GENETIC POPULATION STRUCTURE AND MATING SYSTEM IN CHONDRUS CRISPUS (RHODOPHYTA)1

Chondrus crispus Stackh. has been intensely studied, yet no study to date has elucidated its population structure or mating system despite many populations in which there was a haploid bias and lack of male gametophytes. Therefore, 12 nuclear microsatellite loci were identified in this red alga. Microsatellite markers were developed and tested against a panel of specimens collected from two shore levels at two sites in Brittany, France: Pointe de Primel and Pointe de la Jument, Concarneau. Single locus genetic determinism was verified at eight polymorphic loci, as only one band was observed for haploid genotypes, whereas one or two bands were observed for diploids. These markers enabled the detection of unique genotypes within sampled populations, indicating that very few fronds shared the same multilocus genotype. This finding suggests that asexual reproduction was not the prevailing mode of reproduction. In addition, we explored the hierarchical population structure showing that gene flow is restricted at small spatial scales (<50 m) between upper and lower Chondrus‐range populations within a shore. Sexual reproduction predominated in the populations of C. crispus studied, but probably due to fine‐scale spatial substructuring, inbreeding was also significant. In conclusion, this study reveals that fine‐scale genetic variation is of major importance in C. crispus, suggesting that differences between microhabitats should be essential in understanding evolutionary processes in this species.     

The demography of fronds of Chondrus crispus Stackhouse

A demographic analysis was done of an intertidal stand of Chondrus crispus Stackhouse at Pubnico Point, Nova Scotia. The distribution of gametophytic and tetrasporophytic fronds was assessed. Fronds were placed in one of four size-classes. Size-specific measurements for fronds are presented. Gametophytic fronds dominated the stand. Fronds in Size-Class 2 exhibited high survivorship. Survivorship fell sharply when fronds entered Size-Class 3 and Size-Class 4. Fronds became fertile and highly branched when in the third and fourth size-classes. It is suggested that these two factors contribute to the higher mortality rates of such individuals.Monthly spore release rates·m^?2 for gametophytes and tetrasporophytes were measured. The annual release rate of carpospores exceeded the annual release rate of tetraspores by a ratio of 4.7:1. Rates did not fall below 10⁶ spores released·m^?2·month^?1 for either phase.     

Demographic models to simulate the stable ratio between ecologically similar gametophytes and tetrasporophytes in populations of the Gigartinaceae (Rhodophyta)

In populations of the Gigartinaceae (Rhodophyta), gametophytes often predominate numerically over tetrasporophytes. Several hypotheses have been proposed to explain this dominance, based on the usually implicit assumption that the stable ratio between gametophytes and tetrasporophytes (G:T ratio) should be 1 if both reproductive phases are ecologically similar. We developed demographic models to test this assumption, for which we considered that both phases are ecologically similar. Defining ecologic similarity for most demographic rates is relatively straightforward, except for rates of spore output. The first set of models considered the same spore output per thallus of both phases as representing ecologic similarity. Model iterations led to stable G:T ratios of 1 for triennial and for perennial thalli, regardless of the initial G:T ratio, but not for annual thalli with initial G:T ratios different from 1. However, equal spore output may not represent ecologic similarity, due to size differences between carpospores and tetraspores. The second set of models considered the lowest possible spore output for each phase, according to the life history of this family: only one carposporangium, with one carpospore, is produced from every two gametophytes and only one tetrasporangium, with four tetraspores, is produced by every tetrasporophyte. Model iterations led to stable G:T ratios of 2.8 for most cases, a ratio of 1 being obtained only every 2 years for annual thalli with an initial G:T ratio of 1. Increasing absolute spore output, without altering the relative output between phases and incorporating density-independent mortality through a matrix model, given the same mortality rate for both phases, did not modify results. We suggest that the combination of both modeling and field research may uncover more rapidly than otherwise the most relevant ecologic differences between phases, if any, that underlie the G:T ratio observed for a given population.     

Composes halogenes d'une algue rouge,Falkenbergia rufolanosa tetrasporophyte d' Asparagopsis armata

Water extraction of fresh Falkenbergia rufolanosa followed by water-ether partition, yielded halomethanes, polyhalo ethyl and methyl acetates and especially polyhalo acetones. It is the first example of polyhalo compounds extracted from a tetrasporophyte in the Bonnemaisoniaceae.     

Carrageenan patterns in the Gigartinaceae

Carrageenans of known reproductive phases of gigartinacean species are shown to differ: gelling κ (τ)-type carrageenan occurs in all instances in gametophytes, and viscous non-gelling λ-carrageenan or its variant ξ- or π-carrageenan in tetrasporophytes. Multiple analyses demonstrate that the carrageenan type is a species characteristic, with little difference between individual samples. No difference exists between the carrageenans of male and female plants of each species. Carrageenan chemistry combined with morphological, reproductive and life history feature is useful for defining the taxonomic limits of this family and these genera.     

Oceanic rafting by a coastal community

Oceanic rafting is thought to play a fundamental role in assembling the biological communities of isolated coastal ecosystems. Direct observations of this key ecological and evolutionary process are, however, critically lacking. The importance of macroalgal rafting as a dispersal mechanism has remained uncertain, largely owing to lack of knowledge about the capacity of fauna to survive long voyages at sea and successfully make landfall and establish. Here, we directly document the rafting of a diverse assemblage of intertidal organisms across several hundred kilometres of open ocean, from the subantarctic to mainland New Zealand. Multispecies analyses using phylogeographic and ecological data indicate that 10 epifaunal invertebrate species rafted on six large bull kelp specimens for several weeks from the subantarctic Auckland and/or Snares Islands to the Otago coast of New Zealand, a minimum distance of some 400–600 km. These genetic data are the first to demonstrate that passive rafting can enable simultaneous trans-oceanic transport and landfall of numerous coastal taxa.     

Fronts,jumps and secondary introductions suggested as different invasion patterns in marine species,with an increase in spread rates over time

Not all introduced (invasive) species in a region will spread from a single point of introduction. Long-distance dispersal or further introductions can obscure the pattern of spread, but the regional importance of such processes is difficult to gauge. These difficulties are further compounded when information on the multiple scale process of invasive species range expansion is reduced to one-dimensional estimates of spread (e.g. km yr⁻¹). We therefore compared the results of two different metrics of range expansion: maximum linear rate of spread and accumulation of occupied grid squares (50 × 50 km) over time. An analysis of records for 54 species of introduced marine macrophytes in the Mediterranean and northeast Atlantic revealed cases where the invasion process was probably missed (e.g. Atlantic Bonnemaisonia hamifera) and suggested cases of secondary introductions or erratic jump dispersal (Dasysiphonia sp. and Womersleyella setacea). A majority of species analysed showed evidence for an accumulation of invaded sites without a clear invasion front. Estimates of spread rate are increasing for more recent introductions. The increase is greater than can be accounted for by temporally varying search effort and implies a historical increase in vector efficiency and/or a decreased resistance of native communities to invasion.     

Female Competition over Core Areas in <Emphasis Type=Italic>Pan troglodytes schweinfurthii</Emphasis>, Kibale National Park,Uganda

Aggression is rare among wild female chimpanzees. However, in the Kanyawara chimpanzee community in Kibale National Park, Uganda, stable use of food-rich core areas is linked to increased reproductive success, suggesting that contest competition might occur over access to the highest-quality ranges. To examine this hypothesis, we studied aggression and dominance relationships among Kanyawara females during a 10-yr period that included the immigration of 5 females into the community. We tested 2 predictions: 1) that female-female aggression should intensify when immigrants enter the community because this is when core area access is determined and 2) that the quality of core areas should reflect relative female dominance relationships. In support of the first prediction, female-female aggression increased 4-fold when new immigrants were in the community, with rates peaking when there were multiple immigrants. This pattern was due primarily to aggression by resident mothers toward immigrants and featured coalitionary aggression, a rare behavior among female chimpanzees. In support of the second prediction, females occupying core areas high in foraging quality ranked high overall and higher than expected for their ages, whereas females occupying low-quality core areas were lower-ranking and ranked lower than expected for their ages. Together, the data indicate that though female aggression does not regularly occur in chimpanzees, contest competition continues to play an important role in determining long-term access to resources, an important correlate of reproductive success.     

TEMPORAL VARIATION IN ISOMORPHIC PHASE AND SEX RATIOS OF A NATURAL POPULATION OF ULVA PERTUSA (CHLOROPHYTA)1

The green macroalga Ulva L. is well known as having an alternation of isomorphic biphases: gametophyte and sporophyte. However, an examination of the temporal alternation in phase dominance has not been carried out. By inducing reproduction of thallus samples in the laboratory, this study reports the temporal changes in the two phases and sex ratios in a natural population of Ulva pertusa Kjellm. in the Seto Inland Sea, Japan, over a period of >3 years. The results showed that a temporal alternation in phase dominance occurred after 11–20 months; seasonal changes in phase dominance were not observed in the Ulva population. The sex ratio of male and female gametophytes remained ～1:1 throughout the investigated period, although skewed sex ratios were observed in several collections.