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    Ichthyology III

    2021-07-23   09:15 - 10:00

    Moderator: Tom Turner

    1.  09:15  IN-PERSON    Is the Indo-Pacific a Museum or a Cradle for Biological Diversity in Seahorses, Dragonets, Goatfishes and Allies (Teleostei: Syngnatharia)? Aintzane Santaquiteria*, The University of Oklahoma; Ricardo Betancur-R., The University of Oklahoma

    The possible drivers explaining species diversity gradient patterns, both latitudinally and longitudinally, have been studied on a variety of terrestrial and marine organisms. Many extant reef-associated fish clades show a clear longitudinal discontinuity of species richness across the oceans, with the Indo-Pacific harboring higher taxonomic richness relative to the Atlantic and the eastern Pacific. The goal of this study is to understand the factors that may explain the extraordinary diversity of Syngnatharia (trumpetfishes, goatfishes, seahorses, and relatives) in the Indo-Pacific by assessing whether this region has acted as a “museum” or a “cradle”. To test these (non-mutually exclusive) hypotheses, we first expanded our recent phylogenomic analysis for the group sequences from public repositories to include data from a total of 323 species or ~50% of the clade’s total diversity. We then examined the influence of the geographic distribution on lineage diversification in this group across the three major oceanic realms. Area-dependent lineage diversification analyses (GeoHiSSE) suggest rate constancy across the three areas, supporting the “museum” or time-for-speciation hypothesis. Thus, higher levels of syngnatharian diversity in the Indo-Pacific are explained by earlier colonization of ancestral lineages into this region from the Tethys Sea, their center of origin. Ultimately, our results are in agreement with recent studies showing that time is one of the most important factors explaining uneven diversities of clades across regions.

    2.  09:30  IN-PERSON    A Textbook Heterochronic Shift in the Development of the Catfish Skeleton. Kole Kubicek*, Texas A&M University; Ralf Britz, Senckenberg Natural History Collections; Kevin Conway, Texas A&M University

    Sequence heterochrony, or the evolutionary shift of the events in an ontogenetic sequence, has been shown in tetrapods to be associated with major changes in morphology, function and life history. Despite the greater potential of and likelihood for heterochronic shifts in bony fishes as a result of the larger number and greater complexity of skeletal elements, studies of sequence heterochrony are surprisingly rare. Catfishes (Siluriformes) are characterized by several skeletal autapomorphies, including extreme modifications to certain elements, among them the pectoral-fin spine. The uniquely modified skeleton of catfishes makes them ideal candidates to investigate the potential role of heterochrony in the evolution of a diverse group of fishes. In order to investigate the evolutionary role of sequence heterochrony in the catfish skeleton, we compare complete ossification sequences that we generated for two loricarioid (Ancistrussp. and Corydoras panda) and two siluroid catfishes (Ictalurus punctatusand Noturus gyrinus) to those available for other otophysans (Danio rerio, Enteromius holotaenia and Salminus brasiliensis). We determine which heterochronic changes in skeletal development, if any, characterize loricarioid and siluroid catfishes as well as siluriforms in general. We also assess whether heterochrony has played a role in the evolution of derived characteristics, in particular those which are highly modified in siluriforms.

    3.  09:45  VIRTUAL    Carnivorous Grazers Part Deux! Form and function in scale-feeding and fin-feeding Neotropical fishes. Matthew Kolmann*, University of Michigan; Leo MacLeod, University of Washingon; John Racy, Friday Harbor Labs; Jonathan Huie, George Washington University; Cassandra Donatelli, University of Ottawa; Adam Summers, Friday Harbor Labs

    Parasitic vertebrates, like vampire bats or cuckoos, are rare yet charismatic. But there is an unappreciated host of ectoparasitic vertebrates (feeding/living on the external surface of the host), and they are predominantly ray finned fishes. For example, scale-feeding evolved at least 19 times in teleosts. Here we probe the ecological and evolutionary phenomena that give rise to ectoparasitism in fishes, and our notions of the traits necessary for such bizarre niches as fin-feeding, scale-feeding, and mucus-feeding. We present two case studies at distinctive levels of evolutionary scale: (1) fin and scale-feeding in piranhas, using a densely sampled phylogeny to examine feeding trait evolution. This study contextualizes ectoparasite feeding performance side-by-side with the biomechanical demands incurred by prey materials (fin-clipping). The other (2) explores hypotheses regarding potential ecological precursors to ectoparasitism across Characiformes. We visualized feeding morphology from contrast-stained museum specimens using micro-computed tomography scanning. We find few traits distinguish ectoparasitic fishes from confamilials; however, robust extraoral teeth are important for scraping scales and clipping fins from prey. We propose that fin- and scale-feeding arise because they are energetically affordable, particularly for small fishes like juvenile piranhas, as the forces required to remove fins are well within published bite force estimates for piranhas. Within the diverse characiform fishes alone, scale- and fin-feeding has arisen some 15 times independently, suggesting that prior approximations regarding the abundance of ectoparasitic fishes are considerable underestimates.

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