Biomedical subjects

Bas J Zwaan

Publications and source records attributed to Bas J Zwaan.

7 recordsLinked to original sources

PubMed2004

Butterfly selected lines explore the hormonal basis of interactions between life histories and morphology.

Hormonal mechanisms underlie many life-history traits and their interactions. We studied the role of ecdysteroids with regard to wing pattern and development time of the polyphenic butterfly Bicyclus anynana. Ecdysteroid titers and sensitivity to ecdysone injection were assayed for two-trait selected lines (ventral eyespot size and development time concurrently). These two traits are genetically and phenotypically coupled, having a common endocrinal basis. Two-trait selection had been applied both antagonistically (opposite the correlation) and synergistically (in the same direction as the correlation). Although selected lines had diverged most in eyespot size, the widest differences in timing of ecdysteroid titers were observed between the development time selection regimes; fast selected lines had an earlier hormonal increase after pupation than slow selected lines (even when corrected for differential pupal times). This endocrine peak was also earlier for females than for males. Furthermore, sensitivity to ecdysone injection as measured by a subsequent decrease in pupal time was significantly lower for slow selected lines than for fast or unselected lines. We conclude that the observed response in eyespot size to artificial selection must have been achieved via alteration of, or selection on, other developmental mechanisms, because the dynamics of the alternative, hormonal, pathway were dictated by development time selection. The developmental system is flexible enough to allow evolution in directions opposing the correlation between wing pattern and developmental time, and responses to selection are not constrained by a shared hormonal system.

Animals↗

PubMed2004

Genetic diversity and Wolbachia infection of the Drosophila parasitoid Leptopilina clavipes in western Europe.

Wolbachia are maternally transmitted bacteria that alter their arthropod hosts' reproduction in various ways, including parthenogenesis induction (PI). Wolbachia-induced parthenogenesis can have drastic effects on the genetic structure of its host because it potentially reduces populations to clones without genetic exchange. However, Wolbachia-induced parthenogenesis does not inevitably result in a reduction of genetic variation of infected populations vs. uninfected populations, because the parthenogenetic populations are initially derived from uninfected populations and can thus show similar genetic variation. Here we investigate these issues in infected and uninfected populations of the Drosophila parasitoid Leptopilina clavipes in western Europe. Wasps from 19 sites in the Netherlands, France and northern Spain were screened for Wolbachia and analysed using amplified fragment length polymorphism (AFLP) markers. All the populations from the Netherlands and mid-France were infected with the same two strains of Wolbachia, whereas populations from the Pyrenees were not infected. The infected and uninfected populations show identical levels of genetic variation, but have clearly diverged genetically, indicating the presence of a barrier that prevents gene flow. Within the infected wasps two distinct genotypes were found at multiple localities, indicating the coexistence of multiple clones. The conditions promoting clonal coexistence in L. clavipes are discussed.

Animals↗

PubMed2004

Cytology of Wolbachia-induced parthenogenesis in Leptopilina clavipes (Hymenoptera: Figitidae).

Parthenogenesis induced by cytoplasmatically inherited Wolbachia bacteria has been found in a number of arthropod species, mainly Hymenoptera. Previously, two different forms of diploidy restoration have been reported to underlie parthenogenesis induction in Hymenoptera by Wolbachia. Both are a form of gamete duplication, but each differs in their timing. We investigated the cytology of the early embryonic development of a Wolbachia-infected strain of the parasitoid wasp Leptopilina clavipes and compared it with that of an uninfected sexual strain. Both strains have a similar meiosis. In the infected parthenogenetic strain, diploidy is restored by anaphase restitution during the first somatic mitosis, similar to Trichogramma, but not to Muscidifurax. Our results confirm the occurrence of different cytological mechanisms of diploidy restoration associated with parthenogenesis-inducing Wolbachia in the order Hymenoptera.

Animals↗

PubMed2004

The genetic basis of male fertility in relation to haplodiploid reproduction in Leptopilina clavipes (Hymenoptera: Figitidae).

Traits under relaxed selection are expected to become reduced or disappear completely, a process called vestigialization. In parthenogenetic populations, traits historically involved in sexual reproduction are no longer under selection and potentially subject to such reduction. In Leptopilina clavipes, thelytokous (parthenogenetic) populations are infected by Wolbachia bacteria. Arrhenotokous populations do not harbor Wolbachia. When antibiotics are applied to infected females, they are cured from their infection and males arise. Such males are capable of producing offspring with uninfected females, but with lower fertilization success than sexual males. This can be attributed to the lack of selection on male fertility in thelytokous lines. In this study we used this variation in L. clavipes male fertility to determine the genetic basis of this trait. Males from cured thelytokous populations were crossed to females from uninfected populations. Using AFLP markers, a genetic linkage map was generated, consisting of five linkage groups and spanning a total distance of 219.9 cM. A single QTL of large effect (explaining 46.5% of the phenotypic variance) was identified for male fertility, which we call male fertility factor (mff). We discuss possible mechanisms underlying the effect of mff, as well as mechanisms involved in vestigialization of traits involved in sexual reproduction.

Animals↗

PubMed2003

Linking development and aging.

Evolutionary theory predicts that the different life stages of organisms are coordinated to achieve maximal reproductive output. Moreover, aging can be seen as an evolutionary side effect of this selective process that applies to many living organisms. Hence, genetic, developmental, and physiological mechanisms resulting from this selection are expected to be conserved in diverse lineages. The insulin/insulin-like growth factor signaling (INS) pathway appears to be such a mechanism that regulates life span and reproduction in a variety of model organisms. Here I argue that the experimental tools of environmental manipulation and gene by environment interaction should be used more often both during the experimental organism's development and its adult life. This approach will help us to fully understand the functions of longevity-determining pathways and will determine the life stages during which these pathways exert their effects on adult life. These points are raised because of a recent Aging Cell publication by Tu and Tatar, in which the larval food environment was manipulated to determine the effects on adult reproduction, life span, aging, and INS. The results of this study are a promise of the usefulness of this approach for understanding the aging process.

Aging↗

PubMed2003

Cooler butterflies lay larger eggs: developmental plasticity versus acclimation.

We use a full factorial design to investigate the effects of maternal and paternal developmental temperature, as well as female oviposition temperature, on egg size in the butterfly Bicyclus anynana. Butterflies were raised at two different temperatures and mated in four possible sex-by-parental-temperature crosses. The mated females were randomly divided between high and low oviposition temperatures. On the first day after assigning the females to different temperatures, only female developmental temperature affected egg size. Females reared at the lower temperature laid larger eggs than those reared at a higher temperature. When eggs were measured again after an acclimation period of 10 days, egg size was principally determined by the prevailing temperature during oviposition, with females ovipositing at a lower temperature laying larger eggs. In contrast to widely used assumptions, the effects of developmental temperature were largely reversible. Male developmental temperature did not affect egg size in either of the measurements. Overall, developmental plasticity and acclimation in the adult stage resulted in very similar patterns of egg size plasticity. Consequently, we argue that the most important question when testing the significance of acclamatory changes is not at which stage a given plasticity is induced, but rather whether plastic responses to environmental change are adaptive or merely physiological constraints.

Acclimatization↗

PubMed2003

Simultaneous selection on two fitness-related traits in the butterfly Bicyclus anynana.

Theory about the role of constraints in evolution is abundant, but few empirical data exist to describe the consequences a bias in phenotypic variation has for micro evolution. Responses to natural selection can be severely hampered by a genetic correlation among a suite of traits. Constraints can be studied using antagonistic selection experiments, that is, two-trait selection in opposition to this correlation. The two traits studied here were development time and wing pattern (eyespot size) in the butterfly Bicyclus anynana, both of which have a clear adaptive significance. Rates of response were higher for eyespot size than for development time, but were independent of the concurrent selection (either in the same direction as the correlation or perpendicular to it). Regimes differed in both traits in all directions after 11 generations of selection. The uncoupling lines had higher relative responses than the synergistic lines in development time and equal relative responses in eyespot size. The patterns for eyespot size (reaction norms) were consistent across different rearing temperatures. Differences in lines selected for fast and slow development time were more pronounced at lower temperatures, irrespective of the direction of joint wing pattern selection. Furthermore, correlated responses in pupal weight and growth rate were observed; lines selected for a slower development had higher pupal weights, especially at lower temperatures. The response of the uncoupling lines was not hampered by a lack of selectable genetic variation, and the relative response in the development time was larger than expected based on response in the coupled direction and quantitative genetic predictions. This suggests that the structure of the genetic architecture does not constrain the short-term, independent evolution of both wing pattern and development time.

Animals↗