The birth process with immigration,and the genealogical structure of large populations

This paper studies a version of the birth and immigration process in which families are followed in the order of their appearance. This age structure is related to a number of results from population genetics, in particular the genealogical structure of the infinitely-many neutral alleles model. The asymptotic behavior of this genealogy is an easy consequence of the structure of the age-ordered family size process.     

Age structure and dynamics of Rhododendron ferrugineum L. populations in the northwestern French Alps

Abstract. The ericaceous shrub Rhododendron ferrugineum occupies large areas at the subalpine level (1600–2200 m) of the northwestern French Alps. It frequently reaches 90–100 % cover, accumulates 60–70t/ha (dry weight) above-ground biomass and is able to dominate many subalpine landscapes by outcompeting other species. We formulated the hypothesis that the species shows a rapid and invasive seedling establishment and a fast population development. We investigated the age structure and development of two populations. Although classic colonization stages can be identified, and variation did occur depending on the site, R. ferrugineum populations showed a surprisingly slow development compared with other ericaceous species. Curves obtained from polynomial regression equations of cover on age allowed us to predict the future development of populations. Thus, depending on the site, it would take 150 to 250 yr to achieve total cover. We discuss the factors involved that could explain this slow development and discuss which biotic and abiotic factors may be responsible for the large extension of this species in the subalpine belt.     

Pollen-derived history of timber exploitation from the Roman period onwards in the Romanche valley, central French Alps

The history of forestry in the Romanche river valley, south-east of Grenoble, France, is reconstructed for the past ca. 3000 years on the basis of detailed pollen analysis and AMS¹⁴C dating. Three deforestation phases are recorded during the last two millennia, each phase showing different features and also contrasting woodland succession in the post-clearance period. The first major deforestation is recorded at the Roman time whenAbies alba (fir) was selectively exploited, presumably for use by peoples living downstream of the site. Apart from the deforestation, there appears to have been little human activity in the vicinity of the site at this time. After the clearance fir gradually, and more or less fully, recovered. The second deforestation phase occurred in ca. the 5^th and 6^th century A.D. when there is also substantial evidence for local farming. At this time, both fir and beech (Fagus sylvatica) were non-selectively exploited and probably used locally. Beach subsequently recovers but there is no further regeneration of fir. The third deforestation phase in ca. the 12^th century A.D. is similar to the preceding phase but this time beech does not recover. With the decline in human activity, secondary forest that included spruce (Picea) and pine (Pinus), developed. Forest dynamics were controlled by local human activity and also the economic relationships between the local area and the wider region and especially the region downstream from the site.     

Pinus cembra L. (arolla pine), a common tree in the inner French Alps since the early Holocene and above the present tree line: a synthesis based on charcoal data from soils and travertines

Aim In this study, charcoal‐based data for Pinus cembra L. (arolla pine) were gathered from soil and travertine sequences in order to reconstruct its historical biogeography at the landscape level in the inner western Alps during the Holocene. Location The study sites are located between 1700 and 2990 m a.s.l., in the southern (Queyras Massif and Ubaye Valley) and the northern (Maurienne Valley) parts of the inner French Alps. Methods Charcoal fragments were extracted from sediments by water sieving, using meshes of 5, 2, 0.8 and 0.4 mm. The charcoal mass of P. cembra was determined in each charcoal assemblage. Accelerator mass spectrometry and conventional ¹⁴C measurements were used to date the fragments. Results Supported by 40 ¹⁴C datings, the fragments show that, over 2000 m a.s.l., P. cembra accounts for around 40% (mean value) of identified fragments. Data reveal that arolla pine once extended between 260 and 375 m above the present‐day local tree lines. It was established in the southern and the northern French Alps from at least c. 9000 and 6000 cal yr bp , respectively. Main conclusions While present‐day populations of P. cembra are very fragmented in the inner French Alps, charcoal records indicate large past occurrences of this tree since the early Holocene. Human disturbance since the Neolithic seems to be the main reason for the regression of the arolla pine woodlands. On the south‐facing slopes of the study sites, currently deforested, this species extended up to 2800 m a.s.l. In the northern areas, charcoal records of the P. cembra expansion are consistent with the regional pollen archives, but in the southern massifs charcoal records indicate its presence c. 2600 years earlier than other palaeobotanical studies suggest. This discrepancy highlights the necessity to crosscheck data using several different proxies in order to assess the validity of conclusions regarding tree development in space and time.     

Temporal variation in reproductive costs and payoffs shapes the flowering strategy of a neotropical milkweed, <Emphasis Type="Italic">Asclepias curassavica</Emphasis>

A central goal of evolutionary ecology is to understand the factors that select for particular life history strategies, such as delaying reproduction. For example, environmental variation and reproductive costs to survival and growth often select for reproductive delays in semelparous and iteroparous species. In this study, we examine how variation in reproductive cost, which we define as a reduction to growth, survival, or future reproduction after a reproductive event, may select for reproductive delay in an iteroparous Neotropical milkweed with no obvious reproductive season. We analyzed demographic data collected every 3 months for 3 years from four populations of Asclepias curassavica in Monteverde, Costa Rica. We detected costs of flowering to survival and growth that varied in magnitude between our 12 transition periods without a seasonal pattern. The populations also exhibited temporal variation in reproductive payoffs measured as seedling establishment. We incorporated these reproductive costs into demographic projection models, which predicted a delayed flowering strategy only when we included temporal variation in costs and payoffs. Temporal variation in reproductive costs and payoffs is an important selective force in the evolution of delayed flowering in iteroparous species. Further, a lack of predictable seasonal pattern to reproductive costs and payoffs may contribute to the lack of seasonal reproductive patterns observed in our study species and other Neotropical species.     

The importance of reproductive interference in ecology and evolution: from organisms to communities

Knowledge of species interactions is vital to understand ecological and evolutionary patterns in nature. Traditional species interactions (e.g., competition, predation, symbiosis) have received a great deal of deserved attention and their general importance in shaping the evolution of populations and structure of communities is unquestioned. Recently, reproductive interference has been receiving attention as an important species interaction. Reproductive interference is defined as interspecific reproductive activities that decrease the fitness of at least one of the species involved in the interaction. Reproductive interference has the potential to affect the evolutionary trajectories of populations and structure of communities. Here, I comment on seven papers that make up this special feature on reproductive interference. Along the way I highlight key discoveries of these studies and areas of research that may contribute to our understanding of the causes and consequences of reproductive interference.     

Differential human impact and vegetation history in two adjacent Pyrenean valleys in the Ariège basin,southern France,from 3000 B.P. to the present

Detailed palynological studies in two adjoining French Pyrenean valleys, complemented by the study of archives, demonstrate that under similar climatic conditions, the forest history of each valley from the Bronze Age to present time was essentially determined by socio-economical constraints, possibly modified by natural characteristics such as topography. The studies show why the expansion of Fagus (beech) at c. 4000 B.P. was asynchronous on the northern slope of the Pyrenees and emphasize the effects of the human impact on the recent lowering of the tree-line.A contribution to the 8th IPC, Aix-en-Provence, 1992     

Adding new pieces to the Azadinium (Dinophyceae) diversity and biogeography puzzle: Non-toxigenic Azadinium zhuanum sp. nov. from China,toxigenic A. poporum from the Mediterranean,and a non-toxigenic A. dalianense from the French Atlantic

The marine planktonic dinophyceaen genus Azadinium is a primary source of azaspiracids, but due to their small size its diversity may be underestimated and information on its biogeography is still limited. A new Azadinium species, A. zhuanum was obtained from the East China Sea and Yellow Sea of China by incubating surface sediments. Five strains were established by isolating single germinated cells and their morphology was examined with light microscopy and scanning electron microscopy. Azadinium zhuanum was characterized by a plate pattern of Po, cp, X, 4′, 2a, 6′′, 6C, 5S, 6′′′, 2′′′′, by a distinct ventral pore at the junction of Po, the first and fourth apical plates, and a conspicuous antapical spine. Moreover, Azadinium poporum was obtained for the first time from the Mediterranean by incubating surface sediment collected from Diana Lagoon (Corsica) and a new strain of Azadinium dalianense was isolated from the French Atlantic. The morphology of both strains was examined. Small subunit ribosomal DNA (SSU rDNA), large subunit ribosomal DNA (LSU rDNA) and internal transcribed spacer (ITS) sequences were obtained from cultured strains. In addition, LSU sequences were obtained by single cell sequencing of two presumable A. poporum cells collected from the French Atlantic. Molecular phylogeny based on concatenated SSU, LSU and ITS sequences revealed that A. zhuanum was closest to A. polongum. French A. poporum from Corsica (Mediterranean) and from the Atlantic showed some genetic differences but were nested within one of the A. poporum ribotypes together with other European strains. Azadinium dalianense from France together with the type strain of the species from China comprised a well resolved clade now consisting of two ribotypes. Azaspiracid profiles were analyzed for the cultured Azadinium strains using LC–MS/MS and demonstrate that the Mediterranean A. poporum strain produced AZA-2 and AZA-2 phosphate with an amount of 0.44 fg cell⁻¹. Azadinium zhuanum and A. dalianense did not produce detectable AZA. Results of the present study support the view of a high diversity and wide distribution of species belonging to Azadinium. The first record of AZA-2 producing A. poporum from the Mediterranean suggests that this species may be responsible for azaspiracid contaminations in shellfish from the Mediterranean Sea.     

Circadian rhythm of photosensitivity and the adaptation of reproductive function to the environment in two populations of Arvicanthis niloticus from Mali and Burkina Faso.

Previous studies have shown that there is a circadian rhythm of photosensitivity in different rodent species of the Sahel (Burkina Faso) and that, despite the low amplitude of seasonal variations in daylength, the photoperiod may control reproductive function. The present investigation of Arvicanthis niloticus provides additional support for this hypothesis. Populations of Arvicanthis niloticus from two regions at the same latitude 1000 km apart but with different climates were studied. Oursi, Burkina Faso, has an arid climate (annual rainfall 315 mm) and Kamalé, Mali has a wetter climate (annual rainfall 1114 mm). The circadian rhythm of photosensitivity had the same features in both populations, involving inhibition of testicular activity, but the photosensitive phase began 11 h 30 min after dawn in the population from Burkina Faso and 45 min later in that from Mali. Comparison of these results with the annual variation of daylength showed that the photoperiod inhibits the reproductive activity of A. niloticus from April to December in Burkina Faso and only from mid-May to mid-August in Mali. The population of Arvicanthis niloticus living in an environment with a large and seasonally stable food supply (Mali) thus has a longer reproductive period. This corroborates results from field studies on annual variations of population density.     

Plant size,breeding system,and limits to reproductive success in two sister species of Ferocactus (Cactaceae)

Plant reproductive output can be limited by a variety of factors, bothintrinsic and extrinsic. I investigated the reproductive biologies of twospecies of unbranched short-columnar cacti, Ferocactuscylindraceus and F. wislizeni. I recordedfemalereproductive output (flowers produced, fruit set, seeds per fruit and seedmass), plant size and growth, and used hand-pollination experiments todeterminebreeding systems and pollen limitation. In both species, the ability to selfvaried among individuals, but self-pollination resulted in very few seeds,suggesting strong inbreeding depression. Neither species was pollen-limited.Numbers of flowers produced increases with plant size for both species, andseeds per fruit may also be related to plant size, although the relationship isunclear. Seed mass is not correlated with plant size. Flower production wassimilar in both species, but F. cylindraceus producedfewerseeds per fruit than F. wislizeni, and its seeds weighedless. Fruit set by F. cylindraceus was heavily impacted bya florivorous lepidopteran. Fruit set was very high (94 to 96%) inF. wislizeni, suggesting that architectural constraints(e.g., meristem limitation) are more limiting than resource levels or the levelof pollinator services. In F. cylindraceus, numbers ofseeds per fruit was positively correlated with seed mass, whereas inF. wislizeni, the relationship was negative (tradeoff).Thegrowth rates of F. wislizeni are affected by rainfall theprevious season, and growth rates increase as the plant ages.Ferocactus cylindraceus and F.wislizeni are thought to be sister species, meaning that observeddifferences between them are more likely to be the result of recentevolutionaryprocesses in their lineages rather than differing phylogenetic histories.     

Segregation and linkage analyses in two complex populations derived from the citrus rootstock Cleopatra mandarin. Inheritance of seed reproductive traits

Two complex populations derived from the salt-tolerant citrus rootstock Cleopatra mandarin were used to investigate (1) the genomic regions affected by segregation distortion and (2) gene segregation heterogeneity and their causes and to obtain (3) a Citrus reshni linkage map to genetically analyze (4) the duration of the juvenility period and the seed embryony type. Both populations differed in the extent and origin of segregation distortion. The population derived from the cross between C. reshni and Poncirus trifoliata (R?×?Pr) showed 75?% of codominant markers with distorted segregation. The origin of this distortion was prezygotic in most cases. Meanwhile, 100?% of codominant markers in the self-pollinated population [F₂(R?×?Pr)] showed genotypic distortion, and the origin of such distortion was mostly postzygotic, with the heterozygote being the most frequent genotype in all cases. In the R?×?Pr population, where two pollinator varieties were used, allele segregation was significantly heterogeneous not only in P. trifoliata (28.6?% of markers) but also in C. reshni (19.5?%). The results on segregation heterogeneity in the F₂(R?×?Pr) suggest the presence at linkage group 4c of a postfertilization system of balanced lethal factors that reduces homozygosis in self-compatible hybrids. Four low to medium contributing quantitative trait loci (QTLs) were detected for the duration of juvenility period by both Kruskal?CWallis and interval mapping methodologies. For seed embryony type, three QTLs were detected by both methodologies, with the previously reported Apo2 being the QTL contributing the most. CR14,290 and TAA15 are good markers for early selection of polyembryonic rootstocks in progenies derived from C. reshni, Citrus aurantium, and Citrus volkameriana.     

Morphological differences between,and reproductive isolation of,two populations of the jellyfish Cyanea in Long Island Sound,USA

Two populations of Cyanea, one in the Niantic River estuary and the other in the adjacent Niantic Bay portion of Long Island Sound, were studied for more than a decade. The estuary and the bay are connected by a narrow channel: this and hydrographic features constrain transport between them. Specimens from each site exhibit morphological and seasonal differences comparable to those which distinguish C. capillata from C. lamarckii in European waters. Reproducing River medusae never cooccurred with reproducing Bay medusae. Estuarine jellyfish are sometimes found in the Bay, but reproducing individuals have not been seen there. Reproductively mature Bay jellyfish occasionally appear in the River, but benthic samples show that they do not deposit planulae at this site and thus do not contribute to the next generation of medusae in the River. Such differences suggest an absence of gene flow between these two populations, indicating that the River medusae and Bay medusae might be separate species.     

Intraspecific genetic differentiation of Leporinus friderici (Anostomidae, Pisces) in French Guiana and Brazil: a genetic approach to the refuge theory

A genetic study was carried out on a neotropical fish species to illustrate the refuge theory, whose main principles are summarized. The geographical structure of the anostomid species Leporinus friderici was analysed in French Guiana and Brazil by horizontal starch gel electrophoresis. Fifteen enzymatic systems corresponding to 21 loci were studied, revealing the following particularities: (1) specimens of fish from six independent coastal rivers of French Guiana form two groups geographically situated on either side of the Kourou River; (2) two alleles can serve as geographic markers, Ldh2 ( l30 ) showing an affinity between the populations in eastern French Guiana and Brazil, and Me 1 ( 300 ) being specific to the west.
These observations are probably related to the refuges that were formed in the Quaternary in South America, especially on the Guiana Shield. We consider that the populations of French Guiana are separated into two groups at the boundary between the two migratory flows, one arising in the west from the refuge of the Guiana Shield and the other in the east from a nearby undetermined Amazonian refuge.     

Contrasting effects of herbivory on plant size and reproductive performance in two populations of the Critically Endangered species,Euphorbia clivicola R. A. Dyer

Euphorbia clivicola R.A. Dyer is a Critically Endangered Northern Province endemic confined to two populations that have declined drastically over the last decade. One population is protected within a Nature Reserve, while the other occurs in a peri-urban area. In order to determine the causes of the population declines, herbivory damage to plants in both the protected and urban populations was quantified and the effects of herbivory on various aspects of the population biology were assessed. Mountain reedbuck are believed to have been responsible for the herbivory in the protected population. Herbivory on the above-ground branches probably caused the small sizes of protected plants. These were on average less than half the size of urban plants. Herbivory caused a reduction in the number of flowers and fruit produced per protected plant and may have prevented the maturation of flowers into fruit, thereby reducing the total regenerative output of the population. An eight-year absence of fire had resulted in the build-up of a dense moribund grass layer. The selection of E. clivicola plants by mountain reedbuck may therefore have been due to their relatively high nutritional value and accessibility in the thick moribund grass layer. Fencing off the population to prevent entry of herbivores, and implementing a more suitable fire management programme is recommended, as is the adoption of a new IUCN status for the species of Critically Endangered (CR A1).     

Hybridization of two forms of ninespine stickleback,Pungitius pungitius and P. platygaster,under experimental conditions and an attempt to predict the consequences of their contact in nature

Synopsis In aquaria and in ponds crosses were made between two closely related allopatric forms of ninespine stickleback of the genus Pungitius (P. pungitius and P. platygaster). There were no ethological isolation mechanisms; F₁, F₂ and F₃ hybrids are fertile; experimental hybrid stocks as well as backcrosses maintain themselves for at least three generations. F₁ hybrids are readily distinguishable from parental forms by a combination of morphological characters; F₂ hybrids grown in the north near the Arctic circle, are morphologically similar to P. pungitius. The southern form P. platygaster does not survive in northern conditions; eggs of the northern form P. pungitius die at a temperature of 28°C, normal for the spawning of the southern form. By 9 out of 19 studied morphological characters there are distinctions between the two forms. Therefore, ecologically and morphologically the two forms have diverged rather significantly. On the other hand, ethologically and genetically (as judged by the absence of postmating isolating mechanisms) the forms have diverged only slightly. As a result, the differences between the two forms are considered not to exceed the subspecies or at least semispecies rank.In recent years, due to a disturbance of the ranges of both these forms in Eurasia, a tendency for a secondary contact between P. pungitius and P. platygaster appeared in the basins of the rivers Volga and Irtysh. In the immediate future the two forms are expected to come into contact. From our data we predict possible introgressive hybridization between the northern and sourthern forms in natural conditions.     

Technique,task definition,and the transition from genetics to molecular genetics: Aspects of the work on protein synthesis in the laboratories of J. Monod and P. Zamecnik

In biology proteins are uniquely important. They are not to be classed with polysaccharides, for example, which by comparison play a very minor role. Their nearest rivals are the nucleic acids....The main function of proteins is to act as enzymes....In the protein molecule Nature has devised a unique instrument in which an underlying simplicity is used to express great subtlety and versatility; it is impossible to see molecular biology in proper perspective until this peculiar combination of virtues has been clearly grasped.