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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 around.

1. Nosema bombi is a microsporidian parasite of bumblebees that is of potentially great ecological and economic importance. Nosema bombi has been shown to have detrimental fitness effects on the bumblebee Bombus terrestris under laboratory conditions. The present study investigates whether N. bombi also has negative fitness effects under natural conditions. 2. A field experiment was conducted with B. terrestris spring queens caught from the wild. In the laboratory these queens were assigned to either infected or control treatment groups. On the emergence of workers, colonies were placed in the field and a number of fitness and life-history traits were measured.3. The size of colonies produced by infected queens was significantly smaller than those of control queens. None of the 14 infected colonies produced sexual offspring, whereas four of the 14 control colonies reached the male production stage. Results of the field experiment are in agreement with prior laboratory-based results, and even imply that such effects are amplified under natural conditions. 4. The evidence suggests that, on entering the colony early, N. bombi has a highly detrimental effect on the fitness of its host. It would seem that this parasite reduces its opportunities to transmit into the next host generation.

The rapid evolution of ejaculate components is considered to be largely driven by sexual selection. Less attention has been paid to the fact that sperm and microorganisms frequently meet; we consequently predict selection for substances that protect a male's ejaculate. We report, for the first time, bacteriolytic activity (lysozyme-like immune activity [LLA]) in the ejaculate of an animal, the common bedbug Cimex lectularius. We also show that in almost half the males LLA in the seminal fluid exceeded LLA in the hemolymph. We detected no antimicrobial peptide activity in seminal fluid. Because lysozymes degrade only bacteria, our results suggest that sperm-microbe interactions are probably important in the evolution of ejaculate components and thereby provide a route for natural selection to account for some of the diversity of seminal components.

Summary1. Ejaculate substances are hugely diverse among and within species. The functional significance of this diversity has been little studied except for a few accessory gland proteins. These studies suggest that ejaculate components evolve mainly by sexual selection, that is, sperm competition, male-female co-evolution or by female choice for paternal investment. However, male benefits of protecting sperm from microbial harm, that is, antimicrobial ejaculate protection, has received little attention in the evolutionary literature, while it has been discussed in the human and livestock literature. 2. Here, we examine in the common bedbug, Cimex lectularius, the two basic components of the antimicrobial ejaculate protection hypothesis: 1) microbes damage sperm cells and 2) antimicrobial ejaculate substances prevent such microbe-induced sperm damage. We found that environmental microbes, which are sexually transmitted in bedbugs, induce sperm mortality. Sperm mortality was high (increased 40% compared with controls without bacteria) and very rapid (within 10 min) in vitro. Consistent with the antimicrobial sperm protection hypothesis, a lysozyme dose equivalent to the amount of antibacterial lysozyme-like activity that is transferred in the seminal fluid during a single mating was sufficient to reduce sperm mortality to control levels. 3. While this result is not necessarily predicted by the paternal investment hypothesis, it is plausible that female benefits of male immune substances may evolve under the male-female co-evolution hypothesis. We found that weekly physiological lysozyme doses equivalent to the observed lysozyme-like activity in seminal fluid benefit females to some extent, indicating that immune-active ejaculate substances may have a secondary gift function and may release females from a trade-off between reproduction and immunity. Lysozyme seems to stimulate early egg-laying above the female optimum and later cause earlier reproductive senescence, which is not consistent with the idea of an overall direct benefit but is consistent with the idea that males transfer manipulative substances to the females. 4. Our data are consistent with antimicrobial sperm protection. They support the idea of a naturally selected origin of ejaculate components and provide a mechanistically well-defined pathway how sexual selection can affect ejaculate composition via antimicrobial sperm protection. As sperm and microbes frequently encounter each other in many species, antimicrobial sperm protection may be a common phenomenon and has the potential to inform models of male and female co-evolution and biological diversification.

Many insect species, including social insects, are currently declining in abundance and diversity. Pollutants such as pesticides, heavy metals, or airborne fine particulate matter from agricultural and industrial sources are among the factors driving this decline. While these pollutants can have direct detrimental effects, they can also result in negative interactive effects when social insects are simultaneously exposed to multiple stressors. For example, sublethal effects of pollutants can increase the disease susceptibility of social insects, and thereby jeopardize their survival. Here we review how pesticides, heavy metals, or airborne fine particulate matter interact with social insect physiology and especially the insects’ immune system. We then give an overview of the current knowledge of the interactive effects of these pollutants with pathogens or parasites. While the effects of pesticide exposure on social insects and their interactions with pathogens have been relatively well studied, the effects of other pollutants, such as heavy metals in soil or fine particulate matter from combustion, vehicular transport, agriculture, and coal mining are still largely unknown. We therefore provide an overview of urgently needed knowledge in order to mitigate the decline of social insects.

1. Microbes associated with reproductive organs of animals are either sexually transmitted or opportunistic. Both can affect host defence, immunity, and future colonisation with other microbes. There are only few studies on the microbiota of reproductive organs in insects and how they are affected by copulation.2. This study examines the bacterial communities associated with reproductive organs in the common bedbug Cimex lectularius, a well‐established insect model for the effects of microbes on male and female reproduction. Combining a metagenomic approach with a controlled mating scheme, we found 31 sequence variants (SVs) across 55 organ samples, with on average three SVs in each sample. Male and female reproductive organs harboured distinct bacterial communities in terms of present SVs.3. Using a community ecology approach, we found three potential indications of sexual transmission of bacteria in the common bedbug: (i) copulation increased the similarity of the communities of male and female organs; (ii) mated individuals harboured bacteria that were found in non‐mated individuals of the opposite sex but not in non‐mated individuals of the same sex; and (iii) bacterial communities showed a high SV turnover between non‐mated and mated individuals, suggesting a mating‐induced replacement of bacteria.4. Our findings show that the community ecology approach is useful to examine the bacterial dynamics on reproductive organs, especially when combined with studies that quantify the frequency of transmission and/or estimate the effect of the transmitted microbes on the host immune system and the host endosymbionts.