Anna Nordén

Sex chromosome evolution: historical insights and future perspectives

Many separate-sexed organisms have sex chromosomes controlling sex determination. Sex chromosomes often have reduced recombination, specialized (frequently sex-specific) gene content, dosage compensation and heteromorphic size. Research on sex determination and sex chromosome evolution has increased over the past decade and is today a very active field. However, some areas within the field have not received as much attention as others. We therefore believe that a historic overview of key findings and empirical discoveries will put current thinking into context and help us better understand where to go next. Here, we present a timeline of important conceptual and analytical models, as well as empirical studies that have advanced the field and changed our understanding of the evolution of sex chromosomes. Finally, we highlight gaps in our knowledge so far and propose some specific areas within the field that we recommend a greater focus on in the future, including the role of ecology in sex chromosome evolution and new multilocus models of sex chromosome divergence.

Linking intra- and interspecific assortative mating : Consequences for asymmetric sexual isolation

Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within‐species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male–male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.

Effects of Exclusion from a Conservation Policy: Negative Behavioral Spillovers from Targeted Incentives

A critical issue in the design of incentive mechanisms is the choice of whom to target. For forests, the leading rules are (1) target locations with high ecosystem-service density; (2) target additionality, i.e., locations where conservation would not occur without the incentive; and, (3) at least effectively reward previous private choices to conserve forest. We use a field experiment to examine the changes in contributions to forest conservation when we introduce each of these selection rules. For individuals who are selected, we find that targeting additionality (rule 2) is the only scheme to increase contributions. However, that selection rule intentionally excludes those who contributed most previously, and it is the only one to generate significant “behavioral leakage,” i.e., negative spillovers or a decrease in contributions by those who are excluded (and who face no price or income changes). Our results demonstrate a tradeoff in targeting and a challenge for optimal policy design.

Has Forest Certification Reduced Forest Degradation in Sweden

This paper estimates the effects of certification of nonindustrial private forest owners on forest degradation in Sweden—one of the countries with the largest total area of certified forests. We rely on official forest inventory data, information on certification status, and impact evaluation methods to identify the causal effect of certification on three key environmental outcomes. We find that certification has not halted forest degradation in that it has not improved any of the environmental outcomes. Moreover, for forest certification to have an effect, the standards should be tightened and the monitoring and enforcement of forest certification schemes strengthened. (JEL Q23, Q28)