Association between Wolbachia and Spiroplasma within Drosophila neotestacea: an emerging symbiotic mutualism?

Interspecific mutualism can evolve when specific lineages of different species tend to be associated with each other from one generation to the next. Different maternally transmitted endosymbionts occurring within the same cytoplasmic lineage fulfil this requirement. Drosophila neotestacea is infected with maternally transmitted Wolbachia and Spiroplasma, which are cotransmitted at high frequency in natural populations. Molecular phylogenetic evidence indicates that both endosymbionts have been present in D. neotestacea for considerable evolutionary periods. Thus, conditions are suitable for the evolution of mutualism between them. In support of this possibility, there is a significant positive association between Wolbachia and Spiroplasma infection in many samples of D. neotestacea from natural populations. Theoretically, such a positive association can result from either mutualism between these endosymbionts or recent spread. Collections from present‐day populations suggest that recent spread and mutualism have both operated to generate the positive association between Wolbachia and Spiroplasma. If selection acts on the combination of these two endosymbionts, they may be in the early stages of evolution of a more complex, cooperative association.     

MHC heterozygosity and survival in red junglefowl

Genes of the major histocompatibility complex (MHC) form a vital part of the vertebrate immune system and play a major role in pathogen resistance. The extremely high levels of polymorphism observed at the MHC are hypothesised to be driven by pathogen‐mediated selection. Although the exact nature of selection remains unclear, three main hypotheses have been put forward; heterozygote advantage, negative frequency‐dependence and fluctuating selection. Here, we report the effects of MHC genotype on survival in a cohort of semi‐natural red junglefowl (Gallus gallus) that suffered severe mortality as a result of an outbreak of the disease coccidiosis. The cohort was followed from hatching until 250 days of age, approximately the age of sexual maturity in this species, during which time over 80% of the birds died. We show that on average birds with MHC heterozygote genotypes survived infection longer than homozygotes and that this effect was independent of genome‐wide heterozygosity, estimated across microsatellite loci. This MHC effect appeared to be caused by a single susceptible haplotype (CD_c) the effect of which was masked in all heterozygote genotypes by other dominant haplotypes. The CD_c homozygous genotype had lower survival than all other genotypes, but CD_c heterozygous genotypes had survival probabilities equal to the most resistant homozygote genotype. Importantly, no heterozygotes conferred greater resistance than the most resistant homozygote genotype, indicating that the observed survival advantage of MHC heterozygotes was the product of dominant, rather than overdominant processes. This pattern and effect of MHC diversity in our population could reflect the processes ongoing in similarly small, fragmented natural populations.     

Intra-guild predation and variation in egg defence between sympatric and allopatric populations of two species of ladybird beetles

Abstract.  1. Ladybird eggs are defended chemically against intra-guild predation, and are unsuitable to varying degrees as food for other ladybirds.
2. Ladybird eggs [ Coccinella septempunctata (Cs) and Harmonia axyridis (Ha); Coleoptera: Coccinellidae] from local Japanese versus North American populations were compared as food for two ladybirds (Cs and Ha) co-occurring in Japan.
3. Larvae of Cs exhibited high mortality, slow development, and reduced egg consumption and weight gain when they fed on Ha versus conspecific eggs, especially when Ha eggs were from the local (Japanese) population versus a distant (North American) population of Ha.
4. Larvae of Ha survived equally well on a diet of Cs or conspecific eggs, but developed more slowly and gained less weight on Cs eggs. Ha larvae were more reluctant to eat eggs from the local (Japanese) population of Cs than eggs from the distant (North American) population of Cs; however, other measures of performance did not differ significantly.
5. These results indicate greater egg chemical defence of Ha eggs against Cs larvae than vice versa, as expected from field observations of greater temporal overlap between Cs larvae and Ha eggs than between Ha larvae and Cs eggs. Furthermore, results also indicate that local populations of eggs are better defended than eggs from elsewhere against locally occurring intra-guild predators. Thus, it appears that the effectiveness of chemical defence of ladybird eggs reflects the degree to which specific pairings of ladybirds have the potential to interact in nature through egg predation.     

The development of a model to assess the effects of rabbit grazing on grass

Grass for use as silage is widely grown in the UK. However there is little information on the effects of rabbit grazing on crop yield. In a three‐year trial, grass was grown in six enclosures following current agronomic procedures and was subjected to grazing by two population densities of rabbits. The annual yield loss at the end of the trial was found to be 1% per rabbit ha^?1. The yield loss per rabbit was calculated to be around 200 kg and the financial loss was calculated as £3.40 per rabbit at 1998 prices (approx. £17 t^?1). This new information provides farmers with a better understanding of the economics of damage caused by rabbits enabling them to make more informed decisions as to whether their rabbit population needs to be managed, or whether their crop needs to be protected by some other means.     

Effect of Pituitary and Ovarian Hormones on Human Melanocytes In Vitro

Normal human melanocytes in culture became enlarged and dendritic after a 2-day incubation with either the pituitary (β-MSH, a potent analog of α-MSH, ACTH, FSH and LH) or the ovarian (estradiol, estriol and progesterone) hormones. Under the same experimental conditions, pituitary hormones also increased both the tyrosinase activity and tyrosinase-related protein-1 (TRP-1) while ovarian hormones increased TRP-1 but not tyrosinase activity. The results suggest that pituitary and ovarian hormones possibly induce hyperpigmentation of the skin by stimulating the melanogenesis in epidermal melanocytes, and that estradiol and progesterone may be involved in the pathogenesis of melasma (chloasma) usually developing between early adulthood and menopause in which a high concentration of serum ovarian hormones was maintained.     

A simple, sterile food source for rearing the larvae of Lucilia sericata (Diptera: Calliphoridae)

arvae of the sheep blowfly Lucilia sericata (Meigen) were reared on various mixtures of puréed liver, agar, brewer's yeast and trypsin, in order to develop a simple, sterile, tissue-based diet. Growth and survival rates of larvae reared on a sterile 1:1 mixture of puréed liver with 3% Bacto agar equalled or exceeded those of larvae reared on raw liver. The addition of yeast and/or trypsin to the medium was of no additional benefit. This sterile, homogenous, tissue-based substrate offers a simple, convenient, inexpensive growth medium for rearing larvae for maggot therapy, and for testing the effects of various chemicals and dietary constituents on necrophagous insect larvae. It may be useful, therefore, in studies of myiasis, forensic entomology, and toxicology. This rearing medium also has the advantage that it can be stored for many months at room temperature without progressive decomposition or offensive odour.     

Effect of Fetal Bovine Serum Glycoproteins on the In Vitro Proliferation of the Oyster Parasite Perkinsus marinus: Development of a Fully Defined Medium

ABSTRACT. The oyster parasite Perkinsus marinus replicates in our medium consisting of Dulbecco modified Eagle's medium: Ham's F12 nutrient mixture (1:1) supplemented with 1–5% fetal bovine serum, with a doubling time of 24 hours during the exponential phase of the culture. Fetal bovine serum concentrations above 5% dramatically reduced parasite proliferation in a dose-dependent manner. We tested the individual effects of the three major protein components of fetal bovine serum (fetuin, transferrin and albumin) on the replication of the parasite in a serum-free medium. At the concentrations tested, fetuin enhanced parasite growth, whereas albumin had a modest positive effect and transferrin was inhibitory. Proteolytic digestion of fetuin, strongly diminished its growth-enhancing properties, indicating that the overall glycoprotein architecture may be required for activity. On the contrary, desialylation of fetuin slightly enhanced its growth-promoting activity. The addition of fetuin at 1.7 mg/ml to the serum-free DME: Ham's F12 medium yielded growth rates that are comparable to those obtained with our standard culture methodology. This has resulted in a fully defined culture medium that will allow for a rigorous characterization of excretory/secretory products involved in modulating or blocking the host's humoral and cellular defense mechanisms.