Demographic Contraction Research Articles

The regeneration policy and housing issue. The Italian case read through the history of Foggia (IT)

Urban regeneration is aimed at improving settlement contexts, and indirectly at solving the housing issue. In Italy there is no national regulation on urban regeneration, but many policies from 2000 up to now have resorted to it with the aim of intervening and containing the housing problem. The work examines the city of Foggia, in southern Italy, an area in a demographic contraction, but equally characterized by “high housing tension”, indeed there are numerous eviction proceedings, in the private and public sector of the house, and, as a consequence, phenomena of illegal occupation housing, abandoned buildings, informal settlements. The research will look at how in the last 20 years various national public funding (among these, the last PNRR—Piano Nazionale di Ripresa e Resilienza derived from the Next Generation EU) and regional ones have resorted to urban regeneration strategies to address the problem, reporting failures, gaps and relevant issues.

Genetic divergence and migration patterns of a galatheoid squat lobster highlight the need for deep-sea conservation.

Information on genetic divergence and migration patterns of vent- and seep-endemic macrobenthos can help delimit biogeographical provinces and provide scientific guidelines for deep-sea conservation under the growing threats of anthropogenic disturbances. Nevertheless, related studies are still scarce, impeding the informed conservation of these hotspots of deep-sea biodiversity. To bridge this knowledge gap, we conducted a population connectivity study on the galatheoid squat lobster Shinkaia crosnieri - a deep-sea foundation species widely distributed in vent and seep ecosystems in the Northwest Pacific. With the application of an interdisciplinary methodology involving population genomics and oceanographic approaches, we unveiled two semi-isolated lineages of S. crosnieri with limited and asymmetrical gene flow potentially shaped by the geographic settings, habitat types, and ocean currents - one comprising vent populations in the Okinawa Trough, with those inhabiting the southern trough area likely serving as the source; the other being the Jiaolong (JR) seep population in the South China Sea. The latter might have recently experienced a pronounced demographic contraction and exhibited genetic introgression from the Okinawa Trough lineage, potentially mediated by the intrusion of the North Pacific Intermediate Water. We then compared the biogeographic patterns between S. crosnieri and two other representative and co-occurring vent- and seep-endemic species using published data. Based on their biogeographical subdivisions and source-sink dynamics, we highlighted the southern Okinawa Trough vents and the JR seep warrant imperative conservation efforts to sustain the deep-sea biodiversity in the Northwest Pacific.

Adaptive differentiation on serpentine soil in diploid versus autotetraploid populations of Biscutella laevigata (Brassicaceae)

Serpentine soils exhibit extreme properties (e.g. high magnesium content) influencing plant growth and survival, and have been repeatedly documented to promote adaptive edaphic differentiation in plants. Individuals from four pairs of nearby diploid and autotetraploid populations of Biscutella laevigata sampled on serpentine versus non‐serpentine soils in a factorial design are used to assess the genetic and phenotypic changes associated with edaphic origin and ploidy level. Individual samples from natural populations were subjected to soil elemental analysis and genotyping using restriction site‐associated DNA sequences (RAD‐seq) to link genetic variation with contrasting soils and ploidy levels. In diploids, genetic variation was consistent with demographic contraction and a pattern of isolation by environment with respect to the ratio of calcium/magnesium concentrations, whereas tetraploids presented evidence of expansion with limited edaphic differentiation. The genetic basis of tolerance and adaptation to serpentine was further assessed experimentally on seed‐grown individuals from all populations subjected to high (serpentine‐like) versus low (control) concentrations of magnesium in hydropony. Fitness‐related phenotypic traits under experimental cultivation were consistent with adaptive differentiation among diploid ecotypes but not among the tetraploids that similarly grow in both habitats and consistently present higher investment in roots. Further work comparing experimentally resynthesized polyploids to natural diploids and polyploids would help to tease the role of whole genome duplication apart from the effects of post‐polyploidy evolution.

FINAL NEOLITHIC AND BRONZE AGE FUNERARY PRACTICES AND POPULATION DYNAMICS IN BELGIUM, THE IMPACT OF RADIOCARBON DATING CREMATED BONES

ABSTRACTThe Final Neolithic and the Bronze Age (3000–800 BC) are periods of great transformations in the communities inhabiting the area of modern-day Belgium, as testified by archaeological evidence showing an increasing complexity in social structure, technological transformations, and large-scale contacts. By combining 599 available radiocarbon dates with 88 new 14C dates from 23 from funerary sites, this paper uses kernel density estimates to model the temporality in the use of inhumation vs. cremation burials, cremation deposits in barrows vs. flat graves, and cremation grave types. Additionally, by including 78 dates from settlements, changes in population dynamics were reconstructed. The results suggest a phase of demographic contraction around ca. 2200–1800 BC highlighted by a lack of dates from both settlements and funerary contexts, followed by an increase in the Middle Bronze Age, with the coexistence of cremation deposits in barrows and, in a lower number, in flat graves. At the end of the 14th–13th century BC, an episode of cultural change with the almost generalized use of flat graves over barrows is observed. Regional differentiations in the funerary practices and the simultaneous use of different grave types characterize the Late Bronze Age.

Using genetic tools to inform conservation of fragmented populations of Asian elephants (Elephas maximus) across their range in China.

A herd of 15 Chinese elephants attracted international attention during their 2021 northward trek, motivating the government to propose establishment of an Asian elephant national park. However, planning is hampered by a lack of genetic information on the remaining populations in China. We collected DNA from 497 dung samples from all 5 populations encompassing the entire range of elephants in China and used mitochondrial and microsatellite markers to investigate their genetic and demographic structure. We identified 237 unique genotypes (153 females, 84 males), representing 81% of the known population. However, the effective population size was small (28, range 25-32). Historic demographic contraction appeared to account for low haplotype diversity (Hd = 0.235), but moderate nucleotide and nuclear diversity (π = 0.6%, He = 0.55) was attributable to post-bottleneck recovery involving recent population expansion plus historical gene exchange with elephants in Myanmar, Lao PDR, and Vietnam. The 5 populations fell into 3 clusters, with Nangunhe elephants differing consistently from the other 4 populations (FST = 0.23); elephants from Mengyang, Simao, and Jiangcheng belonged to a single population (henceforth, MSJ), and differed from the Shangyong population (FST = 0.11). Interpopulation genetic variation reflected isolation by distance and female-biased dispersal. Chinese elephants should be managed as 2 distinct units: Nangunhe and another combining Shangyong and MSJ; their long-term viability will require restoring gene flow between Shangyong and MSJ, and between elephants in China and neighboring countries. Our results have the potential to inform conservation planning for an iconic megafaunal species.

A continental approach to jaguar extirpation: A tradeoff between anthropic and intrinsic causes

Human impacts are blamed for range contraction in several animal species worldwide. Remarkably, carnivores and particularly top predators are threatened by humans despite their key role in maintaining ecosystem balance and functions. Conservation strategies to allow human-carnivore coexistence are urgently needed. These strategies must be built on evidence and driven by knowledge of population risk at a broad scale. However, knowledge on wide distributed species is often based on regional expert opinions in which uncertainty is not quantifiable, making data incomparable across regions. Here we develop a method to assess the endangerment status of a species based on its range contractions and the main threats using the jaguar Panthera onca as model. The use of GLM with the main intrinsic and extrinsic drivers of jaguar extinction allowed us to assess the endangerment status at continental and population scale. We found this method to be a valuable tool to obtain a broad picture of human-induced endangerment in animal species. Intrinsic traits (summarized in the demographic contraction theory) and anthropic traits (based on agriculture, cattle and human densities) explained jaguar extinction highlighting the particular importance of livestock activity. Our results suggest that livestock ranching has a pervasive effect on the species likely due to habitat loss combined with retaliatory hunting. We highlight the need to rethink policies, practice and law enforcement in relation to livestock and suggest the development of action plans based in local evidence in those countries where endangered populations have been detected. We also recommend involving and encouraging land owners and private companies in the conservation of private lands that comprise much of the endangered jaguar range.

ДЕПОПУЛЯЦИЯ ГЕОСТРАТЕГИЧЕСКИХ ТЕРРИТОРИЙ РОССИЙСКОЙ ФЕДЕРАЦИИ В ЗЕРКАЛЕ ПРОСТРАНСТВЕННОЙ ДЕМОГРАФИИ: ТЕОРЕТИКО-МЕТОДОЛОГИЧЕСКИЕ АСПЕКТЫ

Actual problems of the geostrategic territories’ demographic development are remaining a serious challenge for the socio-economic development of the Russian Federation. Demographic contraction, a drop in the birth rate and an outflow of the population lead to depopulation and desertification of key regions and hinder effective development and economic activity. Solving the most complex problems related to issues of spatial development requires the use of new theoretical and methodological approaches to the study of demographic processes in the territorial context, as well as modern tools for spatial analysis. The article deals with the current demographic problems of the geostrategic and border areas of Russian Federation through the prism of spatial demography, a scientific direction that is practically not represented in Russia. The main attention of the authors is paid to the study of definitions and methodological apparatus of spatial demography in foreign science. Differences in the subject of research between population geography, regional demography and spatial demography are considered. The author's definition of spatial demography, its subject and research approaches are formulated. The authors propose an alternative approach to the study of the problems of the demographic development of the territory, using methods of spatial analysis (including cartographic materials and GIS models). The paper presents both the theoretical aspects of the concept of «spatial demography» and the assessment of the current demographic situation of the geostrategic regions of the country based on the proposed methodology and mapping of key trends in the demographic development of Russia's geostrategic territories. The authors paid special attention to the study of demographic trends in the municipalities of the geostrategic territories of Siberia and the Far East in the context of their special geographical and resource potential, as well as the complexity of the demographic situation.

Parallel genomic responses to historical climate change and high elevation in East Asian songbirds

Parallel evolution can be expected among closely related taxa exposed to similar selective pressures. However, parallelism is typically stronger at the phenotypic level, while genetic solutions to achieve these phenotypic similarities may differ. For polygenic traits, the availability of standing genetic variation (i.e., heterozygosity) may influence such genetic nonparallelism. Here, we examine the extent to which high-elevation adaptation is parallel-and whether the level of parallelism is affected by heterozygosity-by analyzing genomes of 19 Paridae species distributed across East Asia with a dramatic east-west elevation gradient. We find that western highlands endemic parids have consistently lower levels of heterozygosity-likely the result of late-Pleistocene demographic contraction-than do parids found exclusively in eastern lowlands, which remained unglaciated during the late Pleistocene. Three widespread species (east to west) have high levels of heterozygosity similar to that observed in eastern species, although their western populations are less variable than eastern ones. Comparing genomic responses to extreme environments of the Qinghai-Tibet Plateau, we find that the most differentiated genomic regions between each high-elevation taxon and its low-elevation relative are significantly enriched for genes potentially related to the oxygen transport cascade and/or thermogenesis. Despite no parallelism at particular genes, high similarity in gene function is found among comparisons. Furthermore, parallelism is not higher in more heterozygous widespread parids than in highland endemics. Thus, in East Asian parids, parallel functional response to extreme elevation appears to rely on different genes, with differences in heterozygosity having no effect on the degree of genetic parallelism.

Genotyping-in-Thousands by sequencing of archival fish scales reveals maintenance of genetic variation following a severe demographic contraction in kokanee salmon

Historical DNA analysis of archival samples has added new dimensions to population genetic studies, enabling spatiotemporal approaches for reconstructing population history and informing conservation management. Here we tested the efficacy of Genotyping-in-Thousands by sequencing (GT-seq) for collecting targeted single nucleotide polymorphism genotypic data from archival scale samples, and applied this approach to a study of kokanee salmon (Oncorhynchus nerka) in Kluane National Park and Reserve (KNPR; Yukon, Canada) that underwent a severe 12-year population decline followed by a rapid rebound. We genotyped archival scales sampled pre-crash and contemporary fin clips collected post-crash, revealing high coverage (> 90% average genotyping across all individuals) and low genotyping error (< 0.01% within-libraries, 0.60% among-libraries) despite the relatively poor quality of recovered DNA. We observed slight decreases in expected heterozygosity, allelic diversity, and effective population size post-crash, but none were significant, suggesting genetic diversity was retained despite the severe demographic contraction. Genotypic data also revealed the genetic distinctiveness of a now extirpated population just outside of KNPR, revealing biodiversity loss at the northern edge of the species distribution. More broadly, we demonstrated GT-seq as a valuable tool for collecting genome-wide data from archival samples to address basic questions in ecology and evolution, and inform applied research in wildlife conservation and fisheries management.

Demographic contraction as an indicator of the problems of single-industry municipalities

Migration processes associated with the outflow of the population from single-industry municipalities (monotowns) are becoming one of the components of global demographic changes on the territory of the Russian Federation. One of the tools to curb demographic contraction in the territory of single-industry municipalities can be the strengthening of diversification of the economy of monotowns, which should contribute to improving the quality of life of the population, including through a change in the structure of employment. The article analyzes the existing trends in the socio-economic development of single-industry towns of various types and shows that a significant number of them are characterized by demographic contraction, caused, among other things, by outflow of the working age population. Correlation analysis for a number of indicators characterizing demographic processes in single-industry municipalities showed a weak connection between them. Population survey data for 2016 and 2019 indicate a low assessment of measures to support single-industry towns by the population. The most significant factors for residents, indicating a favourable level of socio-economic development of the single-industry entity, in the opinion of the respondents, are employment opportunities, a decent level of wages, the quality of medical care, the quality of housing and utilities, and the ecological situation.

Taxonomic hypotheses and the biogeography of speciation in the Tiger Whiptail complex (Aspidoscelis tigris: Squamata, Teiidae)

Biodiversity in southwestern North America has a complex biogeographic history involving tectonism interspersed with climatic fluctuations. This yields a contemporary pattern replete with historic idiosyncrasies often difficult to interpret when viewed from through the lens of modern ecology. The Aspidoscelis tigris (Tiger Whiptail) complex (Squamata: Teiidae) is one such group in which taxonomic boundaries have been confounded by a series of complex biogeographic processes that have defined the evolution of the clade. To clarify this situation, we first generated multiple taxonomic hypotheses, which were subsequently tested using mitochondrial DNA sequences (ATPase 8 and 6) evaluated across 239 individuals representing five continental members of this complex. We then evaluated the manner by which our models parsed phylogenetic and biogeographic patterns. We found considerable variation among species ‘hypotheses,’ which we interpret as reflecting inflated levels of inter-population genetic divergence caused by historical demographic expansion and contraction cycles. Inter-specific boundaries with A. marmoratus juxtaposed topographically with the Cochise Filter Barrier that separates Sonoran and Chihuahuan deserts (interpreted herein as an example of ‘soft’ allopatry). Patterns of genetic divergence were consistent across the Cochise Filter Barrier, regardless of sample proximity. Surprisingly, this also held true for intraspecific comparisons that spanned the Colorado River. These in turn suggest geomorphic processes as a driver of speciation in the A. tigris complex, with intraspecific units governed by local demographic processes.

Comparison of adult census size and effective population size support the need for continued protection of two Solomon Island endemics

ABSTRACT Because a population’s ability to respond to rapid change is dictated by standing genetic variation, we can better predict a population’s long-term viability by estimating and then comparing adult census size (N) and effective population size (Ne ). However, most studies only measure N or Ne , which can be misleading. Using a combination of field and genomic sequence data, we here estimate and compare N and Ne in two range-restricted endemics of the Solomon Islands. Two Zosterops White-eye species inhabit the small island of Kolombangara, with a high elevation species endemic to the island (Z. murphyi) and a low elevation species endemic to the Solomon Islands (Z. kulambangrae). Field observations reveal large values of N for both species with Z. kulambangrae numbering at 114,781 ± 32,233 adults, and Z. murphyi numbering at 64,412 ± 15,324 adults. In contrast, genomic analyses reveal that Ne was much lower than N, with Z. kulambangrae estimated at 694.5 and Z. murphyi at 796.1 individuals. Further, positive Tajima’s D values for both species suggest that they have experienced a demographic contraction, providing a mechanism for low values of Ne . Comparison of N and Ne suggests that Z. kulambangrae and Z. murphyi are not at immediate threat of extinction but may be at genetic risk. Our results provide important baseline data for long-term monitoring of these island endemics, and argue for measuring both population size estimates to better gauge long-term population viability.

Contractions in Chinese Fertility and Savings: Long Run Domestic and Global Implications

Following three decades of rapid but unbalanced economic growth, China's reform and policy agenda are set to rebalance the economy toward consumption while maintaining a rate of GDP growth near seven per cent. Among the headwinds it faces is a demographic contraction that brings slower, and possibly negative, labour force growth and relatively rapid ageing. While the lower saving rates that result from consumption-oriented policies and rising aged dependency may contribute to a rebalancing of the economy, in the long run they will reduce both GDP growth and per capita income. Moreover, while an effective transition from the one-child policy to a two-child policy would help sustain growth and eventually mitigate the aged dependency problem, it would set real per capita income on a still lower path. These conundrums are examined using a global economic and demographic model, which embodies the main channels through which fertility and saving rates impact on economic performance. The results quantify the associated trade-offs and show that continuing demographic and saving contractions in China would alter the trajectory of the global economy as well.

Urban development and negative differential rent [Lo sviluppo urbano e la rendita differenziale negativa

The growth of building land does not always produce a positive differential rent on the existing building stock. The essay aims to discuss the case where urban expansion has negative effects on the rent of existing building plots and constructions. In other words, the differential rent assumes negative values that increase over time, lowering the value of existing properties. This occurs when the expansion of the city does not correspond to a real need for new housing. Generally, it happens in the presence of urban centres already in an advanced phase of demographic contraction, when the existing building stock would be sufficient to satisfy the real estate demand. This expansion (sometimes achieved through urban plans or building programs, others in the total absence of plans) is a phenomenon that, since the 1960s, has affected (and still affects) many smaller towns in Italy. While in the cities that attract population, urban expansion led to the creation of a positive and growing rent (absolute and differential), in the centres suffering from depopulation the same type of expansion had adverse effects on the existing building stock.

Comparative phylogeography of two sister species of snowcock: impacts of species-specific altitude preference and life history

BackgroundPhylogeographical patterns and population dynamics are usually interpreted by environmental disturbances and geographic barriers of the past. However, sister species may exhibit disparate patterns of genetic structures and population dynamics due to their habitat preference and altitude segregation. In this study, we tested how species-specific altitude habitat affected phylogeographical patterns in two sister snowcock species, Tibetan (Tetraogallus tibetanus) and Himalayan Snowcocks (T. himalayensis).MethodsA panel of seven microsatellite loci and a fragment of Mitochondrial DNA Control Region were used to investigate genetic structures and population dynamics in hope of revealing the underlying evolutionary processes through the identification of possible past demographic events.ResultsOur results suggest that T. himalayensis showed a significant phylogeographical signal in mtDNA (FST = 0.66, p < 0.001) and microsatellite (FST = 0.11, p < 0.001) data and is stable during the glacial-interglacial cycles in the Pleistocene and followed demographic contraction until 0.003 million years (Mys) ago. The phylogeographical signal of T. tibetanus is lower than the level of genetic difference among populations in mtDNA (FST = 0.41, p < 0.001) and microsatellite (FST = 0.09, p < 0.001) data, likely benefiting from stable habitats over a long period of time. T. tibetanus has been experiencing expansion since 0.09 Mys ago. However, an abnormally haplotype H9 from T. himalayensis clustering with T. tibetanus was spotted.ConclusionOur results indicate that differences in habitat preference and altitude specialities were reflected in the genetic structure patterns and population dynamics of these two species. These dissimilarities in life history traits might have affected the dispersal and survival abilities of these two species differently during environmental fluctuations. The results of this study also enriched our knowledge on population differentiation and connectivity in high altitude mountain ecosystems.

Territoriality and the organization of technology during the Last Glacial Maximum in southwestern Europe.

Climate changes that occurred during the Last Glacial Maximum (LGM) had significant consequences in human eco-dynamics across Europe. Among the most striking impacts are the demographic contraction of modern humans into southern refugia and the potential formation of a population bottleneck. In Iberia and southern France transformations also included the occurrence of significant technological changes, mostly marked by the emergence of a diverse set of bifacially-shaped stone projectiles. The rapid dissemination of bifacial technologies and the geographical circumscription of specific projectile morphologies within these regions have been regarded as evidence for: (1) the existence of a system of long-distance exchange and social alliance networks; (2) the organization of human groups into cultural facies with well-defined stylistic territorial boundaries. However, the degree and modes in which cultural transmission have occurred within these territories, and how it may have influenced other domains of the adaptive systems, remains largely unknown. Using southern Iberia as a case-study, this paper presents the first quantitative approach to the organization of lithic technology and its relationship to hunter-gatherers’ territorial organization during the LGM. Similarities and dissimilarities in the presence of morphological and metric data describing lithic technologies are used as a proxy to explore modes and degrees of cultural transmission. Statistical results show that similarities in technological options are dependent on the chronology and geographical distance between sites and corroborate previous arguments for the organization of LGM settlement in Southern Iberia into discrete eco-cultural facies.

Fine-scale genetic structure and conservation status of American badgers at their northwestern range periphery

Peripheral populations are often characterized by small population size and low genetic diversity, with many at risk of extirpation. These characteristics may be even more pronounced in human-modified landscapes that further reduce the resiliency of populations to environmental change. Situated at the northwestern edge of the species’ range, the western American badger (Taxidea taxus jeffersonii) is an endangered mammal in Canada, where it inhabits the interior grassland and open forest ecosystems of British Columbia (BC) and continues to be threatened by severe vehicle-induced mortality rates and other anthropogenic factors. Here, we collected mitochondrial DNA haplotypic and microsatellite genotypic data to investigate the extent and distribution of American badger genetic variation within and among sites in British Columbia, and relative to adjacent populations in the USA, including in Washington state. From these data, we reconstructed population structure and connectivity, and examined current designatable unit status. Patterns of genetic variation for American badgers in British Columbia were as expected for peripheral populations, including reduced genetic diversity, increased population differentiation, and evidence of demographic contraction. Furthermore, we found limited connectivity between regional populations in our study area and identified significant substructure isolating the most northwestern sampling unit (Cariboo), findings that starkly contrast with the high levels of gene flow observed between populations across the species’ range core. These results have important implications for current designatable unit status for western American badgers in British Columbia and emphasize the need for further population monitoring and mitigation of potential barriers to gene flow.

Mitochondrial Introgression, Color Pattern Variation, and Severe Demographic Bottlenecks in Three Species of Malagasy Poison Frogs, Genus Mantella.

Madagascar is a biodiversity hotspot particularly rich in amphibian diversity and only a few charismatic Malagasy amphibians have been investigated for their population-level differentiation. The Mantella madagascariensis group is composed of two rainforest and three swamp forest species of poison frogs. We first confirm the monophyly of this clade using DNA sequences of three nuclear and four mitochondrial genes, and subsequently investigate the population genetic differentiation and demography of the swamp forest species using one mitochondrial, two nuclear and a set of nine microsatellite markers. Our results confirm the occurrence of two main mitochondrial lineages, one dominated by Mantella aurantiaca (a grouping supported also by our microsatellite-based tree) and the other by Mantella crocea + Mantella milotympanum. These two main lineages probably reflect an older divergence in swamp Mantella. Widespread mitochondrial introgression suggests a fairly common occurrence of inter-lineage gene flow. However, nuclear admixture seems to play only a limited role in this group, and the analyses of the RAG-1 marker points to a predominant incomplete lineage sorting scenario between all five species of the group, which probably diverged relatively recently. Our demographic analyses show a common, severe and recent demographic contraction, inferred to be in temporal coincidence with the massive deforestation events that took place in the past 1000 years. Current data do not allow to conclusively delimit independent evolutionary units in these frogs, and we therefore refrain to suggest any taxonomic changes.

Complex population evolutionary history of four cold-tolerant Notopterygium herb species in the Qinghai-Tibetan Plateau and adjacent areas

Historical geological and climatic events are the most important drivers of population expansions/contractions, range shifts, and interspecific divergence in plants. However, the species divergence and spatiotemporal population dynamics of alpine cold-tolerant herbal plants in the high-altitude Qinghai-Tibetan Plateau (QTP) and adjacent areas remain poorly understood. In this study, we investigated population evolutionary history of four endangered Notopterygium herb species in the QTP and adjacent regions. We sequenced 10 nuclear loci, 2 mitochondrial DNA regions, and 4 chloroplast DNA regions in a total of 72 natural populations from the 4 species, and tested the hypothesis that the population history of these alpine herbs was markedly affected by the Miocene–Pliocene QTP uplifts and Quaternary climatic oscillations. We found that the four Notopterygium species had generally low levels of nucleotide variability within populations. Molecular dating and isolation-with-migration analyses suggested that Notopterygium species diverged ~1.74–7.82 million years ago and their differentiation was significantly associated with recent uplifts of the eastern margin of the QTP. In addition, ecological niche modeling and population history analysis showed that N. incisum and N. franchetii underwent considerable demographic expansions during the last glacial period of the Pleistocene, whereas a demographic contraction and a expansion occurred for N. forrestii and N. oviforme during the antepenultimate interglacial period and penultimate glacial period, respectively. These findings highlight the importance of geological and climatic changes during the Miocene–Pliocene and Pleistocene as causes of species divergence and changes in population structure within cold-tolerant herbs in the QTP biodiversity hotspot.

Demographic Expansion and Contraction in a Neotropical Fish during the Late Pleistocene-Holocene

Demographic changes during the late Pleistocene-Holocene left signatures in the DNA of contemporary populations. These signatures reveal demographic phenomena like the increase or decrease in effective population size. In this paper we searched for signatures of demographic change in the DNA of the Neotropical freshwater fish Poecilia vivipara. Also, we investigated whether demographic changes are correlated with palaeoclimatic events of the late Pleistocene-Holocene, in particular, if changes in effective population size are correlated with expansion and contraction of available habitats, induced by global ice-volume changes and sea-level fluctuations. We used Bayesian Skyline Plot (BSP) analysis with sequences from the mitochondrial gene cytochrome b to estimate the ancestral demography of the Neotropical freshwater fish P. vivipara. To test the assumptions of neutrality and absence of population structure we used Tajima’s D and Spatial Analysis of Molecular Variance (SAMOVA), respectively. Effective population size of P. vivipara remained stable until 75,000 years ago, increased by 10-fold reaching a maximum at approximately 25,000 years ago, then suddenly declined at the Pleistocene-Holocene boundary. Variation in effective population size in P. vivipara correlates with expansion and contraction of habitats induced by sea-level fluctuations, caused by the advance and retreat of ice sheets during the Last Glacial Maximum (LGM).