Entomopathogenic Nematodes as a Model System for Advancing the Frontiers of Ecology

Entomopathogenic nematodes (EPNs) in the families Heterorhabditidae and Steinernematidae have a mutualistic–symbiotic association with enteric γ-Proteobacteria (Steinernema–Xenorhabdus and Heterorhabditis–Photorhabdus), which confer high virulence against insects. EPNs have been studied intensively because of their role as a natural mortality factor for soil-dwelling arthropods and their potential as biological control agents for belowground insect pests. For many decades, research on EPNs focused on the taxonomy, phylogeny, biogeography, genetics, physiology, biochemistry and ecology, as well as commercial production and application technologies. More recently, EPNs and their bacterial symbionts are being viewed as a model system for advancing research in other disciplines such as soil ecology, symbiosis and evolutionary biology. Integration of existing information, particularly the accumulating information on their biology, into increasingly detailed population models is critical to improving our ability to exploit and manage EPNs as a biological control agent and to understand ecological processes in a changing world. Here, we summarize some recent advances in phylogeny, systematics, biogeography, community ecology and population dynamics models of EPNs, and describe how this research is advancing frontiers in ecology.     

Placental transfer of dexamethasone in near-term sheep

The placental transfer of 3H-dexamethasone was studied in six near-term sheep. The placental clearance of 3H-dexamethasone was 18.8 +/- 3.5 ml/min per kg of fetal weight. The clearance of dexamethasone by the fetal tissues was 9.3 +/- w.5 ml/min per kg. The maximum placental clearance was 285 +/- 24 ml/min and the degree of diffusion limitation to the placental transfer of dexamethasone was 78 +/- 4%. The placental transfer of dexamethasone is therefore limited primarily by the nature of the placental barrier.     

The costs of leaving home: ants disperse myrmecochorous seeds to low nutrient sites

Summary Leucospermum conocarpodendron (L.) Buek (Proteaceae) seedlings were excavated several months after a fire in Cape fynbos. Seedlings under burnt parental skeletons had short hypocotyls (mean 25 mm) indicating passive dispersal whereas seedlings in the open were more deeply buried (mean 48 mm) by ants. Soil nutrient concentrations at the site of germination were negatively related to depth of burial and distance from parent. Ant dispersal resulted in seedlings emerging in soils with lower nutrient concentrations than passively dispersed seeds. Tissue analysis supported the soil results with lower P content in seedlings from open (ant dispersed) sites. Seedling survival in the first year of establishment was also lower in open sites, but not significantly so. However seedlings were slightly taller in the open. The results of this study, the first on naturally occurring intraspecific variation in myrmecochory, strongly contradict current explanations for the high incidence of myrmecochory in nutrient poor environments.     

Levels of Intraspecific Variation Within the Catarrhine Skeleton

The amount of phenotypic variation between conspecifics is largely a result of the opposing forces of constraint and plasticity. Because selection is the product of competition between individuals of the same species, understanding the interactions between these forces is vital to understanding evolution. We investigated levels of intraspecific variation in the catarrhine skeleton using a morphometric analysis of 245 crania and 189 appendicular postcranial skeletons. We identified regions of interest from the literature and made comparisons of intraspecific variation between the appendicular postcranium and cranium, the forelimb and hind limb, the diaphyses and epiphyses of long bones, and the diaphyses of the proximal and distal segments of the limbs. We confirmed that variation is significantly higher in the appendicular postcranium than in the cranium, in the forelimb compared to the hind limb, and in the diaphyses compared to the epiphyses. Further, we found that this pattern was repeated in 12 species spanning the infraorder, suggesting a characteristic of catarrhines in general. The relatively low level of variation in the cranium suggests that constraint is more widespread in this region compared to the appendicular postcranium, which is more plastic, especially in the diaphyses of the forelimb. In contrast to previous studies, we found the diaphyses of the distal segment to be more variable than the diaphyses of the proximal segment. The results from this study, which show regional differences in intraspecific variation, will aid the interpretation of evolutionary and plastic influences on morphological variation and inform decisions about which skeletal regions are suitable for answering specific evolutionary questions.     

Aplasia of the thumbs and great toes as the outstanding feature of Yunis and Varon syndrome. A new entity. A new observation

Aplasia of the thumbs and great toes, and aplasia of terminal and dysplasia of middle phalanges with absence of nails were noted in the child of related parents, who died at the age of 3 months from cardiorespiratory insufficiency. This is the 7th case of an (AR) genetic syndrome called after Yunis and Varon.     

A phylogenetic analysis of the 18S ribosomal RNA sequence of the coelacanth Latimeria chalumnae

Synopsis Approximately 98% of the sequence of the 18S ribosomal RNA (rRNA) of the coelacanth Latimeria chalumnae was determined by a combination of direct RNA sequencing and sequencing of rRNA genes amplified by the polymerase chain reaction. This sequence was compared with 18S rRNA sequences of similar length from seven other vertebrate species, representing the taxa Petromyzontiformes, Holocephali, Elasmobranchii, Actinopterygii, Dipnoi, Amphibia, and Amniota, in order to determine the most likely sister group of the coelacanth. Maximum parsimony analysis of these sequences resulted in a single most parsimonious tree containing a number of anomalous relationships among these groups. A bootstrap analysis showed that none of the relationships in this tree was significantly supported at the 95% level, however. Addition of data from 15 other vertebrates (providing multiple representatives of most of the higher taxa) resulted in similar ambiguous groupings, as did a number of methods of editing the sites compared (designed to eliminate rapidly evolving positions). These results may be due to a relatively rapid radiation of the major lineages of osteichthyans, the resolution of which will require molecular information from a larger portion of the coelacanth genome.