Evolutionary trade-offs of insect resistance to Bacillus thuringiensis crops: fitness cost affecting paternity

Evolution of resistance to insecticides provides a useful model for examining fitness trade-offs associated with adaptation to stress. Here, we examined male reproductive costs in pink bollworm (Pectinophora gossypiella) resistant to an insecticidal protein of Bacillus thuringiensis (Bt) produced by transgenic cotton, using contrasts between two pairs of related susceptible and resistant strains. Without competition for access to females, no costs affecting reproductive success of resistant males were observed. Resistant and susceptible males had similar mating frequency and fertility. Additionally, fecundity of females mated to resistant and susceptible males was comparable. In competition for matings with virgin females, resistant and susceptible males had comparable success in one strain, whereas susceptible males tended to mate more often than resistant males in the other. However, irrespective of strain origin, resistant males that mated first sired significantly less offspring than susceptible males that mated first. The reduced first-male paternity in resistant males may involve reduced sperm precedence caused by mutations in a cadherin gene linked with resistance to Bt cotton.     

Sex, mutation and fitness: asymmetric costs and routes to recovery through compensatory evolution

A wild-type population of Drosophila melanogaster was used to assess the impact of a known deleterious mutation, nub(1), when it had (1) evolved for up to 180 generations with the mutation or (2) recently had the same mutant allele introgressed into it. Relative to this benchmark, we observed much stronger initial fitness depression in males (-74%) than in females (-38%) and also relatively greater fitness recovery by evolved males (+55%) than females (+17%). Experimental assays revealed amelioration in both juvenile and adult fitness and suggested that the greater relative recovery of male fitness was from gains through sexual selection. These evolutionary changes in male fertility depended on pairing with their coevolved mates for both mate choice and post-copulatory components of sexual selection. Without replication at the population level, these results are used to motivate a general hypothesis rather than definitively test it: Differences in reproductive optima may generally skew mutational effects towards the more strongly sexually-selected sex due to genic capture and condition dependence.     

Relatedness and investment in children in South Africa

Investment in children is examined using a nationally representative sample of 11,211 black (African) households in South Africa. I randomly selected one child from each household in the sample and calculated the average genetic relatedness of the other household members to the focal child. Using multivariate statistical analysis to control for background variables such as age and sex of child, household size, and socioeconomic status, I examine whether the coefficient of relatedness predicts greater household expenditures on food, on health care, and on children’s clothing. I also test whether relatedness is associated with health and schooling outcomes. The results are consistent with an inclusive fitness model: Households invest more in children who are more closely related. Two exceptions were found: in rural areas, genetic relatedness was negatively associated with money spent on food and on health care. Explanations for these results are discussed. Preliminary versions of this paper were presented at the 2003 Human Behavior and Evolution Society annual meeting in Lincoln, Nebraska, and at the 2003 Human Behavioral Ecology Workshop in Bangor, Maine. Kermyt G. Anderson is Assistant Professor at the Department of Anthropology at the University of Oklahoma. He received his Ph.D. from the University of New Mexico in 1999 and was a postdoctoral research fellow at the Population Studies Center at the University of Michigan for three years. His research focuses on biosocial models of fertility, parental investment, paternity confidence, marriage/divorce, and children’s outcomes. He is currently involved in a long-term longitudinal survey of young adults in Cape Town, South Africa, and in several projects examining the effects of HIV/AIDS in the U.S.     

Quantitative trait locus mapping in natural populations: progress, caveats and future directions

Over the last 15 years quantitative trait locus (QTL) mapping has become a popular method for understanding the genetic basis of continuous variation in a variety of systems. For example, the technique is now an integral tool in medical genetics, livestock production, plant breeding and population genetics of model organisms. Ten years ago, it was suggested that the method could be used to understand continuous variation in natural populations. In this review I: (i) clarify what is meant by natural population in the QTL context, (ii) discuss whether evolutionary biologists have successfully mapped QTL in natural populations, (iii) highlight some of the questions that have been addressed by QTL mapping in natural populations, (iv) describe how QTL mapping can be conducted in unmanipulated natural populations, (v) highlight some of the limitations of QTL mapping and (vi) try to predict some future directions for QTL mapping in natural populations.     

Poor competitive fitness of transgenically mitigated tobacco in competition with the wild type in a replacement series

Transgenic crops can interbreed with other crop cultivars or with related weeds, increasing the potential of the hybrid progeny for competition. To prevent generating competitive hybrids, we previously tested tobacco (Nicotiana tabacum L.) as a model for validating the transgenic mitigation (TM) concept using tandem constructs where a gene of choice is linked to mitigating genes that are positive or neutral to the crop, but deleterious to a recipient under competition. Here, we examine the efficacy of the TM concept at various ratios of transgenically mitigated tobacco in competition with the wild type tobacco in an ecological replacement series. The dwarf/herbicide-resistant TM transgenic plants cultivated alone under self-competition grew well and formed many more flowers than the tall wild type, which is an indication of greater reproductivity. In contrast to the wild type, TM flowering was almost completely suppressed in mixed cultures at most TM/wild type ratios up to 75% transgenic, as the TM plants were extremely unfit to reproduce. In addition, homozygous TM progeny had an even lower competitive fitness against the wild type than hemizygous/homozygous TM segregants. Thus, the TM technology was effective in reducing the risk of transgene establishment of intraspecific transgenic hybrids at different competitive levels, at the close spacing typical of weed populations.     

How is female mate choice affected by male competition?

The plethora of studies devoted to the topics of male competition and female mate choice belie the fact that their interaction remains poorly understood. Indeed, on the question of whether competition should help or hinder the choice process, opinions scattered throughout the sexual selection literature seem unnecessarily polarised. We argue, in the light of recent theoretical and empirical advances, that the effect of competition on mate choice depends on whether it results in the choosy sex attaining high breeding value for total fitness, considering both direct and indirect fitness benefits. Specifically, trade-offs may occur between different fitness benefits if some are correlated with male competitive ability whilst others are not. Moreover, the costs and benefits of mating with competitive males may vary in time and/or space. These considerations highlight the importance of injecting a life-history perspective into sexual selection studies. Within this context, we turn to the sexual selection literature to try to offer insights into the circumstances when competition might be expected to have positive or negative implications for pre-copulatory female choice. In this regard, we elaborate on three stages where competition might impact upon the choice process: (i) during mate detection, (ii) mate evaluation, and (iii) in dictating actual mating outcomes. We conclude by offering researchers several potentially rewarding avenues for future research.     

Environments and evolution: interactions between stress, resource inadequacy and energetic efficiency

Evolutionary change is interpreted in terms of the near-universal ecological scenario of stressful environments. Consequently, there is a premium on the energetically efficient exploitation of resources in a resource-inadequate world. Under this environmental model, fitness can be approximated to energetic efficiency especially towards the limits of survival. Furthermore, fitness at one stage of the life-cycle should correlate with fitness at other stages, especially for development time, survival and longevity; 'good genotypes' under stress should therefore be at a premium. Conservation in the wild depends primarily on adaptation to abiotically changing habitats since towards the limits of survival, genomic variation is rarely restrictive. The balance between energetic costs under variable environments and energy from resources provides a model for interpreting evolutionary stasis, punctuational and gradual change, and specialist diversification. Ultimately, a species should be in an equilibrium between the physiology of an organism and its adaptation to the environment. The primary key to understanding evolutionary change should therefore be ecological, highlighting energy availability in a stressed world; this approach is predictive for various patterns of evolutionary change in the living and fossil biota.     

Serological investigation of Bartonella henselae infections in clinically cat-scratch disease-suspected patients,patients with cardiovascular diseases,and healthy veterinary students in Japan

Seroprevalence of Bartonella henselae was investigated in Japan in 48 individuals clinically suspected of having cat-scratch disease (CSD), 159 patients with cardiovascular diseases, and 129 healthy veterinary students. Of 48 CSD-suspected patients examined, 19 (39.6%) were positive for B. henselae-IgG and 4 (8.3%) for B. henselae-IgM. Of 159 patients with cardiovascular diseases, 5 (3.1%) were positive for B. henselae-IgG. In healthy veterinary students, 14 of 129 (10.9%) were positive for B. henselae-IgG and 1 (0.8%) for B. henselae-IgM. The positive rates of B. henselae-IgG and -IgM in CSD-suspected patients were significantly higher than in other sources. Most CSD-suspected and healthy individuals who were positive for B. henselae antibody had had some contacts with cats. In CSD-suspected patients, the B. henselae positive rate in females was significantly higher than in males, and high seropositive rates to B. henselae were found in younger age groups.     

Male size, sperm transfer, and colony fitness in the western harvester ant, Pogonomyrmex occidentalis

Mating success in the western harvester ant, Pogonomyrmex occidentalis, increases with male size. We tested the hypothesis that increased mating success increases male fitness and the fitness of colonies that make large males by comparing the sperm content of males prior to and at the conclusion of the mating swarm. The number of sperm a male initially possesses is a function of male size, and large males transfer a greater proportion of their sperm than do small males. For colonies, the payoff per unit of investment is an increasing function of male size, and investment in large males is not equivalent to investing in a larger number of small males. Allocation ratios in species that show size variation in reproductives may need to be modified by the individual fitness functions.