Beyond Cuticular Hydrocarbons: Chemically Mediated Mate Recognition in the Subsocial Burying Beetle Nicrophorus vespilloides.

Burying beetles have fascinated scientists for centuries due to their elaborate form of biparental care that includes the burial and defense of a vertebrate carcass, as well as the subsequent feeding of the larvae. However, besides extensive research on burying beetles, one fundamental question has yet to be answered: what cues do males use to discriminate between the sexes? Here, we show in the burying beetle Nicrophorus vespilloides that cuticular lipids trigger male mating behavior. Previous chemical analyses have revealed sex differences in cuticular hydrocarbon (CHC) composition; however, in the current study, fractionated-guided bioassay showed that cuticular lipids, other than CHCs, elicit copulation. Chemical analyses of the behaviorally active fraction revealed 17 compounds, mainly aldehydes and fatty acid esters, with small quantitative but no qualitative differences between the sexes. Supplementation of males with hexadecanal, the compound contributing most to the statistical separation of the chemical profiles of males and females, did not trigger copulation attempts by males. Therefore, a possible explanation is that the whole profile of polar lipids mediates sex recognition in N. vespilloides.

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.

Size Exclusion High Performance Liquid Chromatography: Re-Discovery of a Rapid and Versatile Method for Clean-Up and Fractionation in Chemical Ecology.

Solvent extraction of bioactive molecules from glands, tissues, or whole organisms is a common first step in chemoecological studies. Co-extraction of a surplus of high boiling materials such as triacylglycerides (TAGs) and other lipids with higher molecular weight might hamper the identification of volatile or medium-volatile semiochemicals by high resolution chromatographic and spectroscopic techniques. Therefore, effective clean-up procedures are needed to separate potential semiochemicals from the accompanying materials. Size exclusion high performance liquid chromatography (SE-HPLC), a technique often disregarded by chemoecologists, has proved to be a rapid and efficient clean-up method for complex crude extracts. We demonstrated that TAGs can be baseline separated from typical semiochemicals within less than 10 min on a porous gel stationary phase based on highly cross-linked polystyrene/divinylbenzene. We applied the method as a rapid one-step clean-up procedure for the analysis of juvenile hormone III in insect hemolymph by gas chromatography-mass spectrometry. We furthermore introduced some recent application examples on insect pheromones to demonstrate that SE-HPLC is not only an effective method for the purification of crude extracts, but can as well be used as a first fractionation step for the bioassay-guided identification of behavior modifying natural products. SE-HPLC can be well operated with low-boiling solvents such as dichloromethane, and results in fraction volumes of typically less than one ml, which decreases the danger of losing volatile analytes during subsequent concentration steps.

Acceptance threshold theory can explain occurrence of homosexual behaviour.

Same-sex sexual behaviour (SSB) has been documented in a wide range of animals, but its evolutionary causes are not well understood. Here, we investigated SSB in the light of Reeve's acceptance threshold theory. When recognition is not error-proof, the acceptance threshold used by males to recognize potential mating partners should be flexibly adjusted to maximize the fitness pay-off between the costs of erroneously accepting males and the benefits of accepting females. By manipulating male burying beetles' search time for females and their reproductive potential, we influenced their perceived costs of making an acceptance or rejection error. As predicted, when the costs of rejecting females increased, males exhibited more permissive discrimination decisions and showed high levels of SSB; when the costs of accepting males increased, males were more restrictive and showed low levels of SSB. Our results support the idea that in animal species, in which the recognition cues of females and males overlap to a certain degree, SSB is a consequence of an adaptive discrimination strategy to avoid the costs of making rejection errors.