Reproductive interference in live-bearing fish: the male guppy is a potential biological agent for eradicating invasive mosquitofish

The eradication of invasive exotic species is desirable but often infeasible. Here, we show that male guppies are a potential biological agent for eradicating invasive mosquitofish through the mechanism of reproductive interference, which is defined as any sexual behavior erratically directed at a different species that damages female and/or male fitness. Together with decades of data on species distribution, our field surveys suggest that mosquitofish initially became established on Okinawa Island before being replaced by the more recently introduced guppies. More importantly, our laboratory experiments suggest that reproductive interference was one of the mechanisms underlying this species exclusion, and that in this case, the negative effects were asymmetric, i.e., they only impacted mosquitofish. Reproductive interference may offer a safer and more convenient method of biological control than the traditional sterile male release method because radiation is not necessary.

Abnormality in sarcoplasmic reticulum-dependent arterial contraction in responses to caffeine and noradrenaline in spontaneously hypertensive rats

We studied caffeine- and noradrenaline-induced contraction in tail arteries from 4-week-old male SHR and age- and sex-matched WKY. After the sarcoplasmic reticulum Ca2+ had been depleted by the Ca(2+)-free EGTA (0.1 mmol/l) solution, the caffeine (10 mmol/l)-induced contractions in a low-Ca2+ (0.5 mmol/l) solution were smaller in SHR than in WKY. After the sarcoplasmic reticulum had been loaded with Ca2+ in physiological Ca2+ (2.5 mmol/l) solution, caffeine- and noradrenaline (10(-5) mol/l)-induced contractions in a Ca(2+)-free EGTA solution were smaller in SHR than in WKY. The Ca2+ concentration-tension relationship in skinned arterial fibres was similar in WKY and SHR. These data suggest that the ability of the sarcoplasmic reticulum to take up Ca2+ and store Ca2+ is decreased in SHR. The decreased take up and store of Ca2+ may increase cytosolic Ca2+, which elevates arterial resistance and develops hypertension in gene hypertension.

Ontogenetic stage-specific quantitative trait loci contribute to divergence in developmental trajectories of sexually dimorphic fins between medaka populations

Sexual dimorphism can evolve when males and females differ in phenotypic optima. Genetic constraints can, however, limit the evolution of sexual dimorphism. One possible constraint is derived from alleles expressed in both sexes. Because males and females share most of their genome, shared alleles with different fitness effects between sexes are faced with intralocus sexual conflict. Another potential constraint is derived from genetic correlations between developmental stages. Sexually dimorphic traits are often favoured at adult stages, but selected against as juvenile, so developmental decoupling of traits between ontogenetic stages may be necessary for the evolution of sexual dimorphism in adults. Resolving intralocus conflicts between sexes and ages is therefore a key to the evolution of age-specific expression of sexual dimorphism. We investigated the genetic architecture of divergence in the ontogeny of sexual dimorphism between two populations of the Japanese medaka (Oryzias latipes) that differ in the magnitude of dimorphism in anal and dorsal fin length. Quantitative trait loci (QTL) mapping revealed that few QTL had consistent effects throughout ontogenetic stages and the majority of QTL change the sizes and directions of effects on fin growth rates during ontogeny. We also found that most QTL were sex-specific, suggesting that intralocus sexual conflict is almost resolved. Our results indicate that sex- and age-specific QTL enable the populations to achieve optimal developmental trajectories of sexually dimorphic traits in response to complex natural and sexual selection.