The formation of blastomeres by the newly fertilized egg has been studied by many authors, who have found the process a convenient avenue for attacking the general problem of cell division. By far the greater part of the work has been carried out on the eggs of marine invertebrates, and, in spite of their great suitability for most types of experimental embryological investigation, the eggs of ...

Nest placement affects the risk of predation on both eggs and incubating parents and determines the microclimate for incubation, two functions that may be in conflict, especially in hot deserts. We studied the roles of microclimate and nest predation on nest site selection by Hoopoe Larks (Alaemon alaudipes) in the Arabian Desert. Hoopoe Larks build nests in three microsites: on the gravel plai...

1. Patterns of resource allocation in different times of the year can provide insights into the effects of simultaneous environmental constraints on reproduction and survival of desert birds. Field metabolic rate (FMR), water influx rate (WIR) and patterns of time allocation of Hoopoe Larks ( Alaemon alaudipes Desfontaines) were investigated during spring, when larks were rearing offspring, and...

We tested the role of interspecific competition in driving species distribution at multiple spatial scales using two sibling species of Galerida larks (G. cristata and G. theklae) in Morocco (sympatry), Balearic islands (G. theklae only) and Israel (G. cristata only). We first investigated regional-scale determinants by contrasting allopatric versus sympatric patterns in five distinct habitat t...

T H E mechanism of differentiation presents one of the central problems of embryology, and it seems reasonable to assume that the development of tissue and organ specificities, in a chemical sense, mirrors differentiation as recognized by the classical methods of embryonic grafting and histological analysis. It is now well established that it is possible, by means of immunological techniques, t...

Many organisms avoid habitats posing risks of parasitism. Parasites are not generally conspicuous, however, which raises the question what cues individuals use to detect parasitism risk. Here, we provide evidence in alpine newts ( Ichthyosaura alpestris ) that non-visual from parasite-exposed conspecifics inform habitat avoidance. Alpine breed aquatic and occasionally move among adjacent terres...

Ectodermal explants from gastrulae of Triturus alpestris were exposed to tritiated cytochalasin B (5 and 10 mug/ml) for 1/2-2 1/2 h. The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yo...