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Bird-mediated seed dispersal is crucial for the regeneration and viability of ecosystems, often resulting in complex mutualistic species networks. Yet, how this mutualism drives the evolution of seed dispersing birds is still poorly understood. In the present study we combine whole genome re-sequencing analyses and morphometric data to assess the evolutionary processes that shaped the diversification of the Eurasian nutcracker (Nucifraga), a seed disperser known for its mutualism with pines (Pinus). Our results show that the divergence and phylogeographic patterns of nutcrackers resemble those of other non-mutualistic passerine birds and suggest that their early diversification was shaped by similar biogeographic and climatic processes. The limited variation in foraging traits indicates that local adaptation to pines likely played a minor role. Our study shows that close mutualistic relationships between bird and plant species might not necessarily act as a primary driver of evolution and diversification in resource-specialized birds.
Th¬e main principle of holism – "the whole is more than the sum of its parts" – can be traced back to ancient philosophical studies. Although the term itself was coined by Jan Christiaan Smuts in 1926, the earliest formulations can already be found in Taoism, in the philosophy of Lao Tzu, as well as in Aristotle's 'Metaphysics'. However, a complete and profound sense of the principle has only been revealed in such theories as Gestalt psychology (Kurt Koffka, Max Wertheimer and others), the general systems theory (Ludwig von Bertalanffy), and the theory of complexity (synergetics) as formulated by the Moscow school of synergetics (Sergey Pavlovich Kurdyumov), to name just a few. ¬inking in this direction, from the whole to the parts (subsystems), is quite unusual for classical science which, in its course of analysis, usually moves from distinct parts to the whole. In synergetics, according to Hermann Haken, order parameters determine how parts (subsystems) of complex systems behave. A select few order parameters, as Haken says, encompass the complex behavior of diverse parts and, therefore, lead to enormously reducing the complexity in a description of a given system.
The implementation of HTS (high-throughput sequencing) approaches is rapidly changing our understanding of the lichen symbiosis, by uncovering high bacterial and fungal diversity, which is often host-specific. Recently, HTS methods revealed the presence of multiple photobionts inside a single thallus in several lichen species. This differs from Sanger technology, which typically yields a single, unambiguous algal sequence per individual. Here we compared HTS and Sanger methods for estimating the diversity of green algal symbionts within lichen thalli using 240 lichen individuals belonging to two species of lichen-forming fungi. According to HTS data, Sanger technology consistently yielded the most abundant photobiont sequence in the sample. However, if the second most abundant photobiont exceeded 30% of the total HTS reads in a sample, Sanger sequencing generally failed. Our results suggest that most lichen individuals in the two analyzed species, Lasallia hispanica and L. pustulata, indeed contain a single, predominant green algal photobiont. We conclude that Sanger sequencing is a valid approach to detect the dominant photobionts in lichen individuals and populations. We discuss which research areas in lichen ecology and evolution will continue to benefit from Sanger sequencing, and which areas will profit from HTS approaches to assessing symbiont diversity.