Nuestro último artículo, publicado en PLoS ONE

 

The ancient and helical architecture of Elasmobranchii's spermatozoa enables progressive motility in viscous environments

Serhii Boryshpolets, Borys Dzyuba, Pablo García-Salinas, Hermes Bloomfield-Gadêlha, Victor Gallego, Anatoliy Sotnikov, Juan F. Asturiano

Abstract

Subclass Elasmobranchii belongs to an old evolutionary class of Chondrichthyes that diverged 450 mya, presenting a wide diversity of reproductive strategies while preserving the ancient mode of internal fertilization. Despite such evolutionary success, many species in this group are at serious risk of extinction. Understanding the principles of sperm progressive motility and physiology of such an ancient group of vertebrates is essential for developing future assisted reproductive techniques to protect this species and is also critical for our general understanding of reproduction evolution. Elasmobranchii species possess big spermatozoa (compared to bony fishes) with an elongated helical head and tail similar to one currently existing (but later diverged) in birds, reptiles, and amphibians, which can be considered an evolutionary ancient. These structures may be associated with the necessity to penetrate viscous ovarian fluid or the jelly layer of eggs, suggesting environmental viscosity as the driving pressure shaping large-sized sperm heads into helical shapes through evolution. We observed spermatozoa motility with high-speed video microscopy to capture sperm and flagellar motion in three Elasmobranchii species: the freshwater ray Potamotrygon motoro, the marine skate Raja asterias and the shark Scyliorhinus canicula. We investigated the effect of viscosity on spermatozoa motility parameters and its ability to break free from spermatozeugmata, move progressively, and perform directional changes. After 20 min of observation, the spermatozeugmata conserved their structure in a low viscosity medium of 1000 mOsm/kg osmolality. In comparison, no remaining structure of spermatozeugmata could be found in high-viscosity medium 2% methylcellulose (MC) in all three species due to progressive spermatozoa motility. We find that spermatozoa's unique helical head-to-flagellum architecture is specific to promote locomotion in high-viscosity fluid; they cannot move progressively in low viscosity. The highest velocity for shark sperm was observed at 0.75% MC and 1% MC for ray and skate sperm. Viscosity stabilizes the flagellar propagation, producing rotational forces and allowing the helical head to screw into the media. Our observations suggest that the surrounding viscosity is critical to allowing spermatozoa progressive motility and enabling spermatozoa to control direction via head buckling in high viscosity. As such, the viscosity may be a key element controlling and regulating sperm performance during fertilization in the Elasmobranchii species.

PLoS ONE 22(2): e0319354, 2025

doi: 10.1371/journal.pone.0319354

 

Entre mares y océanos: una historia entre ballenas, tortugas y tiburones

El pasado miércoles 12 de febrero, nuestro compañero Victor Gallego impartió una conferencia de carácter divulgativo, organizada por la Universidad Sénior de la UPV, y en la que habló de algunos de los proyectos que se desarrollan en la UPV, entre los que se encuentra el Proyecto ELASMOREP.  La conferencia "Entre mares y océanos: una historia entre ballenas, tortugas y tiburones", a la que asistieron más de 200 personas, versó sobre la vida marina y la importancia de los ecosistemas acuáticos en el planeta. 

A lo largo de los últimos años varios equipos de la UPV han realizado destacadas investigaciones en especies marinas, que engloban desde pequeños tiburones hasta grandes ballenas, intentando estudiar aspectos sobre su biología y ecología. En esta conferencia se abordó el papel crucial estos seres vivos en el ecosistema, viendo aspectos claves de su ciclo vital como las migraciones, o el estatus actual de sus poblaciones. Además, los asistentes tuvieron la oportunidad de ver en directo crías de tiburón y huevos recién eclosionados.

Nuestro último artículo, publicado en Marine Environmental Research

Sex-specific reproductive impairment in Pacific oysters (Magallana gigas) exposed to TiO₂ NPs: a focus on gonadal quality

Fátima Fernández-García, Ana Marques, Soraia Jerónimo, Isabel B. Oliveira, Ana Carvalhais, Vitoria Pereira, Juan F. Asturiano, Mário Pacheco, Cláudia Mieiro

Abstract

Environmentally realistic concentrations of titanium dioxide nanoparticles (TiO₂ NPs) are considered reprotoxic for marine bivalves. However, further investigation is needed to understand their impact on gonadal health, particularly concerning sex-specific responses. Thus, this study aimed to understand sex-based effects of TiO₂ NPs environmentally realistic concentrations in the gonad of Pacific oysters (Magallana gigas). Oysters were exposed to 10 and 100 μg.L^-1 of TiO₂ NPs for 3 and 7 days. Morphological parameters (condition index, sex and gametogenic stage), energy-related responses (carbohydrates, lipids, proteins, and electron transport system (ETS) activity), digestive function (alpha-amylase activity), and oxidative stress profile (antioxidants and damage) were assessed to address gonadal status. The results revealed sex-specific responses based on duration and concentration. Females reflected a drop in carbohydrate levels after 3 days at 100 μg.L^-1, suggesting mobilization of this energy reserve to counteract TiO₂ NP effects, followed by recovery after 7 days. Males showed reduced metabolic activity after 3 days at 10 μg.L^-1, marked by ETS depletion, independently of oxidative stress demonstrating a compensatory response to TiO₂ NP exposure. After 7 days, both concentrations triggered male lipid peroxidation despite carbohydrate mobilization at 10 μg.L^-1, indicating oxidative damage in testes. These findings revealed that TiO₂ NPs are reprotoxic for male oysters at 10 μg.L^-1, through oxidative stress pathways, while females reflected vulnerability to 100 μg.L^-1. This study provides valuable insights into understanding TiO₂ NP's reprotoxicity at environmental concentrations, highlighting gonads as a target for these NPs, and their potential risks to marine bivalves.

doi: 10.1016/j.marenvres.2025.107008

Nuestro último artículo, publicado en Fishes

 

Heat shock factors in the European eel: gene characterization and expression response to different environmental conditions and to induced sexual maturation

Leonor Ferrão, Luz Pérez, Juan F. Asturiano, Marina Morini

Abstract

Heat shock factors (HSF) are transcription factors that regulate responses to environmental changes and play roles in physiological mechanisms like spermatogenesis. This study analyzed the HSF gene family and their expression profiles in the European eel under different environmental conditions and during testis maturation. Six HSF genes were identified in the studied vertebrates, in which the eel presents two HSF1 paralogs (HSF1a and HSF1b), likely resulting from the teleost whole-genome duplication event, while only one paralog is present for the other HSF (HSF2, HSF4 and HSF5). All five HSF genes were highly expressed in the testis, but some were also detected in the brain, intestine, and gills. Our findings showed that HSF1 changed their expression in response to different temperature and salinity conditions, suggesting that these may support males in perceiving the temperature and salinity changes possibly found during reproductive migration. During hCGrec induced spermatogenesis, HSF genes presented a decreasing expression profile throughout testis maturation (with significant differences in HSF1a and HSF4), except HSF5, which showed the highest levels after 4 weeks of hormonal treatment. Our study indicates that HSF genes are potentially implicated in the response to environmental changes perception and during gonadal maturation.

doi: https://doi.org/10.3390/fishes10020073

Nuestro último artículo, publicado en Reviews in Fish Biology and Fisheries

Cryopreservation of pufferfish sperm in small and large volumes: the effect on kinetic parameters, and fertilization and hatching rates

Juan F. Asturiano, Manabu Yoshida, Luz Pérez, Victor Gallego

Abstract

Cryopreservation of fish gametes has many potential applications for ecological, scientific and aquaculture purposes, and cryobank management has been established for many freshwater and marine fish. Nevertheless, there are no studies for the long-term conservation of pufferfish (Takifugu alboplumbeus) sperm, thus the objectives of this work were (i) to develop a new cryopreservation protocol for pufferfish sperm using different sperm:extender ratios and vials; and (ii) to assess the fertilization capacity of cryopreserved sperm. Results showed that cryopreserved sperm samples showed excellent postthawing motility results when they were frozen in straws, reaching values over 60% with both 1:20 and 1:50 sperm:extender dilution ratios. Samples frozen in cryotubes showed slightly lower motility results (around 50%) than those obtained in the straws. Due to the excellent results obtained in the cryopreservation trials, in vitro fertilization trials were undertaken using different sperm:egg ratios with both fresh and cryopreserved sperm. High fertilization (FR) and hatching (HR) rates (over 90%) were reached using high 1:10⁵ and 1:10⁶ ratios. However, when the spermatozoa amount was limited in the fertilization micro-environment (using lower egg:sperm ratios of 1:10³ and 1:10⁴), the cryopreserved sperm generated lower values of FR and HR than the fresh sperm. These results suggest that for achieving high FR and HR, it is essential to use 10 times more cryopreserved sperm than fresh sperm. We then recommend using egg:sperm ratios of 1:10⁴ and 10⁵ (for fresh and cryopreserved sperm, respectively) for "Takifugu" species in order to optimize the amount of gametes collected during aquaculture procedures. This study has laid the basis for the establishment of cryopreservation protocols in pufferfish, that will be helpful for further reproduction in captivity programs and genetic cryobanking.

doi: 10.1007/s11160-024-09912-9