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Notes: The ultrastructural and enzyme cytochemical features of two follicular ameloblastomas were investigated. The peripherial cells of the follicular areas in both lesions had several types of tall columnar cells which were highly polarized and showed varying degrees of cellular differentiation. These polarized cells had their nuclei situated away from the basal lamina, and often contained dilated strands of endoplasmic reticulum in the subnuclear cytoplasm. Some of these cells also contained dense-cored secretory granules, condensing granules and coated vesicles in the cytoplasm adjacent to the basal plasma membrane. These cells bore a striking resemblance to pre-ameloblasts and early secretory ameloblasts. Alkaline phosphatase and ATPase cytochemistry supported these morphologic observations. Interestingly, the central cells of the follicular areas were consistently negative for alkaline phosphatase activity as were the peripheral cells, while both cell types had ATPase activity demonstrable at their cell surface.

Notes: Abstract Genetic differentiation within the intertidal zone was examined in six populations of the asexually reproducing alga Enteromorpha linza growing in the Long Island Sound, USA. Four of the five populations sampled in 1981 showed significant differentiation between high and low intertidal positions with respect to the GOT-2 locus. The pattern of differentiation was consistent for samples collected at several times during the year with some seasonal modifications. Four additional polymorphic loci, resolved in 1982, identified a total of 13 five-locus genotypes or clones. Four of the six populations sampled in 1982 showed significant differences in clone frequency between high and low intertidal positions. Laboratory experiments revealed differences in response to temperature among the clones. At 24°C a high intertidal associated clone showed an increase in growth, while low intertidal associated clones showed decreased growth compared to growth at 15°C. These results suggest that the microgeographic differentiation observed for E. linza in the intertidal zone may in part be due to the differential adaptation of clones to different intertidal environments. Additional demographic information is needed for individual clones in order to determine the role longevity, reproductive output, recruitment and interclonal competition play in maintaining the observed differentiation.

Notes: Abstract Limited sampling of Mytilus spp. in eastern Newfoundland has suggested that M. trossulus Gould and M. edulis L. are distributed as pure populations or mixtures of both species. In 1989 and 1990 we collected a wider series of samples of Mytilus spp. from 16 sites in eastern Newfoundland in order to determine the genetic structure based on four polymorphic enzyme loci (Est, Pgm, Lap, Ap). Associations among loci (particularly Pgm and Est), and a bimodal distribution of individual principal-component scores (based on fourlocus genotypes) provided evidence for the presence of both M. trossulus and M. edulis. Most of the sites consisted of a mixture of the two species. The relative frequency of each species in the samples varied on both a macro- and microgeographic scale. Two wave-exposed sites had the highest frequency (〉90%) of M. trossulus. The distribution of hybrid index scores, based on three partially diagnostic loci (Est, Pgm, Lap), provided no evidence for hybridization.

Notes: Abstract Allopatric populations of Mytilus species show distinct shell morphology which may be due to genetic and/or environmental effects. Sympatric populations of Mytilus species show similar shell morphology which may be due to hybridization eroding morphological differences and/or the influence of common environmental conditions. The present study examined shell morphology and shell shape from 16 sites in eastern Newfoundland where M. edulis L. and M. trossulus Gould coexist in common environments with limited hybridization. Shell morphology was based on measurements of eight characters, and shell shape was quantified by elliptic Fourier analysis of shell outlines. Significant differences were observed between species for both shell morphology and shell shape across 16 sites sampled. The relatively small differences in morphology and shape between the species were probably due to exposure to common environments rather than hybridization. Shell shape for M. edulis was more eccentric compared to M. trossulus which was more elongated. Shell shape analysis of a range of size classes at one site showed a change from an eccentric to an elongated shape going from the smaller to the larger size classes. Both species showed a similar trend, with the larger M. edulis more eccentric and the larger M. trossulus more elongated.

Notes: Abstract Mytilus trossulus Gould and M. edulis L. coexist in mixed populations in Atlantic Canadian waters. Although there is evidence that the two species hybridize in natural populations and that hybrids produce progeny through backcrosses, no study of the microgeographic distribution of the two forms and their hybrids has been made. Here we examine subtidal samples of mussels taken in July 1997 from two locations in eastern Newfoundland (Canada) and from wave-exposed and protected environments within each location. Shell lengths ranged from 15 to about 90 mm. Mussels were classified as pure forms or hybrids (F1, F2 and from backcrosses) based on four diagnostic markers, two allozyme loci (Mpi and Est-D) and two nuclear PCR-based DNA markers (ITS and Glu-5). In addition, a PCR-based mtDNA marker (COIII) was used to characterize the distribution of mtDNA mitotypes among pure and hybrid individuals. There were differences in the proportions of pure M. edulis and M. trossulus between sites and between environments at one location. M. trossulus was the predominant species at one of the two exposed sites. In all four samples, M. trossulus was also the predominant form among small individuals. The frequency of hybrids was 26% overall and did not differ among samples. Hybrids consisted mostly of backcrosses that were M. trossulus-biased among small mussels and M. edulis-biased among large ones. We conclude that both intrinsic genetic factors and extrinsic environmental factors influence the relative frequency of M. edulis, M. trossulus and their hybrids.

Notes: Abstract We estimated the broad-sense heritability of larval size in 20 full-sib families of the giant scallop, Placopecten magellanicus (Gmelin, 1791) grown in laboratory culture in August and September 1991. The goal was to compare scallops with other bivalves which have been shown to have significant heritabilities for larval growth. Secondly, we estimated the lipid content of occytes from female parents, since this is hypothesized to affect larval growth and survival. Finally, we estimated the among-family variation in mortality from 4 to 21 d as a test of possible genetic variation for viability among larval scallops. Significant genetic variation (h2=1.10 to 1.24) was estimated for larval shell length at 4, 14, and 21 d. There was a significant correlation (r=0.66) between larval size at 4 d and lipid content of oocytes, but only when two females with high levels of lipid oocyte−1 were excluded as outliers. There was no correlation between larval size at 14 and 21 d and lipid content of oocytes. Mortality among families from 4 to 21 d was high (69 to 97%), and was significantly different among families. These results indicate that there is significant heritability for larval growth which is largely independent of the lipid content of the oocytes. A high heritability for larval growth may indicate that this trait is only weakly correlated with fitness.

Notes: Abstract There is significant differentiation at five polymorphic loci ofMytilus edulis among certain geographical areas of the Atlantic coast of North America. Non-metric multidimensional numerical methods distinguished three population groups: (I) populations south of Cape Cod, (II) populations throughout the Gulf of Maine, Gulf of St. Lawrence, areas of both southern and northern Newfoundland, and southern Hudson Bay, and (III) populations in southeastern Nova Scotia, northern Newfoundland and Hudson Strait, Quebec. Each subset consists of populations that exhibit characteristic multilocus, multiple allele genotypes. Populations in Groups II and III are spatially interdigitated among each other. At least one geographical area of mixing between genetically distinct populations occurs in northeastern Newfoundland. There is no evidence for interbreeding among genetically distinct individuals in mixed populations, suggesting the possibility that populations in the Atlantic Canadian Provinces and areas of northern Canada may consist of two distinct species.

Notes: Abstract Thirteen asexually reproducing clones of Enteromorpha linza were found in samples collected from March to September 1982 in Long Island Sound, USA, based on variation at five enzyme loci. Significant differences in the relative frequency of each clone were observed among samples from 16 localities. There was a tendency for localities at the eastern end of the Sound to form a group genetically differentiated from localities at the western end, but in general there was no strong relationship between geographic distance and genetic distance. Areas separated by only a few hundred meters were genetically differentiated, despite the presence of a dispersing spore stage in this species. Samples from areas of low salinity were genetically similar but distinct from adjacent high salinity areas. One clone restricted to high salinity localities and one associated with low salinity localities were tested for growth under high and low salinity conditions in the laboratory. The clone from the high salinity habitat grew more slowly under low salinity conditions. However, there was no evidence for a detrimental effect of high salinity on the low salinity associated clone. Additional environmental factors, as well as biological factors such as limited recruitment and competitive interactions among clones, may also be important determinants of genetic differentiation among populations of E. linza. Temporal shifts in clone frequency were observed within some localities and may be due to seasonal-dependent regeneration from microscopic holdfasts for different clones or a seasonal recruitment of new clones from other areas. The pattern of differentiation among populations of E. linza in Long Island Sound appears to be maintained by factors operating on a microgeographic scale.

Notes: Abstract Most of the information for genetic differentiation among populations of marine algae is from studies on ecotypic variation. Physiological ecotypes have been described for individuals showing different responses to temperature and salinity conditions. Morphological ecotypes have also been found associated with areas differing in wave exposure or different intertidal positions. Little is known on how genetic variation is organized within and between populations of marine algae. The occurrence of ecotypic variation in some species is evidence for genetic differentiation among populations resulting from selection by the local environment. The rate of dispersal and subsequent gene flow will also affect the level of differentiation among populations. In species with low dispersal, differentiation can arise through chance founder events or random genetic drift. The few studies available have shown that species of algae exhibit a range of dispersal capabilities. This information can be useful for predicting the potential level of genetic differentiation among populations of these species. Crossing experiments with several species of algae have shown that populations separated by a considerable distance can be interfertile. In some cases individuals from these populations have been found to be morphologically distinct. Crosses have been used to study the genetic basis of this variation and are evidence for genetic differentiation among the populations sampled. Genetic variation of enzyme proteins detected by electrophoresis provides an additional method for measuring genetic variation within and between populations of marine algae. Electrophoretic methods have previously been used to study systematic problems in algae. However, there have been few attempts to use electrophoretic variation to study the genetic structure of populations of marine algae. This approach is outlined and includes some of the potential problems associated with interpreting electrophoretic data. Studies of electrophoretic variation in natural populations ofEnteromorpha linza from Long island Sound are used as an example. This species was found to reproduce only asexually. Despite a dispersing spore stage, genetic differentiation was found on a microgeographic scale and was correlated with differences in the local environment of some of the populations. Similar studies on other species, and especially sexually reproducing species, will add to a growing understanding of the evolutionary genetics of marine algae.