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.

Mistimed feeding disrupts circadian rhythms of male mating behavior and female preovulatory LH surges in mice

In rodents, eating at atypical circadian times, such as during the biological rest phase when feeding is normally minimal, reduces fertility. Prior findings suggest this fertility impairment is due, at least in part, to reduced mating success. However, the physiological and behavioral mechanisms underlying this reproductive suppression are not known. In the present study, we tested the hypothesis that mistimed feeding-induced infertility is due to a disruption in the normal circadian timing of mating behavior and/or the generation of pre-ovulatory luteinizing hormone (LH) surges (estrogen positive feedback). In the first experiment, male+female mouse pairs, acclimated to be food restricted to either the light (mistimed feeding) or dark (control feeding) phase, were scored for mounting frequency and ejaculations over 96 hours. Male mounting behavior and ejaculations were distributed much more widely across the day in light-fed mice than in dark-fed controls and fewer light-fed males ejaculated. In the second experiment, the timing of the LH surge, a well characterized circadian event driven by estradiol (E2) and the SCN, was analyzed from serial blood samples taken from ovariectomized and E2-primed female mice that were light-, dark-, or ad-lib-fed. LH concentrations peaked 2h after lights-off in both dark-fed and ad-lib control females, as expected, but not in light-fed females. Instead, the normally clustered LH surges were distributed widely with high inter-mouse variability in the light-fed group. These data indicate that mistimed feeding disrupts the temporal control of the neural processes underlying both ovulation and mating behavior, contributing to subfertility.

Experimental evolution under varying sex ratio and nutrient availability modulates male mating success in Drosophila melanogaster

Biased population sex ratios can alter optimal male mating strategies, and allocation to reproductive traits depends on nutrient availability. However, there is little information on how nutrition interacts with sex ratio to influence the evolution of pre-copulatory and post-copulatory traits separately. To address this omission, here we test how male mating success and reproductive investment evolve under varying sex ratios and adult diet in Drosophila melanogaster using an experimental evolution approach. We found that sex ratio and nutrient availability interacted to determine male pre-copulatory performance. Males from female-biased populations were slow to mate when they evolved on a protein-restricted diet. On the other hand, we found direct and non-interacting effects of sex ratio and nutrient availability on post-copulatory success, without interactions between them. Males that evolved on a protein-restricted diet were poor at suppressing female remating. Males that evolved under equal sex ratios fathered more offspring and were better at supressing female remating, relative to males from male-biased or female-biased populations. These results support the idea that sex ratios and nutrition interact to determine the evolution of pre-copulatory mating traits, but independently influence the evolution of post-copulatory traits.

Neuropeptide signalling shapes feeding and reproductive behaviours in male C. elegans

Sexual dimorphism occurs where different sexes of the same species display differences in characteristics not limited to reproduction. For the nematode Caenorhabditis elegans, in which the complete neuroanatomy has been solved for both hermaphrodites and males, sexually dimorphic features have been observed both in terms of the number of neurons and in synaptic connectivity. In addition, male behaviours, such as food-leaving to prioritise searching for mates, have been attributed to neuropeptides released from sex-shared or sex-specific neurons. In this study, we show that the lury-1 neuropeptide gene shows a sexually dimorphic expression pattern; being expressed in pharyngeal neurons in both sexes but displaying additional expression in tail neurons only in the male. We also show that lury-1 mutant animals show sex differences in feeding behaviours, with pharyngeal pumping elevated in hermaphrodites but reduced in males. LURY-1 also modulates male mating efficiency, influencing motor events during contact with a hermaphrodite. Our findings indicate sex-specific roles of this peptide in feeding and reproduction in C. elegans, providing further insight into neuromodulatory control of sexually dimorphic behaviours.

The better, the choosier: a meta-analysis on inter-individual variation of male mate choice

Male mate choice occurs in several animal species, but we know little about the factors that influence the expression of this behaviour. Males vary in their capacity to acquire mates (i.e. male quality), which could be crucial to male mate choice expression but it is often overlooked. Using a meta-analytical approach, we explore inter-individual variation in the expression of male mate choice by comparing the mating investment of males of different qualities and phenotypes to high- and low-quality females. We used two datasets that together contained information from 60 empirical studies, comprising 52 species. We found that males of all qualities and phenotypes prefer high-quality females, but differ in the strength of such preference. High- and medium-quality males are choosier than low-quality males. Similarly, males that are larger or in greater body condition are choosier than their counterparts. In contrast, male body mass and age are not associated with changes in male mate choice. We also show that experimental design may influence our understanding of male mating investment patterns, which may limit the generalization of our findings. Nonetheless, we argue that male quality may be an important feature in the expression of male mate choice.

CRISPR/Cas9 mutagenesis against sex pheromone biosynthesis leads to loss of female attractiveness in Spodoptera exigua, an insect pestt

Virgin female moths are known to release sex pheromones to attract conspecific males. Accurate sex pheromones are required for their chemical communication. Sex pheromones of Spodoptera exigua, a lepidopteran insect, contain unsaturated fatty acid derivatives having a double bond at the 12th carbon position. A desaturase of S. exigua (SexiDES5) was proposed to have dual functions by forming double bonds at the 11th and 12th carbons to synthesize Z9,E12-tetradecedienoic acid, which could be acetylated to be a main sex pheromone component Z9,E12-tetradecenoic acetate (Z9E12-14:Ac). A deletion of SexiDES5 using CRISPR/Cas9 was generated and inbred to obtain homozygotes. Mutant females could not produce Z9E12-14:Ac along with Z9-14:Ac and Z11-14:Ac. Subsequently, pheromone extract of mutant females did not induce a sensory signal in male antennae. They failed to induce male mating behavior including hair pencil erection and orientation. In the field, these mutant females did not attract any males while control females attracted males. These results indicate that SexiDES5 can catalyze the desaturation at the 11th and 12th positions to produce sex pheromone components in S. exigua. This study also suggests an application of the genome editing technology to insect pest control by generating non-attractive female moths.

Blue Cod, Parapercis Colias, Maturity, Fecundity, Sex Change, and Potential Drivers of Sex Ratio in The Marlborough Sounds

<p>Blue cod, Parapercis colias (Pinguipedidae), are widely considered to be the most important recreational finfish species in the South Island. However, blue cod have been declining in abundance in the Marlborough Sounds for many years, and currently, sex ratios are highly male- biased. Blue cod are believed to be a socially structured hermaphroditic species whose populations are prone to local depletion. A potting survey in the Marlborough Sounds was carried out by NIWA in 2013, and along with environmental measurements, 3247 blue cod were measured, weighed, sexed, and stage of sexual maturity was classified macroscopically at sea. Gonads from a subsample of these fish were removed and preserved. In Chapter Two, the preserved gonads were processed histologically and a species-specific histological maturity key was developed. Histological and macroscopic maturity classifications and length-at-maturity estimates were compared. Additionally, estimates of spawning frequency and batch fecundity were made using histological and gravimetric methods. In Chapter Three, possible drivers of sex ratio were investigated using the survey data. Density, large male influence, and environmental factors were considered. In Chapter Four, the feasibility of using digital imaging software to age blue cod otoliths was investigated using the OtolithM application in ImagePro Premier. There was poor agreement between macroscopic and histological maturity classifications (20%, overall). Macroscopic methods overestimated the proportion of mature fish at length in the larger sample, which led to biased length-at-50% maturity (L₅₀) estimates. Macroscopic L₅₀ estimates differed markedly from histology estimates. Using histological data, male L₅₀ was 26 cm TL. Histology indicated that there was no length at which 100% of females were mature. Therefore, a three-parameter capped logistic model was used. Histologically, female L₅₀ was 23.6 cm TL, and the Cap was 0.78, indicating the proportion of mature females reached an asymptote at 0.78. Spawning frequency was 4.6 days, and mean relative batch fecundity was 6.5 hydrated oocytes per gram body weight (SD = 3.3). Hermaphroditism was confirmed for blue cod and was macroscopically identifiable. The analyses in Chapter Three indicated that density had some effect on sex ratio, and large males influenced local sex ratios. Finally, the imaging software could not accurately estimate age compared to an expert reader, and it produced highly variable age estimates. This research found that the macroscopic maturity classifications for blue cod were inaccurate, and revision of the macroscopic key is suggested. The biased estimates of L₅₀ from macroscopic data could lead to biased estimates of spawning stock biomass (SSB). Batch fecundity was markedly lower than the previously reported estimates. The finding of a macroscopically identifiable hermaphroditic stage suggested that ‘hermaphrodite’ should be added as a sex class in the macroscopic key. From the GLM in Chapter Three, in more dense populations, the proportion of males increased. This may have been from changes to male mating strategies, or density may influence the occurrence of primary and secondary males. Finally, areas with males > 45 cm TL had a higher proportion of females, suggesting that large males should be protected in order to help balance sex ratios.</p>

Blue Cod, Parapercis Colias, Maturity, Fecundity, Sex Change, and Potential Drivers of Sex Ratio in The Marlborough Sounds

<p>Blue cod, Parapercis colias (Pinguipedidae), are widely considered to be the most important recreational finfish species in the South Island. However, blue cod have been declining in abundance in the Marlborough Sounds for many years, and currently, sex ratios are highly male- biased. Blue cod are believed to be a socially structured hermaphroditic species whose populations are prone to local depletion. A potting survey in the Marlborough Sounds was carried out by NIWA in 2013, and along with environmental measurements, 3247 blue cod were measured, weighed, sexed, and stage of sexual maturity was classified macroscopically at sea. Gonads from a subsample of these fish were removed and preserved. In Chapter Two, the preserved gonads were processed histologically and a species-specific histological maturity key was developed. Histological and macroscopic maturity classifications and length-at-maturity estimates were compared. Additionally, estimates of spawning frequency and batch fecundity were made using histological and gravimetric methods. In Chapter Three, possible drivers of sex ratio were investigated using the survey data. Density, large male influence, and environmental factors were considered. In Chapter Four, the feasibility of using digital imaging software to age blue cod otoliths was investigated using the OtolithM application in ImagePro Premier. There was poor agreement between macroscopic and histological maturity classifications (20%, overall). Macroscopic methods overestimated the proportion of mature fish at length in the larger sample, which led to biased length-at-50% maturity (L₅₀) estimates. Macroscopic L₅₀ estimates differed markedly from histology estimates. Using histological data, male L₅₀ was 26 cm TL. Histology indicated that there was no length at which 100% of females were mature. Therefore, a three-parameter capped logistic model was used. Histologically, female L₅₀ was 23.6 cm TL, and the Cap was 0.78, indicating the proportion of mature females reached an asymptote at 0.78. Spawning frequency was 4.6 days, and mean relative batch fecundity was 6.5 hydrated oocytes per gram body weight (SD = 3.3). Hermaphroditism was confirmed for blue cod and was macroscopically identifiable. The analyses in Chapter Three indicated that density had some effect on sex ratio, and large males influenced local sex ratios. Finally, the imaging software could not accurately estimate age compared to an expert reader, and it produced highly variable age estimates. This research found that the macroscopic maturity classifications for blue cod were inaccurate, and revision of the macroscopic key is suggested. The biased estimates of L₅₀ from macroscopic data could lead to biased estimates of spawning stock biomass (SSB). Batch fecundity was markedly lower than the previously reported estimates. The finding of a macroscopically identifiable hermaphroditic stage suggested that ‘hermaphrodite’ should be added as a sex class in the macroscopic key. From the GLM in Chapter Three, in more dense populations, the proportion of males increased. This may have been from changes to male mating strategies, or density may influence the occurrence of primary and secondary males. Finally, areas with males > 45 cm TL had a higher proportion of females, suggesting that large males should be protected in order to help balance sex ratios.</p>

Thermal plasticity in behavioural traits mediates mating and reproductive dynamics in an ectotherm

Global changes in temperature potentially influence sexual selection by restricting opportunities for activity. However, explicit tests of the behavioural mechanisms linking thermal variation to mating and reproductive performance are rare. We address this gap in a temperate lizard by combining social network analysis with molecular pedigree reconstruction in a large-scale thermal manipulation experiment. Populations exposed to a more restrictive (cooler) thermal regime presented fewer high activity days compared to populations exposed to a warmer regime. While plasticity in thermal activity responses masked overall differences in activity levels, prolonged restriction nevertheless affected the timing and consistency of male-female interactions. Less active females in the cool thermal regime were significantly less likely to reproduce, which subsequently limited male mating. Surprisingly, this did not correspond to a heightened intensity of sexual selection or shifts in the targets of sexual selection. Thus, populations facing thermal activity restriction may possess limited potential for evolutionary response.