Recalde, N. M. | bioRxiv Science

bioRxiv2024

Islands promote diversification within the silvereye clade: a phylogenomic analysis of a great speciator

Geographic isolation plays a pivotal role in speciation by restricting gene flow between populations through distance or physical barriers. However, the speciation process is complex, influenced by the interplay between dispersal ability and geographic isolation, especially in "great speciators" - bird species present on multiple islands that, at the same time, have many subspecies. Comparing population differentiation in both continental and insular settings can help us to understand the importance of geographical context in the emergence of great speciators. The highly diverse white-eye family Zosteropidae includes several great speciators, including the silvereye (Zosterops lateralis) which consists of 16 subspecies, 11 occurring on islands. The distribution of the silvereye on the Australian continent and numerous southwest Pacific islands allows us to explore the influence of different forms of geographic isolation on population divergence. To do this, we conducted a comprehensive phylogenomic analysis of the silvereye and compared patterns of population divergence in insular versus continental silvereye populations. We estimate that the silvereye lineage emerged approximately 1.5 million years ago, followed by the split of the two main silvereye clades: Southern Melanesia and the broader South Pacific (encompassing Australia, New Zealand, and outlying islands). Continental populations show low genetic population structure, which suggests that they can overcome multiple forms of geographic barriers across long distances. In contrast, most island populations are highly structured even over relatively short distances. Divergence statistics further support the idea that water barriers lead to a higher population differentiation when compared to continental distances. Our results indicate that islands promote divergence and provide an empirical example of the geographical conditions that result in the emergence of great speciators.

evolutionary biology↗

bioRxiv2023

The demographic drivers of cultural evolution in bird song: a multilevel study

Social learning within communities sometimes leads to behavioural patterns that persist over time, which we know as culture. Examples of culture include learned bird and whale songs, cetacean feeding techniques, and avian and mammalian migratory routes. Shaped by neutral and selective forces, animal cultures evolve dynamically and lead to cultural traditions that differ greatly in their diversity and stability. These cultural traits can influence individual and group survival, population structure, and even inform conservation efforts, underscoring the importance of understanding how other population processes interact with social learning to shape culture. Although the impact of social learning mechanisms and biases has been extensively explored, the role of demographic factors--such as population turnover, immigration, and age structure--on cultural evolution has received theoretical attention but rarely been subject to empirical investigation in natural populations. Doing so requires very complete trait sampling and detailed individual life history data, which are hard to acquire in combination. To this end, we built a multi-generational dataset containing over 109,000 songs from >400 individuals from a population of Great Tits (Parus major), which we study using a deep metric learning model to re-identify individuals and quantify song similarity. We show that demographic variation at the small spatial scales at which learning takes place has the potential to strongly impact the pace and outcome of animal cultural evolution. For example, age distributions skewed towards older individuals are associated with slower cultural change and increased diversity, while higher local population turnover leads to elevated rates of cultural change. Our analyses support theoretical expectations for a key role of demographic processes resulting from individual behaviour in determining cultural evolution, and emphasize that these processes interact with species-specific factors such as the timing of song acquisition. Implications extend to large-scale cultural dynamics and the formation of dialects or traditions.

animal behavior and cognition↗