Sperm precedence in zebra finches does not require special mechanisms of sperm competition

Competition between the spermatozoa of different males to fertilize the eggs of a single female acts as a selection pressure on the behaviour of males and females. However, quantitative predictions about behaviour fan only be made if the paternity consequences of different patterns of copulation are known. Because exhaustive empirical measurement of these consequences may be impractical, interest has centred on determining the mechanisms by which sperm competition occurs, knowledge of which may allow consequences to be calculated. One method of elucidating mechanisms of sperm competition is to use mathematical models to determine which mechanisms are necessary or sufficient to account for empirical observations. We use this approach for zebra finches Taeniopygia guttata and show that empirically measured rates of disappearance of sperm from the reproductive tract, and differences in the number of sperm in the first and subsequent ejaculates of each male, are sufficient to account for observed levels of sperm precedence. Special mechanisms of sperm competition, such as displacement or stratification of sperm, are therefore unnecessary to explain sperm precedence in this species

Sexual conflict

Parental care includes a wide variety of traits that enhance offspring development and survival. It is taxonomically widespread and is central to the maintenance of biodiversity through its close association with other phenomena such as sexual selection, life-history evolution, sex allocation, sociality, cooperation and conflict, growth and development, genetic architecture, and phenotypic plasticity. This novel book provides a fresh perspective on the study of the evolution of parental care based on contributions from some of the top researchers in the field. It provides evidence that the dynamic nature of family interactions, and particularly the potential for co-evolution among family members, has contributed to the huge diversity of parental care behaviours expressed across as well as within taxa. The Evolution of Parental Care aims to stimulate students and researchers alike to pursue exciting new directions in this fascinating and important area of behavioural and evolutionary biology.

A theoretical framework for sex-biased parental care

I present game theory models for parental care by male and female-parents of male and female offspring. The models include the effects of Fisherian frequency dependence (FFD), the trade- off between offspring fitness and-the residual fitness of the parent, and the conflict between the two parents. The models are used to make predictions about the factors selecting for biases in parental care with respect to either offspring or parental sex. The models predict that: (1) male and female offspring will receive different amounts of care when the offspring functions (relating fitness accrued;through an offspring to the amount of care that it receives, excluding the effects of FFD) differ between the male and female offspring; (2) male and female parents will give different amounts of care;when either (a) the parental functions (relating the loss in residual fitness to the total amount of care given by the parent, excluding the effects of FFD) differ between male and female parents, or (b) offspring functions differ between male and female offspring and FFD also acts on residual fitness of parents; and (3) there will be an interaction between offspring and parental Sex on: the amount of care received (a) by an offspring within a family when the offspring functions are not the same for male and female parents (but then the sex bias is extreme and one parent does not care for one sex of offspring), and (b) by the family in relation to its sex ratio when offspring functions differ between male and female offspring (but not necessarily between male and female parents) and parental functions differ between male and female parents. (C) 1998 The Association for the Study of Animal Behaviour. [KEYWORDS: Offspring sex; ratio; warblers; size]

Putting Resource Dynamics into Continuous Input Ideal Free Distribution Models

Continuous input models of the ideal free distribution usually assume that resources are consumed immediately that they enter a patch. This paper presents models of constant continuous input in which this assumption is relaxed, so that predictions can be made about the standing crops of resources and the density relationship of prey mortality caused by the consumers. These models suggest that: (1) the input matching rule is not dependent on the assumption that resources are consumed immediately that they enter a patch, and holds whether or not there is interference competition but not when there is an alternative source of mortality; (2) exploitation competition is fundamental to the continuous input model. Whether or not interference competition occurs can be determined in experimental situations by measuring the standing crops of resources in patches with different resource input rates; (3) interference models are not an alternative to continuous input models but represent a 'snapshot' of time from either continuous input or depletion models; (4) in continuous input models prey mortality is density independent in the absence of interference because all patches have the same standing crop of resources. When there is interference between consumers prey mortality is density dependent, unless the interference is extremely strong. [KEYWORDS: Individual decisions; patchy environment; predators; strategy]

Why Are Males Bad for Females? Models for the Evolution of Damaging Male Mating Behavior

One explanation for the cost to mating for females caused by damaging male mating behavior is that this causes the females to adaptively modify their subsequent life histories in a way that also increases male fitness. This might occur because the reduction in residual reproductive value of the female increases her optimal oviposition rate or because an increase in the current level of damage increases the female's optimal remating interval. In this article, I present models of a stochastic dynamic game in which males choose the level of mating damage that they inflict on females and females choose their oviposition rate and whether to remate. The models show that some level of damage is always an evolutionarily stable strategy and may even provoke females into making terminal reproductive investment (and hence a semelparous life history), that nondamaging populations are always invaded by damaging male mutants, and that damage evolves because of its effect on oviposition rate and despite its effect on remating interval. [KEYWORDS: sexual conflict ; cost of mating ; manipulation]

Evolutionary biology - More mutations in males

Mutations are believed to introduce genetic novelty and so are considered a crucial process in evolution. Nearly 50 years ago it was postulated that if... [KEYWORDS: Driven molecular evolution; sex]

Parentally biased favouritism: why should parents specialize in caring for different offspring?

'Parentally biased favouritism' occurs when the two parents differentially care for individual offspring or kinds of offspring. Examples in birds include brood division and differential investment by the two parents in relation to the size or sex of the offspring. This paper uses mathematical models to investigate which ideas can, in theory, explain parentally biased favouritism. One previous explanation is that the parents differ in their cost of reproduction and that the parent who consequently invests least concentrates its care on the more valuable offspring. However, a mathematical model predicts the total care given by each parent and received by each offspring, not how much each parent cares for each offspring, and hence does not explain parentally biased favouritism. Parentally biased favouritism towards particular types of offspring can be explained by a difference between the parents in the benefits of caring for a given type of offspring or in the effort incurred in providing care to a given type of offspring, but then it is extreme, with at least one of the parents providing care to only one type of offspring. Parentally biased favouritism towards particular individual offspring (brood division) can be explained by parent-offspring conflict or sexual conflict. [KEYWORDS: parental favouritism, parental investment, parental care, parent-offspring conflict, sibling competition, sexual conflict]