Información - Evolutionary Biology - # Sperm-Epithelium Interactions and Sperm Behavior in the Female Reproductive Tract of House Mice

The Sperm Hook in House Mice: Its Role in Sperm Migration and Self-Organized Behavior within the Female Reproductive Tract

Q: How do the structural and mechanical characteristics of the colliculus tubarius (CT) and intramural UTJ lumen evolve in relation to the sperm hook morphology across different murine rodent species?

The structural and mechanical characteristics of the colliculus tubarius (CT) and intramural utero-tubal junction (UTJ) lumen are intricately linked to the morphology of the sperm hook across various murine rodent species. The sperm hook, a distinctive feature of murine spermatozoa, is believed to have evolved as an adaptation to enhance sperm competition and migration efficiency within the female reproductive tract. In species with a more pronounced sperm hook, the CT and UTJ may exhibit narrower luminal spaces and more complex mucosal folds, which can serve to regulate sperm entry and selection. This structural adaptation may facilitate the anchoring of spermatozoa via their hooks, allowing them to navigate through the constricted spaces of the CT while minimizing backward slipping. Conversely, species with less pronounced sperm hooks may have wider luminal spaces, potentially allowing for easier sperm passage but at the cost of reduced control over sperm selection. The evolutionary pressures exerted by sperm competition and cryptic female choice likely drive these morphological variations, as females may benefit from a more selective sperm entry mechanism that can be influenced by the sperm hook's morphology. Thus, the interplay between sperm hook characteristics and the structural features of the CT and UTJ reflects a co-evolutionary dynamic shaped by reproductive strategies and the need for effective sperm competition.

Q: What are the potential fitness costs and benefits for females associated with the ease of sperm passage through the CT, and how does this influence the evolutionary arms race between the sexes?

The ease of sperm passage through the colliculus tubarius (CT) presents both fitness costs and benefits for females, significantly influencing the evolutionary arms race between the sexes. On one hand, a more accessible CT may enhance the likelihood of successful fertilization by allowing a greater number of spermatozoa to enter the intramural UTJ, thereby increasing the chances of encountering viable eggs. This can be particularly advantageous in species with high levels of sperm competition, where multiple males may mate with a single female. However, the fitness costs associated with this ease of passage include the risk of polyspermy, where multiple sperm fertilize a single egg, potentially leading to developmental issues or reduced offspring viability. Additionally, a more open CT may facilitate the entry of sperm from rival males, increasing competition and potentially reducing the reproductive success of the female's preferred mate. This dynamic creates a selective pressure for females to evolve mechanisms that can regulate sperm entry, such as structural adaptations in the CT that can selectively filter sperm based on quality or genetic compatibility. This interplay between the benefits of increased fertilization success and the costs of potential reproductive complications drives the evolutionary arms race between male and female reproductive strategies. Males may evolve traits that enhance sperm motility and competitive ability, such as more pronounced sperm hooks or increased sperm production, while females may develop anatomical features that control sperm passage and selection, thereby influencing the overall reproductive success of both sexes.

Q: Could the self-organized sperm behaviors observed in this study, such as unidirectional clustering and synchronized beating, play a role in sperm competition by obstructing the migration of rival males' spermatozoa within the female reproductive tract?

Yes, the self-organized sperm behaviors observed in this study, including unidirectional clustering and synchronized beating, could significantly influence sperm competition by obstructing the migration of rival males' spermatozoa within the female reproductive tract. These behaviors suggest a form of cooperative strategy among spermatozoa that enhances their collective ability to navigate the complex environment of the female reproductive tract. Unidirectional clustering allows spermatozoa to aggregate, potentially creating a physical barrier that can impede the movement of competing sperm from other males. This clustering behavior may also facilitate synchronized beating, which can generate localized fluid flows that further disrupt the migration of rival sperm. By effectively blocking or redirecting the flow of competing sperm, these self-organized behaviors can enhance the likelihood of successful fertilization by the spermatozoa from the male that the female has mated with. Moreover, the ability of sperm to self-organize and synchronize their movements may reflect an evolutionary adaptation to maximize reproductive success in the face of intense sperm competition. This suggests that the morphology of the sperm hook, which aids in these behaviors, may have evolved not only for efficient migration but also for facilitating cooperative interactions among spermatozoa, thereby enhancing their competitive advantage within the female reproductive tract. Overall, these findings highlight the complex dynamics of sperm competition and the potential for cooperative behaviors to influence reproductive outcomes in murine rodents.

Conceptos Básicos

The sperm hook in house mice plays a crucial role in facilitating sperm migration and interactions with the female reproductive tract epithelium, enabling successful sperm transport and self-organized sperm behaviors.

Resumen

This study investigates the function of the sperm hook in the migration of spermatozoa through the female reproductive tract of the house mouse (Mus musculus) using a custom-built two-photon microscope for live imaging.

Key insights:

The sperm hook acts as a pivot, allowing spermatozoa to alter their travel direction upon reaching the uterine wall. Spermatozoa preferentially orient their hook towards the uterine wall (pro-wall-hook direction), facilitating migration along the wall.
The sperm hook provides an anchor-like function, securing spermatozoa to the epithelium of the uterus and the entrance of the intramural utero-tubal junction (UTJ). This anchoring prevents spermatozoa from being swept away by fluid flow.
Spermatozoa can squeeze through the narrow gaps at the UTJ entrance by using their thin head and hooked structure, aiding their passage into the UTJ.
The authors observed spontaneous unidirectional rearrangement and synchronization of sperm beating along the uterine wall, suggesting the sperm hook may facilitate self-organized sperm behaviors.
In contrast to the "sperm cooperation hypothesis" via sperm train formation, the authors did not find evidence that sperm trains swim faster than unlinked spermatozoa in house mice.
The study proposes that the asymmetrical sperm head shape with the apical hook has evolved to facilitate sperm migration and self-organized behaviors within the female reproductive tract, reconciling the "cooperation" and "migration" hypotheses.

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biorxiv.org

Estadísticas

Spermatozoa located close to the uterine wall moved faster, exhibiting higher curvilinear velocity (VCL) and straight-line velocity (VSL) compared to those further away from the wall.
When spermatozoa swam parallel to the uterine wall, they not only moved faster (higher VCL and VSL) but also followed a straighter path (higher linearity of forward progression, LIN, and straight line-to-sideward movement ratio, SWR).

Citas

"The sperm hook interacted with the wall and acts as a pivot that influences the direction of sperm travel."
"The sperm hook was affixed to the epithelium, thereby securing the spermatozoa on the epithelia. We defined this securing of the spermatozoa on the epithelia by the sperm hook as an anchor-like function of the hook."
"The asymmetrical head shape in the house mouse, therefore, may have evolved not only to facilitate sperm migration but also to facilitate such sperm self-organised behaviours including unidirectional clustering and following beating synchrony."

Ideas clave extraídas de

The sperm hook in house mice: a functional adaptation for migration and self-organised behaviour

by Ryu,H., Nam,... a las www.biorxiv.org 02-21-2024

https://www.biorxiv.org/content/10.1101/2024.02.19.581047v3

Consultas más profundas

How do the structural and mechanical characteristics of the colliculus tubarius (CT) and intramural UTJ lumen evolve in relation to the sperm hook morphology across different murine rodent species?

The structural and mechanical characteristics of the colliculus tubarius (CT) and intramural utero-tubal junction (UTJ) lumen are intricately linked to the morphology of the sperm hook across various murine rodent species. The sperm hook, a distinctive feature of murine spermatozoa, is believed to have evolved as an adaptation to enhance sperm competition and migration efficiency within the female reproductive tract. In species with a more pronounced sperm hook, the CT and UTJ may exhibit narrower luminal spaces and more complex mucosal folds, which can serve to regulate sperm entry and selection. This structural adaptation may facilitate the anchoring of spermatozoa via their hooks, allowing them to navigate through the constricted spaces of the CT while minimizing backward slipping.
Conversely, species with less pronounced sperm hooks may have wider luminal spaces, potentially allowing for easier sperm passage but at the cost of reduced control over sperm selection. The evolutionary pressures exerted by sperm competition and cryptic female choice likely drive these morphological variations, as females may benefit from a more selective sperm entry mechanism that can be influenced by the sperm hook's morphology. Thus, the interplay between sperm hook characteristics and the structural features of the CT and UTJ reflects a co-evolutionary dynamic shaped by reproductive strategies and the need for effective sperm competition.

What are the potential fitness costs and benefits for females associated with the ease of sperm passage through the CT, and how does this influence the evolutionary arms race between the sexes?

The ease of sperm passage through the colliculus tubarius (CT) presents both fitness costs and benefits for females, significantly influencing the evolutionary arms race between the sexes. On one hand, a more accessible CT may enhance the likelihood of successful fertilization by allowing a greater number of spermatozoa to enter the intramural UTJ, thereby increasing the chances of encountering viable eggs. This can be particularly advantageous in species with high levels of sperm competition, where multiple males may mate with a single female.
However, the fitness costs associated with this ease of passage include the risk of polyspermy, where multiple sperm fertilize a single egg, potentially leading to developmental issues or reduced offspring viability. Additionally, a more open CT may facilitate the entry of sperm from rival males, increasing competition and potentially reducing the reproductive success of the female's preferred mate. This dynamic creates a selective pressure for females to evolve mechanisms that can regulate sperm entry, such as structural adaptations in the CT that can selectively filter sperm based on quality or genetic compatibility.
This interplay between the benefits of increased fertilization success and the costs of potential reproductive complications drives the evolutionary arms race between male and female reproductive strategies. Males may evolve traits that enhance sperm motility and competitive ability, such as more pronounced sperm hooks or increased sperm production, while females may develop anatomical features that control sperm passage and selection, thereby influencing the overall reproductive success of both sexes.

Could the self-organized sperm behaviors observed in this study, such as unidirectional clustering and synchronized beating, play a role in sperm competition by obstructing the migration of rival males' spermatozoa within the female reproductive tract?

Yes, the self-organized sperm behaviors observed in this study, including unidirectional clustering and synchronized beating, could significantly influence sperm competition by obstructing the migration of rival males' spermatozoa within the female reproductive tract. These behaviors suggest a form of cooperative strategy among spermatozoa that enhances their collective ability to navigate the complex environment of the female reproductive tract.
Unidirectional clustering allows spermatozoa to aggregate, potentially creating a physical barrier that can impede the movement of competing sperm from other males. This clustering behavior may also facilitate synchronized beating, which can generate localized fluid flows that further disrupt the migration of rival sperm. By effectively blocking or redirecting the flow of competing sperm, these self-organized behaviors can enhance the likelihood of successful fertilization by the spermatozoa from the male that the female has mated with.
Moreover, the ability of sperm to self-organize and synchronize their movements may reflect an evolutionary adaptation to maximize reproductive success in the face of intense sperm competition. This suggests that the morphology of the sperm hook, which aids in these behaviors, may have evolved not only for efficient migration but also for facilitating cooperative interactions among spermatozoa, thereby enhancing their competitive advantage within the female reproductive tract. Overall, these findings highlight the complex dynamics of sperm competition and the potential for cooperative behaviors to influence reproductive outcomes in murine rodents.