Phenotypic variation along a cline in allozyme and karyotype frequencies, and its relationship with habitat, in the dog-whelk Nucella lapillus, L.

The dog-whelk Nucella lapillus exhibits a number of phenotypic variations and genetic polymorphisms which correlate with habitat-specific environmental pressures, especially those associated with wave action and temperature. This study investigates the relationship between genetic composition (karyotypic and electrophoretic variation) and phenotypic differentiation in N. lapillus sampled at 15 points along an 8 km stretch of coastline. Coincident clinal variation in gene frequencies and shell shape is described; they covary with differences in karyotype and also with growth. Laboratory-reared young show that differences in phenotype (shell shape and growth) are inherited. Experimental evidence is presented that specific shell shapes are adaptive under conditions of thermal stress. Together with the well-established correlations between shell shape and shore exposure, this association provides an argument for a relationship between genetic composition, phenotype and habitat in this species.     

REPRODUCTIVE SYSTEM AND SPERMATOGENESIS IN THE OPISTHOBRANCH GASTROPOD RETUSA OBTUSA (MONTAGU)

The cephalaspidean opisthobranch Retusa obtusa has an ovotestissimultaneously producing eggs and spermatozoa. Reproductiveorgans are characterized by the hermaphrodite duct and seminalreceptacle together joining the pallial glandular duct whichis differentiated anteriorly to form the ‘albumen’gland, membrane or capsule gland, and mucus gland. The ductof a copulatory bursa joins the common central chamber of thiscomplex. Eggs presumably pass through extended tracts in the3 glands to emerge at a hermaphrodite aperture in the rightside of the mantle cavity. Spermatozoa also emerge at this apertureto a ciliated seminal groove along the right side of the headwhich, in turn, joins copulatory organs folded within the headand opening close behind the right cephalic tentacle: a muscularpenial sac receives 4 elements of prostate gland. Spermatophoreswere never seen. Oocytes, surrounded by several thin folliclecells, reach 150–330 µ, m diameter in larger wintersnails, mostly in the periphery of theovotestis. Spermatocytesand spermatids develop as clusters in association with accessory(Sertoli) cells. The acrosome appears in the centre of a denseanterior plaque, develops as a domed acrosome vesicle on a shortpeduncle and eventually becomes a terminal spike on the nucleustip. The Golgi complex is seen sometimes near the early acrosomebut more often behind the nucleus. Mitochondria aggregate firstahead of the nucleus but then form a mitochondrial derivative,with a glycogen helix, spiralled around the axoneme throughoutthe mid-piece of the tail. This region is marked off from theend-piece of the tail by the annulus. The nucleus becomes long,spiralled with a strong keel, and surrounds the centriolar derivativeat the base of the axoneme.     

Early Ordovician bathyurid province lithofacies, biofacies, and correlations -their relationship to a proto-Atlantic Ocean

The Early Ordovician bathyurid faunal province includes North America, Greenland, Spitsbergen, Scotland, and western Ireland and Norway. Dominant provincial lithofacies and biofacies include a Dolomite Suite with molluscan-stromatolite fossil content rimmed by Limestone Belts with dominantly trilobite-brachiopod faunas on a platform. Shale Belt rocks bearing graptolites, deposited on the platform slopes, rim the Limestone Belts. Volcanic rock-rich terrain partly borders the Shale Belts. Correlation between the lithofacies indicates that change from an expansion to contraction phase of a proto-Atlantic coincided with uplift of the carbonate platform and with tectonic activity in the Atlantic volcanic rock rich terrain. Brachiopods replaced trilobites as dominant faunal elements in more shallow platform waters at the same time. High trilobite diversity remained in deeper waters near platform margins. The changes took place in Earliest Mohawk-ian (Latest Arenig-Earliest Llanvirn).     

Effects of rubidium, potassium and gibberellic acid on plant growth

Growth retardation, measured as internode shortening, was observedin bean and tomato plants when grown in culture solutions towhich Rb had been added. The Rb effect was more pronounced inthe presence of low (0.5 meq/liter) K than high (8 meq/liter)K. Gibberellic acid, added to the solutions, ameliorated thegrowth retardation due to Rb. Epinastic symptoms similar tothose observed with auxin treatment also appeared on the tomatoplants treated with Rb. (Received October 2, 1968; )     

Inherited changes in enzyme patterns within parthenogenetic clones of Aphis fabae

An account is given of changes in esterase enzyme patterns occurring in Aphis fabae populations breeding parthenogenetically.