Biology subjects

Hook, K. A.

Publications and source records attributed to Hook, K. A..

6 recordsLinked to original sources

bioRxiv2022

Female reproductive fluid composition differs based on mating system in Peromyscus mice

Post-copulatory sexual selection is theorized to favor female traits that allow them to control sperm use and fertilization, leading to the prediction that female reproductive traits that influence sperm migration should differ between polyandrous and monogamous species. Here we exploit natural variation in the female mating strategies of closely related Peromyscus mice to compare female traits that influence sperm motility - the viscosity, pH, and calcium concentration of fluids in the reproductive tract - between polyandrous and monogamous species. We find that the viscosity and pH, but not calcium concentration, of fluids collected from both the uterus and the oviduct significantly differ between species based on mating system. Our results demonstrate the existence of a viscosity gradient within the female reproductive tract that increases in monogamous species but decreases in polyandrous species. Both species have a more alkaline environment in the uterus than oviduct, but only in the polyandrous species did we observe a decrease in calcium in the distal end of the tract. These results suggest that fluid viscosity and pH in the female reproductive tracts of these mice may be influenced by post-copulatory sexual selection and provide a promising potential mechanism for female sperm control given their importance in modulating sperm behavior.

evolutionary biology↗

bioRxiv2020

The social shape of sperm: Using an integrative machine-learning approach to examine sperm ultrastructure and collective motility

Sperm are one of the most morphologically diverse cell types in nature, yet they also exhibit remarkable behavioral variation, including the formation of collective groups of cells that swim together for motility or transport through the female reproductive tract. Here we take advantage of the natural variation in sperm traits observed across Peromyscus mice to test the hypothesis that the morphology of the rodent sperm head influences their sperm aggregation behavior. Using machine learning and traditional morphometric approaches to quantify and analyze their complex shapes, we show that the elongation of the sperm head is the most distinguishing morphological trait in these rodents and, as predicted, significantly associates with collective sperm movements obtained from in vitro observations. We then successfully use neural network analysis to predict the size and proportion of sperm aggregates from sperm head morphology and show that species whose sperm feature relatively wider heads aggregate more often and form larger groups, providing support for the theoretical prediction that an adhesive region around the equatorial region of the sperm head mediates these unique gametic interactions. Together these findings advance our understanding of how even subtle variation in sperm design can drive differences in sperm function and performance. Subject AreasEvolution, Cellular Biology, Behavior

evolutionary biology↗

bioRxiv2020

Collective sperm movements are shaped by post-copulatory sexual selection and phylogenetic history in Peromyscus mice

In some species, sperm form coordinated groups that are hypothesized to improve their swimming performance in competitive contexts or to navigate through the viscous fluids of the female reproductive tract. Here we investigate sperm aggregation across closely-related species of Peromyscus mice that naturally vary by mating system to test the predictions that sperm aggregates (1) are faster than solitary sperm in species that females mate multiply to aid cells in sperm competition, and (2) outperform solitary sperm cells in viscous environments. We find significant variation in the size of sperm aggregates, which negatively associates with relative testis mass, a proxy for sperm competition risk, suggesting that post-copulatory sexual selection has a stabilizing effect on sperm group size. Moreover, our results show that sperm aggregates are faster than solitary sperm in some, but not all, species, and this can vary by fluid viscosity. Of the two species that produce the largest and most frequent groups, we find that sperm aggregates from the promiscuous P. maniculatus are faster than solitary sperm in every experimentally viscous environment but aggregation provides no such kinematic advantage under these same conditions for the monogamous P. polionotus. The reduced performance of P. polionotus aggregates is associated with less efficient aggregate geometry and the inclusion of immotile or morphological abnormal sperm. Our cross-species comparison yields insight into the evolution of sperm social behaviors, provides evidence of extensive variation in the Peromyscus lineage, and reveals that differences in sperm aggregate quality associate with post-copulatory sexual selection.

evolutionary biology↗

bioRxiv2018

No support for the sexy-sperm hypothesis in the seed beetle: sons of monandrous females fare better in post-copulatory competition

The sexy-sperm hypothesis posits that polyandrous females derive an indirect fitness benefit from multi-male mating because they increase the probability their eggs are fertilized by males whose sperm have high fertilizing efficiency, which is assumed to be heritable and conferred on their sons. However, whether this process occurs is contentious because father-to-son heritability may be constrained by the genetic architecture underlying traits important in sperm competition within certain species. Previous empirical work has revealed such genetic constraints in the seed beetle, Callosobruchus maculatus, a model system in sperm competition studies in which female multi-male mating is ubiquitous. Using the seed beetle, I tested a critical prediction of the sexy-sperm hypothesis that polyandrous females produce sons that are on average more successful under sperm competition than sons from monandrous females. Contrary to the prediction of the sexy-sperm hypothesis, I found that sons from monandrous females had significantly higher relative paternity in competitive double matings. Moreover, post-hoc analyses revealed that these sons produced significantly larger ejaculates when second to mate, despite being smaller. This study is the first to provide empirical evidence for post-copulatory processes favoring monandrous sons and discusses potential explanations for the unexpected bias in paternity.

evolutionary biology↗

bioRxiv2018

Sibling rivalry: Males with more brothers develop larger testes

When females mate with multiple partners in a reproductive cycle, the relative number of competing sperm from rival males is often the most critical factor in determining paternity. Gamete production is directly related to testis size in most species, and is associated with both mating behavior within a system and perceived risk of competition. Peromyscus maniculatus is naturally promiscuous and males invest significantly more in sperm production than males of P. polionotus, their monogamous sister-species. Here we show that the relatively larger testes in P. maniculatus are retained, even after decades of enforced monogamy in captivity. While these results suggest that differences in sperm production between species with divergent evolutionary histories can be maintained, we also show that the early rearing environment of males can strongly influence their testis size as adults. Using a second-generation hybrid population to increase variation in testis size, we show that males reared in litters with more brothers develop larger testes as adults. Importantly, this difference in testis size is also associated with increased fertility. Together, our findings suggest that sperm production may be both broadly shaped by natural selection over evolutionary timescales and also finely tuned during early development.

evolutionary biology↗

bioRxiv2018

Cellular geometry controls the efficiency of motile sperm aggregates

Teams of cooperating sperm have been found across several vertebrate and invertebrate species, ranging from sperm pairs to massive aggregates containing hundreds of cells. Although the biochemical mechanisms involved in sperm-sperm adhesion are unclear, aggregation can enhance the motility of the cells. Here, we report a thorough computational investigation on the role of cellular geometry in the performance of sperm aggregates. The sperm head is modeled as a persistent random walker characterized by a non-trivial three-dimensional shape and equipped with an adhesive region where cell-cell binding occurs. By considering both a simple parametric head shape and a computer reconstruction of a real head shape based on morphometric data, we demonstrate that the geometry of the head and the structure of the adhesive region crucially affect both the stability and motility of the aggregates. Our analysis further suggests that the apical hook, commonly found in the sperm of most muroid rodents, might serve to shield portions of the adhesive region and promote efficient alignment of the velocities of the interacting cells.

evolutionary biology↗