Montana, K. O. | Search bioRxiv

bioRxiv2024

Why didnt the nudibranch cross the ocean? Understanding biogeographic and evolutionary relationships of Hermissenda (Nudibranchia: Myrrhinidae) Bergh, 1878

In the aftermath of the 2011 east Japanese earthquake and tsunami, anthropogenic debris from the east coast of Japan floated across the Pacific Ocean to the west coast of North America. One such vessel from Iwate Prefecture arrived on the coast of Oregon, and the fouling community included specimens identified as the nudibranch Hermissenda crassicornis, which was previously thought to range from Japan to Baja California but has since been split into three species: H. crassicornis (Alaska to southern CA), H. opalescens (British Columbia to Baja California), and H. emurai (Japan, Korea, Russian Far East). Previous work suggested that all of the motile invertebrates found in the tsunami debris fouling community were either pelagic or Japanese in origin. Our study sought to determine whether the nudibranch specimens collected from the Iwate vessel were, according to the new classification system, only H. emurai or whether the Eastern Pacific Hermissenda were present as well. Results from DNA sequencing and morphological analysis suggest that specimens of H. crassicornis, as it is currently recognized, and H. opalescens were found on the vessel. This finding indicates either that these species settled after arrival to the west coast of North America or that H. crassicornis and H. opalescens is found in Japan, suggesting Hermissenda ranges need to be investigated further. Occurrence data shared on the iNaturalist platform were also used to assess current ranges. Our phylogenetic tree and haplotype network constructed from COI data from all Hermissenda species indicate that H. opalescens and H. emurai are most closely related with H. opalescens sister to the clade that contains H. opalescens and H. emurai. This study demonstrates the power of combining volunteer naturalist data with lab-collected data to understand evolutionary relationships, species ranges, and biogeography.

zoology↗

bioRxiv2022

Characterizing Potential Tetrodotoxin Resistance in Domain IV of the Voltage-Gated Sodium Channel Nav1.4 of Pacific Chorus Frogs, Pseudacris regilla

Animals that frequently encounter toxins often select for mechanisms of toxin resistance. Both predators that consume toxic prey and organisms in physical contact with a toxin or pollutant in their environment may experience natural selection for resistance. Based on field observations that Pacific Chorus Frogs (Pseudacris regilla) sometimes eat and mistakenly amplect tetrodotoxin (TTX)-defended Taricha newts, we predicted that P. regilla may possess resistance to TTX. We tested this prediction by comparing the amino acid sequences of the molecular target of TTX, the muscle voltage-gated sodium channel gene SCN4A (NaV1.4), in populations of P. regilla that are sympatric and allopatric with Taricha. We identified a single substitution in NaV1.4 of P. regilla in a conserved site near the pore loop where TTX binds. Although the role of this site in TTX resistance has not been functionally assessed, both allopatric and sympatric P. regilla had this substitution, suggesting that it may be unrelated to TTX exposure from Taricha. Thus, there is no conclusive evidence that P. regilla has selected for TTX resistance encoded by amino acid substitutions in this domain. In addition, California occurrence data from the last 50 years indicate that Taricha activity peaks in January while the activity of P. regilla peaks in April. These relatively distinct activity patterns suggest that P. regilla may not be exposed to levels of TTX from Taricha that are high enough to select for mutations in the sodium channel. Nevertheless, other unidentified mechanisms of TTX resistance could be present in P. regilla and other species that are sympatric with toxic newts. ResumenLos animales que tienen contacto frecuente con toxinas suelen desarrollar mecanismos de resistencia a las mismas. Tanto los depredadores que consumen presas toxicas como los organismos en contacto cercano con una toxina o contaminante en su entorno pueden experimentar una presion de seleccion que los lleva a evolucionar resistencia a toxinas. Basandose en las observaciones de que las ranas coro del Pacifico (Pseudacris regilla) a veces comen por error y/o amplexan salamandras del genero Taricha que poseen tetrodotoxina (TTX), se planteo la hipotesis de que P. regilla podria poseer resistencia a la TTX. Esta prediccion fue probada comparando las secuencias de aminoacidos en el loop del poro del dominio IV en el gen del canal de sodio voltaje dependiente muscular SCN4A (proteina NaV1.4) en poblaciones de P. regilla que son simpatricas y alopatricas con Taricha. Se identifico una unica sustitucion en el NaV1.4 de P. regilla en un sitio conservado cerca del loop del poro donde se une la TTX. Aunque el papel de este sitio en la resistencia a la TTX no ha sido evaluado funcionalmente, tanto el P. regilla alopatrico como el simpatrico tienen esta sustitucion, lo que sugiere que no esta relacionado con la exposicion a la TTX secretada por Taricha. Por lo tanto, no hay evidencias concluyentes de que P. regilla haya evolucionado resistencia a la TTX por medio de sustituciones de aminoacidos en este dominio. Por otro lado, los datos de ocurrencia en California de la actividad de Taricha en los ultimos 50 anos indican alcanza su maximo en enero, mientras que la de P. regilla lo hace en abril. Estos patrones de actividad relativamente distintos sugieren que P. regilla puede no estar expuesta a niveles de TTX provenientes de Taricha que sean lo suficientemente altos como para inducir la evolucion de mutaciones en el canal de sodio. Sin embargo, otros mecanismos no identificados de resistencia a la TTX podrian estar presentes en P. regilla y en otras especies simpaticas a los salamandras toxicas. Palabras clave: Resistencia a las toxinas; California; Toxinas ambientales; Insensibilidad en el sitio de union; Salamandras; Ecologia quimica

evolutionary biology↗