Susan L. Hull

Littorina neglecta Bean: ecotype or species?

The taxonomic status of the littoral prosobranch Littorina neglecta has been investigated using animals from the northeast coast of England. Rough periwinkles were collected from barnacle-covered rock platforms near the northern (Ness Point) and southern (Old Peak) ends of Robin Hoods Bay, and from small and large boulders at the southern end. Shape was analysed in shells from all sites, and the activity levels and heat stability of aspartate aminotransferase (Aat) and alanine aminotransferase (Alat) were determined in samples from Peak Steel and a nearby boulder habitat. Of the shells from Ness Point, 98% could be separated visually, using colour, sculpturing and banding, into three categories (the oviparous L. arcana, and the ovoviviparous L. saxatilis and L. neglecta). The categories were confirmed using discriminant analysis on shell measurements and cross-validation indicates at least 70% accuracy. On Peak Steel L. saxatilis breeds at a small size and its shells are visually quite distinct from thos...

Heat stability and activity levels of aspartate aminotransferase and alanine aminotransferase in British Littorinidae

Aspartate aminotransferase and alanine aminotransferase activity levels were determined in crude homogenates of Littorina arcana, Littorina littorea, Littorina compressa, Littorina neglecta, Littorina obtusata, Littorina fabalis, Melarhaphe neritoides and three forms of Littorina saxatilis; high shore thin-shelled H, midshore thick-shelled M and barnacle dwelling B. In all the groups investigated, aspartate aminotransferase activity was higher than alanine aminotransferase, and high shore species appeared to have higher activity levels of aspartate aminotransferase relative to alanine aminotransferase than did low shore species. Aspartate aminotransferase was more heat stable than alanine aminotransferase at 45°C, and it was more heat stable in high shore than in low shore groups. Heat stability also varied within a species; the enzymes of L. saxatilis H were more heat stable than those of L. saxatilis M from the same site. The enzymes of a small-barnacle dwelling form of L. saxatilis showed greater heat stability than sympatric samples of L. neglecta. The possible factors involved in these differences are discussed.

Intertidal ostracod (Crustacea: Ostracoda) abundance and assemblage structure within and between four shores in north-east England

Triplicate samples of rockpool algae were collected at each of three tidal elevations (upper, mid and low) from four shores on the north-east coast of England. Two moderately exposed (Ravenscar, the exposed shore at Filey Brigg), and two moderately sheltered (Selwicks Bay, the sheltered shore at Filey Brigg) shores were sampled during one week of spring tides during June 1996. A total of 6866 individual ostracods comprising of 26 ostracod species were recovered from the algal samples. Some species showed significant differences in abundance with tidal elevation across the four shores, e.g. Hirschmannia viridis was significantly more abundant in the upper shore pools. Other species, e.g. Heterocythereis albomaculata , showed no significant difference in abundance either with tidal elevation or between shores. Significant differences in abundance occurred between shores at a given tidal height in some species, e.g. Semicytherura nigrescens was absent from Selwicks Bay but abundant on the remaining shores. Other species had markedly disjunct distributions, e.g. Callistocythere badia only occurred in the exposed upper shore pools at Filey Brigg. Ostracods were significantly less abundant in the low shore pools. Cluster analysis showed that low shore samples had a high degree of similarity between the four shores whereas the upper and mid-shore samples clustered primarily to shore. A two-way ANOSIM indicated that there was a significant difference in assemblage similarity between the four shores and also between the different tidal elevations.

Seasonal patterns in the reproductive activity of barnacle-dwelling littorinids

The reproductive activity of a population of barnacle-dwelling littorinids at Peak Steel, on the north-east coast of England, was investigated. Variation in the number of mature males and females, expressed as a percentage of the whole population, showed a marked difference among the barnacle-dwelling littorinids. Littorina neglecta displayed a distinct seasonal component to its reproductive activity, with a peak in early summer. Littorina arcana B also displayed a distinct seasonal component, with a lull in the summer months. However, L. saxatilis B maintained its reproductive activity all year, but with an increase in output in the summer. The reproductive activity of both L. arcana B and L. saxatilis B follow similar patterns of reproductive activity as their typical non barnacle-dwelling forms, suggesting that these are true barnacle-dwelling ecotypes. The controversy surrounding the specific status of L. neglecta is also discussed.

Reproduction in four populations of brooding periwinkle ( Littorina ) at Ravenscar, North Yorkshire: adaptation to the local environment?

The current study examines the reproductive patterns found within four ovoviviparous, brooding periwinkle populations on one shore in the north-east coast of England; the boulder dwelling populations Littorina saxatilis H (upper-shore form with thin shell and large aperture) and L. saxatilis M (mid-shore form with thick shell and small aperture), and the barnacle-dwelling L. saxatilis B (small form similar in morphology to L. saxatilis M) and L. neglecta . Littorina saxatilis H showed distinct seasonality in reproductive activity, unlike L. saxatilis M, and produced significantly larger eggs and embryos than the latter population. Littorina saxatilis M maintained a significantly higher weight-specific fecundity and reproductive activity throughout the year than L. saxatilis H and produced a larger number of small embryos. The two barnacle-dwelling populations also showed distinct seasonality in reproductive activity and neither of the populations contained reproductively active females during the winter months. There was no significant difference in egg size between the two populations, but L. saxatilis B produced larger crawlaways than did L. neglecta . Even though L. saxatilis B was significantly larger in body and shell size, L. neglecta had a higher weight-specific fecundity than the former population. The possibility that the observed differences in egg and juvenile size, fecundity and seasonality between the four populations can be attributed to microscale adaptation to the local environment is discussed.

Sex-biased colour polymorphism in the marine ostracod Paradoxostoma variabile (Crustacea)

Samples of four species of algae were collected from three mid-shore pools on each of three shores on the north-east coast of England in order to describe colour polymorphism in the common intertidal ostracod Paradoxostoma variabile. Eight different colour morphs were found within the populations. On all shores, male P. variabile occurred in significantly higher densities than did the females, and males exhibited a significantly higher colour morph diversity and colour morph richness than females. On two out of three shores, males showed a significant association in colour morph frequency with algal species (but the pattern was not consistent between shores), but no such association was found in the female populations. In either sex, colour morph diversity did not vary between algal species but samples of male ostracods from the shore at Holbeck contained a significantly higher diversity of colour morphs than samples from the other two shores. In the laboratory, neither sex demonstrated a specific association with algal species suggesting that habitat selection is not an important factor in maintaining colour morph frequencies in this species.

Clonal diversity and rockpool size in the marine ostracod, Callistocythere badia

Samples containing the marine ostracod Callistocythere badia were collected from upper shore rockpools on Filey Brigg, north-east England in order to examine the life cycle and genetic structure of the species. Reproduction occurred during spring/summer after which the adults died; juveniles over-wintered as A-1 instars. No males were ever found during the study. Analysis at three polymorphic loci (Gpi, Pgm and Mpi), showed significant deviations from Hardy-Weinberg equilibrium, and significant linkage equilibrium at and between all loci. The genetic data and absence of males confirm that Callistocythere is an asexual species. There was a significant positive relationship between the number of clones found within a pool and rockpool size, but not with algal habitat heterogeneity.

The occurrence of abnormal embryos in two ovoviviparous barnacle-dwelling littorinids

The occurrence of developmental abnormalities in two ovoviviparous littorinids (Littorina neglecta and a barnacle-dwelling form of L. saxatilis) inhabiting the barnacle zone at Peak Steel, Ravenscar on the north-east coast of England was investigated. In general developmental abnormalities appeared to be a rare occurrence in both taxa. However, L. neglecta was found to have a significantly greater proportion of deformed embryos in their brood pouches than L. saxatilis B (Figure 1), A distinct seasonal variation in the number of developmental abnormalities was observed in L. neglecta, and it is suggested this is a result of broods developing outside of the main reproductive season being more prone to deformity.