Harbor porpoise losing its edges: genetic time series suggests a rapid population decline in Iberian waters over the last 30 years

Impact of climate changes on species is expected to be especially visible at the extremities of the species distribution, where they meet sub-optimal conditions. In Mauritania and Iberia, two genetically isolated populations of harbor porpoises form a distinct ecotype and are presumably locally adapted to the upwelling waters. By analyzing the evolution of mitochondrial genetic variation in the Iberian population between two temporal cohorts (1990-2002 vs. 2012-2015), we report a dramatic decrease in genetic diversity. Phylogenetic analyses including neighboring populations identified two porpoises in southern Iberia carrying a divergent haplotype close to the Mauritanian population, yet forming a distinctive lineage. This suggests that Iberian porpoises may not be as isolated as previously thought with immigration from Mauritania or an unknown population in between, but none from the northern ecotype. The rapid decline in the Iberian mitochondrial diversity may be driven by either genetic drift, or by a dramatic decline in census population size possibly resulting from environmental stochasticity, prey depletion, or acute fishery bycatches. These results illustrate the value of genetics time series to inform demographic trends and emphasize the urgent need for conservation measures to ensure the viability of this small harbor porpoise population in Iberia.

PSIII-13 Genetic assessment of isolated reindeer (Rangifer Tarandus) population from Tuva, Russia

Reindeer herding is traditional in Tuva, Russia. This region is located in the southern part of the country, on the border with Mongolia and isolated from the other reindeer herding areas of Russia. During the last three decades, the census population size of Tuva reindeer has decreased drastically, from 15,000 to 1,500 heads. The aim of our study was to assess genetic characteristics of Tuva population of reindeer. Samples of Tuva reindeer (n = 12) were genotyped using Illumina BovineHD BeadChip. To perform the comparison with other ecotypes of domestic reindeer we added samples of all the breeds, which are officially recognized in Russia: the Chukotka (n = 12), the Nenets (n = 31), the Even (n = 12) and the Evenk from Yakutia (n = 12) and Krasnoyarsk region (n = 19). Reindeer from Mongolia (n = 11) as well as the wild reindeer from Yakutian and Taimyr tundra (n = 20), and Baikal and Amur taiga (n = 9) were added to our dataset. After quality control, 7,202 SNPs were selected for subsequent analyses. On PCA plot Tuva reindeer were clustered together with Mongolian reindeer. The FST genetic distance was lowest between these two groups – 0.039 comparing to FST values between Tuva and other groups of domestic reindeer, which ranged from 0.092 (the Evenk from Yakutia) to 0.137 (the Chukotka) and were highest between Tuva and wild reindeer populations (0.146). Allelic richness was lowest in Mongolia (1.288±0.004) and Tuva reindeer (1.301±0.004). In other breeds this parameter ranged from 1.323±0.004 (the Chukotka) to 1.356±0.004 (the Evenk from Yakutia). In our study, it was shown that reindeer from Tuva do not belong to any official breed of Russia and genetically are very close to Mongolian ecotype. Our results should be considered at developing programs for restoration of Tuva reindeer. This work was supported by Russian Science Foundation grant 16-16-10068-P

Mitochondrial DNA Sequence Diversity in Mammals: A Correlation between the Effective and Census Population Sizes

What determines the level of genetic diversity of a species remains one of the enduring problems of population genetics. Because neutral diversity depends upon the product of the effective population size and mutation rate, there is an expectation that diversity should be correlated to measures of census population size. This correlation is often observed for nuclear but not for mitochondrial DNA. Here, we revisit the question of whether mitochondrial DNA sequence diversity is correlated to census population size by compiling the largest data set to date, using 639 mammalian species. In a multiple regression, we find that nucleotide diversity is significantly correlated to both range size and mass-specific metabolic rate, but not a variety of other factors. We also find that a measure of the effective population size, the ratio of nonsynonymous to synonymous diversity, is also significantly negatively correlated to both range size and mass-specific metabolic rate. These results together suggest that species with larger ranges have larger effective population sizes. The slope of the relationship between diversity and range is such that doubling the range increases diversity by 12–20%, providing one of the first quantifications of the relationship between diversity and the census population size.

COVID-19 epidemic severity is associated with timing of non-pharmaceutical interventions

Background: Unprecedented public health interventions including travel restrictions and national lockdowns have been implemented to stem the COVID-19 epidemic, but the effectiveness of non-pharmaceutical interventions is still debated. International comparisons are hampered by highly variable conditions under which epidemics spread and differences in the timing and scale of interventions. Cumulative COVID-19 morbidity and mortality are functions of both the rate of epidemic growth and the duration of uninhibited growth before interventions were implemented. Incomplete and sporadic testing during the early COVID-19 epidemic makes it difficult to identify how long SARS-CoV-2 was circulating in different places. SARS-CoV-2 genetic sequences can be analyzed to provide an estimate of both the time of epidemic origin and the rate of early epidemic growth in different settings. Methods: We carried out a phylogenetic analysis of more than 29,000 publicly available whole genome SARS-CoV-2 sequences from 57 locations to estimate the time that the epidemic originated in different places. These estimates were cross-referenced with dates of the most stringent interventions in each location as well as the number of cumulative COVID-19 deaths following maximum intervention. Phylodynamic methods were used to estimate the rate of early epidemic growth and proxy estimates of epidemic size. Findings: The time elapsed between epidemic origin and maximum intervention is strongly associated with different measures of epidemic severity and explains 46% of variance in numbers infected at time of maximum intervention. The reproduction number is independently associated with epidemic severity. In multivariable regression models, epidemic severity was not associated with census population size. The time elapsed between detection of initial COVID-19 cases to interventions was not associated with epidemic severity, indicating that many locations experienced long periods of cryptic transmission. Interpretation: Locations where strong non-pharmaceutical interventions were implemented earlier experienced much less severe COVID-19 morbidity and mortality during the period of study.

Mitochondrial DNA Sequence Diversity in Mammals: a Correlation Between the Effective and Census Population Sizes

What determines the level of genetic diversity of a species remains one of the enduring problems of population genetics. Since, neutral diversity depends upon the product of the effective population size and mutation rate there is an expectation that diversity should be correlated to measures of census population size. This correlation is often observed for nuclear but not for mitochondrial DNA. Here we revisit the question of whether mitochondrial DNA sequence diversity is correlated to census population size by compiling the largest dataset to date from 639 mammalian species. In a multiple regression we find that nucleotide diversity is significantly correlated to both range size and mass-specific metabolic rate, but not a variety of other factors. We also find that a measure of the effective population size, the ratio of non-synonymous to synonymous diversity, is also significantly negatively correlated to both range and mass-specific metabolic rate. These results together suggest that species with larger ranges have larger effective population sizes. The slope of the relationship between diversity and range is such that doubling the range increases diversity by 12 to 20%, providing one of the first quantifications of the relationship between effective and census population sizes.

The determinants of genetic diversity in butterflies – Lewontin’s paradox revisited

Under the neutral theory genetic diversity is expected to be a simple function of population size. However, comparative studies have consistently failed to find any strong correlation between measures of census population size and genetic diversity. Instead, a recent comparative study across several animal phyla identified propagule size as the strongest predictor of genetic diversity, suggesting that r-strategists that produce many offspring but invest little in each, have greater long-term effective population sizes. We present a comparison of genome-wide levels of genetic diversity across 38 species of European butterflies (Papilionoidea). We show that across butterflies, genetic diversity varies over an order of magnitude and that this variation cannot be explained by differences in abundance, fecundity, host plant use or geographic range. Instead, we find that genetic diversity is negatively correlated with body size and positively with the length of the genetic map. This suggests that variation in genetic diversity is determined both by fluctuation in Ne and the effect of selection on linked neutral sites.

Low genetic variation is associated with low mutation rate in the giant duckweed

Mutation rate and effective population size (Ne) jointly determine intraspecific genetic diversity, but the role of mutation rate is often ignored. We investigate genetic diversity, spontaneous mutation rate andNein the giant duckweed (Spirodela polyrhiza). Despite its large census population size, whole-genome sequencing of 68 globally sampled individuals revealed extremely low within-species genetic diversity. Assessed under natural conditions, the genome-wide spontaneous mutation rate is at least seven times lower than estimates made for other multicellular eukaryotes, whereasNeis large. These results demonstrate that low genetic diversity can be associated with large-Nespecies, where selection can reduce mutation rates to very low levels, and accurate estimates of mutation rate can help to explain seemingly counterintuitive patterns of genome-wide variation.One Sentence SummaryThe low-down on a tiny plant: extremely low genetic diversity in an aquatic plant is associated with its exceptionally low mutation rate.