Biomedical subjects

Daniel D Wiegmann

Publications and source records attributed to Daniel D Wiegmann.

3 recordsLinked to original sources

PubMed2005

Mating system and demographic constraints on the opportunity for sexual selection.

In monogamous systems the fitness difference between males due to competition for mates is limited to one female. This constraint presumably impedes the action of sexual selection relative to polygynous systems. In this paper, we use formal selection theory to show how population size and the adult sex ratio constrain the force of sexual selection and phenotypic evolution under monogamy and polygyny. The force of sexual selection is ultimately constrained by the number of males in a population and the theoretical limit to the rate of male phenotypic evolution is realized if a single male mates with one or many females. These results imply that the force of sexual selection is not strictly constrained by monogamy. The constraint on female phenotypic evolution is typically higher than the constraint on males under polygyny and similar to selection on males in monogamous systems. The sexual asymmetry in the force of selection under polygyny--not necessarily weak sexual selection on males of monogamous systems--may explain the prominence of sexual dimorphism in polygynous systems.

Animals↗

PubMed2004

Negative maternal or paternal effects on tactic inheritance under a conditional strategy.

Alternative behavioral and life-history tactics are common in animal populations. The conditional strategy model provides a powerful explanation for the evolution and persistence of such tactics, as it allows alternative tactics to be perpetuated even if there is tactic inheritance and tactics yield unequal mean fitness. In many biological systems negative maternal or paternal effects complicate the inheritance of condition and, hence, the inheritance of alternative tactics. Indeed, the inheritance of condition may result in the alternation of tactics across generations. In this paper, we show that the conditional strategy is robust to these effects on progeny condition. There is a unique and stable proportion of tactics under standard inheritance and unequal tactic fitness, and these two important properties of the conditional strategy hold even if negative maternal or paternal effects on progeny condition cause tactics to alternate across generations. However, the dynamics of tactic proportions pursuant to a perturbation of the equilibrium tactic proportions depend on the form of tactic inheritance. An application of our theoretical results to data from a population of smallmouth bass (Micropterus dolomieu) in which negative paternal effects dictate progeny condition reveals that age at first reproduction in males alternates regularly across generations. Furthermore, the model indicates that the population would return rapidly to equilibrium if the proportions of males that mature early or late in life were perturbed from the equilibrium within the system. This example shows how the model of the conditional strategy can be used to gain insight into tactic dynamics in situations where some of the model parameters are difficult or impossible to measure empirically.

Adaptation, Physiological↗

PubMed2003

Effects of a reward downshift on the consummatory behavior and flower choices of bumblebee foragers.

Insect foragers often exhibit flower constancy, the tendency to visit single flower types rather than sample alternative flowers that provide equal or higher levels of reward. We employed a negative incentive contrast procedure to examine whether a decrease of sucrose concentration in a regularly visited flower type affects bumblebee (Bombus impatiens) consummatory or choice behavior. Subjects were trained to enter a test arena where they foraged on a single, red, artificial flower that contained 140 microl of sucrose solution. Subjects were reinforced with a concentration of either 0.50 or 0.20 sucrose solution in 20 trials and in 12 subsequent test trials subjects were given a choice between a red and yellow flower that each contained 140 microl of 0.20 sucrose solution. Subjects that experienced a downshift of reward showed an abrupt disruption in consumption of sucrose solution from the red flower. These subjects were also significantly more likely to visit the novel yellow flower than subjects that were reinforced with 0.20 sucrose solution in red flowers in all trials. However, the effects of the downshift of reward were transient and appeared to disrupt consummatory behavior more strongly than flower preferences. These results support the idea that bumblebee foragers form expectations of reward in flowers--as is implied by the results of studies of honeybees--and suggest that unrealized expectations of reward may cause foragers to sample alternative flowers or to fly considerable distances in search of particular types of flowers.

Animals↗