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1. Nonadaptive host‐use specificity in tropical armored scale insects

   https://doi.org/10.1002/ece3.6867  

   Peterson, Daniel A. ; Hardy, Nate B. ; Morse, Geoffrey E. ; Itioka, Takao ; Wei, Jiufeng ; Normark, Benjamin B. ( November 2020 , Ecology and Evolution)

   Most herbivorous insects are diet specialists in spite of the apparent advantages of being a generalist. This conundrum might be explained by fitness trade‐offs on alternative host plants, yet the evidence of such trade‐offs has been elusive. Another hypothesis is that specialization is nonadaptive, evolving through neutral population‐genetic processes and within the bounds of historical constraints. Here, we report on a striking lack of evidence for the adaptiveness of specificity in tropical canopy communities of armored scale insects. We find evidence of pervasive diet specialization, and find that host use is phylogenetically conservative, but also find that more‐specialized species occur on fewer of their potential hosts than do less‐specialized species, and are no more abundant where they do occur. Of course local communities might not reflect regional diversity patterns. But based on our samples, comprising hundreds of species of hosts and armored scale insects at two widely separated sites, more‐specialized species do not appear to outperform more generalist species.

    

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2. Multidimensional specialization and generalization are pervasive in soil prokaryotes

   https://doi.org/10.1038/s41559-023-02149-y  

   Hernandez, Damian J. ; Kiesewetter, Kasey N. ; Almeida, Brianna K. ; Revillini, Daniel ; Afkhami, Michelle E. ( September 2023 , Nature Ecology & Evolution)

   Habitat specialization underpins biological processes from species distributions to speciation. However, organisms are often described as specialists or generalists based on a single niche axis, despite facing complex, multidimensional environments. Here, we analysed 236 environmental soil microbiomes across the United States and demonstrate that 90% of >1,200 prokaryotes followed one of two trajectories: specialization on all niche axes (multidimensional specialization) or generalization on all axes (multidimensional generalization). We then documented that this pervasive multidimensional specialization/generalization had many ecological and evolutionary consequences. First, multidimensional specialization and generalization are highly conserved with very few transitions between these two trajectories. Second, multidimensional generalists dominated communities because they were 73 times more abundant than specialists. Lastly, multidimensional specialists played important roles in community structure with ~220% more connections in microbiome networks. These results indicate that multidimensional generalization and specialization are evolutionarily stable with multidimensional generalists supporting larger populations and multidimensional specialists playing important roles within communities, probably stemming from their overrepresentation among pollutant detoxifiers and nutrient cyclers. Taken together, we demonstrate that the vast majority of soil prokaryotes are restricted to one of two multidimensional niche trajectories, multidimensional specialization or multidimensional generalization, which then has far-reaching consequences for evolutionary transitions, microbial dominance and community roles. 

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3. The roles of ecology, behaviour and effective population size in the evolution of a community

   https://doi.org/10.1111/mec.14152  

   Hung, Chih‐Ming ; Drovetski, Sergei V. ; Zink, Robert M. ( June 2017 , Molecular Ecology)

   Organismal traits such as ecological specialization and migratory behaviour may affect colonization potential, population persistence and degree of isolation, factors that determine the composition and genetic structure of communities. However, studies focusing on community assembly rarely consider these factors jointly. We sequenced 16 nuclear genes and one mitochondrial gene from Caucasian and European populations of 30 forest‐dwelling avian species that represent diverse ecological (specialist–generalist) and behavioural (migratory‐resident) backgrounds. We tested the effects of organismal traits on population divergence and community assembly in the Caucasus forest, a continental mountain island setting. We found that (i) there is no concordance in divergence times between the Caucasus forest bird populations and their European counterparts, (ii) habitat specialists tend to be more divergent than generalists and (iii) residents tend to be more divergent than migrants. Thus, specialists and residents contribute to the high level of endemism of Caucasus forest avifauna more than do generalists and migrants. Patterns of genetic differentiation are better explained by differences in effective population sizes, an often overlooked factor in comparative studies of phylogeography and speciation, than by divergence times or levels of gene flow. Our results suggest that the Caucasus forest avifauna was assembled through time via dispersal and/or multiple vicariant events, rather than originating simultaneously via a single isolation event. Our study is one of the first multilocus, multispecies analyses revealing how ecological and migratory traits impact the evolutionary history of community formation on a continental island.

    

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4. Fluctuating selection facilitates the discovery of broadly effective but difficult to reach adaptive outcomes in yeast

   https://doi.org/10.1093/evlett/qrad055  

   Fasanello, Vincent J. ; Liu, Ping ; Fay, Justin C. ; Botero, Carlos A. ( November 2023 , Evolution Letters)

   Evolutionary compromises are thought to be common under fluctuating selection because the mutations that best enable adaptation to one environmental context can often be detrimental to others. Yet, prior experimental work has shown that generalists can sometimes perform as well as specialists in their own environments. Here we use a highly replicated evolutionary experiment (N = 448 asexual lineages of the brewer’s yeast) to show that even though fluctuation between two environmental conditions often induces evolutionary compromises (at least early on), it can also help reveal difficult to reach adaptive outcomes that ultimately improve performance in both environments. Specifically, we begin by showing that yeast adaptation to chemical stress can involve fitness trade-offs with stress-free environments and that, accordingly, lineages that are repeatedly exposed to occasional stress tend to respond by trading performance for breadth of adaptation. We then show that on rare occasions, fluctuating selection leads to the evolution of no-cost generalists that can even outcompete constant selection specialists in their own environments. We propose that the discovery of these broader and more effective adaptive outcomes under fluctuating selection could be partially facilitated by changes in the adaptive landscape that result from having to deal with fitness trade-offs across different environmental conditions. Overall, our findings indicate that reconciling the short- and long-term evolutionary consequences of fluctuating selection could significantly improve our understanding of the evolution of specialization and generalism.

    

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5. The evolution of siphonophore tentilla for specialized prey capture in the open ocean

   https://doi.org/10.1073/pnas.2005063118  

   Damian-Serrano, Alejandro ; Haddock, Steven H. ; Dunn, Casey W. ( February 2021 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   Predator specialization has often been considered an evolutionary “dead end” due to the constraints associated with the evolution of morphological and functional optimizations throughout the organism. However, in some predators, these changes are localized in separate structures dedicated to prey capture. One of the most extreme cases of this modularity can be observed in siphonophores, a clade of pelagic colonial cnidarians that use tentilla (tentacle side branches armed with nematocysts) exclusively for prey capture. Here we study how siphonophore specialists and generalists evolve, and what morphological changes are associated with these transitions. To answer these questions, we: a) Measured 29 morphological characters of tentacles from 45 siphonophore species, b) mapped these data to a phylogenetic tree, and c) analyzed the evolutionary associations between morphological characters and prey-type data from the literature. Instead of a dead end, we found that siphonophore specialists can evolve into generalists, and that specialists on one prey type have directly evolved into specialists on other prey types. Our results show that siphonophore tentillum morphology has strong evolutionary associations with prey type, and suggest that shifts between prey types are linked to shifts in the morphology, mode of evolution, and evolutionary correlations of tentilla and their nematocysts. The evolutionary history of siphonophore specialization helps build a broader perspective on predatory niche diversification via morphological innovation and evolution. These findings contribute to understanding how specialization and morphological evolution have shaped present-day food webs. 

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