Evidence for serial founder events during the colonization of North America by the yellow fever mosquito, Aedes aegypti

Megaherbivores are primary consumers who provide unique ecosystem services. Given their body size, they are disproportionately threatened in the Anthropocene. Asian elephants are the largest extant terrestrial megaherbivores native to Asia, with 60% of the population found in India. Despite their ecological and cultural importance, the management/conservation units, genetic history, diversity and threats remain understudied. We re-sequenced 31 whole genomes (between 11X - 32X) from all known elephant landscapes in India, and identified five management/conservation units corresponding to elephants in northern India, central India and three in southern India. The genetic data reveal signatures of serial colonisation, and a dilution of diversity from north to south of India. The northern populations diverged from other populations more than 70,000 years ago, and have the highest genetic diversity, with low inbreeding/high effective size (Pi = 0.39, SD:0.2; FROH> 1MB= 0.09, SD:0.03). Two of three populations in southern India have low diversity and are inbred with much lower effective sizes than current populations sizes (Pi = 0.25, SD:0.29 and 0.29, SD:0.23; FROH> 1MB= 0.25, SD:0.09 and 0.17, SD:0.02). Additionally, future generations are expected to be more inbred since pairs of extant elephants have large tracts of the genome that are already identical. Analyses of genetic load reveals purging of potentially high-effect deleterious alleles in the southern populations and potential dilution of all deleterious alleles from north to south in India. However, southern Indian elephants are highly homozygous for all the deleterious alleles that persist, despite dilution and purging. High homozygosity of deleterious alleles, coupled with low neutral genetic diversity make them high priority for conservation and management attention. Most surprisingly, our study suggests that patterns of genetic diversity and genetic load can correspond to geographic signatures of serial founding events even in large mobile endangered species.

In the centuries following Christopher Columbus’s 1492 journey to the Americas, transoceanic voyages opened unprecedented pathways for global pathogen circulation. Yet no biological transfer is a single, discrete event. We use mathematical modeling to quantify historical risk of shipborne pathogen introduction, exploring the respective contributions of journey time, ship size, population susceptibility, transmission intensity, density dependence, and pathogen biology. We contextualize our results using port arrivals data from San Francisco, 1850–1852, and from a selection of historically significant voyages, 1492–1918. We offer numerical estimates of introduction risk across historically-realistic journey times and ship population sizes, and show that steam travel and shipping regimes that involved frequent, large-scale movement of people both substantially increased risk of transoceanic pathogen circulation.

The mosquitoAedes albopictusis a vector species of Dengue, yellow fever, and Zika among other diseases. The species originated in Southeast Asia and has spread widely and rapidly in the last century. The species has been reported in localities from the Gulf of Guinea since the early 2000s, but systematic sampling has been scant. We sampledAe. albopictusbetween 2013 and 2023 across the altitudinal gradient in São Tomé and found that the species was present in all sampled years at altitudes up to 680 meters. We also find some evidence of increases in proportional representation compared toAe. aegyptiover time. We report the presence of the species in Príncipe for the first time, suggesting that the range ofAe. albopictusis larger than previously thought. Finally, we use bioclimatic niche modeling to infer the potential range ofAe. albopictusand infer that the species has the potential to spread across a large portion of São Tomé and Príncipe. Our results suggest thatAe. albopictushas established itself as a resident species of the islands of the Gulf of Guinea and should be incorporated into the list of potential vectors that need to be surveyed and controlled.