Mating status regulates post‐mating refractory period in Striacosta albicosta females

In polyandrous insect species, males may transfer substances to reduce sperm competition by affecting female sexual receptivity. In this study, we determined the incidence of polyandry in females of Western bean cutworm (WBC), Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), and investigated the influence of both previous female and male mating history on the duration of mating, the female refractory period, and subsequent calling behavior of females under controlled laboratory conditions. The mating status of WBC males influenced mating duration, with copulations involving previously mated males taking longer, possibly related to the time required to produce an ejaculate. The duration of the female refractory period and the onset time of recalling during the scotophase were both affected by female mating history, but not by that of the males. Females had a shorter refractory period and resumed calling activity earlier after their second and third matings than after their first mating. The earlier onset of calling by previously mated females could reduce competition with virgin females and their shorter refractory period could explain the high incidence of polyandry observed in nature.     

Quantifying inbreeding avoidance through extra-pair reproduction

Extra-pair reproduction is widely hypothesized to allow females to avoid inbreeding with related socially paired males. Consequently, numerous field studies have tested the key predictions that extra-pair offspring are less inbred than females’ alternative within-pair offspring, and that the probability of extra-pair reproduction increases with a female's relatedness to her socially paired male. However, such studies rarely measure inbreeding or relatedness sufficiently precisely to detect subtle effects, or consider biases stemming from failure to observe inbred offspring that die during early development. Analyses of multigenerational song sparrow (Melospiza melodia) pedigree data showed that most females had opportunity to increase or decrease the coefficient of inbreeding of their offspring through extra-pair reproduction with neighboring males. In practice, observed extra-pair offspring had lower inbreeding coefficients than females’ within-pair offspring on average, while the probability of extra-pair reproduction increased substantially with the coefficient of kinship between a female and her socially paired male. However, simulations showed that such effects could simply reflect bias stemming from inbreeding depression in early offspring survival. The null hypothesis that extra-pair reproduction is random with respect to kinship therefore cannot be definitively rejected in song sparrows, and existing general evidence that females avoid inbreeding through extra-pair reproduction requires reevaluation given such biases.     

Sexual rest and post‐meiotic sperm ageing in house mice

Fertilization by aged sperm can result in adverse fitness consequences for both males and females. Sperm storage during male sexual rest could provide an environment for post‐meiotic sperm senescence causing a deterioration in the quality of stored sperm, possibly impacting on both sperm performance (e.g. swimming ability) and DNA quality. Here, we compared the proportion of sperm with fragmented DNA, an indicator of structural damage of DNA within the sperm cell, among males that had been sexually rested for approximately 2 months, to that of males that had mated recently. We found no evidence of intra‐epididymal sperm DNA damage or any impairment in sperm performance, and consequently no evidence of post‐meiotic sperm senescence. Our results suggest that male house mice are likely to possess mechanisms that function to ensure that their sperm reserves remain stocked with ‘young’, viable sperm during periods of sexual inactivity. We also discuss the possibility that our experimental design leads to no difference in the age of sperm among males from the two mating treatments. Post‐meiotic sperm senescence is especially relevant under sperm competition. Thus, we sourced mice from populations that differed in their levels of post‐copulatory sexual selection, enabling us to gain insight into how selection for higher sperm production influences the rate of sperm ageing and levels of DNA fragmentation. We found that males from the population that produced the highest number of sperm also had the smallest proportion of DNA‐fragmented sperm and discuss this outcome in relation to selection acting upon males to ensure that they produce ejaculates with high‐quality sperm that are successful in achieving fertilizations under competitive conditions.     

Environmental variation and population responses to global change

Species' responses to environmental changes such as global warming are affected not only by trends in mean conditions, but also by natural and human‐induced environmental fluctuations. Methods are needed to predict how such environmental variation affects ecological and evolutionary processes, in order to design effective strategies to conserve biodiversity under global change. Here, we review recent theoretical and empirical studies to assess: (1) how populations respond to changes in environmental variance, and (2) how environmental variance affects population responses to changes in mean conditions. Contrary to frequent claims, empirical studies show that increases in environmental variance can increase as well as decrease long‐term population growth rates. Moreover, environmental variance can alter and even reverse the effects of changes in the mean environment, such that even if environmental variance remains constant, omitting it from population models compromises their ability to predict species' responses to changes in mean conditions. Drawing on theory relating these effects of environmental variance to the curvatures of population growth responses to the environment, we outline how species' traits such as phylogenetic history and body mass could be used to predict their responses to global change under future environmental variability.     

Cold truths: how winter drives responses of terrestrial organisms to climate change

Winter is a key driver of individual performance, community composition, and ecological interactions in terrestrial habitats. Although climate change research tends to focus on performance in the growing season, climate change is also modifying winter conditions rapidly. Changes to winter temperatures, the variability of winter conditions, and winter snow cover can interact to induce cold injury, alter energy and water balance, advance or retard phenology, and modify community interactions. Species vary in their susceptibility to these winter drivers, hampering efforts to predict biological responses to climate change. Existing frameworks for predicting the impacts of climate change do not incorporate the complexity of organismal responses to winter. Here, we synthesise organismal responses to winter climate change, and use this synthesis to build a framework to predict exposure and sensitivity to negative impacts. This framework can be used to estimate the vulnerability of species to winter climate change. We describe the importance of relationships between winter conditions and performance during the growing season in determining fitness, and demonstrate how summer and winter processes are linked. Incorporating winter into current models will require concerted effort from theoreticians and empiricists, and the expansion of current growing‐season studies to incorporate winter.     

Engineering of 2-Cys peroxiredoxin for enhanced stress-tolerance

A typical 2-cysteine peroxiredoxin (2-Cys Prx)-like protein (PpPrx) that alternatively acts as a peroxidase or a molecular chaperone in Pseudomonas putida KT2440 was previously characterized. The dual functions of PpPrx are regulated by the existence of an additional Cys(112) between the active Cys(51) and Cys(171) residues. In the present study, additional Cys residues (Cys(31), Cys(112), and Cys(192)) were added to PpPrx variants to improve their enzymatic function. The optimal position of the additional Cys residues for the dual functionality was assessed. The peroxidase activities of the S31C and Y192C mutants were increased 3- to 4-fold compared to the wild-type, while the chaperone activity was maintained at > 66% of PpPrx. To investigate whether optimization of the dual functions could enhance stress-tolerance in vivo, a complementation study was performed. The S31C and Y192C mutants showed a much greater tolerance than other variants under a complex condition of heat and oxidative stresses. The optimized dual functions of PpPrx could be adapted for use in bioengineering systems and industries, such as to develop organisms that are more resistant to extreme environments.     

Sperm competition does not influence sperm hook morphology in selection lines of house mice

Sperm show a remarkable degree of variation in size, shape and complexity. Murine rodents exhibit a sperm head morphology that differs greatly from the ovoid shape that is characteristic of most mammals. These rodents have sperm that bear one or more apical hooks, the function of which is currently surrounded by much controversy. It has been suggested that the hook serves to facilitate the formation of sperm groups, which in some species exhibit relatively faster velocities than single cells and thus, may provide an advantage when ejaculates are competing for fertilisations. In support of this hypothesis, a comparative study reported a positive association between the strength of sperm competition (estimated from testes size) and the curvature of the sperm hook amongst 37 murine species. Here, we assessed whether sperm competition influences sperm hookedness at the intra-specific level. Following 16 generations of selection, we used geometric morphometry (GM) to describe sperm head morphology in selection lines of house mice evolving with (polygamous) and without (monogamous) sperm competition. Although the GM analysis returned two relative warps that described variation in the curvature of the sperm hook, we found no evidence of divergence between the selection lines. Thus, we can conclude that sperm competition does not influence the degree of sperm hookedness in house mice.     

No reversion to single mating in a socially parasitic ant

Social Hymenoptera are ideal biological models for the study of the selective forces affecting the evolution of multiple mating (polyandry), because sister species can evolve different lifestyles and mating strategies. Single mating is predicted in workerless social parasites, because the key benefit of multiple mating in social insects, that is, the increase in genetic diversity among worker offspring, does not hold for workerless species. We compared the queen mating frequency between the ant Plagiolepis pygmaea and its derived social parasite P. xene. Previous studies showed that queens of the host P. pygmaea are obligately polyandrous. Here, pedigree analyses of mother–offspring combinations indicate that queens of the parasite P. xene did not revert to single mating; more than 50% of queens mated multiply, with 2–4 males. This result shows that reversal from multiple to single mating may be not selected in polyandrous social insect workerless parasites. We propose that such reversion does not occur when multiple mating is virtually cost free.     

Allocation of maternal- and ejaculate-derived proteins to reproduction in female crickets, Teleogryllus oceanicus

Female fitness has traditionally been thought to be maximized with one or a few matings. More recent research suggests that polyandry, mating with two or more males, can generate an increase in the viability of offspring females produce. However, the mechanism(s) underlying enhanced offspring viability remain largely unknown. The Australian field cricket Teleogryllus oceanicus has proved a useful model for examining the evolutionary significance of polyandry. Embryo viability appears to be associated with a male's investment in accessory gland tissue, implicating a role for seminal fluid. Here, I used amino acids labelled with different radio isotopes to identify proteins manufactured by males and females before they engaged in reproduction. Males incorporated 95% of the radiolabel into the testes, accessory glands and the ejaculate that was transferred to the female at mating. Male ejaculate compounds were incorporated predominantly into the female's somatic tissue. Relatively more female compounds were incorporated into the ovaries and into laid eggs than ejaculate compounds, and relatively fewer female compounds were sequestered in the somatic tissue than ejaculate compounds. The patterns observed suggest that while ejaculate compounds may be incorporated directly into eggs, they are likely to have a larger effect on maternal allocation to offspring.