial plants (which reproduce more than once) are favored depends on the cost of a produced seed. The second example concerns perennial plants that reproduce vegetatively. It is shown that whether monocarpic or polycarpic perennial plants are favored depends on the cost of a seed and that where vegetative reproduction is common, polycarpic perennials with no seed reproduction are favored.

A graphical analysis of life history evolution in biennial plants

Graphical analysis was done on the lfie history evolution of biennials (or monocarpic perennials). The age of seed production (x), the probability of surviving to agex [l(x)], and the number of seeds produced at agex[b(x)] determine the ultimate rate of population increase (r). The ages whenr=max andr=0 define the optimal and critical age for seed production, respectively, which depend on the shape and combination of thel(x) andb(x) curves. The otpimal age of seed production appears only for the convex function of the natural logarithm of the net reproductive rate [R0(x)], while the critical age appears irrespective of the shape of theR0(x) curves. The effects of environmental change on the optimal and critical ages are, analyzed, with the conclusion that in an environment imposing higher mortality or lower fecundity, delayed reproduction is favored. Age- and size-dependent productions of seeds have different effects on the variation ofr in a changing environment.

A Quantitative Genetic Theory of Life History Evolution

Dynamic models of quantitative (polygenic) characters are more generally applicable in the analysis of life history evolution than are static optimization methods or one and two locus genetic models. A dynamic theory of life history evolution is derived by synthesizing population demography with quantitative genetics. In a population under weak selection with a nearly stable age distribution, the relative fitness of individuals with a particular life history phenotype can be approximated as an average of age—specific relative fecundity and mortality rates, weighted respectively by the present productivity and future reproductive value of each age—class. An adaptive topography is constructed showing that, with phenotype— and age—specific fecundity and mortality rates constant in time, evolution of the mean life history maximizes the intrinsic rate of increase of a population. However, the rate and direction of evolution in response to selection are strongly influenced by genetic correlations among characters. Negative genetic correlations among major components of fitness are often obscured phenotypically by positive environmental correlations, but commonly constitute the ultimate constraint on life history evolution, as illustrated by artificial selection experiments. Methods are suggested for measuring selective forces and evolutionary constraints that effect life history characters in natural populations.