How to escape from the host nest: imperfect chemical mimicry in eucharitid parasitoids and exploitation of the ants' hygienic behavior

Effects of genotype and host environment on the cuticular hydrocarbon profiles of Lysiphlebus parasitoids and aggression by aphid-tending ants

Parasitoids in the genus Lysiphlebus specialize on ant-tended aphids and have previously been reported to mimic the cuticular hydrocarbon (CHC) profiles of their aphid hosts to avoid detection by ants. However, the precise mechanisms that mediate reduced ant aggression toward Lysiphlebus spp. are not known, nor is it clear whether such mechanisms are broadly effective or specialized on particular aphid hosts. Here we explore the effects of wasp genotype and host environment on Lysiphlebus CHC profiles and ant aggression. Rearing asexual Lysiphlebus lines in different host aphid environments revealed effects of both wasp line and aphid host on wasp CHCs. However, variation in genotype and host affected different features of the CHC profile, with wasp genotype explaining most variation in linear and long-chain methyl alkanes, while aphid host environment primarily influenced short-chain methyl alkanes. Subsequent behavioural experiments revealed no effects of host environment on ant aggression, but strong evidence for genotypic effects. The influence of genotypic variation on experienced ant aggression and relevant chemical traits is particularly relevant in light of recent evidence for genetic divergence among Lysiphlebus parasitoids collected from different aphid hosts.

Chemical and behavioural strategies along the spectrum of host specificity in ant-associated silverfish

Background

Host range is a fundamental trait to understand the ecological and evolutionary dynamics of symbionts. Increasing host specificity is expected to be accompanied with specialization in different symbiont traits. We tested this specificity-specialization association in a large group of 16 ant-associated silverfish species by linking their level of host specificity to their degree of behavioural integration into the colony and to their accuracy of chemically imitating the host’s recognition system, i.e. the cuticular hydrocarbon (CHC) profile.

Results

As expected, facultative associates and host generalists (targeting multiple unrelated ants) tend to avoid the host, whereas host-specialists (typically restricted to Messor ants) were bolder, approached the host and allowed inspection. Generalists and host specialists regularly followed a host worker, unlike the other silverfish. Host aggression was extremely high toward non-ant-associated silverfish and modest to low in ant-associated groups. Surprisingly, the degree of chemical deception was not linked to host specificity as most silverfish, including facultative ant associates, imitated the host’s CHC profile. Messor specialists retained the same CHC profile as the host after moulting, in contrast to a host generalist, suggesting an active production of the cues (chemical mimicry). Host generalist and facultative associates flexibly copied the highly different CHC profiles of alternative host species, pointing at passive acquisition (chemical camouflage) of the host’s odour.

Conclusions

Overall, we found that behaviour that seems to facilitate the integration in the host colony was more pronounced in host specialist silverfish. Chemical deception, however, was employed by all ant-associated species, irrespective of their degree of host specificity.

Co-occurrence in ant primary parasitoids: a Camponotus rectangularis colony as host of two eucharitid wasp genera

Different assemblages of parasitoids may attack a given host species and non-random distribution patterns in parasitoid species assemblages have been reported on various occasions, resulting in co-occurrence at the population, colony, or even individual host levels. This is the case for different closely related species of eucharitid wasps (a family of specialized ant parasitoids) sharing similar niches and co-occurring on the same host at different levels. Here we reviewed all known associations between eucharitid wasps and the ant host genus Camponotus Mayr, 1861 and reported new ant-parasitoid associations. In addition, we report a new case of co-occurrence in eucharitid wasps, at the host colony level, involving a new undescribed species of Pseudochalcura Ashmead, 1904 and an unidentified species of Obeza Heraty, 1985, which attack the common but very poorly known neotropical arboreal ant Camponotus rectangularis Emery, 1890. Most attacks were solitary, but various cocoons were parasitized by two (16%) or three (8%) parasitoids. Globally, parasitism prevalence was very low (3.7%) but showed an important variability among samples. Low parasitism prevalence along with host exposure to parasitoid attack on host plants and overlapping reproductive periods of both parasitoid species may have allowed the evolution of co-occurrence. We also provided some additional data regarding the host ant nesting habits, the colony composition and new symbiotic associations with membracids and pseudococcids. The seemingly polydomous nesting habits of C. rectangularis could play a part in the reduction of parasitism pressure at the population level and, combined with occasionally important local parasitism rates, could also contribute to some parts of the colonies escaping from parasites, polydomy possibly representing an effective parasitism avoidance trait.

Context dependent life-history shift in Macrodinychus sellnicki mites attacking a native ant host in Colombia

Ant parasitoidism has been reported in seven of the 26 recognized species of the mite genus Macrodinychus (Machrodynichidae). Macrodynichus sellnicki, previously reported as a parasitoid of the invasive ant Nylanderia fulva in Colombia, is now reported, in the same region, as attacking a native host, Ectatomma sp. 2 (E. ruidum complex). The mite develops within the protective silk cocoon of an Ectatomma pupa and waits for the emergence of the young ant before leaving the cocoon, unmolested. Overall nest prevalence was relatively high (34.6% of the 52 nests containing cocoons) but pupae prevalence was low (4.0%, n = 1401 cocoons). Mite life-history (parasite or parasitoid) was context dependent, shifting according to the intensity of the attack on a same host. Contrary to the strictly parasitoidic association of M. sellnicki with N. fulva, single mite attacks against E. ruidum did not result in host killing and solitary M. sellnicki (78.6% of the cases) behaved as parasites. However, in 21.4% of the attacks (0.9% of all available host pupae) more than one mite was involved and behaved as parasitoids, draining the host of its internal fluids and killing it. This is the first association of a macrodinychid mite with a species of the subfamily Ectatomminae, and the first ant associated mite for which such a context dependent life-style shift is described.

Fine-tuned intruder discrimination favors ant parasitoidism

A diversity of arthropods (myrmecophiles) thrives within ant nests, many of them unmolested though some, such as the specialized Eucharitidae parasitoids, may cause direct damage to their hosts. Ants are known to discriminate between nestmates and non-nestmates, but whether they recognize the strength of a threat and their capacity to adjust their behavior accordingly have not been fully explored. We aimed to determine whether Ectatomma tuberculatum ants exhibited specific behavioral responses to potential or actual intruders posing different threats to the host colony and to contribute to an understanding of complex ant-eucharitid interactions. Behavioral responses differed significantly according to intruder type. Ants evicted intruders that represented a threat to the colony's health (dead ants) or were not suitable as prey items (filter paper, eucharitid parasitoid wasps, non myrmecophilous adult weevils), but killed potential prey (weevil larvae, termites). The timing of detection was in accordance with the nature and size of the intruder: corpses (a potential source of contamination) were detected faster than any other intruder and transported to the refuse piles within 15 min. The structure and complexity of behavioral sequences differed among those intruders that were discarded. Workers not only recognized and discriminated between several distinct intruders but also adjusted their behavior to the type of intruder encountered. Our results confirm the previously documented recognition capabilities of E. tuberculatum workers and reveal a very fine-tuned intruder discrimination response. Colony-level prophylactic and hygienic behavioral responses through effective removal of inedible intruders appears to be the most general and flexible form of defense in ants against a diverse array of intruders. However, this generalized response to both potentially lethal and harmless intruders might have driven the evolution of ant-eucharitid interactions, opening a window for parasitoid attack and allowing adult parasitoid wasps to quickly leave the natal nest unharmed.

Drosophila parasitoid wasps bears a distinct DNA transposon profile

BACKGROUND

The majority of Eukaryotic genomes are composed of a small portion of stable (non-mobile) genes and a large fraction of parasitic mobile elements such as transposable elements and endogenous viruses: the Mobilome. Such important component of many genomes are normally underscored in genomic analysis and detailed characterized mobilomes only exists for model species. In this study, we used a combination of de novo and homology approaches to characterize the Mobilome of two non-model parasitoid wasp species.

RESULTS

The different methodologies employed for TE characterization recovered TEs with different features as TE consensus number and size. Moreover, some TEs were detected only by one or few methodologies. RepeatExplorer and dnaPipeTE estimated a low TE content of 5.86 and 4.57% for Braconidae wasp and 5.22% and 7.42% for L. boulardi species, respectively. Both mobilomes are composed by a miscellaneous of ancient and recent elements. Braconidae wasps presented a large diversity of Maverick/Polintons Class II TEs while other TE superfamilies were more equally diverse in both species. Phylogenetic analysis of reconstructed elements showed that vertical transfer is the main mode of transmission.

CONCLUSION

Different methodologies should be used complementarity in order to achieve better mobilome characterization. Both wasps genomes have one of the lower mobilome estimates among all Hymenoptera genomes studied so far and presented a higher proportion of Class II than Class I TEs. The large majority of superfamilies analyzed phylogenetically showed that the elements are being inherited by vertical transfer. Overall, we achieved a deep characterization of the mobilome in two non-model parasitoid wasps improving our understanding of their evolution.

Chemical and behavioral integration of army ant-associated rove beetles - a comparison between specialists and generalists

Host-symbiont interactions are embedded in ecological communities and range from unspecific to highly specific relationships. Army ants and their arthropod guests represent a fascinating example of species-rich host-symbiont associations where host specificity ranges across the entire generalist - specialist continuum. In the present study, we compared the behavioral and chemical integration mechanisms of two extremes of the generalist - specialist continuum: generalist ant-predators in the genus Tetradonia (Staphylinidae: Aleocharinae: Athetini), and specialist ant-mimics in the genera Ecitomorpha and Ecitophya (Staphylinidae: Aleocharinae: Ecitocharini). Similar to a previous study of Tetradonia beetles, we combined DNA barcoding with morphological studies to define species boundaries in ant-mimicking beetles. This approach found four ant-mimicking species at our study site at La Selva Biological Station in Costa Rica. Community sampling of Eciton army ant parasites revealed that ant-mimicking beetles were perfect host specialists, each beetle species being associated with a single Eciton species. These specialists were seamlessly integrated into the host colony, while generalists avoided physical contact to host ants in behavioral assays. Analysis of the ants' nestmate recognition cues, i.e. cuticular hydrocarbons (CHCs), showed close similarity in CHC composition and CHC concentration between specialists and Eciton burchellii foreli host ants. On the contrary, the chemical profiles of generalists matched host profiles less well, indicating that high accuracy in chemical host resemblance is only accomplished by socially integrated species. Considering the interplay between behavior, morphology, and cuticular chemistry, specialists but not generalists have cracked the ants' social code with respect to various sensory modalities. Our results support the long-standing idea that the evolution of host-specialization in parasites is a trade-off between the range of potential host species and the level of specialization on any particular host.

Arthropods Associate with their Red Wood ant Host without Matching Nestmate Recognition Cues

Social insect colonies provide a valuable resource that attracts and offers shelter to a large community of arthropods. Previous research has suggested that many specialist parasites of social insects chemically mimic their host in order to evade aggression. In the present study, we carry out a systematic study to test how common such chemical deception is across a group of 22 arthropods that are associated with red wood ants (Formica rufa group). In contrast to the examples of chemical mimicry documented in some highly specialized parasites in previous studies, we find that most of the rather unspecialized red wood ant associates surveyed did not use mimicry of the cuticular hydrocarbon recognition cues to evade host detection. Instead, we found that myrmecophiles with lower cuticular hydrocarbon concentrations provoked less host aggression. Therefore, some myrmecophiles with low hydrocarbon concentrations appear to evade host detection via a strategy known as chemical insignificance. Others showed no chemical disguise at all and, instead, relied on behavioral adaptations such as particular defense or evasion tactics, in order to evade host aggression. Overall, this study indicates that unspecialized myrmecophiles do not require the matching of host recognition cues and advanced strategies of chemical mimicry, but can integrate in a hostile ant nest via either chemical insignificance or specific behavioral adaptations.

Rediscovery and reclassification of the dipteran taxon Nothomicrodon Wheeler, an exclusive endoparasitoid of gyne ant larvae

The myrmecophile larva of the dipteran taxon Nothomicrodon Wheeler is rediscovered, almost a century after its original description and unique report. The systematic position of this dipteran has remained enigmatic due to the absence of reared imagos to confirm indentity. We also failed to rear imagos, but we scrutinized entire nests of the Brazilian arboreal dolichoderine ant Azteca chartifex which, combined with morphological and molecular studies, enabled us to establish beyond doubt that Nothomicrodon belongs to the Phoridae (Insecta: Diptera), not the Syrphidae where it was first placed, and that the species we studied is an endoparasitoid of the larvae of A. chartifex, exclusively attacking sexual female (gyne) larvae. Northomicrodon parasitism can exert high fitness costs to a host colony. Our discovery adds one more case to the growing number of phorid taxa known to parasitize ant larvae and suggests that many others remain to be discovered. Our findings and literature review confirm that the Phoridae is the only taxon known that parasitizes both adults and the immature stages of different castes of ants, thus threatening ants on all fronts.