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1. Linking Ecological Specialization to Its Macroevolutionary Consequences: An Example with Passerine Nest Type

   https://doi.org/10.1093/sysbio/syac083  

   Zenil-Ferguson, Rosana; McEntee, Jay P; Burleigh, J Gordon; Duckworth, Renée A (May 2023, Systematic Biology)

   Ruane, Sara (Ed.)

   Abstract A long-standing hypothesis in evolutionary biology is that the evolution of resource specialization can lead to an evolutionary dead end, where specialists have low diversification rates and limited ability to evolve into generalists. In recent years, advances in comparative methods investigating trait-based differences associated with diversification have enabled more robust tests of this idea and have found mixed support. We test the evolutionary dead end hypothesis by estimating net diversification rate differences associated with nest-type specialization among 3224 species of passerine birds. In particular, we test whether the adoption of hole-nesting, a nest-type specialization that decreases predation, results in reduced diversification rates relative to nesting outside of holes. Further, we examine whether evolutionary transitions to the specialist hole-nesting state have been more frequent than transitions out of hole-nesting. Using diversification models that accounted for background rate heterogeneity and different extinction rate scenarios, we found that hole-nesting specialization was not associated with diversification rate differences. Furthermore, contrary to the assumption that specialists rarely evolve into generalists, we found that transitions out of hole-nesting occur more frequently than transitions into hole-nesting. These results suggest that interspecific competition may limit adoption of hole-nesting, but that such competition does not result in limited diversification of hole-nesters. In conjunction with other recent studies using robust comparative methods, our results add to growing evidence that evolutionary dead ends are not a typical outcome of resource specialization. [Cavity nesting; diversification; hidden-state models; passerines; resource specialization.] 

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2. Linking ecological specialization to its macroevolutionary consequences: An example with passerine nest type

   https://doi.org/10.5281/zenodo.7459509  

   Zenil-Ferguson, Rosana; McEntee, Jay; Burleigh, Gordon; Duckworth, Renée (January 2022, Zenodo)

   A long-standing hypothesis in evolutionary biology is that the evolution of resource specialization can lead to an evolutionary dead end, where specialists have low diversification rates and limited ability to evolve into generalists. In recent years, advances in comparative methods investigating trait-based differences associated with diversification have enabled more robust tests of this idea and have found mixed support. We test the evolutionary dead end hypothesis by estimating net diversification rate differences associated with nest site specialization among 3,224 species of passerine birds. In particular, we test whether the adoption of hole-nesting, a nest site specialization that decreases predation, results in reduced diversification rates relative to nesting outside of holes. Further, we examine whether evolutionary transitions to the specialist hole-nesting state have been more frequent than transitions out of hole-nesting. Using diversification models that accounted for background rate heterogeneity and different extinction rate scenarios, we found that hole-nesting specialization was not associated with diversification rate differences. Furthermore, contrary to the assumption that specialists rarely evolve into generalists, we found that transitions out of hole-nesting occur more frequently than transitions into hole-nesting. These results suggest that interspecific competition may limit adoption of hole-nesting, but that such competition does not result in limited diversification of hole-nesters. In conjunction with other recent studies using robust comparative methods, our results add to growing evidence that evolutionary dead ends are not a typical outcome of resource specialization. 

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3. The Evolutionary History of Siphonophore Tentilla: Novelties, Convergence, and Integration

   https://doi.org/10.1093/iob/obab019  

   Damian-Serrano, A; Haddock, S H; Dunn, C W (January 2021, Integrative Organismal Biology)

   null (Ed.)

   Abstract Synopsis Siphonophores are free-living predatory colonial hydrozoan cnidarians found in every region of the ocean. Siphonophore tentilla (tentacle side branches) are unique biological structures for prey capture, composed of a complex arrangement of cnidocytes (stinging cells) bearing different types of nematocysts (stinging capsules) and auxiliary structures. Tentilla present an extensive morphological and functional diversity across species. While associations between tentillum form and diet have been reported, the evolutionary history giving rise to this morphological diversity is largely unexplored. Here we examine the evolutionary gains and losses of novel tentillum substructures and nematocyst types on the most recent siphonophore phylogeny. Tentilla have a precisely coordinated high-speed strike mechanism of synchronous unwinding and nematocyst discharge. Here we characterize the kinematic diversity of this prey capture reaction using high-speed video and find relationships with morphological characters. Since tentillum discharge occurs in synchrony across a broad morphological diversity, we evaluate how phenotypic integration is maintaining character correlations across evolutionary time. We found that the tentillum morphospace has low dimensionality, identified instances of heterochrony and morphological convergence, and generated hypotheses on the diets of understudied siphonophore species. Our findings indicate that siphonophore tentilla are phenotypically integrated structures with a complex evolutionary history leading to a phylogenetically-structured diversity of forms that are predictive of kinematic performance and feeding habits. 

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4. Shifts in bee diet breadths are associated with gene gains and losses and positive selection across olfactory receptors

   https://doi.org/10.1093/g3journal/jkaf105  

   Singh, Avehi; Pope, Nathaniel S; López-Uribe, Margarita M (July 2025, G3: Genes, Genomes, Genetics)

   Whitehead, A (Ed.)

   Abstract Bees are palynivorous insects that vary widely in the number of plant families from which they collect pollen. Their evolutionary history has been marked by multiple transitions in diet breadth between specialists that only visit specific plant genera (narrow diet breadth) and generalists that visit multiple large plant families (broad diet breadth). Understanding the evolution of sensory systems associated with changes in the detection, discrimination, and gustation of different pollen in bees can shed light on the underlying genetic mechanisms associated with transitions between narrow and broad diet breadths. We conducted a comparative study of three families of insect olfactory receptor genes (odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs)) linked to diet breadth across 51 bee species. We calculated rates of gene gains and losses and identified genes experiencing positive selection across specialist and generalist bees. Our results show that broad generalists exhibit high rates of OR gene losses and GR gene gains. We observed accelerated rates of evolution in seven orthologous groups of genes across specialists and one group in generalists. Several orthogroups showed diversification in putative ligand-binding domains of proteins, indicating potential shifts in functional properties of the receptors. Taken together, these results indicate that dietary specialization in bees requires chemosensory system diversification of existing genes while dietary generalization is associated with the loss of ORs and gain of GRs. Our study provides important insights into the genetic architecture underlying shifts in niche occupancy across insects. 

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5. Temporal Diversification and Evolutionary History of the Cribellum in Marronoid Spiders

   Mottershead, S. D.; Riquelme, F. C.; Esposito, L. A.; Gorneau, J. A. (October 2023, Society for the Advancement of Chicanos/Hispanics and Native Americans in Science - 2023 NDiSTEM)

   Webs play many essential roles in spider biology, including communication, prey capture, locomotion, and reproduction. One interesting morphological feature of many spiders is the cribellum, a plate located near the silk-producing structures called spinnerets, and used to create a special type of matted silk that captures prey mechanically, instead of with glue droplets used by many orb-weaving spiders. The cribellum is hypothesized to have been present in the ancestor of all araneomorph spiders, but lost multiple times over the course of spider evolution. One group of spiders, the ‘marronoids’, shows a pattern of repeated loss and gain of this structure, placing them at a transitional position in the evolution of spider webs, with further implications for the web capture strategy, and other ecological conditions such as water-associated habitat. Studying the timing of the loss of the cribellum may yield insight to the cryptic ecology and morphology of the marranoid clade, and more broadly, araneomorph spiders. We use comparative phylogenetic methods to identify ancestral states of morphological and behavioral characters, and examine divergence dates with fossil calibrations. To do this, 98 representative spiders from the marronoid clade were coded by zoogeographic region, distribution proximity to a body of water and type, web type, and observed aquatic behavior. The morphology of the cribellum and spinnerets was assessed using 42 characters with multiple states. We identified patterns of evolution of the cribellum and aquatic habitat associations in the context of phylogeny, and geologic time. 

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