Mitochondria,maternal inheritance,and asymmetric fitness: Why males die younger

Mitochondrial function is achieved through the cooperative interaction of two genomes: one nuclear (nuDNA) and the other mitochondrial (mtDNA). The unusual transmission of mtDNA, predominantly maternal without recombination is predicted to affect the fitness of male offspring. Recent research suggests the strong sexual dimorphism in aging is one such fitness consequence. The uniparental inheritance of mtDNA results in a selection asymmetry; mutations that affect only males will not respond to natural selection, imposing a male‐specific mitochondrial mutation load. Prior work has implicated this male‐specific mutation load in disease and infertility, but new data from fruit flies suggests a prominent role for mtDNA in aging; across many taxa males almost invariably live shorter lives than females. Here we discuss this new work and identify some areas of future research that might now be encouraged to explore what may be the underpinning cause of the strong sexual dimorphism in aging. Editor's suggested further reading in BioEssays: Mitonuclear match: Optimizing fitness and fertility over generations drives ageing within generations Abstract Mitochondrial manoeuvres: Latest insights and hypotheses on mitochondrial partitioning during mitosis in Saccharomyces cerevisiae Abstract Mitochondria and the culture of the Borg Abstract     

Delineating the roles of males and females in sperm competition

Disentangling the relative roles of males, females and their interactive effects on competitive fertilization success remains a challenge in sperm competition. In this study, we apply a novel experimental framework to an ideally suited externally fertilizing model system in order to delineate these roles. We focus on the chinook salmon, Oncorhynchus tshawytscha, a species in which ovarian fluid (OF) has been implicated as a potential arbiter of cryptic female choice for genetically compatible mates. We evaluated this predicted sexually selected function of OF using a series of factorial competitive fertilization trials. Our design involved a series of 10 factorial crosses, each involving two ‘focal’ rival males whose sperm competed against those from a single ‘standardized’ (non-focal) rival for a genetically uniform set of eggs in the presence of OF from two focal females. This design enabled us to attribute variation in competitive fertilization success among focal males, females (OF) and their interacting effects, while controlling for variation attributable to differences in the sperm competitive ability of rival males, and male-by-female genotypic interactions. Using this experimental framework, we found that variation in sperm competitiveness could be attributed exclusively to differences in the sperm competitive ability of focal males, a conclusion supported by subsequent analyses revealing that variation in sperm swimming velocity predicts paternity success. Together, these findings provide evidence that variation in paternity success can be attributed to intrinsic differences in the sperm competitive ability of rival males, and reveal that sperm swimming velocity is a key target of sexual selection.     

Assessing the utility of marine filter feeders for environmental DNA (eDNA) biodiversity monitoring

Aquatic environmental DNA (eDNA) surveys are transforming how marine ecosystems are monitored. The time-consuming preprocessing step of active filtration, however, remains a bottleneck. Hence, new approaches that eliminate the need for active filtration are required. Filter-feeding invertebrates have been proven to collect eDNA, but side-by-side comparative studies to investigate the similarity between aquatic and filter-feeder eDNA signals are essential. Here, we investigated the differences among four eDNA sources (water; bivalve gill-tissue; sponges; and ethanol in which filter-feeding organisms were stored) along a vertically stratified transect in Doubtful Sound, New Zealand using three metabarcoding primer sets targeting fish and vertebrates. Combined, eDNA sources detected 59 vertebrates, while concurrent diver surveys observed eight fish species. There were no significant differences in alpha and beta diversity between water and sponge eDNA and both sources were highly correlated. Vertebrate eDNA was successfully extracted from the ethanol in which sponges were stored, although a reduced number of species were detected. Bivalve gill-tissue dissections, on the other hand, failed to reliably detect eDNA. Overall, our results show that vertebrate eDNA signals obtained from water samples and marine sponges are highly concordant. The strong similarity in eDNA signals demonstrates the potential of marine sponges as an additional tool for eDNA-based marine biodiversity surveys, by enabling the incorporation of larger sample numbers in eDNA surveys, reducing plastic waste, simplifying sample collection, and as a cost-efficient alternative. However, we note the importance to not detrimentally impact marine communities by, for example, nonlethal subsampling, specimen cloning, or using bycatch specimens.