Selection on Sperm Count, but Not on Sperm Morphology or Velocity, in a Wild Population of Anolis Lizards

Oral administration of antimicrobial peptide MPX can effectively regulate LPS-mediated testicular oxidative stress and blood‒testis barrier damage

Oxidative stress and disruption of blood‒testis barrier permeability are considered key factors in the pathogenesis of testicular inflammation, degeneration, and functional impairment, which play crucial roles in male infertility. Antimicrobial peptides (AMPs) are internationally recognized as some of the most promising alternatives to antibiotics. However, the molecular mechanisms by which AMPs regulate oxidative stress and the blood‒testis barrier in the testis are still poorly understood. In this study, we orally administered 0.5 mg/kg antimicrobial peptide MPX (MPX) to mice for 20 and 40 days and evaluated its effects on Lipopolysaccharide LPS-induced testicular oxidative stress and blood‒testis barrier repair, and elucidateed the pharmacokinetics of MPX in mice. The experiment was divided into six groups, control, LPS, MPX, MPX + LPS, Polymyxin and Polymyxin + LPS, respectively. The results showed that oral administration of MPX effectively increased testicular Glutathione (GSH), Total superoxide dismutase (T-SOD), and Catalase (CAT) levels and reduced Nitric oxide (NO) and Malondialdehyde (MDA) levels in the testes and Lactate dehydrogenase (LDH) levels in serum; these findings were consistent with the oxidative stress parameters in the liver. MPX significantly upregulated the expression of Kelch-like ECH-associated protein 1 (Keap1), Nuclear factor erythroid 2-related factor 2 (Nrf2), and Glutamate cysteine ligase, modifier (GLCM) in the testes while downregulating the expression of Glutamate cysteine ligase, catalytic (GCLC) and Inducible nitric oxide synthase (iNOS), thus exerting a regulatory effect on oxidative stress. MPX also effectively increased sperm count and motility and counteracted the LPS-induced blood‒testis barrier damage, and its molecular mechanism involved upregulating the expression of Slug, which subsequently promoted high expression of Claudin, Occludin, Zonula occludens-1 (ZO-1), N-cadherin, and E-cadherin in the testes. After intragastric administration of FITC-MPX for 30 min, FITC-MPX was mainly distributed in the stomach and thoracic cavity, then showed multi-tissue distribution after 30 min. The fluorescence signal could be detected in the testis 1 h later, which confirmed that MPX had testicular targeting. Moreover, both intraperitoneal and intravenous injection of FITC-MPX also confirmed its testicular targeting ability. In conclusion, this study systematically evaluated the long-term effects of the orally administered antimicrobial peptide MPX on oxidative stress and the blood‒testis barrier in the male reproductive system. This study laid the foundation for the antimicrobial peptide MPX to be used in the treatment of male testicular inflammatory diseases.

Sperm competition favours intermediate sperm size in a hermaphrodite1

Sperm competition is a potent mechanism of postcopulatory sexual selection that has been found to shape reproductive morphologies and behaviours in promiscuous animals. Especially sperm size has been argued to evolve in response to sperm competition through its effect on sperm longevity, sperm motility, the ability to displace competing sperm, and ultimately fertilization success. Additionally, sperm size has been observed to co-evolve with female reproductive morphology. Theoretical work predicts that sperm competition may select for longer sperm but may also favour shorter sperm if sperm size trades-off with number. In this study, we studied the relationship between sperm size and postmating success in the free-living flatworm, Macrostomum lignano. Specifically, we used inbred isolines of M. lignano that varied in sperm size to investigate how sperm size translated into the ability of worms to transfer and deposit sperm in a mating partner. Our results revealed a hump-shaped relationship with individuals producing sperm of intermediate size having the highest sperm competitiveness. This finding broadens our understanding of the evolution of sperm morphology by providing empirical support for stabilizing selection on sperm size under sperm competition.

Sperm morphology and forward motility are indicators of reproductive success and are not age- or condition-dependent in a captive breeding population of endangered snake

The relationship between male ejaculate traits and reproductive success is an important consideration for captive breeding programs. A recovery plan for the endangered Louisiana pinesnake includes captive breeding for the release of young to the wild. Semen was collected from twenty captive breeding male snakes and ejaculate traits of motility, morphology, and membrane viability were measured for each male. Semen traits were analyzed in relation to the fertilization rate of eggs produced from pairings of each male with a single female (% fertility) to determine the ejaculate factors contributing to reproductive success. In addition, we investigated the age- and condition-dependence of each ejaculate trait. We found significant variation in the ejaculate traits of males and normal sperm morphology ([Formula: see text] = 44.4 ± 13.6%, n = 19) and forward motility ([Formula: see text] = 61.0 ± 13.4%, n = 18) were found to be the best predictors of fertility. No ejaculate traits were found to be condition-dependent (P > 0.05). Forward progressive movement (FPM) ([Formula: see text] = 4 ± 0.5, n = 18) was determined to be age-dependent (r2 = 0.27, P = 0.028), but FPM was not included in the best model for rate of fertilization. Male Louisiana pinesnakes do not appear to experience a significant decline in reproductive potential with age (P > 0.05). The observed average rate of fertilization in the captive breeding colony was below 50% and only those pairings with a male having >51% normal sperm morphology avoided a 0% rate of fertilization. Identification of the factors contributing to the reproductive success of captive breeding Louisiana pinesnakes is of considerable conservation value in the recovery of the species, and captive breeding programs should use assessments of ejaculate traits to plan breeding pairs for maximum reproductive output.

On the Origin and Evolution of Sperm Cells

Sperm cells have intrigued biologists since they were first observed nearly 350 years ago by Antonie van Leeuwenhoek and Johan Ham [...].

Nesting in Anolis Lizards: An Understudied Topic in a Well-Studied Clade

Maternal nesting behavior in oviparous species strongly influences the environmental conditions their embryos experience during development. In turn, these early-life conditions have consequences for offspring phenotypes and many fitness components across an individual’s lifespan. Thus, identifying the evolutionary and ecological causes and effects of nesting behavior is a key goal of behavioral ecology. Studies of reptiles have contributed greatly to our understanding of how nesting behavior shapes offspring phenotypes. While some taxonomic groups have been used extensively to provide insights into this important area of biology, many groups remain poorly studied. For example, the squamate genus Anolis has served as a model to study behavior, ecology, and evolution, but research focused on Anolis nesting behavior and developmental plasticity is comparatively scarce. This dearth of empirical research may be attributed to logistical challenges (e.g., difficulty locating nests), biological factors (e.g., their single-egg clutches may hinder some experimental designs), and a historical focus on males in Anolis research. Although there is a gap in the literature concerning Anolis nesting behavior, interest in nesting ecology and developmental plasticity in this group has grown in recent years. In this paper, we (1) review existing studies of anole nesting ecology and developmental plasticity; (2) highlight areas of anole nesting ecology that are currently understudied and discuss how research in these areas can contribute to broader topics (e.g., maternal effects and global change biology); and (3) provide guidelines for studying anole nesting in the field. Overall, this review provides a foundation for establishing anoles as models to study nesting ecology and developmental plasticity.

Sperm Numbers as a Paternity Guard in a Wild Bird

Sperm competition is thought to impose strong selection on males to produce competitive ejaculates to outcompete rival males under competitive mating conditions. Our understanding of how different sperm traits influence fertilization success, however, remains limited, especially in wild populations. Recent literature highlights the importance of incorporating multiple ejaculate traits and pre-copulatory sexually selected traits in analyses aimed at understanding how selection acts on sperm traits. However, variation in a male’s ability to gain fertilization success may also depend upon a range of social and ecological factors that determine the opportunity for mating events both within and outside of the social pair-bond. Here, we test for an effect of sperm quantity and sperm size on male reproductive success in the red-back fairy-wren (Malurus melanocephalus) while simultaneously accounting for pre-copulatory sexual selection and potential socio-ecological correlates of male mating success. We found that sperm number (i.e., cloacal protuberance volume), but not sperm morphology, was associated with reproductive success in male red-backed fairy-wrens. Most notably, males with large numbers of sperm available for copulation achieved greater within-pair paternity success. Our results suggest that males use large sperm numbers as a defensive strategy to guard within-pair paternity success in a system where there is a high risk of sperm competition and female control of copulation. Finally, our work highlights the importance of accounting for socio-ecological factors that may influence male mating opportunities when examining the role of sperm traits in determining male reproductive success.