First report on the pollination of Neotinea maculata (Orchidaceae) by minor worker ants of the Temnothorax exilis group (Hymenoptera: Formicidae)

Ants commonly visit flowers seeking for food resources such as nectar. However, only eight species of orchids are known for having an effective pollinaria removal by ants. In this study, the visit of the orchid Neotinea maculata (Desf.) Stearn by ants is described in one of the three known populations from the province of Valladolid (Spain). Through direct observation, six minor worker ants of Temnothorax exilis (Emery, 1869) (Hymenoptera: Formicidae) group were found visiting flowers of six plants of N. maculata, and four of them were carrying pollinaria on their heads. Other insects were not observed with pollinaria or visiting the flowers. Overall, we found that 33.3% of all the flowers had no pollinaria (96 flowers without pollinaria in a total of 288 flowers). Nevertheless, despite ants observed in the field only promoted cross-pollination between flowers of the same individual (geitonogamy), there is a possibility that the ant will visit another plant’s inflorescence. Thus, ants could be considered not only as visitors but also as true pollinators of N. maculata.

Caste-specific phenotypic plasticity of Asian weaver ants: Revealing the allometric and non-allometric component of female caste system of Oecophylla smaragdina (Hymenoptera: Formicidae) by using geometric morphometrics

In eusocial insects, particularly in ants, caste differentiation is extremely complicated when we rely on traditional taxonomy. In most species, the worker caste does not display any distinct morphological characters neither the caste’s central division according to their morphological size variations. We used a landmark-based geometric morphometric approach to quantify the morphological characteristics of female caste systems (queen, major and minor worker ant) of Oecophylla smaragdina. Our findings suggested that each caste has its unique shape and size. Especially in the worker caste, apart from the size variations, we can use the shape as a prominent tool for distinguishing between them. The O. smaragdina exhibits a triphasic allometry pattern. Studying the allometry and non-allometry components of each caste system revealed a highly complex size and shape relationship in the female caste systems. From the allometric and non-allometric analysis, we concluded that the major worker ants showed a closer relationship with the queen than the minor worker ant. This outcome demonstrated that Asian weaver ant exhibits complex shape variations related to size and is correlated to their functional modular characters. This research sheds new light on caste systems’ taxonomic uncertainties for eusocial hymenopteran groups, especially ants.

Nano-CT characterization reveals coordinated growth of a rudimentary organ necessary for soldier development in the antPheidole hyatti

The growth of imaginal discs in holometabolous insects is coordinated with larval growth to ensure the symmetrical and proportional development of the adult appendages. In ants, the differential growth of these discs generates distinct castes – the winged male and queen castes and the wingless worker caste. In the hyperdiverse ant genusPheidole, the worker caste is composed of two morphologically distinct subcastes: small minor workers and larger, big-headed soldiers. Although these worker subcastes are completely wingless, soldier larvae develop rudimentary forewing discs that are necessary for generating the disproportionate head-to-body scaling of the big-headed soldier subcaste. However, it remains unclear whether rudimentary forewing discs in soldier larvae are coordinated with other imaginal discs, and whether disc growth and coordination patterns vary between the minor worker and soldier subcastes. Here we show, using quantitative nano-CT three-dimensional analyses, that growth of the soldier rudimentary forewing discs is coordinated with the increase in volume of the leg and eye-antennal (head) discs as well as with larval size. We found that the growth rate of the rudimentary forewing discs differs from the leg discs but is similar to the growth of the head (eye-antennal) discs relative to larval size, suggesting that growth of each type of imaginal disc may be differentially regulated. In addition to their larger size, the soldier eye-antennal discs increase in width as they undergo morphogenesis to generate the characteristic shape of the large soldier head, suggesting that the rudimentary forewing discs may regulate their patterning in addition to their growth. Finally, we observe little growth of the leg and eye-antennal discs during the bipotential stage, while in minor worker development these discs grow at similar rates to one another in coordination with larval size to generate the smaller minor worker subcaste. Our results suggest that rudimentary organs with regulatory functions may participate in new patterns of inter-organ coordination and regulation to produce novel phenotypes and complex worker caste systems. We provide characterization of larval development and imaginal disc growth and morphogenesis with the aim of highlighting this as an emerging system for the study of rudimentary organs during development and evolution.

Taxonomic revision of Madagascan species of the Pheidole fervens species-group (Hymenoptera, Formicidae)

Madagascar, one of the top megadiversity regions, hosts one of the highest numbers of endemic and threatened organisms on earth. One of the most spectacular examples of ant radiation on the island has occurred in the hyperdiverse genus Pheidole. To this date, there are 117 described Madagascan Pheidole divided into 16 species-groups, and 97% of them are endemic to the island. Only two of these species-groups contain widely distributed invasive species in addition to native, endemic taxa: megacephala, and fervens species-groups. Here we revise the fervens species-group and discuss updated distribution records of its introduced members on Madagascar. We recognize six species belonging to this group, including five new to science: Pheidole ampangabe sp. nov., P. arivo sp. nov., P. comosa sp. nov., P. indica Mayr, P. mamirapiratra sp. nov., and P. mena sp. nov. Detailed descriptions are supplemented with measurements, diagnoses, identification key, high-resolution images for major and minor worker, and comments on distribution and biology.

A Morphological Integration Perspective on the Evolution of Dimorphism among Sexes and Social Insect Castes

Many species have evolved alternate phenotypes, thus enabling individuals to conditionally produce phenotypes that are favorable for reproductive success. Examples of this phenomenon include sexual dimorphism, alternative reproductive strategies, and social insect castes. While the evolutionary functions and developmental mechanisms of dimorphic phenotypes have been studied extensively, little attention has focused on the evolutionary covariance between each phenotype. We extend the conceptual framework and methods of morphological integration to hypothesize that dimorphic traits tend to be less integrated between sexes or social castes. In the case of social insects, we describe results from our recent study of an ant genus in which workers have major and minor worker castes that perform different behavioral repertoires in and around the nest. In the case of birds, we describe a new analysis of a family of songbirds that exhibits plumage coloration that can differ greatly between males and females, with apparently independent changes in each sex. Ant head shape, which is highly specialized in each worker caste, was weakly integrated between worker castes, whereas thorax shape, which is more monomorphic, was tightly integrated. Similarly, in birds, we found a negative association between dimorphism and the degree of integration between sexes. We also found that integration decreased in fairy wrens (Malurus) for many feather patches that evolved greater dichromatism. Together, this suggests that the process of evolving increased dimorphism results in a decrease in integration between sexes and social castes. We speculate that once a mechanism for dimorphism evolves, that mechanism can create independent variation in one sex or caste upon which selection may act.

Pheidole (Hymenoptera, Formicidae) of Middle American Wet Forest

The ant genus Pheidole is a highly diverse lineage of ants that are dominant elements of tropical and subtropical ecosystems throughout the world. Biodiversity inventory projects in Middle American wet forests (southern Mexico to Costa Rica, lowland rainforest to high montane forest) allow an improved taxonomy of the genus in this region. An identification guide to 234 species in the region is provided, using a "bird guide" approach. Species are arranged in order of minor worker head width and scape length, and each species has a fixed layout that includes habitat and microhabitat information, standard views (minor lateral, minor face, major face), and a distribution map. The following new synonyms are proposed: biconstricta Mayr 1870 (= inermis Mayr 1870), carapuna Mann 1916 (= tristicula Wilson 2003), fimbriata Roger 1863 (= soesilae Makhan 2007), insipida Forel 1899 (= fariasana Wilson 2003, mooreorum Wilson 2003), longiscapa Forel 1901 (= cocciphaga Borgmeier 1934), plebecula Forel 1899 (= perdiligens Wilson 2003, texticeps Wilson 2003), nitidicollis Emery 1896 (= chalcoides Wilson 2003), nubicola Wilson 2003 (= cielana Wilson 2003, petrensis Wilson 2003), simonsi Wilson 2003 (= arctos Wilson 2003, gangamon Wilson 2003, thrasys Wilson 2003), striaticeps Mayr 1870 (= chloe Forel 1908), transversostriata Mayr 1887 (= scalaris Wilson 2003), vafra Santschi 1923 (= laticornis Wilson 2003). The following 57 new species are described: ajaxigibba, andersoni, angustinigra, atitlana, balatro, belonorte, besalon, bicornisculpta, brownampla, cahui, caliginosa, carinitida, corniclypeus, costaricensis, cusuco, depressinoda, eosimilis, familiaparra, fincanaranjo, hansoni, hectornitida, hitoy, huarache, imbrilis, indagarama, kasparii, kelainos, lagunculiminor, lamancha, laselvoides, lineafrons, luteagossamer, machaquila, marmor, moskitia, muralla, musacolor, musinermis, natalie, nephele, obturaculum, passivaeferox, perissothrix, platyscapa, probolonotum, rima, rogeripolita, savegre, sensipelada, sepultura, tapanti, tikal, tinamu, tsontekonwei, tuculutan, xiloa, zannia.

Macroevolutionary integration of phenotypes within and across ant worker castes

Phenotypic traits are often integrated into evolutionary modules: sets of organismal parts that evolve together. In social insect colonies the concepts of integration and modularity apply to sets of traits both within and among functionally and phenotypically differentiated castes. On macroevolutionary timescales, patterns of integration and modularity within and across castes can be clues to the selective and ecological factors shaping their evolution and diversification. We develop a set of hypotheses describing contrasting patterns of worker integration and apply this framework in a broad (246 species) comparative analysis of major and minor worker evolution in the hyperdiverse ant genusPheidole. Using geometric morphometrics in a phylogenetic framework, we inferred fast and tightly integrated evolution of mesosoma shape between major and minor workers, but slower and more independent evolution of head shape between the two worker castes. Thus,Pheidoleworkers are evolving as a mixture of intra- and inter-caste integration and rate heterogeneity. The decoupling of homologous traits across worker castes may represent an important process facilitating the rise of social complexity.

Polymorphism and division of labour in a socially complex ant: neuromodulation of aggression in the Australian weaver ant, Oecophylla smaragdina

Complex social structure in eusocial insects can involve worker morphological and behavioural differentiation. Neuroanatomical variation may underscore worker division of labour, but the regulatory mechanisms of size-based task specialization in polymorphic species are unknown. The Australian weaver ant, Oecophylla smaragdina , exhibits worker polyphenism: larger major workers aggressively defend arboreal territories, whereas smaller minors nurse brood. Here, we demonstrate that octopamine (OA) modulates worker size-related aggression in O. smaragdina . We found that the brains of majors had significantly higher titres of OA than those of minors and that OA was positively and specifically correlated with the frequency of aggressive responses to non-nestmates, a key component of territorial defence. Pharmacological manipulations that effectively switched OA action in major and minor worker brains reversed levels of aggression characteristic of each worker size class. Results suggest that altering OA action is sufficient to produce differences in aggression characteristic of size-related social roles. Neuromodulators therefore may generate variation in responsiveness to task-related stimuli associated with worker size differentiation and collateral behavioural specializations, a significant component of division of labour in complex social systems.

Symbiotic Fungus and Enzymatic Digestion in the Gut of the Termite, Macrotermes barneyi (Light) (Isoptera: Termitidae)

Gut polysaccharidase activity was examined in the fungus-growing termite, Macrotermes barneyi (Light). Rates of enzymatic digestion of 7 polysaccharides and 5 synthetic heterosides were compared among major and minor worker midguts and hindguts and mycotêtes of the Termitomyces fungus. Major workers showed substantially more hindgut polysaccharidase activity than minor workers, though for both worker types midgut activity was substantially higher than in the hindgut. For 10 out of the 12 enzymes tested (including cellulases), activities were significantly higher in the midguts of major workers than in the fungus mycotêtes. Acquired polysaccharidases from the mycotêtes have been suggested to play a role in digestion in the termite midgut in some other Macrotermes species. However, in M. barneyi, our results indicate that for 11 of the 12 enzymes we tested acquired fungal polysaccharidases are probably of relatively little importance.

Natural History of the AntPheidole desertorumWheeler in a Desert Grassland Habitat

Pheidole desertorumcolonies are large for the genus; the number of adult workers in established colonies ranges from 2,460–24,814. They are nocturnal during summer and are predators and scavengers on arthropods. Both minor and major workers forage, although foraging by majors appears to occur primarily when food is abundant. Young major workers may function as repletes. The adult major/minor worker ratio varies greatly among colonies; much of that variance appears explained by colony size and marturity of adult colony reproductive broods. Most colonies produce reproductives each year and colony sex ratios are extremely sex-biased. Mating season begins following summer rainfall, Males and gynes fly prior to sunrise; males form aerial swarms which gynes enter. Mating occurs on the ground, then gynes fly awy, presumably o suitable colony founding sites Colony f0udation is normally haplometrotic, although pleometrotic queen associations with workers are found.