Biology subjects

Hook, K. A.

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

3 recordsLinked to original sources

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↗