Molecular genetics of peripheral populations of Nova Scotian Unionidae (Mollusca: Bivalvia)

Peripheral populations of eight species of freshwater bivalves (Unionidae.) extending their geographic ranges into Nova Scotia, Canada, were examined electrophoretically to determine both the extent of genetic variability within such populations, and whether the hypothesized pathway of colonization across the Isthmus of Chignecto is reflected in patterns of genetic resemblance among these populations. The Nova Scotian species examined could be separated into two groups based on levels of observed heterozygosity and levels of variability in allele frequencies. The first group is characterized by low levels of heterozygosity and polymorphism compared with north-eastern American populations, and in the case of one species, Elliptio complanala, considerable variability in allele frequencies among populations occurring in similar habitats in different drainages. Populations of E. complanata from Nova Scotia can be differentiated from conspecific populations on the southern Atlantic Slope by possession of fast alleles at two loci. Multivariate analyses define subgroups within populations of E. complanata consistent with hypothesis that the species invaded Nova Scotia by way of the Isthmus of Chignecto, and then split into two groups, one of which colonized Cape Breton to the north and the other of which colonized southern areas of the Province. The second group of Nova Scotian species is characterized by little reduction in heterozygosity and polymorphism compared with values observed among north-eastern American conspecifics or congeners, little variability in allele frequencies from population to population, and little evidence to suggest that these species were dependent on the land bridge to invade the Province. The type of dispersal is hypothesized to be responsible, in part, for these differences: larvae of species in the first group rely on a parasitic attachment to fish with territorial habits limited to fresh water, and are thus likely to invade new drainages separated by salt water by chance, in small numbers, and in stepping-stone fashion. Species in the second group parasitize anadromous or saltwater tolerant hosts, are likely to be introduced into new habitats in greater numbers and/or receive greater amounts of gene flow subsequent to colonization, and seem less dependent on land-bridges to colonize new habitats.     

A preliminary examination of genetic variation in a peripheral population of Blanding's turtle, Emydoidea blandingii

Random amplified polymorphic DNA (RAPD) was used to compare the Nova Scotia population of Blanding's turtle (Emydoidea blandingii) with several populations from the species' main range. The Nova Scotia population is believed to have been isolated from the main range for 4000-8000 years. Cluster analysis using a neighbour-joining algorithm produced a dendrogram showing the Nova Scotia population clustering separately from those populations in the main range. Analysis of molecular variance shows 34.28% of total variance to be accounted for between the Nova Scotia population and populations in the main range. While this study is preliminary, the results suggest that the Nova Scotia population of Blanding's turtle may be important to the maintenance of genetic diversity in the species.     

Effect of octanoic acid on ethylene-mediated flower induction in Dutch iris

Treatment of Dutch iris (Iris × hollandica Hoog. cv. Sapphire Beauty) bulbs with ethylene prior to precooling stimulated flowering in bulbs of various sizes. In large sized bulbs exposure to ethylene followed by precooling resulted in 100% flowering over a five months period after planting. Flowering in control bulbs which were not treated with ethylene prior to precooling was limited to 67% during the same five months period. In medium sized bulbs flowering in the ethylene treatment was 90% compared to 75% in the control. However, the biggest stimulation of flowering by ethylene was found in small sized bulbs (from 16 to 56%). Application of octanoic acid for a short time period prior to exposure to ethylene stimulated flowering in all bulb sizes. After five months the final percentage flowering in large and medium sized bulbs of the octanoic acid plus ethylene treatment did not differ from that of the ethylene only treatment. However, the initial rate of flowering was higher in the former treatment. In small bulbs the percentage flowering was much higher in the octanoic acid plus ethylene treatment than in the ethylene only treatment. The results of this study indicate that, just as in certain flowers, fruit and seeds, treatment with octanoic acid stimulates ethylene sensitivity in Dutch iris bulbs. The sensitivity of untreated bulbs to ethylene was highest in large bulbs and lowest in small bulbs. This correlated well with the endogenous octanoic acid content of the bulbs. Octanoic acid levels were highest in large bulbs and lowest in small Bulbs. It appears that the endogenous levels of octanoic acid in the bulbs is determined prior to the onset of dormancy.     

Temporal and intraclonal variation of flowering and pseudovivipary in Poa bulbosa

Background and Aims

Versatility in the reproductive development of pseudoviviparous grasses in response to growth conditions is an intriguing reproduction strategy. To better understand this strategy, this study examined variation in flowering and pseudovivipary among populations, co-occurring clones within populations, and among tillers in individual clones of Poa bulbosa, a summer-dormant geophytic grass that reproduces sexually by seed, and asexually by basal tiller bulbs and bulbils formed in proliferated panicles.

Methods

Clones were collected from 17 populations across a rainfall gradient. Patterns of reproduction were monitored for 11 years in a common garden experiment and related to interannual differences in climatic conditions. Intraclonal variation in flowering and pseudovivipary was studied in a phytotron, under daylengths marginal for flowering induction.

Key Results

Clones showed large temporal variability in their reproductive behaviour. They flowered in some years but not in others, produced normal or proliferated panicles in different years, or became dormant without flowering. Proliferating clones did not show a distinct time sequence of flowering and proliferation across years. Populations differed in incidence of flowering and proliferation. The proportion of flowering clones increased with decreasing rainfall at the site of population origin, but no consistent relationship was found between flowering and precipitation in the common garden experiment across years. In contrast, flowering decreased at higher temperatures during early growth stages after bulb sprouting. Pulses of soil fertilization greatly increased the proportion of flowering clones and panicle production. High intraclonal tiller heterogeneity was observed, as shown by the divergent developmental fates of daughter plants arising from bulbs from the same parent clone and grown under similar conditions. Panicle proliferation was enhanced by non-inductive 8 h short days, while marginally inductive 12 h days promoted normal panicles.

Conclusions

Interannual variation in flowering and proliferation in P. bulbosa clones was attributed to differences in the onset of the rainy season, resulting in different daylength and temperature conditions during the early stages of growth, during which induction of flowering and dormancy occurs.     

Asymmetric competition drives lake use of coexisting salmonids

To what degree are population differences in resource use caused by competition and the occupation of adjacent positions along environmental gradients evidence of competition? Habitat use may be the result of a competitive lottery, or restricted by competition. We tested to what extent population differences in habitat use of two salmonids, cutthroat trout (Oncorhynchus clarki) and Dolly Varden charr (Salvelinus malma) were influenced by interspecific competition. We hypothesized that the depth distribution of Dolly Varden charr would be affected by competition from the more littoral and surface-oriented cutthroat trout, and that the depth distribution of cutthroat trout would be little affected by competition from Dolly Varden charr. Sympatric populations of cutthroat trout and Dolly Varden charr were created by reciprocal transfers of previously allopatric populations in two experimental lakes. We found evidence of asymmetric competition, as Dolly Varden charr were displaced from littoral habitats when sympatric with cutthroat trout, whereas cutthroat trout remained unaffected by the presence of Dolly Varden charr. Evolved differences between the species, and differences between experimental lakes, also contributed to population differences in habitat use, but asymmetric competition remained as the main driver of different depth distributions in sympatry.     

Parasitism and predation as agents of mortality of winter moth populations in neglected apple orchards in Nova Scotia

Abstract.

• 1 This study compared the roles of pupal mortality and parasitism in winter moth (Operophtera brumata) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators.
• 2 The component of pupal mortality termed predation accounted for greater stage-specific mortality of winter moth than parasitism by Cyzenis albicans in four neglected orchards.
• 3 Parasitism by Cyzenis albicans was not spatially density-dependent in any orchard, whereas the predation component of pupal mortality was spatially density-dependent in the two orchards most densely populated by winter moth.
• 4 Field experiments indicated that over 60% of pupal predation may be attributed to beetles, and that about 46% of pupal predation occurred within 4 weeks after pupal drop.
• 5 Mortality of introduced populations of winter moth in Nova Scotia resembles that of native populations in England where density-dependent predation regulates the winter moth population and reduces the parasitoid population to minimal levels. The situation in Nova Scotia appears to have changed appreciably since the establishment of parasitoids into the system in the 1950s.

     

Trends in abundance of rocky intertidal seaweeds and filter feeders across gradients of elevation,wave exposure,and ice scour in eastern Canada

On NW Atlantic rocky shores, the main basal organisms in intertidal communities are seaweeds (Ascophyllum nodosum, Fucus spp. and Chondrus crispus) and filter feeders (barnacles, Semibalanus balanoides, and mussels, Mytilus spp.). Their ecology has been extensively studied in New England (United States), but knowledge gaps exist for northern shores, which are subjected to stronger environmental stress. Therefore, we studied the above organisms on Canadian shores. We quantified the summer abundance of these seaweeds and filter feeders across full vertical (intertidal elevation) and horizontal (wave exposure and winter ice scour) environmental gradients on the Gulf of St. Lawrence and open Atlantic coasts of Nova Scotia. At the regional scale along the open Atlantic coast, seaweeds showed similar abundances in Nova Scotia than values reported for New England. However, both filter feeders were considerably less abundant in Nova Scotia. At the local scale in Nova Scotia, intense winter ice scour (which only occurs on the Gulf of St. Lawrence coast) was associated with a very low abundance of all species except barnacles. Spatial trends in Nova Scotia were similar to patterns known for certain species elsewhere, such as A. nodosum being almost restricted to sheltered habitats, regardless of elevation, and C. crispus being almost restricted to low elevations, regardless of exposure. Other trends were, however, characteristic of Nova Scotia, such as C. crispus being frequent at low elevations in exposed habitats, unlike in New England, where mussels often predominate there because of competitive advantages. In Nova Scotia, mussels were always restricted to cracks and crevices, unlike in New England, where they form extensive intertidal beds on exposed shores. The direct effects of increased environmental stress and indirect effects through altered interspecific interactions might explain the regional differences in local species distribution, which will require experimental validation. Handling editor: K. Martens     

Forest responses to the large-scale east coast fires in Korea

The east coast forest fires of April 2000 were Koreas largest recorded fires. This, along with the fact that they took place in the region most frequently affected by fire, attracted a great deal of attention. Due to the variations in wind, topography and pre-fire forest stands, a heterogeneous landscape mosaic of burn severity was created across the region. It turned out to be an excellent opportunity to study various landscape-scale impacts of fires on forest dynamics. Therefore, we investigated stands in the 23794ha of burned forest region, in terms of burn severity, vegetation regeneration and forested landscape change as a measure of community stability. Using the geographic information system technique, we analyzed the differential severity and post-fire recovery of pre-fire forest types of different stand age both at stand and species level. Analysis showed that pre-fire vegetation was composed of mainly pine (Pinus densiflora) stands that occupied 70% of the whole forested area, while pine-hardwood and hardwood stands occupied only 28% and 3%, respectively. In addition, two-thirds of all stands were less than 30-years-old. Pine stands were the most severely burned, while conversely pine-hardwood and hardwood stands were less vulnerable. This implied that pine forests had fire-prone characteristics. Vegetation recovery went the opposite way; that is, the regenerating vegetation cover was 71% at pre-fire hardwood stands, and 65% and 53% at pine-hardwood and pine stands, respectively. However, these recovery rates were strikingly fast, considering that investigation took place about 3months after the fires. Fire did not initiate successional processes, but tended to accelerate the predicted successional changes by releasing pre-fire understory species that survived the fires and regenerated by sprouting. The dominant pre-fire tree species (P. densiflora) was susceptible to fire and not resilient enough to reestablish in competition with oak species. Contrary to pines, the abilities of oak species, mainly Quercus mongolica and Q. variabilis, to survive fires and to resprout vigorously made them dominant at most post-fire stands. These shifts in species abundance caused drastic changes to the landscape: from pine-dominated to oak-dominated stands without any notable change in species composition. The patterns in forest regeneration that we observed in Korea may be representative of forest responses to any long-term repeated disturbances, including fire.     

Flowering pathway is regulated by bulb size in Lilium longiflorum (Easter lily)

Lilium longiflorum (Easter lily) vegetative propagation occurs through production of underground bulbs containing apical and axillary meristems. In addition, sexual reproduction is achieved by flowering of elongated shoots above the bulb. It is generally accepted that L. longiflorum has an obligatory requirement for vernalisation and that long day (LD) regime hastens flowering. However, the effect of bulb size and origin, with respect to axillary or apical meristems on flowering, as well as the interactions between these meristems are largely unknown. The aim of this study was to explore the effect of bulb size, vernalisation and photoperiod on L. longiflorum flowering. To this end, we applied vernalisation and photoperiod treatments to the different bulb sizes and used a system of constant ambient temperature of 25 °C, above vernalisation spectrum, to avoid cold‐dependent floral induction during plant growth. Vernalisation and LD hasten flowering in all bulbs. Large, non‐vernalised bulbs invariably remained at a vegetative stage. However, small non‐vernalised bulbs flowered under LD conditions. These results demonstrate for the first time that cold exposure is not an obligatory prerequisite for L. longiflorum flowering, and that an alternative flowering pathway can bypass vernalisation in small bulbs. We suggest that apical dominance interactions determine the distinct flowering pathways of the apical and axillary meristems. Similar floral induction is achieved in propagated bulblets from scaling. These innovative findings in the field of geophyte floral induction represent valuable applicative knowledge for lily production.     

Ecological factors affecting gene flow between populations of Anarthrophyllum cumingii (Papilionaceae) growing on equatorial- and polar-facing slopes in the Andes of Central Chile

In the Andes of Central Chile, flowering commences 1–2 months earlier on equatorial-(north-) facing than on polar- (south-) facing slopes, and pollinator assemblages also differ between these habitats. In order to understand the potential influence of these differences on gene flow, we monitored flowering periods and insect visitation rates to flowers of 60 individuals of Anarthrophyllum cumingii (Papilionaceae) on two equatorial- and two polar-facing slopes in the Andes of central Chile (33°35 S;70°32 W). Flowering began about 30 days earlier on equatorial-facing slopes. Flowering periods of individuals on slopes with the same aspect had a mean overlap of 0.52, while those on opposite slopes had a mean overlap of 0.15. On equatorial-facing slopes Yramea lathionoides (Lepidoptera) accounted for 60% of the visits to flowers of A. cumingii, while on polar-facing slopes Centris cineraria (Hymenoptera) was responsible for more than 80% of flower visits. Average similarities of visitor assemblages among individual plants on slopes with the same aspect was 0.83, while the mean similarity between individuals on opposite slopes was only 0.23. Within slopes fluorescent dyes were dispersed up to 40 m from the donor plants, but there was no movements of dyes between individuals growing on opposite slopes, even when they were separated by less than 10 m. Synchronous blooming and a common pollen vector are necessary conditions for pollen exchange between individuals. The overall probability of pollen exchange estimated by multiplying the inter-individual overlap for both factors, was nearly 0.5 for individuals growing on slopes with the same aspect, and less than 0.04 for individuals growing on opposite slopes. Consequently, at equivalent distances, the probability of pollen exchange between individuals growing on slopes of opposite aspect is more than 10-times lower than between those growing on the same slopes. Seed dispersal cannot compensate for restricted gene flow through pollination, because seeds of A. cumingii were dispersed less than 2 m away from a parent plant. Presumably, restricted gene flow could enhance genetic divergence between populations on slopes of contrasting aspects. This factor could be important in contributing to the high diversity and endemism in the Chilean Andes.     

Plant interactions for pollinator visits: a test of the magnet species effect

Summary From 1985–1987, patterns of fruit and seed set were studied in a population of mayapple (Podophyllum peltatum), a clonal, self-incompatible herb found in deciduous woods in eastern North America. Mayapple flowers do not produce nectar, but depend on infrequent visits by nectar-seeking queen bumble bees for pollination. In all years female reproductive success in mayapple colonies was influenced by colony size (number of flowers), by the distance to neighbouring colonies and by proximity to lousewort plants (Pedicularis canadensis), a prolific nectar producer heavily visited by bumble bees. In all years fruit and seed set were greater in mayapple colonies <25 m from lousewort flowers than in matched colonies which were >50 m from lousewort. In 1985 and 1987 the frequency of queen bumble bee visits to flowers in colonies close to lousewort was about four times greater than to distant colonies. In 1986 I removed about 80% of lousewort flowers to test whether the enhanced fruit and seed set in mayapples close to lousewort was pollinator mediated. Mayapple colonies close to flowerless lousewort patches did not differ in fruit or seed set from matched colonies >50 m from lousewort. In contrast, mayapples close to flowering lousewort patches had greater fruit and seed set compared with distant colonies. Over all years, a larger proportion of mayapples close to flowering lousewort patches had enhanced fruit and seed set compared with colonies close to louseworts without flowers. Though rarely documented, this type of facilitative interaction between plants that are highly attractive to pollinators (magnet species), and co-flowering species that are rarely visited by pollinators, may be widespread in plant communities.     

Conservation genetics of Blanding’s turtle and its application in the identification of evolutionarily significant units

Blanding’s turtle is a North American freshwater turtle whose main range occurs south of the Great Lakes; disjunct populations occur east of the Appalachian Mountains from New York to Nova Scotia. The species is listed as threatened or endangered in most of its range. We employed five variable microsatellites to examine samples of 300 individuals in 12 populations. Estimates of F _ST based on pairwise comparisons of populations ranged from 0.000 to 0.465. Phylogenetic analysis of these F _ST values reveals that the Appalachian Mountains and the Hudson River appear to present major barriers to gene flow in Blanding’s turtle. The extent of fine-scale genetic structure previously reported in the Nova Scotian populations was not found in other parts of the species’ range. We recommend that populations separated by the Appalachian Mountains as well as the highly disjunct Nova Scotian populations of Blanding’s turtle be recognized as evolutionarily significant units.     

Contrasting trends in gray seal (Halichoerus grypus) pup production throughout the increasing northwest Atlantic metapopulation

The northwest Atlantic subspecies of gray seal (Halicheorus grypus grypus) has been increasing for more than a half century and has reestablished breeding colonies in Canadian and US waters. In 2016, visual, oblique, and vertical large-format digital photographic surveys were conducted at all known breeding colonies in the northwest Atlantic. Total pup production in the northwest Atlantic was estimated to be 109,000 (SE = 17,500) pups. At 87,500 (SE = 15,100) pups, Sable Island accounts for 80% of total pup production. Regional differences in pup production trends are evident. Pup production in the Gulf of St. Lawrence and along the eastern shore of Nova Scotia has been relatively stable. Since 2004, the rate of increase in pup production at Sable Island has slowed to about 5%–7% per year, while the newer colonies in southwest Nova Scotia and the northeastern United States are increasing rapidly. In 2016, the Muskeget Island (MA) breeding colony produced 3,900 (SE = 200) pups, making it the third largest breeding colony in the northwest Atlantic. This southward shift in production may reflect climate-mediated changes in population growth as well as reestablishment of colonies throughout the former range associated with increased protection.     

Diffusion of nuclear and mitochondrial genes across a zone of secondary contact in the maritime shrew, Sorex maritimensis: implications for the conservation of a Canadian endemic mammal

The maritime shrew, Sorex maritimensis, is a Canadian endemic species with a limited distribution in two provinces in eastern Canada. Phylogeographic analysis of mitochondrial DNA control region and cytochrome b sequences revealed two clades, one found in New Brunswick and the other primarily in Nova Scotia, Canada. We propose that these clades have come back into secondary contact following the Wisconsin glaciation via wetlands on the narrow Isthmus of Chigneto that connects these provinces. Despite evidence of an historic separation of maritime shrew subpopulations in Nova Scotia and New Brunswick, we conclude that shrews in these two regions should be considered a single evolutionary significant unit but separate, semi-isolated management units that should be recognized as such for conservation purposes. The susceptibility of this stenotopic species with limited dispersal capabilities raises concerns about its long-term persistence if climate-change induced habitat fragmentation increases. Maintenance of contiguous wetland habitats is needed to ensure connectivity and gene flow among populations of the maritime shrew.     

Between-year variation in flowering and fruit set in frost-prone and frost-sheltered populations of dioecious Rubus chamaemorus

Summary The flowering and fruiting patterns of the dioecious perennial herb Rubus chamaemorus L. were studied in frost-prone (open) and frost-sheltered (Shaded) habitats in northern Sweden over 6 years. The number of ramets with flower buds, the proportion of flower buds that opened, and fruit set varied markedly between years. In the frost-prone populations, the occurrence or absence of detrimental frosts during the development of flowers and fruit could explain much of the variation, both in the proportion of flower buds that developed into flowers, and in fruit set. In the frost-sheltered populations, most female flowers that did not develop into fruit aborted without any signs of physical damage and before any ovules had begun to enlarge. Flower mortality caused by herbivores feeding on reproductive parts was commonly low, but reached values higher than 10% in one of the shaded populations. Hand-pollination increased the proportion of ovules producing seeds in the mature fruits by about 20%, and in one year also increased fruit set significantly in one population. Fruit-producing female ramets had a higher mortality and a lower probability of flowering in the subsequent year than male ramets and non-fruiting female ramets. In R. chamaemorus, the conditions for fruit maturation are highly unpredictable at the time of flower initiation. It is suggested that the apparent over-initiation of flower buds is advantageous, as it allows the plant to attain a high reproductive success in years favourable for flowering and fruit development.     

Life-history variation in Crepis tectorum (Asteraceae)

Summary Populations of the monocarpic plant Crepis tectorum were grown in a series of uniform environments to test the hypothesis that weedy populations are more r-selected than populations from a more natural habitat. Weedy populations exhibited a combination of r- and K-selected traits. The relatively rapid growth, the potential for a summer annual habit, and the relatively high fecundity that characterized at least one of the two weed populations studied were considered as r-selected traits favored in habitats of unpredictable duration. However, high levels of competition from other weedy species or from the crop in arable fields may explain at least some presumably K-selected traits observed in the weedy populations, e.g. relatively large seeds and late flowering in the summer. Results indicated that stress due to abiotic factors (strong winds, desiccation and nutrient deficiency) has been a more important selective factor than r- or K-selection, in non-weedy populations from calcareous grasslands (alvars) on the Baltic islands.     

Developmental changes and tissue distribution of lectin in Tulipa

A sensitive enzyme-immunoassay was developed to quantify the tulip lectin and used to follow its distribution during the life cycle of tulips cv. Attila.The tulip lectin is predominantly located in the bulbs. At planting time the absolute lectin concentration is approximately the same in all bulb scales. However, as the shoot grows and the plant turns on to flowering, the lectin concentration rapidly decreases, first in the inner bulb scales but later also in the outer bulb scale. Soon after flowering the lectin rapidly accumulates in the new daughter bulbs.Lectin levels in leaves, stems and flowers are very low. The lectin in these tissues is already present before the sprout emerges. During the first two weeks after planting, there is a small increase in lectin concentration, followed by a rapid decrease as the plant turns on to flowering. By flowering time all the lectin has disappeared from the aerial parts.Abbreviations DW dry weight - ELISA enzyme-linked immunosorbent assay - FW fresh weight - PBS phosphate-buffered saline - PBSN phosphate-buffered saline containing 0.02% sodium azide - PBST phosphate-buffered saline containing 0.02% sodium azide and 0.05% Tween 20 - TL tulip lectin - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol