TY - BOOK

T1 - Evolution of Scale Worms

AU - Gonzalez, Brett Christopher

PY - 2016

Y1 - 2016

N2 - Morphologically characterized by the presence of a dorsal covering of paired segmental scales(=elytra), scale worms are well represented throughout the scientific literature, and are a result ofone of the most successful radiations of annelids. However, the phylogenetic relationships ofelytrigerous annelids remain unresolved, in spite of the numerous systematic revisions the grouphas undergone. Since the first morphological cladistic analysis, molecular and combinedinvestigations have shaken up the systematics, yielding surprising character transformationswithin Aphroditiformia, and paraphyly within various groups previously thought to bemonophyletic, highlighting the necessity for further detailed systematic revisions. Herein, weattempt to resolve these controversies within scale worms, by inclusion of previouslyunderrepresented taxa (i.e., caves and interstitium) in order to improve the overall resolution ofthe phylogenetic relationships within Aphroditiformia. To date, this is the largest and most diversephylogenetic sampling of scale worms, being the first to include anchialine as well as severalpreviously neglected interstitial representatives. Using combined and total evidence approaches,our phylogenetic analyses integrated morphological and molecular datasets, with subsequentsensitivity analyses to identify those groups with unstable positioning. Our inclusion of speciesfrom extreme environments showed several independent radiations among the deep sea,(anchialine) caves, and the interstitium, recovering six monophyletic clades withinAphroditiformia: Acoetidae, Aphroditidae, Eulepethidae, Iphionidae, Polynoidae, and Sigalionidae(inclusive of the former ‘Pisionidae’ and ‘Pholoidae’), respectively. Tracing of morphologicalcharacter evolution showed a high degree of homoplasy throughout Aphroditiformia, with severalsecondary losses of scales among the groups. Ultimately, our investigations into cave andinterstitial scale worms have given rise to interesting phylogeographical questions, as these groupshave wide distributions despite their habitat specificity and seemingly low dispersal potential.While anchialine polynoids are highly habitat specific, we found strong geographic structurebetween Bahamian islands, with intra-island gene flow presumably through spelean corridors.Alternatively, our studies of interstitial taxa showed broad distributions associated to geographicalregions, with high levels of homoplasy in group-specific morphological characters. Due to the highlevels of homoplasy found by our cladistics analyses, we performed large-scale phylogeneticcomparative analyses to unravel how ecology correlates to variation across e.g., feeding, motility,and colonization of habitats, especially the subterranean and interstitium. Focusing on theseextreme habitat colonization events, we found evidence of shared morphological adaptations inresponse to aphotic conditions, as trait similarity appeared to be linked to functionality, therebyreflecting a high degree of adaptability and convergent evolution between relatively closelyrelated scale worms. While some morphological and behavioral modifications in cave polynoidsreflected troglomorphism, other modifications like eye loss were found to stem from a commonancestor inhabiting the deep sea, further corroborating the deep sea ancestry of scale worm cavefauna. In conclusion, while morphological characterization across Aphroditiformia appearsdeceptively easy due to the presence of elytra, convergent evolution during multiple earlyradiations across wide ranging habitats have confounded our ability to reconstruct the evolutionof morphological characters. The high morphological variability include from loss of elytra anddevelopment of specialized male copulatory structures, to that of reduced body size andincorporation of elytral brooding. Our combined investigations into adaptation and evolution ofmorphological and molecular characters on species, genera, and across families has illustrated thedegree to which ecology drives morphological plasticity, making it equally important

AB - Morphologically characterized by the presence of a dorsal covering of paired segmental scales(=elytra), scale worms are well represented throughout the scientific literature, and are a result ofone of the most successful radiations of annelids. However, the phylogenetic relationships ofelytrigerous annelids remain unresolved, in spite of the numerous systematic revisions the grouphas undergone. Since the first morphological cladistic analysis, molecular and combinedinvestigations have shaken up the systematics, yielding surprising character transformationswithin Aphroditiformia, and paraphyly within various groups previously thought to bemonophyletic, highlighting the necessity for further detailed systematic revisions. Herein, weattempt to resolve these controversies within scale worms, by inclusion of previouslyunderrepresented taxa (i.e., caves and interstitium) in order to improve the overall resolution ofthe phylogenetic relationships within Aphroditiformia. To date, this is the largest and most diversephylogenetic sampling of scale worms, being the first to include anchialine as well as severalpreviously neglected interstitial representatives. Using combined and total evidence approaches,our phylogenetic analyses integrated morphological and molecular datasets, with subsequentsensitivity analyses to identify those groups with unstable positioning. Our inclusion of speciesfrom extreme environments showed several independent radiations among the deep sea,(anchialine) caves, and the interstitium, recovering six monophyletic clades withinAphroditiformia: Acoetidae, Aphroditidae, Eulepethidae, Iphionidae, Polynoidae, and Sigalionidae(inclusive of the former ‘Pisionidae’ and ‘Pholoidae’), respectively. Tracing of morphologicalcharacter evolution showed a high degree of homoplasy throughout Aphroditiformia, with severalsecondary losses of scales among the groups. Ultimately, our investigations into cave andinterstitial scale worms have given rise to interesting phylogeographical questions, as these groupshave wide distributions despite their habitat specificity and seemingly low dispersal potential.While anchialine polynoids are highly habitat specific, we found strong geographic structurebetween Bahamian islands, with intra-island gene flow presumably through spelean corridors.Alternatively, our studies of interstitial taxa showed broad distributions associated to geographicalregions, with high levels of homoplasy in group-specific morphological characters. Due to the highlevels of homoplasy found by our cladistics analyses, we performed large-scale phylogeneticcomparative analyses to unravel how ecology correlates to variation across e.g., feeding, motility,and colonization of habitats, especially the subterranean and interstitium. Focusing on theseextreme habitat colonization events, we found evidence of shared morphological adaptations inresponse to aphotic conditions, as trait similarity appeared to be linked to functionality, therebyreflecting a high degree of adaptability and convergent evolution between relatively closelyrelated scale worms. While some morphological and behavioral modifications in cave polynoidsreflected troglomorphism, other modifications like eye loss were found to stem from a commonancestor inhabiting the deep sea, further corroborating the deep sea ancestry of scale worm cavefauna. In conclusion, while morphological characterization across Aphroditiformia appearsdeceptively easy due to the presence of elytra, convergent evolution during multiple earlyradiations across wide ranging habitats have confounded our ability to reconstruct the evolutionof morphological characters. The high morphological variability include from loss of elytra anddevelopment of specialized male copulatory structures, to that of reduced body size andincorporation of elytral brooding. Our combined investigations into adaptation and evolution ofmorphological and molecular characters on species, genera, and across families has illustrated thedegree to which ecology drives morphological plasticity, making it equally important

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122461293805763

M3 - Ph.D. thesis

BT - Evolution of Scale Worms

PB - Department of Biology, Faculty of Science, University of Copenhagen

ER -