Homosexual male pairing in Schistosoma mansoni

and 1988. Homosexual male pairing in Schistosoma mansoni.International Journal for Parasitology 18: 1115–1117. To see whether male worms within the gynecophoral canal of another male worm would become feminized (i.e. express vestigial female-associated genes), we established homosexual pairs by twice exposing mice to male cercariae with a 4 or 6-week interval, and perfusing 3–5 weeks later. From 13 to 34% of these worms were found in pairs, compared with 0 to 7% in singly exposed controls. ‘Inner’ males in homosexual pairs showed no histological evidence of female reproductive structures, but were stunted, had poorly developed testes, and the high nuclear density characteristic of mature females. More vitelline follicles occurred in unpaired unisexual males than in homosexually paired males, fewest in bisexually paired males. Uptake of tyrosine, an indicator of vitelline development, occurred in the same relative order. The gynecophoral microenvironment often led to stunting, probably through starvation induced by the relative inaccessibility of host blood to homosexually clasped males.     

What generates the diversity of Wolbachia—arthropod interactions?

Wolbachia are strictly endocellular, vertically transmitted bacteria associated with insects and crustaceans. This group of parasites modify their hosts' reproduction so as to increase their own fitness. This paper reviews the variability of these parasitic alterations and their consequences for host biology and populations. Wolbachia induce cytoplasmic incompatibility (a characteristic apparently specific to Wolbachia) in several insects and one isopod crustacean; parthenogenesis (thelytoky) in haplo-diploid insects; feminization in various isopods. The consequences of these phenomena on speciation, population dynamics and genetic polymorphism are discussed. The variability of the mechanisms of host sex determination is one important factor responsible for the diversity of Wolbachia-host interactions. However, parasite characteristics, such as the capacity to disturb host mitosis, and the ability to be horizontally transferred between hosts, also appear to play a role in this diversity.     

Cytoplasmic feminizing elements in a two-population model: infection dynamics, gene flow modification, and the spread of autosomal suppressors

We investigate the dynamics of a cytoplasmic parasitic element with feminizing effect in a two-population model. We assume that the host species has a ZZ/ZW sex determination system. Our analysis reveals that the feminizer and the W chromosome can stably coexist by dominating different populations if the transmission rate differs significantly between the populations and migration is sufficiently weak. In the equilibrium of coexistence, genetic influx at any host autosomal locus is strongly enhanced in the population where infection is prevalent but not modified in the other population. We further explore conditions for the spread of autosomal suppressor genes that reduce transmission of feminizing elements to the cost of host viability, and compute their equilibrium frequencies. Our results confirm the hypothesis that selfish genetic elements convert infected host populations into genetic sinks, thereby restricting the spread of transmission suppressors.     

THE EVOLUTIONARY IMPLICATIONS OF CONFLICT BETWEEN PARASITES WITH DIFFERENT TRANSMISSION MODES

Understanding the processes that shape the evolution of parasites is a key challenge for evolutionary biology. It is well understood that different parasites may often infect the same host and that this may have important implications to the evolutionary behavior. Here we examine the evolutionary implications of the conflict that arises when two parasite species, one vertically transmitted and the other horizontally transmitted, infect the same host. We show that the presence of a vertically transmitted parasite (VTP) often leads to the evolution of higher virulence in horizontally transmitted parasites (HTPs), particularly if the VTPs are feminizing. The high virulence in some HTPs may therefore result from coinfection with cryptic VTPs. The impact of an HTP on a VTP evolution depends crucially on the nature of the life‐history trade‐offs. Fast virulent HTPs select for intermediate feminization and virulence in VTPs. Coevolutionary models show similar insights, but emphasize the importance of host life span to the outcome, with higher virulence in both types of parasite in short‐lived hosts. Overall, our models emphasize the interplay of host and parasite characteristics in the evolutionary outcome and point the way for further empirical study.     

环境雌激素生态影响的研究进展

环境雌激素(ｅｃｏｅｓｔｒｏｇｅｎ) ,是指能够扰乱动物内分泌活动 ,生理活性与雌激素较为相似的动物体外化学物质 ,包括人工合成化合物以及植物天然雌激素 ,由于目前所发现的干扰动物及人体内分泌系统的有机化合物绝大多数都具有激素特征 ,因此通常又将环境激素称做“干扰内分泌化合物”(ｅｎｄｏｃｒｉｎｅｄｉｓｒｕｐｔｉｎｇｃｈｅｍｉ ｃａｌｓ或ｅｎｄｏｃｒｉｎｅｄｉｓｒｕｐｔｅｒｓ)。环境激素问题只是在最近几年才引起世界关注 ,但由于环境激素污染范围广、影响大 ,对人类生存的威胁更直接 ,目前 ,西方国家将环境激素问题与臭…     

The hormone 17β-estradiol promotes feminization of juveniles protandrous hermaphrodite false clownfish (Amphiprion ocellaris)

The social structure of the false clownfish (Amphiprion ocellaris) typically consists of a pair of functional brooders within a population of individuals which remain as protandrous hermaphrodites usually incapable of breeding. This situation often hampers the commercial scale production of large numbers of clownfish offspring and broodstock. To enhance breeding outputs, protandrous hermaphrodites must be converted to functional brooders with a distinct sex prior to pairing and breeding. In this study, 17β-estradiol (E2) was used to feminize juveniles of A. ocellaris, with groups of fish incubated at 0.1, 0.2, and 0.4 mgL^?1 E2 for 15 days. The gender was substantiated on the basis of gonad histological profiles after 15, 30, and 60 days, work that includes verification of the safety levels of this hormone used in this application. All the treatments employed induced feminization, as shown by histology profiles revealing degenerate male germ cells and testes tissues and several developed ovarian cells at different stages (oogonia, previtellogenic and vitellogenic) 30 days after E2 incubation. Conversely, gonad profiles of non-treated fish did not change. The gonads possessed both ovarian and testicular tissues, a typical characteristic indicating that the fish are still ambisexual. Although E2 was effective in promoting gonad maturation, incubation of fish in high concentrations adversely affected fish survival. Mortalities occurred when E2 exceeded 0.1 mgL^?1. The latter concentration is considered the most appropriate level for inducing feminization and at the same time, maintaining the well-being of the organism.     

β-Glucuronidase activity is present in the microscopic epididymis of the Tfm/Y mouse

The sex-linked recessive gene Tfm in the mouse produces a condition of testicular feminization (androgen insensitivity syndrome, AIS) in hemizygotes, comparable to the condition of the same name in humans. The murine mutant was originally believed to have no derivatives of the mesonephric duct system (MDS), and this absence was ascribed to dependence of these derivatives on androgens for survival. However, microscopical epi-didymides, retia testes, and vasa deferentia were identified in these animals in our laboratory. These micro-organs may play a role in meiosis induction in Tfm/Y animals. The present study was designed to determine whether survival of these organs is due to retention of an ability to respond to androgens, or whether they are unique amongst MDS derivatives in being independent of androgens. Previous studies in our laboratory demonstrated that the enzyme β-glucuronidase (βG) is androgen sensitive in the epididymis of the normal mouse. In the present investigation we used this enzyme as a marker to study androgen sensitivity in the microscopical epididymides of Tfm/Y hemizygotes and in the epididymides of control +/Y litter-mate brothers. Both mutant and control animals were studied with and without exogenous androgen stimulation. Tfm/Y hemizygotes demonstrated low levels of diffuse, cytoplasmic βG activity that appears to be unresponsive to exogenous androgen stimulation. In light of our previous studies, this distribution of βG reaction products suggests some degree of androgen sensitivity. The survival of these micro-organs and their partial androgen sensitivity may be related to the role of the MDS in inducing meiosis.     

Microbial manipulation of host sex determination. Endosymbiotic bacteria can directly manipulate their host's sex determination towards the production of female offspring

A recent study in the lepidopteran Ostrinia scapulalis shows that endosymbionts can actively manipulate the sex determination mechanism of their host. Wolbachia bacteria alter the sex-specific splicing of the doublesex master switch gene. In ZZ males of this female heterogametic system, the female isoform of doublesex is produced in the presence of the bacteria. The effect is a lethal feminization of genotypic males. Curing of ZW females leads to males that die, indicating that the bacteria have an obligate role in proper sex determination and development of their host. Microbial intervention with host sex determination may be a driving force behind the evolutionary turnover of sex determination mechanisms.     

Association with host mitochondrial haplotypes suggests that feminizing microsporidia lack horizontal transmission

The amphipod crustacean Gammarus duebeni hosts two feminizing microsporidian parasites, Nosema granulosis and Microsporidium sp. Samples of G. duebeni were collected from three sites on the Scottish island of Great Cumbrae and screened for microsporidia using polymerase chain reaction. Associations between the prevalence of the two feminizing parasites and haplotypes of the host mitochondrial gene cytochrome oxidase I (COI) were investigated. The prevalence of both parasites varied significantly among the host's COI haplotypes, suggesting that horizontal transmission is rare or absent in the life cycles of the feminizing microsporidia and that all transmission must therefore be vertical. Life cycles in which all transmission is vertical are common among bacterial parasites but have never before been demonstrated in Eukaryotic parasites.