Selfish genes and sexual selection: the impact of genomic parasites on host reproduction

Mating receptivity mediated by endosymbiont interactions in a haplodiploid thrips species

Many arthropods carry maternally inherited endosymbionts that cause cytoplasmic incompatibility (CI), manifested as embryonic mortality in matings of infected males with uninfected females. Infected females, however, do not suffer this cost. Therefore, in populations with mixed endosymbiont infections, selection is expected to favour mechanisms that enable hosts to avoid or mitigate CI. This may include changes in mating behaviour, such as reduced female receptivity to mating and/or remating when approached by incompatible males. Here, we investigated mating behavioural traits in haplodiploid thrips naturally associated with two CI-inducing endosymbionts, Cardinium and Wolbachia. Compared with females with both endosymbionts, those with only Cardinium showed reduced receptivity to males carrying both. However, surprisingly, females without endosymbionts were not less receptive to incompatible males. Furthermore, in contrast to females without endosymbionts, females with Cardinium were far less likely to remate with incompatible than compatible males irrespective of the compatibility type of the first mating. Our results suggest that endosymbiont-specific sexual selection processes occur, whereby females carrying only Cardinium recognize Wolbachia in coinfected males to avoid CI. This may hinder a CI-driven Wolbachia spread. Endosymbiont-mediated mating behaviours may be crucial for the dynamics of CI-inducing endosymbionts and their application in pest management strategies.

Addictive manipulation: a perspective on the role of reproductive parasitism in the evolution of bacteria-eukaryote symbioses

Wolbachia bacteria encompass noteworthy reproductive manipulators of their arthropod hosts. which influence host reproduction to favour their own transmission, also exploiting toxin-antitoxin systems. Recently, multiple other bacterial symbionts of arthropods have been shown to display comparable manipulative capabilities. Here, we wonder whether such phenomena are truly restricted to arthropod hosts. We focused on protists, primary models for evolutionary investigations on eukaryotes due to their diversity and antiquity, but still overall under-investigated. After a thorough re-examination of the literature on bacterial-protist interactions with this question in mind, we conclude that such bacterial 'addictive manipulators' of protists do exist, are probably widespread, and have been overlooked until now as a consequence of the fact that investigations are commonly host-centred, thus ineffective to detect such behaviour. Additionally, we posit that toxin-antitoxin systems are crucial in these phenomena of addictive manipulation of protists, as a result of recurrent evolutionary repurposing. This indicates intriguing functional analogy and molecular homology with plasmid-bacterial interplays. Finally, we remark that multiple addictive manipulators are affiliated with specific bacterial lineages with ancient associations with diverse eukaryotes. This suggests a possible role of addictive manipulation of protists in paving the way to the evolution of bacteria associated with multicellular organisms.

Environmental and Genetic Traffic in the Journey from Sperm to Offspring

Recent advancements in the understanding of how sperm develop into offspring have shown complex interactions between environmental influences and genetic factors. The past decade, marked by a research surge, has not only highlighted the profound impact of paternal contributions on fertility and reproductive outcomes but also revolutionized our comprehension by unveiling how parental factors sculpt traits in successive generations through mechanisms that extend beyond traditional inheritance patterns. Studies have shown that offspring are more susceptible to environmental factors, especially during critical phases of growth. While these factors are broadly detrimental to health, their effects are especially acute during these periods. Moving beyond the immutable nature of the genome, the epigenetic profile of cells emerges as a dynamic architecture. This flexibility renders it susceptible to environmental disruptions. The primary objective of this review is to shed light on the diverse processes through which environmental agents affect male reproductive capacity. Additionally, it explores the consequences of paternal environmental interactions, demonstrating how interactions can reverberate in the offspring. It encompasses direct genetic changes as well as a broad spectrum of epigenetic adaptations. By consolidating current empirically supported research, it offers an exhaustive perspective on the interwoven trajectories of the environment, genetics, and epigenetics in the elaborate transition from sperm to offspring.

Meiotic drive adaptive testes enlargement during early development in the stalk-eyed fly

The sex ratio (SR) X-linked meiotic drive system in stalk-eyed flies destroys Y-bearing sperm. Unlike other SR systems, drive males do not suffer fertility loss. They have greatly enlarged testes which compensate for gamete killing. We predicted that enlarged testes arise from extended development with resources re-allocated from the accessory glands, as these tend to be smaller in drive males. To test this, we tracked the growth of the testes and accessory glands of wild-type and drive males over 5-6 weeks post-eclosion before males attained sexual maturity. Neither of the original predictions is supported by these data. Instead, we found that the drive male testes were enlarged at eclosion, reflecting a greater allocation of resources to the testes during pupation. Testes grow at a higher rate during early adult development in drive males, but there was no evidence that this retards the growth of the accessory glands. Further experiments are proposed to investigate whether smaller accessory glands only arise in drive males post-copulation or when flies are subjected to nutritional stress. Our experimental findings support the idea that enlarged testes in drive males arise as an adaptive allocation of resources to traits that enhance male reproductive success.

Individual Genetic Heterogeneity

Genetic variation has been widely covered in literature, however, not from the perspective of an individual in any species. Here, a synthesis of genetic concepts and variations relevant for individual genetic constitution is provided. All the different levels of genetic information and variation are covered, ranging from whether an organism is unmixed or hybrid, has variations in genome, chromosomes, and more locally in DNA regions, to epigenetic variants or alterations in selfish genetic elements. Genetic constitution and heterogeneity of microbiota are highly relevant for health and wellbeing of an individual. Mutation rates vary widely for variation types, e.g., due to the sequence context. Genetic information guides numerous aspects in organisms. Types of inheritance, whether Mendelian or non-Mendelian, zygosity, sexual reproduction, and sex determination are covered. Functions of DNA and functional effects of variations are introduced, along with mechanism that reduce and modulate functional effects, including TARAR countermeasures and intraindividual genetic conflict. TARAR countermeasures for tolerance, avoidance, repair, attenuation, and resistance are essential for life, integrity of genetic information, and gene expression. The genetic composition, effects of variations, and their expression are considered also in diseases and personalized medicine. The text synthesizes knowledge and insight on individual genetic heterogeneity and organizes and systematizes the central concepts.

The impact of female mating strategies on the success of insect control technologies

Attempts to control insect pests and disease vectors have a long history. Recently, new technology has opened a whole new range of possible methods to suppress or transform natural populations. But it has also become clear that a better understanding of the ecology of targeted populations is needed. One key parameter is mating behaviour. Often modified males are released which need to successfully reproduce with females while competing with wild males. Insect control techniques can be affected by target species' mating ecology, and conversely mating ecology is likely to evolve in response to manipulation attempts. A better understanding of (female) mating behaviour will help anticipate and overcome potential challenges, and thus make desirable outcomes more likely.

Selfish genetic elements and male fertility

Selfish genetic elements (SGEs) are diverse and near ubiquitous in Eukaryotes and can be potent drivers of evolution. Here, we discuss SGEs that specifically act on sperm to gain a transmission advantage to the next generation. The diverse SGEs that affect sperm often impose costs on carrier males, including damaging ejaculates, skewing offspring sex ratios and in particular reducing sperm-competitive success of SGE-carrying males. How males and females tolerate and mitigate against these costs is a dynamic and expanding area of research. The intense intra-genomic conflict that these selfish elements generate could also have implications for male fertility and spermatogenesis more widely. This article is part of the theme issue 'Fifty years of sperm competition'.

Conceptual developments in sperm competition: a very brief synopsis

The past half century has seen the development of the field of post-ejaculatory sexual selection, the sequel to sexual selection for mate-acquisition (pre-ejaculatory) described by Darwin. In richness and diversity of adaptations, post-ejaculatory selection rivals that of pre-ejaculatory sexual selection. Anisogamy-and hence two sexes-likely arose by primeval gamete competition, and sperm competition remains a major force maintaining high sperm numbers. The post-ejaculatory equivalent of male-male competition for matings, sperm competition was an intense ancestral form of sexual selection, typically weakening as mobility and internal fertilization developed in many taxa, when some expenditure became diverted into pre-ejaculatory competition. Sperm competition theory has been relatively successful in explaining variation in relative testes size and sperm numbers per ejaculate and is becoming more successful in explaining variation in sperm phenotype. Sperm competition has generated many other male adaptations such as seminal fluid proteins that variously modify female reproduction towards male interests, and copulatory plugs, prolonged copulations and post-ejaculatory guarding behaviour that reduce female remating probability, many of which result in sexual conflict. This short survey of conceptual developments is intended as a broad overview, mainly as a primer for new researchers. This article is part of the theme issue 'Fifty years of sperm competition'.