Juvenile bimodal length distribution and sea-run migration of the lower modal group in the Pacific Ocean form of three-spined stickleback

Juvenile three-spined stickleback Gasterosteus aculeatus in their nursery pond had a bimodal length distribution after October in their first year of life. A sea-run migration of all individuals belonging to the lower modal group was observed, with a peak in early November. These data suggest that partial migration based on the early status of individual juveniles occurs in the Pacific Ocean form of three-spined stickleback.     

Genetic and morphometric differentiation among island populations of two Norops lizards (Reptilia: Sauria: Polychrotidae) on independently colonized islands of the Islas de Bahia (Honduras)

Aim Anole lizards (Reptilia: Sauria: Polychrotidae) display remarkable morphological and genetic differentiation between island populations. Morphological differences between islands are probably due to both adaptive (e.g. differential resource exploitation and intra‐ or interspecific competition) and non‐adaptive differentiation in allopatry. Anoles are well known for their extreme diversity and rapid adaptive speciation on islands. The main aim of this study was to use tests of morphological and genetic differentiation to investigate the population structure and colonization history of islands of the Islas de Bahia, off the coast of Honduras. Location Five populations of Norops bicaorum and Norops lemurinus were sampled, four from islands of the Islas de Bahia and one from the mainland of Honduras. Methods Body size and weight differentiation were measured in order to test for significant differences between sexes and populations. In addition, individuals were genotyped using the amplified fragment length polymorphism technique. Bayesian model‐based and assignment/exclusion methods were used to study genetic differentiation between island and mainland populations and to test colonization hypotheses. Results Assignment tests suggested migration from the mainland to the Cayos Cochinos, and from there independently to both Utila and Roatán, whereas migration between Utila and Roatán was lacking. Migration from the mainland to Utila was inferred, but was much less frequent. Morphologically, individuals from Utila appeared to be significantly different in comparison with all other localities. Significant differentiation between males of Roatán and the mainland was found in body size, whereas no significant difference was detected between the mainland and the Cayos Cochinos. Main conclusions Significant genetic and morphological differentiation was found among populations. A stepping‐stone model for colonization, in combination with an independent migration to Utila and Roatán, was suggested by assignment tests and was compatible with the observed morphological differentiation.     

"It Was Fine, if You Wanted to Leave": Educational Ambivalence in a Nova Scotian Coastal Community 1963–1998

This article reports on a study of schooling in southwest Nova Scotia. Using Bourdieu's concepts of cultural capital and habitus, I analyze rural men's relationships involving identity, work, place, and schooling to explain continuing high male dropout rates and local traditions of ambivalence and resistance to schooling. I conclude that the tension between formal schooling and place is endemic in many rural communities and that qualitative migration analysis can reveal the complexity of relationships between learning and leaving.     

Female‐biased migration of stream‐dwelling Dolly Varden in the Shiisorapuchi River, Hokkaido, Japan

The first evidence for female‐biased migration in a partially migratory stream‐dwelling salmonid the Dolly Varden Salvelinus malma , a phenomenon well known in sea‐run and lake‐run populations, is presented. Dolly Varden in the Shiisorapuchi River in central Hokkaido, Japan, used both tributaries, of which there are many, and the main stem, but spawned only in tributaries. The size structures of Dolly Varden (≥age 1 + years) in tributaries were unimodal (<100 mm fork length, L _F) during non‐spawning seasons but changed to bimodal during spawning seasons (lower mode <110 mm, upper mode >120 mm L _F). Mature individuals were observed in both modal groups. From the trapping and census data, the small group appeared to be tributary resident and the large group main stem migrant. Males were common in both resident and migrant components. Most females, however, migrated to the main stem to mature, indicating female‐biased migration.     

Environmental factors influencing the vertical migration of planktonic rotifers in a hypereutrophic tarn

The diel vertical migration of planktonic rotifers in a small, hypereutrophic tarn was investigated on four occasions in 1983. When the tarn was isothermal the rotifers were distributed throughout the water column. After stratification, the rotifers were confined to the top 1–2 m of oxygenated water. On all four dates the rotifers were aggregated at specific depths in the water column. On some occasions, the pattern of aggregation changed as the animals performed distinct diurnal migrations. Keratella cochlearis, K. quadrata and Polyarthra vulgaris usually followed the reverse migrations of the phytoplankton. In contrast, the movements of Anuraeopsis fissa were less pronounced and were associated with variations in the depth of the oxycline.     

Breeding system ofDaphniopsis ephemeralis: adaptations to a transient environment

Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction. Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic brood.     

Daphnia size structure,vertical migration,and phosphorus redistribution

The timing and magnitude of diel migration in two daphnid assemblages were determined from a series of vertical profiles of daphnid size distribution. Animals were collected concurrently for gut fullness determination. Only large daphnids (> 1.4 mm) migrated, but these animals could account for substantial vertical and diel differences in phosphorus excretion rate. Gut fullness measurements and time courses of diel vertical migration suggested that large Daphnia can cause a net downward flux of phosphorus during summer in thermally stratified lakes.     

On the origin ofVeronica persica (Scrophulariaceae)—a contribution to the history of a neophytic weed

A character analysis reveals a clearly intermediate position of the tetraploidV. persica (2n = 28) between the two diploid speciesV. polita andV. ceratocarpa (both 2n = 14) which are morphologically rather different and have been placed by several authors in different sections of the genus.V. ceratocarpa is native to subhumid deciduous forests of the Caucasus and of the Elburz mountains (N. Iran);V. polita has its centre of variation in the Elburz range where it grows in therophyte habitats. Three other closely related species,V. bungei, V. siaretensis, andV. francispetae, are endemic to the Elburz range which is the main centre of diversity and variability of theV. agrestis group. This comprises all the above mentioned species and also two more European weeds:V. agrestis andV. opaca. Veronica polita, was probably originally native to open places in deciduous mountain forests, before becoming a weed in neolithic times and migrating to Europe; nowadays it has an almost world-wide distribution. The allotetraploidV. persica combines the ecological characters of its parents, the slightly xerophyticV. polita and the more mesophyticV. ceratocarpa, thus being preadapted to become a highly successful weed with a large ecological range. It has spread rapidly almost all over the world since the early 19th century.Dedicated to Hofrat Univ.-Prof. DrKarl Heinz Rechinger on the occasion of the 80th anniversary of his birthday.