Odor diversity decreases with inbreeding in the ant Hypoponera opacior

Ant cuticular hydrocarbons are heritable and associated with variation in colony productivity

In social insects, cuticular hydrocarbons function in nest-mate recognition and also provide a waxy barrier against desiccation, but basic evolutionary features, including the heritability of hydrocarbon profiles and how they are shaped by natural selection are largely unknown. We used a new pharaoh ant (Monomorium pharaonis) laboratory mapping population to estimate the heritability of individual cuticular hydrocarbons, genetic correlations between hydrocarbons, and fitness consequences of phenotypic variation in the hydrocarbons. Individual hydrocarbons had low to moderate estimated heritability, indicating that some compounds provide more information about genetic relatedness and can also better respond to natural selection. Strong genetic correlations between compounds are likely to constrain independent evolutionary trajectories, which is expected, given that many hydrocarbons share biosynthetic pathways. Variation in cuticular hydrocarbons was associated with variation in colony productivity, with some hydrocarbons experiencing strong directional selection. Altogether, this study builds on our knowledge of the genetic architecture of the social insect hydrocarbon profile and indicates that hydrocarbon variation is shaped by natural selection.

New method for estimating the post-mortem interval using the chemical composition of different generations of empty puparia: Indoor cases

Most flies of forensic importance are in two superfamilies, the Muscoidea and the Oestroidea, with similar life stages including the puparium. Upon completion of metamorphosis the adult fly emerges from the puparium, leaving behind an exuvia that is of potential significance in forensic investigation. The empty puparium is a durable piece of entomological evidence lasting several years. Through the study of chemical compounds, specifically the hydrocarbons of these puparia, it is possible to identify the species, in addition to how long they have been exposed to weathering and for this reason, these parameters can assist forensic entomologists in estimating long-term postmortem interval (minPMI). In corpses that take a relatively longer time to decompose, insects may use the same corpses for several oviposition cycles. Therefore, the aim of this study was to develop a new method to determine the PMI based on chemical compounds of the puparia from different oviposition cycles of the fly Chrysomya megacephala. The chemical composition of 50 puparia from different cycles of oviposition were evaluated by Gas Chromatography–Mass Spectrometry (GC-MS). In total, 60 compounds were identified ranging from C₁₈ to C₃₄, 38 of those were common to all generations. Our results demonstrate that chemical profiles can be used to differentiate puparia collected from successive cycles, and therefore valuable in the estimation of minPMI.

Lifetime inbreeding depression in a leaf beetle

Ongoing habitat loss and fragmentation result in rapid population size reductions, which can increase the levels of inbreeding. Consequently, many species are threatened by inbreeding depression, a loss of individual fitness following the mating of close relatives. Here, we investigated inbreeding effects on fitness-related traits throughout the lifetime of the mustard leaf beetle (Phaedon cochleariae) and mechanisms for the avoidance of inbreeding. Previously, we found that these beetles have family-specific cuticular hydrocarbon profiles, which are likely not used as recognition cue for precopulatory inbreeding avoidance. Thus, we examined whether adult beetles show postcopulatory inbreeding avoidance instead. For this purpose, we determined the larval hatching rate of eggs laid by females mated sequentially with two nonsiblings, two siblings, a nonsibling, and a sibling or vice versa. The beetles suffered from inbreeding depression throughout their entire ontogeny, as evinced by a prolonged larval development, a decreased larval and adult survival and a decreased reproductive output of inbred compared to outbred individuals. The highest larval hatching rates were detected when females were mated with two nonsiblings or first with a sibling and second with a nonsibling. Significantly lower hatching rates were measured in the treatments with a sibling as second male. Thus, the results do not support the existence of postcopulatory inbreeding avoidance in P. cochleariae, but revealed evidence for second male sperm precedence. Consequently, an alternative strategy to avoid inbreeding costs might exist in this beetle, such as a polyandrous mating system, potentially coupled with a specific dispersal behavior.

Male sex pheromone components in Heliconius butterflies released by the androconia affect female choice

Sex-specific pheromones are known to play an important role in butterfly courtship, and may influence both individual reproductive success and reproductive isolation between species. Extensive ecological, behavioural and genetic studies of Heliconius butterflies have made a substantial contribution to our understanding of speciation. Male pheromones, although long suspected to play an important role, have received relatively little attention in this genus. Here, we combine morphological, chemical and behavioural analyses of male pheromones in the Neotropical butterfly Heliconius melpomene. First, we identify putative androconia that are specialized brush-like scales that lie within the shiny grey region of the male hindwing. We then describe putative male sex pheromone compounds, which are largely confined to the androconial region of the hindwing of mature males, but are absent in immature males and females. Finally, behavioural choice experiments reveal that females of H. melpomene, H. erato and H. timareta strongly discriminate against conspecific males which have their androconial region experimentally blocked. As well as demonstrating the importance of chemical signalling for female mate choice in Heliconius butterflies, the results describe structures involved in release of the pheromone and a list of potential male sex pheromone compounds.