Major Transitions in Animal Evolution: A Developmental Genetic Perspective

SYNOPSIS. Several phases of animal evolution have undergoneradical change in developmental mechanisms. I refer to theseas major transitions in animal evolution. The six most importanttransitions in the lineage leading to humans are proposed tobe: the origin of multicellularity, the origin of two-germ layersand radial symmetry, the origin of three-germ layers and bilateralsymmetry, dorsoventral axis inversion, the origin of vertebrates,the origin of gnathostomes. Here I discuss the genetic changesthat may have underlain these transitions. The last two transitionswere accompanied by, and possibly facilitated by, large increasesin gene number. This probably occurred by tetraploidy, withsome of the duplicate genes being subsequently lost. The originof three germ-layers, bilateral symmetry and a through gut alsoprobably involved gene duplication; in this case, duplicationof an ancestral ProtoHox gene cluster to yield two paralogoushomeobox gene clusters, Hox and ParaHox, with roles in patterningdifferent germ layers along the anteroposterior body axis. Thisevent may provide a partial genetic explanation for the Cambrianexplosion.     

Resource provision for farmland gamebirds: the value of beetle banks

Severe declines have occurred in the populations of wild game birds in Britain. This has been attributed to agricultural intensification, leading to the loss of invertebrates vital within chick diets, fewer feeding resources for adults, and inadequate provision of nesting and brood‐rearing habitat. This paper explores the potential value of simple sown grass strips – beetle banks – in providing these resources, and compares results with functionally similar conventional field margins. The data indicate that beetle banks can contribute useful, albeit lower, densities of chick‐food than conventional margins. These resources are more abundant later in the season, which may have implications for early hatched chicks. Beetle banks provide considerable quantities of nesting cover for adults, although sheltering conditions may never be as satisfactory as in well managed hedgerows. Given the ease and low cost of establishment of beetle banks, we suggest that they may be valuable components within a range of game management techniques on the farm, as a ‘spin‐off’ to their primary role as overwintering habitat for polyphagous predators. They may be important particularly where resources for game birds are impoverished, but clearly cannot substitute for suitably managed field margins.     

Enzymes of de novo Pyrimidine Biosynthesis in Babesia rodhaini1

ABSTRACT. The pathway of de novo pyrimidine biosynthesis in the rodent parasitic protozoa Babesia rodhaini has been investigated. Specific activities of five of the six enzymes of the pathway were determined: aspartate transcarbamylase (ATCase: E.C. 2.1.3.2): dihydroorotase (DHOase: E.C. 3.5.2.3): dihydroorotate dehydrogenase (DHO-DHase: E.C. 1.3.3.1); orotate phosphoribosyltransferase (OPRTase: E.C. 2.4.2.10); and orotidine-5′-phosphate decarboxylase (ODCase: E.C. 4.1.1.23). Michaelis constants for ATCase, DHO-DHasc. OPRTase, and ODCase were determined in whole homogenates. Several substrate analogs were also investigated as inhibitors and inhibitor constants determined. N-(phosphonacetyl)-L-aspartate was shown to be an inhibitor of the ATCase with an apparent K, of 7μM. Dihydro-5-azaorotate inhibited the DHO-DHase (K, 16 μM) and 5-azaorotate (K_i, 21 μM) was an inhibitor of the OPRTase. The UMP analog, 6-aza-UMP (K_i, 0.3 μM) was a potent inhibitor of ODCase, while lower levels of inhibition were found with the product. UMP (K_i, 120 μM) and the purine nucleotide, XMP (K₁, 95 μM). Additionally, menoctone, a ubiquinone analog, was shown to inhibit DHO-DHase.     

EFFECTS OF IONOPHORE A23187 ON OOCYTES OF COMANTHUS JAPONICA (ECHINODERMATA: CRINOIDEA)*

Micromolar amounts of divalent cation ionophore A23187 stimulate full grown (but unfertilizable) oocytes of Comanthus japonica to undergo a cortical reaction that is incomplete: first, cortical granule contents ejected at exocytosis do not coalesce but remain as individual blebs just outside the oocyte; and, second, about a fourth of the cortical granule population does not undergo exo-cytosis and remains in the cortical cytoplasm. Of the cortical granules remaining in the oocyte, some have unreacted contents and others have morphologically modified contents. Fine structures are compared among unreacted cortical granules, internally-reacted cortical granules, extracellular blebs of cortical granule material and normal fertilization membranes. The comparison strongly suggests that the outer dense layer and inner fibrous layer of the normal fertilization membrane are derived, respectively, from the dense patches and from the matrices of the cortical granules.     

The Vitamin Requirements of Staphylococci Isolated from Human Skin

The vitamin requirements of 46 strains representing nine species of Staphylococcus isolated from human skin together with nine authentic reference strains of these species were determined using a chemically defined medium. Strains of Staphylococcus saprophyticus and Staphylococcus cohnii were isolated on selective media. All the strains investigated required nicotinic acid and thiamine for growth. Biotin was essential or stimulatory for all coagulase negative strains except one strain of Staphylococcus capitis. Oleic acid substituted for biotin in all cases except with one strain of Staphylococcus haemolyticus. No species pattern of biotin requirement or of the ability of oleic acid to substitute for biotin was apparent. Five out of six strains of Staph. cohnii required pantothenic acid.