Dispersal Phenotype Research Articles

Maternal size and stress and offspring philopatry: An experimental study in the common lizard (Lacerta vivipara)

:During gestation, many morphological, physiological, and behavioural traits are influenced by the maternal environment. Previous experiments on natal dispersal in Lacerta vivipara demonstrated that maternal condition during gestation affects juvenile dispersal behaviour. The mechanisms by which a female may influence her offspring, or offspring respond to changes in the mother’s internal environment, remain largely unknown. In this study, we investigated the role of corticosterone during pregnancy on the production of the dispersal phenotype. Ninety pregnant females were collected from a population at Cévennes (Massif Central) and kept in the laboratory until parturition. We applied a corticosterone solution daily on the back of 58 females and applied a similar solution, but without corticosterone, to the 32 others as a control. We measured dispersal propensity and morphology of the offspring of both groups. Morphology of offspring was not affected by hormonal treatment of their mothers, but dispersal of young from corticosterone-treated mothers was significantly smaller for large-sized (old) mothers and significantly greater for small-sized (young) females compared to the offspring of control females. Corticosterone might not be the only factor affecting the development of the juvenile dispersal phenotype. Maternal effects on juvenile dispersal reflect future survival prospects of the female and/or the quality of her environment; this finding strengthens our previous finding that natal dispersal in L. vivipara results from the integration of multiple factors.

Ecological and evolutionary processes at expanding range margins.

Many animals are regarded as relatively sedentary and specialized in marginal parts of their geographical distributions. They are expected to be slow at colonizing new habitats. Despite this, the cool margins of many species' distributions have expanded rapidly in association with recent climate warming. We examined four insect species that have expanded their geographical ranges in Britain over the past 20 years. Here we report that two butterfly species have increased the variety of habitat types that they can colonize, and that two bush cricket species show increased fractions of longer-winged (dispersive) individuals in recently founded populations. Both ecological and evolutionary processes are probably responsible for these changes. Increased habitat breadth and dispersal tendencies have resulted in about 3- to 15-fold increases in expansion rates, allowing these insects to cross habitat disjunctions that would have represented major or complete barriers to dispersal before the expansions started. The emergence of dispersive phenotypes will increase the speed at which species invade new environments, and probably underlies the responses of many species to both past and future climate change.

EVOLUTION OF DISPERSAL RATES IN METAPOPULATION MODELS: BRANCHING AND CYCLIC DYNAMICS IN PHENOTYPE SPACE.

We study the evolution of dispersal rates in a two patch metapopulation model. The local dynamics in each patch are given by difference equations, which, together with the rate of dispersal between the patches, determine the ecological dynamics of the metapopulation. We assume that phenotypes are given by their dispersal rate. The evolutionary dynamics in phenotype space are determined by invasion exponents, which describe whether a mutant can invade a given resident population. If the resident metapopulation is at a stable equilibrium, then selection on dispersal rates is neutral if the population sizes in the two patches are the same, while selection drives dispersal rates to zero if the local abundances are different. With non-equilibrium metapopulation dynamics, non-zero dispersal rates can be maintained by selection. In this case, and if the patches are ecologically identical, dispersal rates always evolve to values which induce synchronized metapopulation dynamics. If the patches are ecologically different, evolutionary branching into two coexisting dispersal phenotypes can be observed. Such branching can happen repeatedly, leading to polymorphisms with more than two phenotypes. If there is a cost to dispersal, evolutionary cycling in phenotype space can occur due to the dependence of selection pressures on the ecological attractor of the resident population, or because phenotypic branching alternates with the extinction of one of the branches. Our results extend those of Holt and McPeek (1996), and suggest that phenotypic branching is an important evolutionary process. This process may be relevant for sympatric speciation.

A dispersive morph in the naked mole-rat.

Close inbreeding is known for a variety of small mammal species for which a high probability of mortality during dispersal makes helping and delayed maturation a relatively secure fitness option. Prolonged inbreeding, however, is usually associated with lowered fitness, and it has been shown that most highly inbred small mammals and social insects have inbreeding-avoidance mechanisms that promote some degree of outbreeding. However, previous field and laboratory research on the naked mole-rat (Heterocephalus glaber) suggested that this cooperatively breeding rodent is highly inbred, with new colonies forming by fission. Here we report the discovery of a dispersal phenotype that may occasionally promote outbreeding in naked mole-rats. These dispersers are morphologically, physiologically and behaviourally distinct from other colony members. They are laden with fat, exhibit elevated levels of luteinizing hormone, have a strong urge to disperse, and only solicit matings with non-colony members. These findings suggest that, although rare, a dispersive morph exists within naked mole-rat colonies.

The Role of DNA Ploidy in the Differentiation of WEHI-3B D - Leukemia Cells Transfected with the Granulocyte Colony-Stimulating Factor Receptor Gene

Granulocyte colony-stimulating factor (G-CSF) exerts various biological effects through occupancy of its receptor (G-CSFR). WEHI-3B D - myelomonocytic leukemia cells do not express the G-CSFR, do not respond to G-CSF or to retinoic acid by the induction of granulocytic maturation, contain a near tetraploid content of DNA, and form tightly aggregated colonies. However, they still maintain the capacity to differentiate since they respond to vitamin D 3 by the formation of mature cells. Transfection of the G-CSFR gene into WEHI-3B D - cells resulted in three major changes. G-CSFR-expressing clones (a) acquired the capacity to respond to the differentiation-inducing properties of G-CSF and retinoic acid, (b) formed colonies which exhibited a dispersed phenotype, and (c) exhibited near diploid DNA ploidy. In contrast, WEHI-3B D - cells transfected with vector alone behaved like parental WEHI-3B D - cells. The findings imply that the near diploid phenotype is required for WEHI-3B D - leukemia cells to respond to certain inducers of differentiation.

The Evolution of Plant Mating Systems: Multilocus Simulations of Pollen Dispersal

We simulated pollination in a plant population and explored how pollen dispersal distance and allocation among recipient individuals evolved in response to direct selection on three loci coding for dispersal phenotype and in response to indirect selection on two unlinked "genetic congruence" loci. Fitnesses at congruence loci were chosen to model "genetic" and "ecological" mechanisms that have been proposed to explain the observation that an intermediate outcrossing distance maximizes fitness in some plants. Simulations show (1) that dispersal genotype evolves rapidly in response to direct selection, apparently mediated mainly through competition for access to ovules; (2) that selection for intermediate genetic congruence affects final dispersal genotype in largely predictable ways and does not appear to provoke runaway evolution; and (3) that evolution of dispersal type influences the genetic structure of the population, which in turn influences the evolution of dispersal.

Dispersal polymorphisms in subdivided populations

Price's method for analyzing natural selection in subdivided populations is applied to the problem of dispersal polymorphism strategies in a stable habitat. The results agree with the more traditional Mendelian models for this same problem that have recently been published. Further, by using Price's method, the results obtained are simpler and more general, and the causal evolutionary mechanisms underlying the predicted patterns are more easily recognized. The most interesting new result is that the equilibrium proportion of dispersed individuals is a simple function of the risk of dispersing and the regression coefficient of relatedness among individuals who, in the absence of dispersal, would compete for a limited, local resource. This regression coefficient refers to the genotypes that control the dispersal phenotype. For example, when mothers control the phenotype of their progeny, then the regression is from the mother onto an offspring chosen randomly from the local group before dispersal; while when offspring control their own phenotype, the regression is taken directly from offspring onto a randomly chosen cohort member before dispersal. This use of controlling genotypes to calculate regressions explains the form of the parent-offspring conflict over dispersal noted by previous authors. The simplicity and generality of these results suggest that Price's method is a useful approach for studying the class of phenomena known as "games among relatives".

Ectopic peptides released by a human melanoma cell line that modulate the transformed phenotype.

Cells derived from a human melanoma strain by low-serum selection in monolayer were found to be capable of growth in semisolid medium, forming colonies ranging from tight to loose or dispersed. These phenotypes were found to be stable after cloning and retesting. Examination of the biological activities of ectopic peptides produced by a clone that gives rise to loose dispersed colonies revealed the presence of a transforming growth factor beta (TGF-beta; apparent Mr 14,700) and a single TGF-alpha species produced at an unusually high concentration (2.2 ng/ml). Coeluted with the TGF-alpha at approximately 22,500 was a mitogenic activity and a previously undescribed activity capable of modulating the phenotype of induced normal rat kidney fibroblast (NRK-49F) colonies in semisolid medium. This activity can modulate the usual tight colony to express a loose or dispersed phenotype characteristic of the producer cells. Both the possible role these ectopic peptides play in the expression of the transformed phenotype by the tumor cells producing them and the possible correlation between the Mr 22,500 epidermal growth factor-like peptide released by this particular tumor line and high molecular weight epidermal growth factor-like peptides found in the urine of cancer patients are discussed.

Ectopic peptides released by a human melanoma cell line that modulate the transformed phenotype.

Cells derived from a human melanoma strain by low serum selection in monolayer were found to be capable of growth in semi-solid medium, forming colonies ranging from tight, to loose, or dispersed. These phenotypes were found to be stable on cloning and retesting. Examination of the serum-free media conditioned by these clones indicates that the clones release activities capable of inducing agar colonies, in an indicator cell line (NRK, 49F), that express phenotypes similar to those of the melanoma clones used to produce the serum-free conditioned media (SF-CM). These SF-CM contained a transforming growth factor (TGF) beta (apparent Mr 14 700) and a single, apparently high Mr TGF-alpha species. Co-eluting with the TGF-alpha at an Mr of approximately 22 500 was a previously undescribed activity capable of modulating the phenotype of the NRK agar colonies induced by the combination of TFGs alpha and beta. This new activity can modulate the usual tight colony to express a loose or dispersed phenotype characteristic of the producer cells. The possible role these ectopic peptides play in the expression of the transformed phenotype by the tumour cells producing them, and the possible correlation between the 22 500 Mr EGF-like peptide (TGF-alpha) released by this particular tumour line and high Mr EGF-like peptides found in the urine of cancer patients, are both discussed.

Dormancy and dispersal in dimorphic achenes of tansy ragwort, Senecio jacobaea L. (Compositae).

Marginal and central florets of the capitula of tansy ragwort Senecio jacobaea yield different kinds of fruit. The central ("disk") achenes are lighter (x±SE=199±5μg), more numerous (x±SE=58±0.6 achenes per head), and are equipped with a pappus aiding wind transport and rows of trichomes aiding animal transport. The marginal ("ray") achenes are heavier (x±SE=286±7μg), less numerous (virtually invariant at 13 achenes per head), and lack dispersal structures. Whereas disk achenes are relased shortly after they mature, ray achenes are retained by the parent for a period of months following maturity.Germination at constant temperature (20°C) and with alternating light (12 h light: 12 h dark) demonstrated that disk and ray achenes exhibit different germination syndromes. Germination percentage increases linearly with achene fresh weight in both types; for a given weight, disk achenes have a higher germination percentage than ray achenes. Germination time decreases with increasing achene weight in disk achenes, but increases with achene weight in ray achenes.The germination percentages and germination times for disk and ray achenes diverge progressively with increasing achene weight. The divergence in behavior is a result of diverging patterns of dry matter allocation in the two achene types. Increase in the size of disk achenes favors the embryo fraction, thereby speeding germination while reducing protection. Increase in the size of the ray achenes favors the pericarp fraction, thereby increasing protection while delaying germination.Reduced germination percentage and germination speed of the ray achenes were shown by experimental manipulation to be caused by physical inhibition by their thicker pericarps.Dimorphism in ragwort likely speards germination out in space and time, thereby increasing the number of safe sites an individual parent can exploit in disseminating offspring. The syndrome in other heteromorphic composites resembles that of ragwort, generally combining reduced dispersal-delayed germination in the outer achenes and distance dispersal-quick germination in the central achenes. The outer achenes are generally less numerous and larger. Dispersal traits (large numbers, early release and light wieght) are the direct opposite of dormancy traits (small numbers, delayed release and heavier weight). Thus conflicts between the properties determining dormancy and dispersal appear to require separate dormancy and dispersal phenotypes.

Transformation in Tetrahymena thermophila: Development of an inducible phenotype

Tetrahymena thermophila transforms from a pyriform-shaped trophic form to an elongate rapidly swimming, dispersal form under the appropriate conditions of starvation [Nelsen, E. M., and DeBault, L. E. (1978). J. Protozool. 25, 113–119] . The development and control of the dispersal phenotype are examined. After an initial starvation period, the cell replaces its oral structures. During oral replacement, a caudal cilium emerges at the posterior end of the cell. As oral replacement is completed, the cell becomes spindle shaped and the newly-formed oral membranelles are positioned beneath the surface of the cell with somatic ciliary rows exterior to them. The spindle-shaped cell then elongates to become the dispersal form. While the cell is developing the new oral structures, it is also drastically increasing its numbers of somatic basal bodies and cilia. The events in the transformation pathway may be arrested or reversed by feeding the cell, except that once oral replacement has begun, it is completed along with an associated streamlining of the cell. Refed cells revert to the normal vegetative phenotype, except that some shape changes persist for several hours, suggesting that they are compatible with, but independent of, growth. Blockage of protein synthesis with cycloheximide prevents all changes associated with transformation, including the shape changes and elongation of the caudal cilium. The relation between transformation and conjugation has also been examined. Less transformation takes place when mating is possible, but transformed cells may also mate.

BODY SIZE AND METABOLIC RATE

BODY SIZE AND METABOLIC RATE