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    V: ASIH Symposium: Why are there so many kinds of fishes? A showcase of early-career ichthyologists, I

    2021-07-27   08:00 - 10:00

    Moderator: Prosanta Chakrabarty

    1.  08:00  VIRTUAL    Early Career: Why Are There So Many Kinds of Fishes? Two Lessons from Studies of Diversification Rates and Biogeography. Elizabeth Miller*, University of Washington

    There are presently 35,845 species of fishes encompassing half of all vertebrates. Fishes occupy all aquatic habitats including alkaline springs, dark caves, Antarctic seas and the deep ocean. The size and shape diversity of fishes is immense, ranging in length from 8 mm to 12 meters. These observations beg the question, “why are there so many kinds of fishes?” In the first half of this talk, I will introduce the symposium which will explore the taxonomic, morphological, and ecological diversity of fishes. A diversity of viewpoints is needed to answer a complex question. To this end, all speakers in this symposium are early-career researchers (students, postdocs and pre-tenure faculty). Early-career scientists represent over one-third of the membership of ASIH and are a more diverse group of people than tenured faculty. In the second half of the talk, I will share two overarching lessons from my work that will help us move forward towards explaining the diversity of fishes. First, the factors that explain diversification rate variation among clades change with taxonomic scale. Second, diversification rates do not usually explain richness disparities by habitat and geography (such as the latitudinal diversity gradient), so we must look to other explanations.

    2.  08:15  VIRTUAL    Early Career: Perpetual Updates for the Fish Tree of Life. Jonathan Chang*, Los Angeles County Department of Public Health

    Well-sampled phylogenies are a critical resource for comparative biologists and systematicists in understanding the diversity of life. However, the construction of large phylogenies covering the diversity of a group such as ray-finned fishes is a time-consuming task requiring many manual steps. Nearly a decade ago, the PUmPER (phylogenies updated perpetually) pipeline was developed to update existing phylogenies without human intervention. Here we extend the PUmPER pipeline to integrate novel sources of sequence data, and enable human audit, review, and correction of machine actions, to ensure accurate phylogenies that will advance understanding of why there are so many kinds of fishes.

    3.  08:30  VIRTUAL    Early Career: Reproductive mode, sexual selection, and speciation in poeciliid fishes. Andrew Furness*, University of Hull; Bart Pollux, Wageningen University; David Reznick, University of California, Riverside

    The way in which organisms reproduce determines the opportunity for sexual and parent-offspring conflict. Live-bearing fish in the family Poeciliidae show variation amongst species in whether offspring are provisioned prior to fertilization (lecithotrophy) or after fertilization (matrotrophy by means of a placenta). This shift in when females provision their offspring relative to when an egg is fertilized is predicted to cause a fundamental change in when and how conflict is manifested. If eggs are provisioned before fertilization, there should be strong selection for females to choose with whom they mate. Maternal provisioning after fertilization should promote a shift to post-copulatory mate choice. The evolution of maternal provisioning is predicted to have downstream effects on the evolution of male sexually selected traits, the rate at which reproductive isolation evolves, and ultimately speciation. Here, we test for and find that that the evolution of maternal provisioning is associated with and appears to govern the evolution of male traits associated with sexual selection. The evolution of placentas and associated conflict does not cause accelerated speciation, contrary to predictions. Accelerated speciation rate is instead correlated with the evolution of male traits associated with sexual selection, which implies a more prominent role of pre-copulatory reproductive isolation in causing speciation in this family.

    4.  08:45  VIRTUAL    Ecological Evolution and Diversification of Neotropical Freshwater Fishes. Milton Tan*, University of Illinois at Urbana-Champaign; Victor Tagliacollo, University of São Paulo; James Albert, University of Louisiana at Lafayette

    Neotropical freshwaters exhibit the highest species richness and functional trait diversity of any continental aquatic fauna, yet the causal relationships among lineage diversification, ecological diversification, and landscape evolution remain poorly understood. We explore these associations using a newly-assembled dataset of 6,346 species coded for 38 ecological traits corresponding to modal adult diet, macrohabitat, mesohabitat, microhabitat, and water type variables. We ordinated these traits to summarize the multidimensional ecological diversity of Neotropical freshwater fishes, and studied the evolution of these ecological traits in a formal phylogenetic framework using a newly-generated tree from analysis of published gene sequence data for 3,396 species. We interrogated these datasets for associations among rates of ecological evolution, net lineage diversification, and the timing and location of prominent landscape evolution events (e.g. tectonic uplifts, mega-river captures). We found net lineage diversification (speciation minus extinction) heterogeneous through time, and among clades with different ecological traits. Most taxa and all ecological trait states originated during the Paleogene (c. 66 – 23 Ma) in sediment-poor upland (>250 m elevation) habitats of the Guiana and Brazilian shields, and highest rates of lineage diversification and ecological trait evolution in sediment-rich Amazon-Orinoco lowlands (<250 m elevation) during the Neogene (c. 23.0 – 2.6 Ma). We found that rates of lineage diversification and ecological trait evolution are positively associated at higher taxonomic levels but not at the species level, suggesting that the processes of ecological adaptation and speciation have been decoupled in the continental radiations of Neotropical freshwater fishes.

    5.  09:00  VIRTUAL    Phylogenomics and Biogeographic History of Trans-Andean Tetras in the Genus Hyphessobrycon Durbin 1908. Diego J. Elías*, Museum of Natural Science, Department of Biological Sciences, Louisiana State University; Caleb D. McMahan, Field Museum of Natural History; Fernando Alda, Department of Biology, Geology and Environmental Science, University of Tennessee at Chattanooga; Carlos García-Alzate, Museo de colecciones científicas, Universidad del Atlántico; Pamela B. Hart, Museum of Natural Science, Department of Biological Sciences, Louisiana State University; Prosanta Chakrabarty, Museum of Natural Science, Department of Biological Sciences, Louisiana State University

    Hyphessobryconis one of the most species rich genera (136 species) within the family Characidae, with a widespread distribution from Veracruz, Mexico to Argentina. The type species of the genus, H. compressus (Meek 1908), is the most northerly distributed species of Hyphessobrycon. Most of the diversity within Hyphessobrycon is distributed to the east of the Andes; however, nine trans-Andean species are distributed in Middle America and South America (H. compressus,H. tortuguerae, H. bussingi,H. savagei,H. panamensis, H. columbianus,H. condotensis, H. daguae,and H. ecuadorensis). Recent work has highlighted that the currently recognized diversity within Hyphessobrycon is not monophyletic. In this study we test if trans-Andean species of Hyphessobrycon are monophyletic and investigate their biogeographic history within the region. We propose the first phylogenomic hypothesis of the trans-Andean Hyphessobryconthat includes nearly complete taxonomic sampling (seven of nine valid species) using ultraconserved elements (UCEs). We analyzed two datasets consisting of 75% (1683 UCEs) and 95% (886 UCEs) complete matrices, and inferred phylogenomic hypotheses using concatenation and coalescent approaches. Finally, we performed ancestral area estimation to reconstruct the biogeographic history of trans-Andean Hyphessobrycon. Our analyses recovered the monophyly of the trans-Andean Hyphessobrycon, as well as strong support for three species groups and evidence of cryptic diversity within the widespread H. compressus. Our biogeographic inference suggests a single colonization event from East to West of the Andes by Hyphessobrycon followed by diversification from the Pacific slope of South America (Choco block) to northern Middle America (Maya block).

    6.  09:15  VIRTUAL    The Ecology and Evolution of Color Polymorphism in Hawkfishes of the Genus Paracirrhites. Michelle Gaither*, University of Central Florida; Samuel Greaves, University of Central Florida; Darren Coker, KAUST; Samuel Payet, James Cook University; Joseph DiBattista, Australia Museum; Michael Berumen, KAUST

    Non-sex linked color polymorphism is common in animals and can be maintained in populations via balancing selection or, when under diversifying selection, promote divergence. Despite their potential importance in ecological interactions and the evolution of biodiversity, their function and the mechanisms by which these polymorphisms are maintained are still poorly understood. Hawkfishes of the family Cirrhitidae are coral reef-associated mesopredators. In the genus Paracirrhites, at least three of the six species are known to display sympatric color morphs not thought to be linked to sex or ontogeny. Combining field observations with life history and molecular data, we found that the four sympatric color morphs of Paracirrhites forsteri in the central Red Sea inhabit the same reefs, do not show signs of avoidance or aggression between them, and are not linked to sex or ontogeny. A standard barcoding approach examining 1276 bp of the mitochondrial cytochrome c oxidase subunit I and cytochrome b genes could not differentiate the four morphs. However, 36769 ddRADseq-derived SNPs identified 1121 FST outliers that corresponded to distinct population clusters with modest, but significant shifts in allele frequencies and unique alleles between the four morphs. Genetic divergence at these outlier loci was accompanied by differences in growth rate and marginal variation in microhabitat preference. Taken together, these results suggest subtle divergence between the color morphs that mandate further investigation.

    7.  09:30  VIRTUAL    Early Career: The origins of novelty in an adaptive radiation of pupfishes: insights from ecology, genomics, behavior, and fitness landscapes. Christopher Martin*, University of Californiaornia, Berkeley

    Biologists are drawn to the most extraordinary adaptations in the natural world, i.e. evolutionary novelties, yet rarely do we understand the microevolutionary processes underlying the origins of novel traits, behaviors, or ecological niches. Here I discuss insights gained into the origins of novelty from my research program over the past decade on Caribbean pupfishes, spanning biological levels of organization from genotype to fitness landscape. I focus on a case study of the origins of novel trophic specialists on San Salvador Island, a sympatric radiation including the endemic scale-eating and mollusk-eating specialist pupfishes. I highlight questions that can be addressed about the origins of novelty at different biological levels, including the contributions of ecological opportunity, the isolation of novel phenotypes on the fitness landscape, the spatiotemporal origins of adaptive variation contributing to novelty, and form-function relationships for novel traits. Evolutionary novelties are rare, almost by definition, yet integrative case studies can provide insights into this rarity relative to more common adaptations, such as the relative isolation of novel phenotypes on fitness landscapes and the transient availability of ecological, genetic, and behavioral opportunities for novelty.

    8.  09:45  VIRTUAL    Early Career: Biogeography, Habitat Transitions, and Hybridization in a Radiation of South American Silversides Revealed by MtDNA and Genomic Data. Lily C. Hughes*, University of Chicago; Yamila P. Cardoso, Universidad Nacional de la Plata; Julie Sommer, University of Nebraska Medical Center; Roberto Cifuentes, Universidad de Concepción; Mariela Cuello, Universidad Nacional de la Plata; Gustavo M. Somoza, Instituto Tecnológico de Chascomús; Mariano González-Castro, Universidad Nacional de Mar del Plata; Luiz R. Malabarba, Universidade Federal do Rio Grande do Sul; Victor Cussac, Universidad Nacional de Comahue; Evelyn M. Habit, Universidad de Concepción

    Rivers and lake systems in southern South America have been widely influenced by historical glaciations, carrying important implications for the evolution of aquatic organisms, including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes (Odontesthes, 19 species) in the region have been hypothesized to have either transitioned repeatedly into continental waters from the sea or colonized marine habitats following freshwater diversification. New genomic ddRAD data presented here provide a robust framework to investigate the biogeographical history of and habitat transitions in Odontesthes. We show that Odontesthes silversides initially diversified in the Pacific but independently colonized the Atlantic three times, producing three independent marine-to-freshwater transitions. Our results also indicate recent introgression of marine mitochondrial haplotypes into two freshwater clades, with more recurring instances of hybridization among Atlantic- versus Pacific-slope species. In Pacific freshwater drainages, hybridization with a marine species appears to be geographically isolated and may be related to glaciation events. Substantial structural differences of estuarine gradients between these two geographical areas may have influenced the frequency, intensity and evolutionary effects of hybridization events.

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