The allure of cave scale worms: investigating their phylogenetic positions, unique morphologies, and adaptations

Anchialine cave habitats encompass land-locked water bodies of marine origin, partially isolated from the sea and harboring unique endemic fauna that may hold the key to elucidating evolutionary and biogeographic processes. Anchialine fauna are uniquely adapted, persisting under extreme environmental conditions, total darkness, limited oxygen, and particular hydrological and biogeochemical parameters. Unbeknown, crustaceans dominate the biodiversity, but continuous investigations have revealed a large and hidden diversity of annelids, including those known as scale worms (Aphroditiformia).

Scale worms are one of the most diverse families of annelids (<1200) found in all marine habitats, reflecting a complex evolutionary history that has permitted a vast array of adapta-tions and life history traits. Among this diversity are two anchialine scale worms from the family Polynoidae; Gesiella jameensis and Pelagomacellicephala iliffei, found at opposite sides of the Atlantic and in caves born of significantly different age and geology. Together, these anchialine scale worms are of putative deep-sea ancestry, classified within a subfamily known only from bathyal/abyssal depths. Morphological examination of these anchialine cave scale worms revealed similar morphologies, including lack of eyes and pigmentation, elongated sensory appendages, and a swimming lifestyle, all that have been suggested to be troglomorphic (reductive/constructive traits) adaptations to the anchialine cave environ-ment.

Throughout this talk, I will highlight our most recent findings, including ongoing morphological and phylogenetic investigations of scale worms from undersampled extreme environments. Our results represent the first model-based phylogeny to showcase rare anchialine genera (Gesiella and Pelagomacellicephala), being recovered within a clade of strictly deep-sea taxa. These findings support a deep-sea ancestry and a single colonization event into marine subterranean environments prior to the opening of the Atlantic. Furthermore, our access to unique and rare anchialine scale worms has allowed the first investigation among annelids to test for troglomorphism (=cave adaptations) using phylogenetic generalized linear mixed models (PGLMMs) across both behavioral and morphological traits. Results from our PGLMMs showed significant correlation between environment and dorsal cirri length, illustrating that the observed morphology within Gesiella and Pelagomacellicephala represents troglomorphic adaptations to anchialine environments and that of a swimming lifestyle.

Foredraget er på engelsk! The talk is in English!