Two colonisation stages generate two different patterns of genetic diversity within native and invasive ranges of Ulex europaeus

Genetic diversity and the way a species is introduced influence the capacity of populations of invasive species to persist in, and adapt to, their new environment. The diversity of introduced populations affects their evolutionary potential, which is particularly important for species that have invaded a wide range of habitats and climates, such as European gorse, Ulex europaeus. This species originated in the Iberian peninsula and colonised Europe in the Neolithic; over the course of the past two centuries it was introduced to, and has become invasive in, other continents. We characterised neutral genetic diversity and its structure in the native range and in invaded regions. By coupling these results with historical data, we have identified the way in which gorse populations were introduced and the consequences of introduction history on genetic diversity. Our study is based on the genotyping of individuals from 18 populations at six microsatellite loci. As U. europaeus is an allohexaploid species, we used recently developed tools that take into account genotypic ambiguity. Our results show that genetic diversity in gorse is very high and mainly contained within populations. We confirm that colonisation occurred in two stages. During the first stage, gorse spread out naturally from Spain towards northern Europe, losing some genetic diversity. During the second stage, gorse was introduced by humans into different regions of the world, from northern Europe. These introductions resulted in the loss of rare alleles but did not significantly reduce genetic diversity and thus the evolutionary potential of this invasive species.     

A new prenylisoflavone from Ulex jussiaei

A new naturally occurring isoflavone, derrone, was isolated from Ulex jussiaei (Leguminosae) together with the isoflavones ulexins A-C, lupalbigenin, isolupalbigenin, 7-O-methylso-lupalbigenin, isoderrone, ulexone A and isochandalone, the pterocarpans (6aR,11aR)-(-)-maackiain, (6aR,11aR)-(-)-2-methoxymaackiain and (6aR,11aR)-(-)-4-methoxymaackiain, the chalcone 4-hydroxylonchocarpine and the dihydrochalcone crotaramosmine. The antifungal activity of the new compound was tested by a bioautographic method against Cladosporium cucumerinum, and as expected from structural features it proved to have no activity.     

Migratory divides and their consequences for dispersal, population size and parasite-host interactions

Populations of migratory birds differ in their direction of migration with neighbouring populations often migrating in divergent directions separated by migratory divides. A total of 26% of 103 passerine bird species in Europe had migratory divides that were located disproportionately often along a longitudinal gradient in Central Europe, consistent with the assumption of a Quaternary glacial origin of such divides in the Iberian and Balkan peninsulas followed by recolonization. Given that studies have shown significant genetic differentiation and reduced gene flow across migratory divides, we hypothesized that an absence of migratory divides would result in elevated rates of gene flow and hence a reduced level of local adaptation. In a comparative study, species with migratory divides had larger population sizes and population densities and longer dispersal distances than species without migratory divides. Species with migratory divides tended to be habitat generalists. Bird species with migratory divides had higher richness of blood parasites and higher growth rates of Staphylococcus on their eggs during the incubation period. There was weaker cell-mediated immunity in adults and stronger cell lysis in species with migratory divides. These findings may suggest that migratory divides constitute barriers to dispersal with consequences for ecology and evolution of distributions, population sizes, habitats and parasite-host interactions. They also suggest that migratory divides may play a role in local adaptation in host-parasite interactions.     

Races of the Barley Root-Knot Nematode,Meloidogyne naasi. III. Reproduction and Pathogenicity on Creeping Bentgrass

Reproduction and pathogenicity of the five known races of Meloidogyne naasi on two selections of creeping bentgrass were compared. Toronto C-15 was a host for Races 3, 4 and 5, whereas Northmoor 9 supported reproduction of all five races. Differences in susceptibility and population increase demonstrated that the races could be separated by degree of reproduction on the two selections. Root weights generally were unaffected. Based on cumulative dipping weights, all but Race 1 were pathogenic on at least one of the selections; Race 3 stunted top growth of both. Slight differences in degree of pathogenicity, associated with final populations, were not broad enough to be useful in race separation.     

Ulex europaeus agglutinin-I binds to developing gastrin cells

 We have previously reported that antropyloric gastrin (G) and somatostatin (D) cells derive from precursor (G/D) cells that coexpress both hormones. We have now analyzed this endocrine cell pedigree for binding of Ulex europaeus agglutinin-I (UEA-I), which previously has been reported to represent a useful marker for cell differentiation. Subpopulations of G/D, D, and G cells were all found to express UEA-I binding. Labelling with bromodeoxyuridine showed that UEA-I positive G cells possessed a higher labelling index than UEA-I negative G cells. These data suggest that the UEA-I positive G cells represent maturing cells still involved in DNA synthesis and cell division. Electron microscopically, specific UEA-I binding sites were localized to the secretory granules and the apical cell membrane of G cells. We conclude that UEA-I represents a differentiation marker for G cells. Moreover, the presence of UEA-I binding sites in these cells may be relevant for Helicobacter pylori-mediated disturbances of gastric acid secretion and gastrin hypersecretion. Accepted: 19 August 1997     

Connecting geographical distributions with population processes

The geographical distribution of a species is determined by a large number of complex processes operating over spatial scales spanning 10 orders of magnitude. Patterns in population processes have been described at numerous scales. We show that two patterns, measured at different scales, jointly allow us to infer heretofore unknown patterns in the distribution of demographic patterns across the geographical range of a species. The resulting model describes three fundamentally different modes of geographical variation in vital rates of populations. One mode is characterized by a positive nonlinear relationship between the maximum rate of population growth and the intensity of intraspecific competition across a geographical range. That is, populations that grow rapidly are also those where individuals experience the greatest per capita negative effect of the presence of other individuals. The second mode of behaviour is described by a negative nonlinear relationship between maximum growth rate and density dependence. Under this scenario, populations with low capacity to grow rapidly have highest intensities of intraspecific competitive effects. A third mode of behaviour is characterized by a weak positive relationship between growth rate and intraspecific competition, with very little geographical variation in maximum growth rate. A survey of studies relating temporal means and variances in population abundance for a variety of species indicate that the second mode of geographical variation in population dynamics across species ranges is the most common, though a few species appear to be characterized by the third mode.     

Widespread latitudinal asymmetry in the performance of marginal populations: A meta-analysis

Aim

Range shifts are expected to occur when populations at one range margin perform better than those at the other margin, yet no global trend in population performances at range margins has been demonstrated empirically across a wide range of taxa and biomes. Here we test the prediction that, if impacts of ongoing climate change on performance in marginal populations are widespread, then populations from the high-latitude margin (HLM) should perform as well as or better than central populations, whereas low-latitude margin (LLM) populations should perform worse.

Location

Global.

Time period

1995–2019.

Major taxa studied

Plants and animals.

Methods

To test our prediction, we used a meta-analysis to quantify empirical support for asymmetry in the performance of high- and low-latitude margin populations compared to central populations. Performance estimates (survival, reproduction, or lifetime fitness) for populations occurring in their natural environment were derived from 51 papers involving 113 margin-centre comparisons from 54 species and 705 populations from the Americas, Europe, Africa and Australia. We then related these performance differences to climatic differences among populations. We also tested whether patterns are consistent across taxonomic kingdoms (plants vs animals) and across realms (marine vs terrestrial).

Results

Populations at margins performed significantly worse than central populations, and this trend was primarily driven by the low-latitude margin. Although the difference was of small magnitude, it was largely consistent across biological kingdoms and realms. Differences in performance were weakly (p = .08) related to the difference in average temperatures between central and marginal populations.

Main conclusions

The observed asymmetry in performance in marginal populations is consistent with predictions about the effects of global climate change, though further research is needed to confirm the effect of climate. It indicates that changes in demographic rates in marginal populations can serve as early-warning signals of impending range shifts.     

Local adaptation,dispersal evolution,and the spatial eco‐evolutionary dynamics of invasion

Local adaptation and dispersal evolution are key evolutionary processes shaping the invasion dynamics of populations colonizing new environments. Yet their interaction is largely unresolved. Using a single‐species population model along a one‐dimensional environmental gradient, we show how local competition and dispersal jointly shape the eco‐evolutionary dynamics and speed of invasion. From a focal introduction site, the generic pattern predicted by our model features a temporal transition from wave‐like to pulsed invasion. Each regime is driven primarily by local adaptation, while the transition is caused by eco‐evolutionary feedbacks mediated by dispersal. The interaction range and cost of dispersal arise as key factors of the duration and speed of each phase. Our results demonstrate that spatial eco‐evolutionary feedbacks along environmental gradients can drive strong temporal variation in the rate and structure of population spread, and must be considered to better understand and forecast invasion rates and range dynamics.     

The population ecology of rare species

There is no general theory of rarity, although one is sorely needed both to understand population dynamics and to determine conservation priorities. Here we suggest some of the strands that might be woven into such a theory. They include relationships between local abundance, geographic range size and body size of species, and the determinants of minimum viable population sizes. In each of these areas much can still be learnt from the classical 'compare and contrast' approach using assemblages of species from a variety of taxa. Freshwater fish have contributed relatively little to the broad ecological literature in this respect. We perform some tentative analyses for this group of species, and speculate on how they might fit into our current understanding of rarity.     

Phylogenetic distributions of British birds of conservation concern

Recent studies suggest that species' life histories and ecology can be used to forecast future extinction risk. Threatened species often share similar traits such that if a trait predisposing a species to decline or extinction is evolutionarily conserved, then close relatives of threatened species are themselves likely to be at risk. The phylogenetic distribution of current threat has been argued to provide insight into the species that could be threatened in the future when trait data are not available. Conservation criteria are typically based on multiple indices that capture different symptoms of threat including population trends and range contraction. However, there is no reason to assume consistent phylogenetic distributions of different symptoms. I construct a molecular phylogeny of 249 species of British birds (more than 93% of the breeding and wintering species) and use this to show that the species that are threatened due to population declines are phylogenetically more closely related than expected by chance alone. However, species that are listed for other reasons, including range contraction, are distributed randomly with respect to phylogeny. I suggest that while phylogeny can be informative with respect to identifying clades that are susceptible to some measures of extinction risk, such patterns are likely to be idiosyncratic with respect to symptom and taxa.     

Pleistocene climatic fluctuations drive isolation and secondary contact in the red diamond rattlesnake (Crotalus ruber) in Baja California

Aim

Many studies have investigated the phylogeographic history of species on the Baja California Peninsula, and they often show one or more genetic breaks that are spatially concordant among many taxa. These phylogeographic breaks are commonly attributed to vicariance as a result of geological or climatic changes, followed by secondary contact when barriers are no longer present. We use restriction‐site associated DNA sequence data and a phylogeographic model selection approach to explicitly test the secondary contact hypothesis in the red diamond rattlesnake, Crotalus ruber.

Location

Baja California and Southern California.

Methods

We used phylogenetic and population clustering approaches to identify population structure. We then used coalescent methods to simultaneously estimate population parameters and test the fit of phylogeographic models to the data. We used ecological niche models to infer suitable habitat for C. ruber at the Last Glacial Maximum (LGM).

Results

Crotalus ruber is composed of distinct northern and southern populations with a boundary near the town of Loreto in Baja California Sur. A model of isolation followed by secondary contact provides the best fit to the data, with both divergence and contact occurring in the Pleistocene. We also identify a genomic signature of northern range expansion in the northern population, consistent with LGM niche models showing that the northern‐most portion of the range of C. ruber was not suitable habitat during the LGM.

Main conclusions

We provide the first explicitly model‐based test of the secondary contact model in Baja California and show that populations of C. ruber were isolated before coming back into contact near Loreto, a region that shows phylogeographic breaks for other taxa. Given the timing of divergence and contact, we suggest that climatic fluctuations have driven the observed phylogeographic structure observed in C. ruber and that they may have driven similar patterns in other taxa.     

Chemotaxonomy of Portuguese Ulex: quinolizidine alkaloids as taxonomical markers

Six species of Portuguese Ulex L. in a total of nineteen populations were studied by GC-EIMS as to their content in quinolizidine alkaloids. Sparteine, beta-isosparteine, jussiaeiine A, N-methylcytisine, cytisine, 5,6-dehydrolupanine, rhombifoline, lupanine, jussiaeiine B, N-formylcytisine, N-acetylcytisine, anagyrine, jussiaeiine C, jussiaeiine D, pohakuline, baptifoline, and epibaptifoline were detected. Analysis of the chromatograms showed that the chemical profile of all species was mainly composed of N-methylcytisine, cytisine, anagyrine, and jussiaeiines A, B, C and D. Therefore a quantification study of these alkaloids in all the populations studied was done by GC. These data were then submitted to cluster analysis and principal component analysis, which allowed the definition of five chemotypes and the recognition of hybrids. N-methylcytisine, cytisine, and jussiaeiines A, C and D are recognized as markers of this genus in Portugal.     

Habitat Association and Social Structure of the Chocolate Hind, <Emphasis Type="BoldItalic">Cephalopholis boenak</Emphasis> (Pisces: Serranidae: Epinephelinae), at Ping Chau Island,Northeastern Hong Kong Waters

Synopsis The chocolate hind, Cephalopholis boenak, is the smallest and last remaining grouper of any abundance in Hong Kong waters. We investigated its habitat association and social structure to understand its sexual pattern and seek possible approaches to protect this species. Juveniles and adults are distributed in the same habitat and strongly associated with corals, in particular, Pavona decussata when available, for settlement and residence. Social groups of C. boenak are relatively small with a single male, one or two smaller females, and varying numbers of sexually inactive individuals (which are mature but sexually inactive, or juvenile). Males defend their boundaries by chasing neighbouring males and have significantly larger home ranges than females. Males visit females and sexually inactive individuals at one or more specific locations, consistently following similar paths. There was a positive linear correlation between body size and home range in individuals ≥90 mm TL. We observed male courtship in the reproductive season, within his home range during the late afternoon. Spawning behaviour is not associated with any particular moon phase and may occur more than once within the reproductive season. Although C. boenak is a diandric, protogynous hermaphrodite, primary and secondary males could not be distinguished by behavioural patterns in the field. Population management of this species should include habitat protection.     

Persistence of British natterjack toad Bufo calamita Laurenti (Anura: Bufonidae) populations despite low genetic diversity

Like other amphibians native to Britain, the natterjack toad Bufo calamita must have colonized the islands during the relatively short period between the end of the last glaciation and the separation of Britain from mainland Europe by rising sea levels. Unlike the other native amphibians, however, B. calamita is a habitat specialist at the north-westerly edge of its biogeographical range and for most of the 8000–10000 years since its colonization has probably been restricted to open dunes, heathlands and upper saltmarshes, as isolated populations in a few discrete areas of the country. We have investigated the genetic diversity and relatedness of six widely separated British natterjack populations by allozyme analysis, and shown that all have very low diversity (Overall P _95%= 2.7%, H = 0.004) by comparison with other anurans, including natterjack populations in mainland Europe and common frogs ( Rana temporaria , L) in Britain. Eighty percent of loci were fixed for the same allele in all six British natterjack populations and genetic differentiation between colonies was extremely low. The possible significance of these findings to the persistence of small isolated populations at range edges is discussed.     

Population and geographic range dynamics: implications for conservation planning

Continuing downward trends in the population sizes of many species, in the conservation status of threatened species, and in the quality, extent and connectedness of habitats are of increasing concern. Identifying the attributes of declining populations will help predict how biodiversity will be impacted and guide conservation actions. However, the drivers of biodiversity declines have changed over time and average trends in abundance or distributional change hide significant variation among species. While some populations are declining rapidly, the majority remain relatively stable and others are increasing. Here we dissect out some of the changing drivers of population and geographic range change, and identify biological and geographical correlates of winners and losers in two large datasets covering local population sizes of vertebrates since 1970 and the distributions of Galliform birds over the last two centuries. We find weak evidence for ecological and biological traits being predictors of local decline in range or abundance, but stronger evidence for the role of local anthropogenic threats and environmental change. An improved understanding of the dynamics of threat processes and how they may affect different species will help to guide better conservation planning in a continuously changing world.     

Genetic drift during the spread phase of a biological invasion

Recent theoretical and experimental models have revealed the role played by evolution during species spread, and in particular have questioned the influence of genetic drift at range edges. By investigating the spread of an aquatic invader in patchy habitats, we quantified genetic drift and explored its consequences for genetic diversity and fitness. We examined the interplay of gene flow and genetic drift in 36 populations of the red swamp crayfish, Procambarus clarkii, in a relatively recently invaded wetland area (30 years, Brière, northwest France). Despite the small spatial scale of our study (15 km²), populations were highly structured according to the strong barrier of land surfaces and revealed a clear pattern of colonization through watercourses. Isolated populations exhibited small effective sizes and low dispersal rates that depended on water connectivity, suggesting that genetic drift dominated in the evolution of allele frequencies in these populations. We also observed a significant decrease in the genetic diversity of isolated populations over only a 2‐year period, but failed to demonstrate an associated fitness cost using fluctuating asymmetry. This study documents the possible strong influence of genetic drift during the spread of a species, and such findings provide critical insights into the current context of profound rearrangements in species distributions due to global change.