Effect of Silt, Water and Periphyton Quality on Survival and Growth of the Mayfly Heptagenia Sulphurea

The herbivorous mayfly Heptagenia sulphurea is characteristic of rivers with stony bottoms. Records from the 20th century showed that this species had disappeared from the Common Meuse in the Netherlands, probably due to river regulation or changes in water quality. A field survey in 2003 showed that H. sulphurea was present in the Geul tributary, approximately 300 m upstream of its confluence with the Common Meuse. H. sulphurea has not recolonized the Common Meuse despite improvements in water quality over the last decades. Concentration of suspended sediments in the River Meuse, however, is still high, much higher than in the beginning of the 20th century. The presence of a silt layer may limit the return of H. sulphurea in this river by reducing availability and quality of its food. The prime objective of this study was to investigate the impact of silt on survival and growth of H. sulphurea in a laboratory experiment. Furthermore, the impact of water and periphyton quality from the Common Meuse on survival and growth of this mayfly was also investigated. Results showed that neither water quality nor cultured periphyton from the Common Meuse reduced survival and growth of H. sulphurea. The presence of a silt layer resulted in a significantly lower growth rate of the mayfly larvae. It is concluded that the silt layer reduces the accessibility of the food. Covering of food is possibly one of the main factors limiting the recolonization of H. sulphurea and probably other benthic grazers in the Common Meuse.     

Anthrax in Western and Central African great apes

During the period of December 2004 to January 2005, Bacillus anthracis killed three wild chimpanzees (Pan troglodytes troglodytes) and one gorilla (Gorilla gorilla gorilla) in a tropical forest in Cameroon. While this is the second anthrax outbreak in wild chimpanzees, this is the first case of anthrax in gorillas ever reported. The number of great apes in Central Africa is dramatically declining and the populations are seriously threatened by diseases, mainly Ebola. Nevertheless, a considerable number of deaths cannot be attributed to Ebola virus and remained unexplained. Our results show that diseases other than Ebola may also threaten wild great apes, and indicate that the role of anthrax in great ape mortality may have been underestimated. These results suggest that risk identification, assessment, and management for the survival of the last great apes should be performed with an open mind, since various pathogens with distinct characteristics in epidemiology and pathogenicity may impact the populations. An animal mortality monitoring network covering the entire African tropical forest, with the dual aims of preventing both great ape extinction and human disease outbreaks, will create necessary baseline data for such risk assessments and management plans.     

Queen-worker differences in spermatheca reservoir of phylogenetically basal ants

Ant queens mate when young and store sperm in their spermatheca to fertilize eggs for several years until their death. In contrast, workers in most species never mate. We have compared the histological organization of spermathecae in 25 poneromorph species exhibiting various degrees of queen-worker dimorphism. The spermathecae of both castes in all species are similar in having a reservoir connected by a sperm duct to the ovary, and a paired gland opening into this duct. The reservoir of queens typically has a columnar epithelium in the hilar region (near the opening of the sperm duct), whereas the epithelium in the distal region is cuboidal. Abundant mitochondria together with apical microvilli and basal invaginations indicate an osmoregulatory function. In contrast, the reservoir epithelium of workers is flattened throughout and lacks these transport characteristics. This single difference shows the importance of a columnar epithelium in the reservoir for sperm storage. However, our data have not revealed inter-specific variations in the development of the hilar region linked with higher fecundity. We have found no consistent differences in associated structures, such as the spermatheca gland or sperm ducts, or in the musculature between queens and workers.This work was funded by IWT, FWO, KULeuven OT and JSPS.     

A simple equation for describing the temperature dependent growth of free-floating macrophytes

Temperature is one of the most important factors determining growth rates of free-floating macrophytes in the field. To analyse and predict temperature dependent growth rates of these pleustophytes, modelling may play an important role. Several equations have been published for describing temperature responses of macrophytes and algae. But they are often complex or are only applicable in a limited range of temperatures. In this paper, we present a simple three-parameter equation for describing the temperature dependent growth rates of pleustophytes. The equation that we developed is tested using results from laboratory growth experiments conducted with three different species of pleustophytes (Lemna minor, Salvinia molesta and Azolla filiculoides). The equation is simple and demonstrates reliable fits (adjusted R² reaching from 0.89 to 0.95). Additionally, our equation primarily uses parameters of biological significance, resulting in estimates of useful cardinal temperatures (minimum and maximum).     

Hormonal correlates of reproductive status in the queenless ponerine ant, Streblognathus peetersi

In colonies of the queenless ant Streblognathus peetersi, dominance interactions produce a reproductive hierarchy in which one individual, the alpha, is capable of producing offspring while her subordinates remain infertile. Based on differences between behaviour and cuticular hydrocarbon profiles, the subordinates can be further divided into high and low ranking workers. Although it had been shown previously that alphas treated with a juvenile hormone analog lose their reproductive status, little was known of the endocrinological basis of dominance in this species. To elucidate the underlying endocrinology of these three ranks, we measured the individual in vitro rate of juvenile hormone (JH) production of excised corpora allata, and the ecdysteroid titer of pooled hemolymph samples. Production of JH was highest in low-ranking workers, intermediate in high rankers, and almost undetectable in alphas. Ecdysteroid titers were low for low rankers, but were more than twice as high for both high rankers and alphas. The results support the hypothesis that JH suppresses ovarian function in these queenless ants, and suggest that ecdysteroids may be responsible for stimulating vitellogenin production. The possible role of these hormones as behavioural modulators is also discussed.     

When David and Goliath share a home: Compound nesting of Pyramica and Platythyrea ants

We documented a commensal association between two phylogenetically distant ant subfamilies (Ponerinae and Myrmicinae). The host (Platythyrea conradti) and its tiny guest (Pyramica maynei) nest in the same hollow branches in West African forests. Brood chambers are adjacent but separate, and the guest scavenges on prey remains of the host, which may benefit from improved nest hygiene. Two mated dealate queens of Pyramica were collected in one small Platythyrea nest, suggesting that they can hunt (non-claustral foundation) in the safe environment provided. An experiment showed that the guest can survive alone and was able to hunt collembolans. Received 14 March 2006; revised 18 May 2006; accepted 24 May 2006.     

Les anthropomorphes du mont Bego aux pieds tournés vers l'intérieur : une hypothèse

Three major figures from the Vallée des Merveilles have the feet turned inward. The extreme rarity of this posture in the plastic arts of all times and the fact it is attributed essentially to major figures indicate the particular significance of this stand for the authors of the engravings. de Lumley et al. (1995, 2003) interpret this feet position as a hieratic attitude, as the mark the figure belongs to the world of the gods. In this study another hypothesis, which doesn't necessarily exclude the first one, is proposed from an ethological point of view based on the reading of body language made by Wex (1993). She claims that the inward turning of the feet represents a protective reaction to a situation which put the person in a fragile or harmful position. This hypothesis, as well other characteristics, questions the divine or human nature of our three anthropomorphic figures. The shamanistic approach (Hedges, 1993; Whitley, 2001) is raised with respect to this issue and the inward feet position.     

Indirect Genetic Effects for Survival in Domestic Chickens (Gallus gallus) Are Magnified in Crossbred Genotypes and Show a Parent-of-Origin Effect

Through social interactions, individuals can affect one another’s phenotype. The heritable effect of an individual on the phenotype of a conspecific is known as an indirect genetic effect (IGE). Although IGEs can have a substantial impact on heritable variation and response to selection, little is known about the genetic architecture of traits affected by IGEs. We studied IGEs for survival in domestic chickens (Gallus gallus), using data on two purebred lines and their reciprocal cross. Birds were kept in groups of four. Feather pecking and cannibalism caused mortality, as beaks were kept intact. Survival time was shorter in crossbreds than in purebreds, indicating outbreeding depression and the presence of nonadditive genetic effects. IGEs contributed the majority of heritable variation in crossbreds (87 and 72%) and around half of heritable variation in purebreds (65 and 44%). There was no evidence of dominance variance, neither direct nor indirect. Absence of dominance variance in combination with considerable outbreeding depression suggests that survival is affected by many loci. Direct–indirect genetic correlations were moderately to highly negative in crossbreds (−0.37 ± 0.17 and −0.83 ± 0.10), but low and not significantly different from zero in purebreds (0.20 ± 0.21 and −0.28 ± 0.18). Consequently, unlike purebreds, crossbreds would fail to respond positively to mass selection. The direct genetic correlation between both crosses was high (0.95 ± 0.23), whereas the indirect genetic correlation was moderate (0.41 ± 0.26). Thus, for IGEs, it mattered which parental line provided the sire and which provided the dam. This indirect parent-of-origin effect appeared to be paternally transmitted and is probably Z chromosome linked.     

Eastern chimpanzees, but not bonobos, represent a simian immunodeficiency virus reservoir

Chimpanzees in west central Africa (Pan troglodytes troglodytes) are endemically infected with simian immunodeficiency viruses (SIVcpzPtt) that have crossed the species barrier to humans and gorillas on at least five occasions, generating pandemic and nonpandemic forms of human immunodeficiency virus type 1 (HIV-1) as well as gorilla SIV (SIVgor). Chimpanzees in east Africa (Pan troglodytes schweinfurthii) are also infected with SIVcpz; however, their viruses (SIVcpzPts) have never been found in humans. To examine whether this is due to a paucity of natural infections, we used noninvasive methods to screen wild-living eastern chimpanzees in the Democratic Republic of the Congo (DRC), Uganda, and Rwanda. We also screened bonobos (Pan paniscus) in the DRC, a species not previously tested for SIV in the wild. Fecal samples (n = 3,108) were collected at 50 field sites, tested for species and subspecies origin, and screened for SIVcpz antibodies and nucleic acids. Of 2,565 samples from eastern chimpanzees, 323 were antibody positive and 92 contained viral RNA. The antibody-positive samples represented 76 individuals from 19 field sites, all sampled north of the Congo River in an area spanning 250,000 km(2). In this region, SIVcpzPts was common and widespread, with seven field sites exhibiting infection rates of 30% or greater. The overall prevalence of SIVcpzPts infection was 13.4% (95% confidence interval, 10.7% to 16.5%). In contrast, none of the 543 bonobo samples from six sites was antibody positive. All newly identified SIVcpzPts strains clustered in strict accordance to their subspecies origin; however, they exhibited considerable genetic diversity, especially in protein domains known to be under strong host selection pressure. Thus, the absence of SIVcpzPts zoonoses cannot be explained by an insufficient primate reservoir. Instead, greater adaptive hurdles may have prevented the successful colonization of humans by P. t. schweinfurthii viruses.