A map of brain neuropils and fiber systems in the ant Cardiocondyla obscurior

A wide spectrum of occupied ecological niches and spectacular morphological adaptations make social insects a prime object for comparative neuroanatomical studies. Eusocial insects have evolved complex societies based on caste polyphenism. A diverse behavioral repertoire of morphologically distinct castes of the same species requires a high degree of plasticity in the central nervous system. We have analyzed the central brain neuropils and fiber tract systems of the worker of the ant Cardiocondyla obscurior, a model for the study of social traits. Our analysis is based on whole mount preparations of adult brains labeled with an antibody against Drosophila-Synapsin, which cross-reacts strongly with synapses in Cardiocondyla. Neuropil compartments stand out as domains with a certain texture and intensity of the anti-Synapsin signal. By contrast, fiber tracts, which are composed of bundles of axons accompanied by glia and are devoid of synapses, appear as channels or sheaths with low anti-Synapsin signal. We have generated a digital 3D atlas of the Cardiocondyla brain neuropil. The atlas provides a reference for future studies of brain polymorphisms in distinct castes, brain development or localization of neurotransmitter systems

Sex- and caste-specific developmental responses to juvenile hormone in an ant with maternal caste determination

Juvenile hormone is considered to be a master regulator of polyphenism in social insects. In the ant Cardiocondyla obscurior, whether a female egg develops into a queen or a worker is determined maternally and caste-specific differentiation occurs in embryos, so that queens and workers can be distinguished in a non-invasive manner from late embryogenesis onwards. This ant also exhibits two male morphs – winged and wingless males. Here, we used topical treatment with juvenile hormone III and its synthetic analogue methoprene, a method that influences caste determination and differentiation in some ant species, to investigate whether hormone manipulation affects the development and growth of male, queen- and worker-destined embryos and larvae. We found no effect of hormone treatment on female caste ratios or body sizes in any of the treated stages, even though individuals reacted to heightened hormone availability with increased expression of krüppel-homolog 1, a conserved JH first-response gene. In contrast, hormone treatment resulted in the emergence of significantly larger males, although male morph fate was not affected. These results show that in C. obscurior, maternal caste determination leads to irreversible and highly canalized caste-specific development and growth

Behavioural interactions between co‐habiting females and their impact on productivity and offspring sex ratios in the coffee berry borer, Hypothenemus hampei

The coffee berry borer (CBB) Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae) has invaded all coffee-producing regions of the world and causes substantial economic losses every year. A single female beetle typically infests one coffee berry, which her offspring consume over the course of development. Offspring then engage in sib-mating before daughters fly off to infest new berries. We assessed infestation rates across different locations in Jamaica and found a strong positive correlation between double infestation and overall infestation rate, suggesting that females prefer to breed alone but will tolerate sharing a berry under resource constraints. Using an artificial habitat to study productivity and behaviour in the laboratory, we found that single females produced significantly more offspring per capita than two females, suggesting that co-habitation is costly. Accordingly, co-habiting females spent a significant proportion of their time engaged in antagonistic interactive behaviours such as pushing. When daughter beetles were given the opportunity to stay with their mothers or to infest a new berry, they tended to leave. In contrast to some related beetle species, which exhibit gregariousness and even cooperative behaviour, beneficial social interactions in the CBB appear to be limited to parental care

Endosymbionts mediate the effects of antibiotic exposure in the tramp ant Cardiocondyla obscurior

1. Bacterial endosymbionts play a fundamental role in insect ecology. Ants host a large diversity of bacterial symbionts, but comparably little is known about how the loss or reduction of symbionts affects ant fitness. 2. We investigated the effects of the rifampicin, a commonly used antibiotic, on colonies from several populations of the globally distributed tramp ant Cardiocondyla obscurior, which differ in their endosymbiont communities. 3. We found that rifampicin treatment negatively affected queen fecundity and colony productivity, even when there was a delay of 3 months between treatment and productivity assessment. In addition, the viability of sperm from males produced in rifampicin-treated colonies was significantly reduced, pointing towards a trans-generational effect of antibiotics on male ant fitness. As expected, rifampicin treatment also led to a significant decrease in the titres of Candidatus Westeberhardia cardiocondylae and Wolbachia sp., the main bacterial endosymbionts of this ant. 4. The negative effects of antibiotic exposure on ant and symbiont fitness were modulated by the presence and strain of symbiotic bacteria, revealing a complex relationship between the microbiome and ant fitness

First Recorded Mating Flight of the Hypogeic Ant, Acropyga epedana, with its Obligate Mutualist Mealybug, Rhizoecus colombiensis

On 26-July, 2005 a mating aggregation of Acropyga epedana Snelling (Hymenoptera: Formicidae) was observed in the Chiricahua Mountains in south-eastern Arizona. This is the first record of a mating flight of A. epedana, the only nearctic member of this pantropical genus. Mating behavior was observed, newly mated queens were collected, and a complete colony was excavated. New information is reported on the natural history and mating behavior of the species. The identity of a mealybug mutualist, Rhizoecus colombiensis (Homoptera: Rhizoecinae) is confirmed. Reproductive females participating in flights all carried mealybugs between their mandibles, indicating a vertical transfer of mealybugs with their ant hosts. No captured foundresses survived long in captivity, most likely due to the death of their mealybugs. The colony excavated had a single queen, though polygyny is common in the genus. Nearly all workers within the nest were heavily parasitized by mites, although males or gynes were not parasitized. These natural history observations are discussed with regard to this poorly understood mutualistic relationship between Acropyga ants and their mealybug partners

Evolution of Social Insect Polyphenism Facilitated by the Sex Differentiation Cascade

The major transition to eusociality required the evolution of a switch to canalize development into either a reproductive or a helper, the nature of which is currently unknown. Following predictions from the 'theory of facilitated variation', we identify sex differentiation pathways as promising candidates because of their pre-adaptation to regulating development of complex phenotypes. We show that conserved core genes, including the juvenile hormone-sensitive master sex differentiation gene doublesex (dsx) and a kruppel homolog 2 (kr-h2) with putative regulatory function, exhibit both sex and morph-specific expression across life stages in the ant Cardiocondyla obscurior. We hypothesize that genes in the sex differentiation cascade evolved perception of alternative input signals for caste differentiation (i.e. environmental or genetic cues), and that their inherent switch-like and epistatic behavior facilitated signal transfer to downstream targets, thus allowing them to control differential development into morphological castes.Peer reviewe