Condition-dependent ejaculate production affects male mating behavior in the common bedbug Cimex lectularius

Food availability in the environment is often low and variable, constraining organisms in their resource allocation to different life‐history traits. For example, variation in food availability is likely to induce condition‐dependent investment in reproduction. Further, diet has been shown to affect ejaculate size, composition and quality. How these effects translate into male reproductive success or change male mating behavior is still largely unknown. Here, we concentrated on the effect of meal size on ejaculate production, male reproductive success and mating behavior in the common bedbug Cimex lectularius. We analyzed the production of sperm and seminal fluid within three different feeding regimes in six different populations. Males receiving large meals produced significantly more sperm and seminal fluid than males receiving small meals or no meals at all. While such condition‐dependent ejaculate production did not affect the number of offspring produced after a single mating, food‐restricted males could perform significantly fewer matings than fully fed males. Therefore, in a multiple mating context food‐restricted males paid a fitness cost and might have to adjust their mating strategy according to the ejaculate available to them. Our results indicate that meal size has no direct effect on ejaculate quality, but food availability forces a condition‐dependent mating rate on males. Environmental variation translating into variation in male reproductive traits reveals that natural selection can interact with sexual selection and shape reproductive traits. As males can modulate their ejaculate size depending on the mating situation, future studies are needed to elucidate whether environmental variation affecting the amount of ejaculate available might induce different mating strategies

Balancing life history investment decisions in founding ant queens

Reproduction is a very critical step in the life of an organism. Females must balance their investment in different life-history traits while reproducing. During the process of colony founding in social organisms, such as ants or bees, a trade-off between reproduction and immunity might be very stringent, because queens might be constrained to invest into immune protection of themselves and their developing offspring until the first workers emerge. Here we investigate how different levels of microbial pressure affect colony founding success of Lasius niger ant queens and whether investment into immune defense traits comes at a substantial cost to the queens. In a first experiment mated queens were exposed to four different environments: sterile housing, autoclaved soil, untreated soil and soil containing two opportunistic pathogens. In this experiment, we investigated an immediate cost, i.e., the success of producing the first brood, and a potential delayed cost, i.e., queen survival and colony founding success after hibernation. For the latter, we removed the first brood after hibernation to reveal hidden costs via the application of an additional stressor. We found that irrespective of the microbial environment all queens successfully managed to start a colony, with queens in the soil treatments showing a higher worker production than the queens in the sterile environment. This suggests that either soil components or soil microbes benefit colony growth. After hibernation queens in microbe soil showed significantly lower survival and could not replace a lost brood. In a second experiment, we investigated whether external immune defense in the form of formic acid use can explain part of the costs imposed on queens. We found that queens used formic acid to sanitize their new nest suggesting that queens founding a colony under high microbial pressure are forced to pay a substantial cost by investing in both reproduction and immunity simultaneously. Our results suggest that early, simultaneous investment in reproduction and immunity can allow colony growth under microbial pressure but may be costly in terms of resistance to later challenges. Ant queens may thus be trading off insurance against future challenges for increased pathogen immunity

Female mouthbrooders in control of pre- and postmating sexual selection

The fertilization mode determines which sex has greater control over the offspring's sires. With internal fertilization, females can strongly influence the chances of different males' ejaculates to fertilize their eggs by the postmating sexual selection process referred to as cryptic female choice. In contrast, when fertilization is external and multiple males compete in this process, the outcome of pre- and postmating sexual selection is largely determined by the competitive quality of males and their sperm. Intermediate modes of fertilization as found in mouthbrooding fishes might allow for a greater maternal influence on her offspring's sire. Here, we show that in the maternal mouthbrooder Ophthalmotilapia ventralis, females collect sperm from different males in their mouth, and males can successfully fertilize eggs even if the female did not lay eggs with them. In the field, 25 of 30 clutches had multiple sires, and the fertilization success was significantly biased toward particular males in most clutches. A mate choice experiment revealed that females prefer to spawn with males possessing strongly elongated pelvic fins, a conspicuous secondary sexual character of males in this cichlid. Additionally, the body length of males partly explained their success in sperm competition within the females' mouth, a factor without apparent influence on female choice of partners with which to lay eggs. Hence, successful sires are determined by a 2-step process that is largely under female control; females select which males to spawn with and from which males they collect additional ejaculates for the subsequent sperm competition in their mout

Cichlids do not adjust reproductive skew to the availability of independent breeding options

Helpers in cooperatively breeding species forego all or part of their reproduction when remaining at home and assisting breeders to raise offspring. Different models of reproductive skew generate alternative predictions about the share of reproduction unrelated subordinates will get depending on the degree of ecological constraints. Concession models predict a larger share when independent breeding options are good, whereas restraint and tug-of-war models predict no effects on reproductive skew. We tested these predictions by determining the share of reproduction by unrelated male and female helpers in the Lake Tanganyika cichlid Neolamprologus pulcher depending on experimentally manipulated possibilities for helper dispersal and independent breeding and depending on helper size and sex. We created 32 breeding groups in the laboratory, consisting of two breeders and two helpers each, where only the helpers had access to a nearby dispersal compartment with (treatment) or without (control) breeding substrate, using a repeated measures design. We determined the paternity and maternity of 1185 offspring from 47 broods using five to nine DNA microsatellite loci and found that: (1) helpers participated in reproduction equally across the treatments, (2) large male helpers were significantly more likely to reproduce than small helpers, and (3) male helpers engaged in significantly more reproduction than female helpers. Interestingly, in four broods, extragroup helper males had fertilized part of the brood. No helper evictions from the group after helper reproduction were observed. Our results suggest that tug-of-war models based on competition over reproduction within groups describe best the reproductive skew observed in our study system. Female breeders produced larger clutches in the treatment compared to the control situation when the large helpers were males. This suggests that male breeder-male helper reproductive conflicts may be alleviated by females producing larger clutches with helpers aroun

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation