Final Adult Size Research Articles

Body Size Variation in Lesser Snow Geese: Environmental Plasticity in Gosling Growth Rates

We examined the influence of timing of reproduction and brood size on growth rates of goslings of nidifugous Lesser Snow Geese (Anser caerulescens) using data collected at La Perouse Bay, Manitoba from 1978 to the present, Gosling growth rates declined significantly during the season, and the declines were independent of the parental genotype. Goslings from larger broods grew significantly faster, but there was no significant annual variation in the seasonal growth rate patterns with either hatch date or brood size. The hatch date and brood size effects could not be accounted for by systematic differences in either egg size or body size of the female parent. Goslings that grew more slowly due to the effects of hatch date or brood size were significantly smaller as adults. Because gosling growth rates influence final adult size, they may have a significant effect on various life history traits in this species.

Overwintering of Africanized, European, and Hybrid Honey Bees in Germany

The survival of Africanized honey bees, Apis mellifera L., in temperate regions was evaluated in Germany during the 1988–1989 winter. Africanized, local European, and Africanized × European colonies were started by queen introductions on 5 August, and all surviving colonies were depopulated on 21 February. Five of nine Africanized colonies had died by the end of the experiment, whereas all eight European and all five Africanized × European colonies survived. Brood production of the three genotypes declined from 18 August until 13 November with significant differences on two of the seven measurement dates. Brood areas were not different among surviving colonies that had resumed brood production by 21 February. Changes in total colony weights through time were not different. Significant differences were found in the rates of colony weight loss (kilograms total weight/average kilograms of adult bees∗time)and in final adult population size. The higher attrition of worker populations and the higher mortality of Africanized colonies suggest a possible reduction of their adverse effect as their range expands northward to temperate areas in the United States. The intermediate values for all characters in the Africanized × European colonies suggest that genes underlying overwintering characters are additive. This additivity will permit different levels of hybridization for different ecological zones, thus complicating predictions about absolute climatic limits.

Changes during the holocene in the size of white-tailed deer ( Odocoileus virginianus) from central Illinois

White-tailed deer ( Odocoileus virginianus) from central Illinois varied in size during the Holocene. The record, which extends back to 8450 yr B.P., indicates small deer through the mid-Holocene until 3650 yr B.P., after which size increases. Although influences of winter climate, seasonality, anthropogenic effects, and other ecological factors should not be discounted, an intriguing possible cause of the deer size shifts is insolation-driven summer climate and its influence on food resources. In the Holocene, small deer size is correlated with high summer insolation and with low winter insolation. Climatic models indicate that in spite of changes in insolation, Holocene winters did not vary greatly through time, especially in contrast to summers, which were dynamic. Physiological constraints peculiar to O. virginianus make critical the quality of summer forage for determining final adult size. Summer temperature averaged 2°C warmer than present during the middle Holocene, which increased evaporation and probably reduced the period of availability of high-quality forage low in fiber and high in protein. Consequently, less fuel for growth was consumed by mid-Holocene deer and only small body size was achieved. Other possible causes (e.g., Bergmann's rule, seasonality) of clinal variation are considered with reference to central Illinois deer, but at present the most parsimonious explanation appears to be the summer insolation hypothesis.

Preservation of motoneuron electrotonic characteristics during postembryonic growth

The postembryonic developmental period of the nervous system involves, among other processes, an increase in the dimensions of individual neurons. In the present study we examine whether the characteristic electronic parameters that underlie the integrative properties of the neuron (L, the electrotonic length; rho, dendritic to somatic conductance ratio; and tau m, the membrane time constant) are established before, during, or after the neurons reach their final adult size. A second aspect that we analyze are the mechanisms by which the neurons adjust their electrotonic parameters during the growth period. The dimensions of the soma and dendrites of the phallic motoneurons (Ph.m.n.) of the cockroach, Periplaneta americana, increase during the last postembryonic developmental stages and metamorphosis to adult by a factor of 1.75 and 1.5, respectively. This increase is not associated with major changes in the morphological outline of the neuron but is associated with a significant decrease in the input resistance (Rin) by a factor of 6 (from 120 to 20 M omega). The dendritic to somatic conductance ratio (rho) is maintained constant. Morphological analysis of cobalt-filled neurons reveals that the neurons can be represented by an equivalent cylinder (Rall, 1969). Calculations of the electrotonic length (L) of the equivalent cylinder from measurements of the time constants tau m and tau 1 (Rall, 1969) revealed that L is constant throughout the period of neuronal growth (1.29 +/- 0.24 lambda in adult, and 1.13 +/- 0.28 lambda in nymph). The mechanism by which the electrotonic parameters are maintained in spite of growth is continuous adjustment of the diameter and length of the various neuronal segments, rather than by changes in the biophysical properties of the neuron. Several implications in relation to mechanisms of integration and input-output relations during growth and development of neurons are discussed in view of our findings.

Ontogenetic approaches to sexual dimorphism in anthropoids

Studies of sexual dimorphism have traditionally focused on the static differences in size and shape between adult males and females. In this paper, I suggest that an investigation of the ontogenetic bases of sexual dimorphism can provide new insights and information unobtainable from studies concerned only with adult endpoints. While growth is often viewed as simply the developmental pathway utilized to attain final adult size and shape, we must recognize that it is the entire pattern of sex-differentiated growth, and not merely the adult endpoints, which is adaptive and the target of natural selection. The importance of an ontogenetic approach to the analysis of sexual dimorphism is also demonstrated by the fact that a given morphologicalresult (e.g., a certain degree of adult weight dimorphism) may be attained by very different developmentalprocesses, signalling selection for quite different factors. The need to analyze the ontogenetic bases of sexual dimorphism in size and shape has recently been recognized by Jarman, in his study of dimorphism in large terrestrial herbivores. Here I combine aspects of Jarman’s approach with those of allometry and heterochrony in an analysis of sexual dimorphism in selected anthropoid primates. It is demonstrated that although all dimorphic anthropoids appear to be characterized by somebimaturism, the degree varies significantly. Marked weight dimorphism in certain species is primarily produced by an increased differentiation of female and male growthrates, while in other species the primary change involves differences in thetime or duration of growth between the sexes. These variations are illustrated with anthropoid genera such asMiopithecus, Cercopithecus, Erythrocebus, Macaca, Papio, Pan, andGorilla. It is suggested that additional ontogenetic investigations of other anthropoids will help clarify some of the socioecological bases of this variation in the ways of attaining an adult dimorphic state. This will contribute to our understanding of the complex factors underlying and producing sexual dimorphism in primates and other mammals.

Density-Dependent Growth in Early Ocean Life of Sockeye Salmon (Oncorhynchus nerka)

Significant decreases in adult body size and marine growth rate occur in seven British Columbia and Bristol Bay, Alaska, sockeye salmon (Oncorhynchus nerka) stocks when large numbers of sockeye are present in the Gulf of Alaska. These density-dependent effects arise mainly during early ocean life and are probably due to competition for food. The total sockeye abundance in the Gulf of Alaska is at least as important as within-stock abundance in determining final adult body size. British Columbia sockeye show a 10–22% decrease in adult body weight at high abundance of conspecifics. Thus, future evaluations of management strategies cannot simply focus on individual stocks, but must take a broader perspective which includes other sockeye populations.

Ontogeny, Timing of Development, and Genetic Variance-Covariances Structure

evolutionary perspective is to regulate a number of ontogenetic processes to arrive eventually at a final adult size. Optimal final size is important since there are a number of processes which, if not dependent on body size, are at least highly correlated with it including metabolic rate, onset of reproductive maturity, and competitive ability for mates. Growth patterns during development are widely thought to be under genetic control and arise mainly from the activation and repression of structural and regulatory genes which vary the metabolic activity and chemical composition of differentiated cells. These activation-repression cycles are responsible for changes in cell number and cell size, fluctuations in enzyme and hormone levels, varying rates of protein and fat accretion, skeletal growth, etc. The timing of ontogenetic cycles of gene activity determines the total length of the developmental process as well as the timing of critical steps during various ontogenetic processes. The evolution of gene regulation patterns during ontogeny and the resultant timing of events for complex, polygenically controlled traits is central to general discussions in evolution and development. Hall (1982, p. 46) stated that do not know when during development, nor by what developmental process, growth of the mandible, or for that matter of any other region of the embryo, is controlled. Bonner (1982, p. 8) states that everyone agrees that the most effective way to elicit big phenotypic changes with the least genetic fuss is by heterochrony. Nevertheless, we seem unable to attack the problem. The inability to attack experimentally the problem of gene regulation in polygenic traits is reflected in the absence of genetic models for ontogenetic changes in polygenic traits. Further, critical genetic data are lacking about general morphogenetic models which emphasize heterochronic phenomena (e.g., Gould 1977; Alberch et al. 1979). This paper provides a discussion of ontogenetic variation in quantitative genetic parameters in mammals, examines the genetic aspects of several general growth phenomena, and describes their relative importance in mammalian growth.

Patterns of growth in Darwin’s finches

Nestling growth was studied in six species of Darwin’s finches, and in two subspecies of one of them, on four islands of the Galápagos archipelago. The results show how the different beak and body size proportions among the adults of the species are brought about in ontogeny. Large species lay large eggs which give rise to large hatchlings, and in general these have higher growth rates than do the nestlings of smaller species. Geospiza difficilis hatches at a proportionally larger size than the other species and then grows at a slow rate. Variation with species tends to decline with nestling age, but this may be partly artefactual. Adult levels of variation are reached by about day 9, but in G. magnirostris bill depth variation increases significantly from day 9 to adulthood owing to differential mortality or growth. Bill depth variation is heritable in G. conirostris , the best-studied species, on every day from day 2 to day 10; heritable variation was demonstrated towards the end of the nestling phase of growth of this species in bill width, tarsus length and mass but not in bill length. In terms of relative growth, i. e. variates in proportion to body mass, there is only minor variation among species in growth rates of wing and tarsus but substantial variation in relative growth of bill dimensions. By extrapolation, this is one source of indirect evidence that pre-hatching growth differs among the species. The other evidence is that bill proportions differ at hatching relative to final adult size among species. In a multiple discriminant function analysis, the best discrimination among the three Geospiza species on Isla Genovesa was achieved by bill dimensions at all stages throughout the nestling period. Rates of relative growth were fastest in those bill dimensions that are most pronounced in adults. Each species changes in beak shape during nestling growth in a unique manner, except that G. difficilis on I. Genovesa and G. fuliginosa on I. Marchena, which are convergent as adults, have the same growth trajectories. The two subspecies of G. difficilis also have the same growth trajectories, and the differences in adult proportions are the allometric consequences of different stopping points along these trajectories. After fledging there is more growth remaining in bill length than in bill depth and width, but G. magnirostris is unique in first growing relatively quicker in bill depth, then in bill length. These results show that the adaptive differentiation of Darwin’s finch species in adult bill morphology and size has been brought about by evolutionary changes in embryonic, nestling and post-fledging growth characteristics. A more comprehensive theory of the differentiation than exists at present could be developed by integrating ontogeny and phylogeny.