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We investigated patterns of within-species genetic variation for traits observed in hybrids (hybrid numbers, hybrid sex ratios, and hybrid male deformities) between two species of flour beetles, Tribolium castaneum and T. freemani. We found genetic variation segregating among four natural populations of T. castaneum as well as within these populations. For some hybrid traits, we observed as much variation among populations 750 km apart as between populations on different continents, suggesting genetic differentiation at a local scale. Within natural populations, the variation segregating among sires is greater than that found in an earlier study for an outbred laboratory population and comparable to that observed between inbred lines derived from the outbred stock by eight generations of brother-sister mating. When sires from T. castaneum are mated to conspecific and heterospecific females, we do not observe a significant correlation at the level of the family mean between the intraspecific and interspecific phenotypes, suggesting the independence of the hybrid traits from comparable traits within species. We discuss our findings in relation to the evolutionary genetics of speciation and the expression of epistatic genetic variance in interspecific crosses.

We use population genetics to model the evolution of a gene with an indirect effect owing to paternal care and with a second pleiotropic, direct effect on offspring viability. We use the model to illustrate how the common empirical practice of considering offspring viability as a component of parent fitness can confound a gene's direct and indirect fitness effects. We investigate when this confounding results in a distorted picture of overall evolution and when it does not. We find that the practice has no effect on mean fitness, W, but it does have an effect on the dynamics of gene frequency change, ∆q. We also find that, for some regions of parameter space associated with fitness trade-offs, the distortion is not only quantitative but also qualitative, obscuring the direction of gene frequency change. Because it affects the evolutionary dynamics, it also affects the expected amount of genetic variation at mutation-selection balance, an important consideration in molecular evolution. We discuss empirical techniques for separating direct from indirect effects and how field studies measuring the value of male paternal care might be improved by using them. [ABSTRACT FROM AUTHOR]

Maternal-zygotic co-evolution is one of the most common examples of indirect genetic effects. I investigate how maternal-zygotic gene interactions affect rates of evolution and adaptation. Using comparably parameterized population genetic models, I compare evolution to an abiotic environment with genotype-by-environment interaction (G × E) to evolution to a maternal environment with offspring genotype-by-maternal environment interaction (G × Gmaternal). There are strong parallels between the 2 models in the components of fitness variance but they differ in their rates of evolution measured in terms of ∆p, gene frequency change, or of ∆W, change in mean fitness. The Price Equation is used to partition ∆W into 2 components, one owing to the genetic variance in fitness by natural selection and a second owing to change in environment. Adaptive evolution is faster in the 2-locus model with G × Gmaternal with free recombination, than it is in the 1-locus model with G × E, because in the former the maternal genetic environment coevolves with the zygotic phenotype adapting to it. I discuss the relevance of these findings for the evolution of genes with indirect genetic effects. [ABSTRACT FROM AUTHOR]

Population genetic methods help propose the anticipated population dynamics of the selfish-gene chromosomal factor Medea in flour beetles. Medea factors extend to fixation for all positive degrees of maternal-effect lethality when there are no harmful effects on gross fertility at a rate that varies with the nature of the effect and with the density. A stable interior polymorphism occurs when medea adversely affects fertility, affecting all offspring genotypes.

Use of quantitative genetic techniques on a laboratory strain of Tribolium castaneum in a study of the genetic basis of variation for the expression of viability reveals genetic variation for two traits of T. castaneum male and T. freemani female hybrids. Variation in hybrid sex ratio and surviving hybrid male fraction with antennal morphological defects increase when T. castaneum animals are inbred. The two traits exhibit a minimal but significant correlation with each other in both the hybrid and inbred lines, indicating that the variation in their expression could arise from the pleiotropic effects of the same set of segregating genes.

The opportunity for sexual selection on males can be influenced by 'female copying', a form of female mate selectionin which females imitate the mate choices of other females. Female copying always increases the opportunity for sexual selection on males because it increases the number of males obtaining no mates, as well as the number of males obtaining many mates. Paracerceis sculpta, a marine isopod crustacean, breeds in intertidal sponges in the Gulf of California. In the field and in laboratory choice tests, females in this species do not exhibit male or sponge preferences, but do prefer to breed in spongocoels containing other females. This tendency for females to aggregate is a form of female copying. Males in this species occur as three genetically distinct morphotypes: large [alpha]-males defend breeding sites in intertidal sponges; small [beta]-males resemble sexually receptive females in behaviour and body form; and tiny [gamma]-males that are effective at entering spongocoels and engaging in sperm competition with other males. [alpha]-Males prefer to guard large aggregations of females. [beta]-Males and [gamma]-males prefer to invade spongocoels containing large female aggregations. This paper reports the degree of femal copying that is sufficient to account for the observed distribution of females in spongocoels in the field. These results also indicate that while female copying increases variance in harem size among [alpha]-males, it also increases the opportunity for [beta]- and [gamma]-males to invade large breeding aggregations. Female aggregation behaviour thus creates a 'mating niche' for [beta]-males and [gamma]-males. The availability of this niche may partially explain the persistence of multiple male morphs in this species.

Abstract Background Maternal RNAs play a critical role in early development. Variation in the diversity and levels of maternally derived gene transcripts may be central to the origin of phenotypic novelty -- a longstanding problem in evolution and development. By studying maternal transcriptomes within and between divergent species, a better understanding of the evolutionary forces acting on maternal RNA allocation is possible. Results We present the first maternal transcriptome of the red flour beetle, Tribolium castaneum. Using a tiled whole-genome microarray, we found that 58.2% of T. castaneum genes are maternally loaded into eggs. Comparison of known Drosophila melanogaster maternal genes to our results showed widespread conservation of maternal expression with T. castaneum. Additionally, we found that many genes previously reported as having sex or tissue specific expression in T. castaneum were also maternally loaded. Identification of such pleiotropy is vital for proper modeling and testing of evolutionary theory using empirical data. The microarray design also allowed the detection of 2315 and 4060 novel transcriptionally active regions greater in length than 100 bp in unfertilized and fertilized T. castaneum eggs, respectively. These transcriptionally active regions represent novel exons of potentially unknown genes for future study. Conclusions Our results lay a foundation for utilizing T. castaneum as a model for understanding the role of maternal genes in evolution.

Abstract Background Although selection favors exploitative competition within groups, a group of hypercompetitive individuals may be less productive than a cooperative group. When competition is costly for group fitness, among-group selection can favor groups with 'policing' individuals who reduce within-group competition at a cost to their own fitness, or groups of individuals who restrain their competitive intensity ('self policing'). We examine these possibilities in a series of explicit population-genetic models. Results By comparing results from models of half and full sib structured populations, we find that increased relatedness increases the strength of among-group selection against competition genotypes, and increases the strength of among group selection favoring policing genotypes. However, the strength of selection favoring costly policing behavior also increases with increased levels of competition. When levels of competition and policing feedback on one another, groups with lower levels of relatedness can favor higher levels of costly policing. Conclusion The result of the joint selection on policing and competition leads to results different from those based on the evolution of policing alone. Our model makes 'long term' predictions equivalent to those of optimization models, but we also show the existence of protected polymorphisms of police and civilians, as well as competitors and non-competitors.

The Fisher prediction, says that sex ratios should be even when the cost of producing each sex is equal. It is found that unbiased sex ratios are predicted to evolve because frequency-dependent selection favours the rarer sex.

Many organisms exhibit phenotypic plasticity; producing alternate phenotypes depending on the environment. Individuals can be plastic (intragenerational or direct plasticity), wherein individuals of the same genotype produce different phenotypes in response to the environments they experience. Alternatively, an individual's phenotype may be under the control of its parents, usually the mother (transgenerational or indirect plasticity), so that mother's genotype determines the phenotype produced by a given genotype of her offspring. Under what conditions does plasticity evolve to have intragenerational as opposed to transgenerational genetic control? To explore this question, we present a population genetic model for the evolution of transgenerational and intragenerational plasticity. We hypothesize that the capacity for plasticity incurs a fitness cost, which is borne either by the individual developing the plastic phenotype or by its mother. We also hypothesize that individuals are imperfect predictors of future environments and their capacity for plasticity can lead them occasionally to make a low‐fitness phenotype for a particular environment. When the cost, benefit and error parameters are equal, we show that there is no evolutionary advantage to intragenerational over transgenerational plasticity, although the rate of evolution of transgenerational plasticity is half the rate for intragenerational plasticity, as predicted by theory on indirect genetic effects. We find that transgenerational plasticity evolves when mothers are better predictors of future environments than offspring or when the fitness cost of the capacity for plasticity is more readily borne by a mother than by her developing offspring. We discuss different natural systems with either direct intragenerational plasticity or indirect transgenerational plasticity and find a pattern qualitatively in accord with the predictions of our model. [ABSTRACT FROM AUTHOR]