When males stop having sex: adaptive insect mating tactics during parental care

Why do males stay in biparental burying beetles?

Biparental associations are rare in most taxa. A second parent should stay with its current brood only to enhance brood fitness or to increase its own future breeding opportunities. I compared the breeding performance of Nicrophorus defodiens pairs and single females while confronting a conspecific male intruder. Pairs fared better than single females in defending a brood, and age had a strong effect on contest outcomes even though defenders and intruders were of the same age. Pairs also produced larger broods than single females, but only on larger carcasses. The results and a review of prior studies suggest that the benefits for a male that stays with a partner during the post-hatch period, whether gains from offspring success or protecting mating opportunities, are observed primarily in the context of intruder pressure, and that paternal care such as regurgitations to young and nest maintenance would not have evolved in a rival-free world.

Sex-specific influence of communal breeding experience on parenting performance and fitness in a burying beetle

Communal breeding, wherein multiple conspecifics live and reproduce together, may generate short-term benefits in terms of defence and reproduction. However, its carry-over effects remain unclear. We experimentally tested the effects of communal breeding on parental care and reproduction in burying beetles (Nicrophorus vespilloides), which use carcasses as breeding resources and provide parental care to offspring. We subjected individuals to communal or non-communal breeding (i.e. pair breeding) during their first breeding event and to non-communal breeding during their second breeding event. We measured the parental care of individuals and of groups and the reproductive success of groups during both breeding events. In communal groups, large individuals became dominant and largely monopolized the carcass, whereas small individuals (i.e. subordinates) had restricted access to the carcass. At the first breeding event, large males in communal groups spent more time providing care than large males in non-communal groups, whereas such an effect was not observed for large females and small individuals. Reproductive successes were similar in communal and non-communal groups, indicating no short-term benefits of communal breeding in terms of reproduction. Compared with males from non-communal groups, males originating from communal groups produced a larger size of brood during their second breeding event, whereas such an effect was not observed for females. Our results demonstrate the sex-specific effects of communal breeding experience on parenting performance and fitness.

Survey of neurotransmitter receptor gene expression into and out of parental care in the burying beetle Nicrophorus vespilloides

Understanding the genetic influences of traits of nonmodel organisms is crucial to understanding how novel traits arise. Do new traits require new genes or are old genes repurposed? How predictable is this process? Here, we examine this question for gene expression influencing parenting behavior in a beetle, Nicrophorus vespilloides. Parental care, produced from many individual behaviors, should be influenced by changes of expression of multiple genes, and one suggestion is that the genes can be predicted based on knowledge of behavior expected to be precursors to parental care, such as aggression, resource defense, and mating on a resource. Thus, testing gene expression during parental care allows us to test expectations of this "precursor hypothesis" for multiple genes and traits. We tested for changes of the expression of serotonin, octopamine/tyramine, and dopamine receptors, as well as one glutamate receptor, predicting that these gene families would be differentially expressed during social interactions with offspring and associated resource defense. We found that serotonin receptors were strongly associated with social and aggression behavioral transitions. Octopamine receptors produced a complex picture of gene expression over a reproductive cycle. Dopamine was not associated with the behavioral transitions sampled here, while the glutamate receptor was most consistent with a behavioral change of resource defense/aggression. Our results generate new hypotheses, refine candidate lists for further studies, and inform the genetic mechanisms that are co-opted during the evolution of parent-offspring interactions, a likely evolutionary path for many lineages that become fully social. The precursor hypothesis, while not perfect, does provide a starting point for identifying candidate genes.

Pheromones Regulating Reproduction in Subsocial Beetles: Insights with References to Eusocial Insects

Beetles have evolved diverse strategies to cope with environmental challenges. Although parents of the vast majority of beetle species do not take care of their offspring, there are some species, in which parents provide elaborate post-hatching care and remain temporarily associated with their offspring to defend them from competitors or to provision them with food. Usually, socially induced reproductive "control" is a core feature of eusocial societies, but here we highlight that already in small family groups, socially induced reproductive regulation can play a fundamental role. By discussing the family life of burying beetles, we illustrate the mechanisms behind such a reproductive "control" and show that - similar to eusocial insects - pheromones can be an important regulating factor. However, apart from burying beetles, our knowledge of pheromones or other signals mediating reproductive regulation is surprisingly rudimentary for social beetles. More data are required to broaden our currently patchy picture.

Pheromones involved in insect parental care and family life

Effective parental care requires recognition and communication processes. Whereas chemical communication has been studied intensively in eusocial organisms, in which the workers (siblings) predominantly provide brood care, insect groups in which parents engage in care have been largely neglected. However, the study of communication in insect families might complement and enhance our understanding not only of the evolution of signaling process involved in social insects, but also of those involved in vertebrate families. In this review, we synthesize the existing information about the pheromones and chemical cues that regulate and affect insect parental care and family life. We will present research dealing with pre-hatching as well as post-hatching parental care and cover interactions between parents and offspring, between male and female parents, and among siblings.

Parental Care: When the Sex Has to Stop

How is sexual conflict during reproduction resolved when parents collaborate to rear offspring? A new study shows that female burying beetles communicate their hormonal status to their male partners to avoid costly superfluous mating, using an anti-aphrodisiac pheromone.

A hormone-related female anti-aphrodisiac signals temporary infertility and causes sexual abstinence to synchronize parental care

The high energetic demand of parental care requires parents to direct their resources towards the support of existing offspring rather than investing into the production of additional young. However, how such a resource flow is channelled appropriately is poorly understood. In this study, we provide the first comprehensive analysis of the physiological mechanisms coordinating parental and mating effort in an insect exhibiting biparental care. We show a hormone-mediated infertility in female burying beetles during the time the current offspring is needy and report that this temporary infertility is communicated via a pheromone to the male partner, where it inhibits copulation. A shared pathway of hormone and pheromone system ensures the reliability of the anti-aphrodisiac. Female infertility and male sexual abstinence provide for the concerted investment of parental resources into the existing developing young. Our study thus contributes to our deeper understanding of the mechanisms underlying adaptive parental decisions.

Parents are faced with the dilemma whether to invest in their current offspring, or potential future young. Here, Engel et al. show that nutritionally-dependent young induce temporary infertility in female burying beetles, which in turn is signalled to the male partner via a hormone-related anti-aphrodisiac.