[All-postdocs] Two Bioseminars this week! Billie J. Swalla (Wednesday) and Serena Sung-Clarke (Thursday)

[Ana Velez]

Woods Hole Oceanographic Institution
Biology Department Seminar

Wednesday, April 2, 2025 - 12:00 pm
Redfield Auditorium

Billie J. Swalla
Professor Emerita, University of Washington

Evolution, Development and Regeneration in the Chordates
The Swalla Lab is interested in the evolution, development and regeneration in the Chordates, a group of animals with a unique body plan within Deuterostomia.  All chordates have a notochord, a muscular tail, and a dorsal central nervous system. Deuterostomia are a monophyletic animal group, consisting of the Ambulacraria, with two phyla, Hemichordata and Echinodermata, and the phylum Chordata, containing the subphyla Cephalochordata (lancelets or Amphioxus), Tunicata (Urochordata) and Vertebrata. Hemichordates and echinoderms are sister groups and are critical for understanding the deuterostome ancestor and the origin and evolution of the chordates within the deuterostomes. Genomic comparisons show that cephalochordates share synteny and a vermiform body plan similar to vertebrates, but phylogenomic analyses place tunicates as the sister group of vertebrates. Tunicates have a U-shaped gut and a very different adult body plan than the rest of the chordates, and all tunicates have small genomes and many gene losses, although the GRNs underlying specific tissues, such as notochord and muscle, are conserved. Echinoderms and vertebrates have extensive fossil records, with fewer specimens found for tunicates and enteropneusts, or worm-like hemichordates. The data is mounting that the deuterostome ancestor was a complex benthic worm, with gill slits, a cartilaginous skeleton, and a CNS. Two extant groups, echinoderms and tunicates, have evolved highly derived adult body plans, remarkably different from the deuterostome ancestor. I will review the current genomic and GRN data on the different groups of deuterostomes' characters to re-evaluate different hypotheses of chordate origins. Notochord loss in echinoderms and hemichordates is as parsimonious as notochord gain in the chordates but has implications for the deuterostome ancestor. The chordate ancestor lost an ancestral nerve net, retained the central nervous system, and evolved neural crest cells.

Wednesday, April 3, 2025 - 12:00 pm
Redfield Auditorium

Serena Sung-Clarke
PhD Student, MIT-WHOI Joint Program

Rapid Sexual Reproduction in a Mixotrophic Dinoflagellate Revealed Through Behavioral Time Partitioning
Dinophysis are specialist mixotrophs that must balance prey capture, cell division, and sexual recombination during blooms. Many Dinophysis species produce diarrhetic shellfish toxins (DSTs) that bioaccumulate in filter-feeding shellfish, causing illness to human and other animal consumers. Relatively little is known about the occurrence and role of sex in their ecology. Here, mating was investigated in D. acuminata through culture and in situ observation in Salt Pond, MA with continuous automated microscopy. Vegetative division and mating were phased on a diel timescale, occurring primarily at night and near dawn, regardless of prey availability. When prey was available, feeding occurred primarily during daylight hours. Confinement of division and mating to nighttime and early morning may minimize conflict with photosynthesis-related metabolism and/or predator exposure. Phasing of mating can also promote genetic connectivity within Dinophysis cell populations. Mating was prevalent in the culture experiment but not associated with zygote accumulation or resting stage formation. Instead, zygotes reverted to haploidy via meiosis within one day, providing a cell reproduction mechanism that bypasses vegetative growth and division. Sexual reproduction is increasingly accessible as blooms intensify and may also alleviate populations' susceptibility to pathogens, parasites, and other threats that are associated with bloom development via genetic recombination, an example of Red Queen dynamics.

For questions, contact:

Ana María Vélez
Biology Pre-Award Administrative Associate
Ph: (+1)(508)289-2334
[signature_1005462319]

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