Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male-female coevolution and male-male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insect

Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male-female coevolution and male-male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insect

Within-ejaculate sperm competition

Sperm competition was defined by Geoff Parker 50 years ago as the competition between sperm from two or more males over the fertilization of a set of eggs. Since the publication of his seminal paper, sperm competition has developed into a large field of research, and many aspects are still being discovered. One of the relatively poorly understood aspects is the importance of selection and competition among sperm within the ejaculate of a male. The sheer number of sperm present in a male's ejaculate suggests that the competition among sibling sperm produced by the same male may be intense. In this review, we summarize Parker's theoretical models generating predictions about the evolution of sperm traits under the control of the haploid gamete as opposed to the diploid male. We review the existing evidence of within-ejaculate competition from a wide range of fields and taxa. We also discuss the conceptual and practical hurdles we have been facing to study within-ejaculate sperm competition, and how novel technologies may help in addressing some of the currently open questions. This article is part of the theme issue 'Fifty years of sperm competition'

Developmental and molecular analysis of sperm in Drosophila pseudoobscura

Drosophila pseudoobscura produce three distinct sperm morphs: a long fertilising morph, the eusperm, and short and medium non-fertilising morphs, parasperm 1 and 2. Parasperm protect the eusperm from female-derived spermicides in the female reproductive tract. Drosophila spermatogenesis follows a well-characterised pattern of differentiation, mitosis, meiosis, elongation and individualisation. The majority of transcription of genes whose products are required during meiosis and post-meiosis occurs during the pre-meiotic primary spermatocyte stage. Prior to this work, little was known regarding the specific molecular and developmental processes required for the production of multiple sperm morphs in D. pseudoobscura. I hypothesised that transcriptional variation would be present between sub-sets of primary spermatocyte cysts, which would contribute to development of the sperm morphs. RNA-seq analysis of single spermatocyte cysts showed transcriptional differences between sub-sets of cysts, prior to the onset of meiosis. Over 1000 genes were identified as differentially expressed between primary spermatocyte cysts. RNA-seq analysis of post-meiotic spermatid cysts suggested that transcriptional differences between cyst types are also present during elongation and individualisation, identifying around 1400 genes. Analysis of cyst RNA-seq data, and subsequent validation by in situ hybridisation, revealed differentially expressed genes with potential functions in transcription, spermatogenesis and spermiogenesis, notably components of the testis meiotic arrest complex (tMAC) and the tMAC regulator kumgang (kmg). A Kmg-GFP fusion revealed that the Kmg protein is also differentially expressed in D. pseudoobscura spermatocytes and may contribute to morph differentiation. I have used immunofluorescence to characterise the structure of the hub and apical proliferation centre in D. pseudoobscura testes, and propose an updated model of hub structure in this species. I have also developed D. pseudoobscura lines expressing endogenous cas9, and describe the results of validation experiments. In this work, I have identified genetic components contributing to the development of the multiple sperm morphs in D. pseudoobscura

Study of genetic factors and temperature influence on sex determination and differentiation in turbot

Sex, as intuitive and simple as it may seem to us, poses some of the most interesting and complex questions when studying life. Sex is an intrinsic characteristic of most eukaryote species which eventually has led to the appearance of two differentiated adult phenotypes or sexes, males and females. This distinction rules a huge part of our lives and is the origin of important evolutionary processes based on intra-sex competition or inter-sex conflict due to sexual antagonism. Furthermore, sex is an important character for a plethora of species involved in human activities, for example in aquaculture many fish species present sex size dimorphisms where one sex grows faster than the other, and so knowing how sex is determined in each species is of the outmost interest. Traditionally, sex determination has been considered a cascade process with a master gene at the top, but recent findings have suggested that, instead, it might be a network process where different genetic and environmental factors can alter gonad fate, which in turn would be connected with a huge number of different sex determination mechanisms in vertebrates, especially in poikiloterms. In this new view of sex, the different players involved in sex differentiation gain relevance and their study may help us understanding how the fate of the gonad is determined. In this work, we have studied sex differentiation in turbot, a flatfish with a marked sex dimorphism where females grow faster than males. This species presents genetic sex determination, but also temperature effects on sex ratios have been reported, which seem to be family-dependant. Our aim was to study sex differentiation in turbot to gain knowledge about how sex is determined in this species and also in a broader sense in fish. This work consists of expression studies in turbot gonads using two different techniques: real-time PCR and microarrays. First of all, the real time PCR technique was setup for gonad development studies in turbot. The different methods available for reference gene stability calculation and efficiency determination were assessed. Then, using this information we performed an extensive expression study on turbot sex differentiation ranging from undifferentiated to differentiated gonads at three different temperatures. We found that the first molecular signs of sex differentiation are observed at 90 days post fertilization and that three genes, cyp19a1a, amh and vasa, can be used to sex turbot at this stage. Furthermore, the expression of genes involved in germ cell development pointed towards their involvement in early sex differentiation and possibly sex determination. Temperature effects on sex differentiation were also assessed in this study. A higher proportion of females was obtained at cold temperatures and several genes showed temperature dependant expression changes. Finally, to complete our study, we also performed a microarray analysis in turbot gonad samples from undifferentiated individuals to male and female juveniles. Female gonads were found to be more different from undifferentiated gonads than those of males, requiring the regulation of a large number of genes and the involvement of different processes including epigenetic mechanisms. Furthermore, the involvement of known sex differentiation genes and previously unrelated genes in sex differentiation was observed. This study has widened our knowledge on sex differentiation in turbot in particular and in fish in general, helping to understand the role of many genes involved in sex differentiation across the whole vertebrate taxa and pointing towards other genes which have been connected with sex for the first time. Our data suggest that a network model might be more accurate to explain sex determination in turbot, where the environment can interact with genetic factors and modify gonad fate

Male Reproductive Anatomy

The male reproductive system, which is made up of the testes, scrotum, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral gland, ejaculatory duct, urethra, and penis, functions mainly in the production, nourishment, and temporary storage of spermatozoa. Epigenetic modifications are essential to regulate normal gonadal development and spermatogenesis. The sperm epigenome is highly susceptible influence by a wide spectrum of environmental stimuli. This book focuses on the male reproductive system, discussing topics ranging from aspects of anatomy and risk factors for male infertility to clinical techniques and management of male reproductive health