Why do sperm carry RNA? Relatedness, conflict, and control

Classically, sperm were seen as transcriptionally inactive vehicles for delivering the paternal haplotype to an egg. Yet, it has become apparent that sperm also carry thousands of different RNAs, and the functions of most of these are unknown. Here, we make four novel suggestions for sperm RNA function. First, they could act as relatedness markers facilitating sperm cooperation. Second, they could act as paternally imposed suppressors of haploid interests. Third, they could act as a nuptial gift, providing the female with resources that entice her to fertilise ova using the sperm of the gift-provider. Fourth, they could represent the contents of a Trojan horse, delivered by males to manipulate female reproduction. We discuss these ideas and suggest how they might be tested

Evolution: escaping the Inevitability of ageing

William Hamilton argued that even species inhabiting the farthest flung corners of the universe should age. However, a recent study shows that to find a species that escapes ageing, you only need to look as far as your local pond

Heritability of three condition surrogates in the yellow dung fly

Condition capture has been proposed as a general mechanism maintaining additive genetic variation, Va, in sexually selected traits under directional selection. It relies on two main assumptions: condition-dependent trait expression and Va in condition. Although there is evidence for the former, direct evidence that condition is heritable is scarce, although this is a requirement of most models of handicap sexual selection. We used a parent-offspring, full-sib, two-container laboratory breeding design in the yellow dung fly Scathophaga stercoraria to demonstrate the broad- and narrow-sense heritability of three surrogates of condition commonly used in sexual selection studies: lipid and glycogen reserves (i.e., physiological condition), body size, and fluctuating asymmetry. All three measures are nutrition dependent and have been linked to sexual selection in free-living yellow dung flies. While lipid reserves and body size were heritable, asymmetry and glycogen reserves were not. Moreover, the evolvability of physiological condition was higher than that of the other two traits. Of the three surrogates, physiological condition is most akin to the original definition, but all have their limitations. We conclude that condition is a useful heuristic concept in evolutionary ecology, but its practical value may be limited by the fact that it cannot be measured directl

Metabolic Physiology of Euthermic and Torpid Lesser Long-Eared Bats, Nyctophilus geoffroyi (Chiroptera: Vespertilionidae)

Thermal and metabolic physiology of the Australian lesser long-eared bat, Nyctophilias geojfroyi, a small (ca. 8 g) gleaning insectivore, was studied using flow-through respirometry. Basal metabolic rate of N. geojfroyi (1.42 ml O2 g−1 h−1) was 70% of that predicted for an 8-g mammal but fell within the range for vespertilionid bats. N. geoffroyi was thermally labile, like other vespertilionid bats from the temperate zone, with clear patterns of euthermy (body temperature >32°C) and torpor. It was torpid at temperatures ≤25°C, and spontaneously aroused from torpor at ambient temperatures ≥5°C. Torpor provided significant savings of energy and water, with substantially reduced rates of oxygen consumption and evaporative water loss. Minimum wet conductance (0.39 ml O2 g−1 h−1 °C−1) of euthermic bats was 108% of predicted, and euthermic dry conductance was 7.2 J g−1 h−1 °C−1 from 5-25°C. Minimum wet and dry conductances of bats that were torpid at an ambient temperature of 15-20°C (0.06 ml O2 g−1 h−1 °C−1 and 0.60 J g−1 h−1 °C−1) were substantially less than euthermic values, but conductance of some torpid bats increased at lower ambient temperatures and approached values for euthermic bats. Metabolic rates of bats torpid at ambient temperatures >10°C and bats euthermic in the thermoneutral zone indicated a metabolic Q10 of 3.9. That high Q10 suggested that there may have been an intrinsic reduction in metabolic rate during torpor, in addition to down-regulation of thermoregulation (which accounted for most of the reduction in metabolic rate) and the normal Q10 effec

Why aren’t signals of female quality more common?

ArticleHighlights In most species females are less ornamented than males. We suggest a novel reason for this pattern. If females signal their sexual quality, they may suffer increased sexual harassment. Ornaments could therefore be especially costly for females.We thank the Editor and the anonymous referees for helpful comments and the Leverhulme Trust, NERC and the Royal Society for funding

Evolution: Lending a Helping Hand in Sperm Competition?

Most females mate with many males. This can be costly, but the benefits to females are often unclear. A new study raises the possibility that females could benefit through an unconventional genetic pathway, while also showing that males can inadvertently increase rival males' fitness in surprising ways

Sexual Selection: Signals to Die for

SummarySexual signals are conspicuous and are typically assumed to be energetically costly, which keeps them honest. A recent study on fireflies has found that signal production is energetically cheap, but signalling remains expensive because of eavesdropping predators

Inbreeding alters intersexual fitness correlations in Drosophila simulans.

PublishedJournal ArticleIntralocus sexual conflict results from sexually antagonistic selection on traits shared by the sexes. This can displace males and females from their respective fitness optima, and negative intersexual correlations (r mf) for fitness are the unequivocal indicator of this evolutionary conflict. It has recently been suggested that intersexual fitness correlations can vary depending on the segregating genetic variation present in a population, and one way to alter genetic variation and test this idea is via inbreeding. Here, we test whether intersexual correlations for fitness vary with inbreeding in Drosophila simulans isolines reared under homogenous conditions. We measured male and female fitness at different times following the establishment of isofemale lines and found that the sign of the association between the two measures varied with time after initial inbreeding. Our results are consistent with suggestions that the type of genetic variation segregating within a population can determine the extent of intralocus sexual conflict and also support the idea that sexually antagonistic alleles segregate for longer in populations than alleles with sexually concordant effects.Foundation for Polish Science (FNP)NER

Artificial selection on walking distance suggests a mobility-sperm competitiveness trade-off

Securing matings is a key determinant of fitness, and in many species, males are the sex that engages in mate searching. Searching for mates is often associated with increased mobility. This elevated investment in movement is predicted to trade-off with sperm competitiveness, but few studies have directly tested whether this trade-off occurs. Here, we assessed whether artificial selection on mobility affected sperm competitiveness and mating behavior, and if increased mobility was due to increased leg length in red flour beetles (Tribolium castaneum). We found that, in general, males selected for decreased mobility copulated for longer, stimulated females more during mating, and tended to be better sperm competitors. Surprisingly, they also had longer legs. However, how well males performed in sperm competition depended on females. Males with reduced mobility always copulated for longer than males with high mobility, but this only translated into greater fertilization success in females from control populations and not the selection populations (i.e. treatment females). These results are consistent with a mate-searching/mating-duration trade-off and broadly support a trade-off between mobility and sperm competitiveness