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1. 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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2. Diversity in olfactory receptor repertoires is associated with dietary specialization in a genus of frugivorous bat

   https://doi.org/10.1093/g3journal/jkab260  

   Yohe, Laurel R ; Leiser-Miller, Leith B ; Kaliszewska, Zofia A ; Donat, Paul ; Santana, Sharlene E ; Dávalos, Liliana M ( July 2021 , G3 Genes|Genomes|Genetics)

   null (Ed.)

   Abstract Mammalian olfactory receptor genes (ORs) are a diverse family of genes encoding proteins that directly interact with environmental chemical cues. ORs evolve via gene duplication in a birth-death fashion, neofunctionalizing and pseudogenizing over time. Olfaction is a primary sense used for food detection in plant-visiting bats, but the relationship between dietary specialization and OR repertoire diversity is unclear. Within neotropical Leaf-nosed bats (Phyllostomidae), many lineages are plant specialists, and some have a distinct OR repertoire compared to insectivorous species. Yet, whether specialization on particular plant genera is associated with the evolution of specialized, less diverse OR repertoires has never been tested. Using targeted sequence capture, we sequenced the OR repertoires of three sympatric species of short-tailed fruit bats (Carollia), which vary in their degree of specialization on the fruits of Piper plants. We characterized orthologous vs duplicated receptors among Carollia species, and explored the diversity and redundancy of the receptor gene repertoire. At the species level, the most dedicated Piper specialist, Carollia castanea, had lower OR diversity compared to the two generalists (C. sowelli and C. perspicillata), but we discovered a few unique sets of ORs within C. castanea with high redundancy of similar gene duplicates. These unique receptors potentially enable C. castanea to detect Piper fruit odorants better than its two congeners. Carollia perspicillata, the species with the most generalist diet, had a higher diversity of intact receptors, suggesting the ability to detect a wider range of odorant molecules. Variation among ORs may be a factor in the coexistence of these sympatric species, facilitating the exploitation of different plant resources. Our study sheds light on how gene duplication and changes in OR diversity may play a role in dietary adaptations and underlie ecological interactions between bats and plants. 

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3. 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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4. Remarkable variation in androecial morphology is closely associated with corolla traits in Western Hemisphere Justiciinae (Acanthaceae: Justicieae)

   https://doi.org/10.1093/aob/mcad068  

   Kiel, Carrie A. ; Manzitto-Tripp, Erin ; Fisher, Amanda E. ; Porter, J. Mark ; McDade, Lucinda A. ( June 2023 , Annals of Botany)

   Few studies of angiosperms have focused on androecial evolution in conjunction with evolutionary shifts in corolla morphology and pollinator relationships. The Western Hemisphere clade of Justiciinae (Acanthaceae) presents the rare opportunity to examine remarkable diversity in staminal morphology. We took a phylogenetically informed approach to examine staminal diversity in this hypervariable group and asked whether differences in anther thecae separation is associated with phylogenetically informed patterns of variation in corolla morphology. We further discuss evidence for associations between anther diversity and pollinators in this lineage.

   For the Dianthera/Sarotheca/Plagiacanthus (DSP) clade of Western Hemisphere Justiciinae, we characterized floral diversity based on a series of corolla measurements and using a model-based clustering approach. We then tested for correlations between anther thecae separation and corolla traits, and for shifts in trait evolution, including evidence for convergence.

   There is evolutionary vagility in corolla and anther traits across the DSP clade with little signal of phylogenetic constraint. Floral morphology clusters into four distinct groups that are, in turn, strongly associated with anther thecae separation, a novel result in Acanthaceae and, to our knowledge, across flowering plants. These cluster groups are marked by floral traits that strongly point to associations with pollinating animals. Specifically, species that are known or likely to be hummingbird pollinated have stamens with parallel thecae, whereas those that are likely bee or fly pollinated have stamens with offset, divergent thecae.

   Our results suggest that anther thecae separation is likely under selection in concert with other corolla characters. Significant morphological shifts detected by our analyses corresponded to putative shifts from insect to hummingbird pollination. Results from this study support the hypothesis that floral structures function in an integrated manner and are likely subject to selection as a suite. Further, these changes can be hypothesized to represent adaptive evolution.

    

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5. 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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