Queen signal should be honest to be involved in maintenance of eusociality: chemical correlates of fertility in Ropalidia marginata

Queens of many social insect species are known to maintain reproductive monopoly by pheromonal signalling of fecundity. Queens of the primitively eusocial wasp Ropalidia marginata appear to do so using secretions from their Dufour's glands, whose hydrocarbon composition is correlated with fertility. Solitary nest foundresses of R. marginata are without nestmates; hence expressing a queen signal can be redundant, since there is no one to receive the signal. But if queen pheromone is an honest signal inextricably linked with fertility, it should correlate with fertility and be expressed irrespective of the presence or absence of receivers of the signal, by virtue of being a byproduct of the state of fertility. Hence we compared the Dufour's gland hydrocarbons and ovaries of solitary foundresses with queens and workers of post-emergence nests. Our results suggest that queen pheromone composition in R. marginata is a byproduct of fertility and hence can honestly signal fertility. This provides important new evidence for the honest signalling hypothesis.

Queens and Workers of the Primitively Eusocial Wasp Ropalidia marginata do not Differ in Their Dufour's Gland Morphology

Ropalidia marginata is a primitively eusocial paper wasp found in peninsular India, where recent work suggests the role of the Dufour's gland hydrocarbons in queen signaling. It appears that the queen signals her presence to workers by rubbing the tip of her abdomen on the nest surface, thereby presumably applying her Dufour's gland secretion to the nest. Since the queen alone produces pheromone from the Dufour's gland and also applies it on the nest surface, the activity level of queen gland should be higher than that of worker gland, as the gland contents would have to get replenished periodically for queens but not for workers. The difference in activity level can be manifested in difference in Dufour's gland morphology, larger glands implying higher activity levels and smaller glands implying lower activity levels, as positive correlation between gland size and gland activity has been reported in exocrine glands of various taxa (including Hymenopteran insects). Hence we investigated whether there is any size difference between Dufour's glands of queens and workers in R. marginata. We found that there was no difference between queens and workers in their Dufour's gland size, implying that Dufour's gland activity and Dufour's gland size are likely to be uncorrelated in this species.

Virgin wasps develop ovaries on par with mated females, but lay fewer eggs

In the primitively eusocial wasp Ropalidia marginata, mating is not necessary for a female wasp to develop her ovaries, lay eggs, and even to become the sole egg layer of her colony despite the presence of other mated nestmates. Here, we show that virgin wasps do not differ from their mated counterparts in the extent and rapidity of their ovarian development, in the proportion of individuals that build a nest and laid eggs, and in the time taken to do so. However, a significantly larger proportion of virgin females showed resorbing oocytes, and laid fewer eggs as compared to mated individuals. Thus, virgin females have the ability to develop ovaries and lay eggs but also to refrain from necessarily laying all mature eggs produced, before mating opportunities arise. This dual ability would be adaptive in haplodiploid, tropical species with perennial nesting cycles and frequent opportunities for workers to become replacement queens or solitary nest foundresses throughout the year.

Function of the Dufour's gland in solitary and social Hymenoptera

The poison gland and Dufour's gland are the two glands associated with the sting apparatus in female Apocrita (Hymenoptera). While the poison gland usually functions as an integral part of the venom delivery system, the Dufour's gland has been found to differ in its function in various hymenopteran groups. Like all exocrine glands, the function of the Dufour's gland is to secrete chemicals, but the nature and function of the secretions varies in different taxa. Functions of the Dufour's gland secretions range from serving as a component of material used in nest building, larval food, and pheromones involved in communicative functions that are important for both solitary and social species. This review summarizes the different functions reported for the Dufour's gland in hymenopterans, illustrating how the Dufour's gland secretions can be adapted to give rise to various functions in response to different challenges posed by the ways of life followed by different taxa. Aspects of development, structure, chemistry and the evolution of different functions are also touched upon briefly.

Nestmate discrimination in the social wasp Ropalidia marginata: chemical cues and chemosensory mechanism

Nestmate discrimination plays an important role in preserving the integrity of social insect colonies. It is known to occur in the primitively eusocial wasp Ropalidia marginata in which non-nestmate conspecifics are not allowed to come near a nest. However, newly eclosed females are accepted in foreign colonies, suggesting that such individuals may not express the cues that permit differentiation between nestmates and non-nestmates. As cuticular hydrocarbons (CHCs) have been implicated as chemosensory cues used in nestmate recognition in other species, we investigated, using bioassays and chemical analyses, whether CHCs can play a role in nestmate recognition in R. marginata. We found that individuals can be differentiated according to colony membership using their CHC profiles, suggesting a role of CHCs in nestmate discrimination. Non-nestmate CHCs of adult females received more aggression than nestmate CHCs, thereby showing that CHCs are used as cues for nestmate recognition. Contrarily, and as expected, CHCs of newly eclosed females were not discriminated against when presented to a foreign colony. Behavioural sequence analysis revealed the behavioural mechanism involved in sensing nestmate recognition cues. We also found that newly eclosed females had a different CHC profile from that of adult females, thereby providing an explanation for why young females are accepted in foreign colonies. (C) 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Breeding in bamboo: a novel anuran reproductive strategy discovered in Rhacophorid frogs of the Western Ghats, India

Amphibians exhibit extraordinarily diverse sets of reproductive strategies among vertebrates. Understanding life history strategies in an evolutionary framework is lacking for many amphibian species in the tropics. Here, we report a novel reproductive mode where adult frogs enter hollow internodes of bamboo via a small opening, deposit direct developing eggs, and provide parental care. This behaviour is observed in two species of the frog genus Raorchestes. The first description of this unique life history and details of nest site characteristics and embryo development are provided along with ecological comparisons. Evolution of novel reproductive modes and parental care are discussed in context of natural selection. Dearth of natural history information on amphibians in the Western Ghats and much of the South-East Asian region is highlighted with suggestions for further studies.(c) 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 1-11.

The influence of termites on soil sheeting properties varies depending on the materials on which they feed

Fungus-growing termites are involved in many ecological processes and play a central role in influencing soil dynamics in the tropics. The physical and chemical properties of their nest structures have been largely described; however less information is available concerning the relatively temporary structures made above-ground to access food items and protect the foraging space (the soil `sheetings'). This study investigated whether the soil physical and chemical properties of these constructions are constant or if they vary depending on the type of food they cover. Soil samples and soil sheetings were collected in a forest in India, from leaves on the ground (LEAF), fallen branches (WOOD), and vertical soil sheetings covering the bark of trees (TREE). In this environment, termite diversity was dominated by Odontotermes species, and especially Odontotermes feae and Odontotermes obesus. However, there was no clear niche differentiation and, for example, O. feae termites were found on all the materials. Compared with the putative parent soil (control), TREE sheetings showed the greatest (and most significant) differences (higher clay content and smaller clay particle sizes, lower C and N content and smaller delta C-13 and delta N-15), while LEAF sheetings were the least modified, though still significantly different than the control soil. We suggest that the termite diversity is a less important driver of potential soil modification than sheeting diversity. Further, there is evidence that construction properties are adapted to their prospective life-span, with relatively long-lasting structures being most different from the parent soil. (C) 2015 Elsevier Masson SAS. All rights reserved.

Influence of soil type on the properties of termite mound nests in Southern India

Termite mounds are conspicuous features in many tropical ecosystems. Their shape and soil physicochemical properties have been suggested to result from the termites ecological need to control the temperature and humidity within their nests and protect themselves from predators. This study aimed to determine the influence of the parent soil properties on the shape and soil physical and chemical properties of termite mounds. Termite mounds built by the fungus-growing termite species Odontotermes obesus were compared in two forests with different soil properties (Ferralsol or Luvisol) in Southern India. Our findings confirm that soil properties influence the physicochemical characteristics of mound material and may affect the shape, but these impacts are mostly independent of the size of the mounds (i.e., the age of the colonies). Mound walls were more enriched in clay and impoverished in C and N in the Luvisol than the Ferralsol. However, their shape was more complex in the Ferralsol than the Luvisol, suggesting a possible link between the clay content in soil and the shape of termite mounds. The results also suggest that clay becomes enriched in O. obesus mound walls through a more passive process rather than solely by particle selection, and that termite mound shape results from the soil properties rather than the ecological needs of termites. In conclusion, although ecologists have mainly focused upon the influence of termite ecological needs on their nest properties, this study highlights the need for a better understanding about the role of the soil pedological properties and, as a consequence, how these properties drive the establishment and survival of termites in tropical ecosystems. (C) 2015 Elsevier B.V. All rights reserved.

Influence of soil pedological properties on termite mound stability

This study investigated the influence of soil properties on the density and shape of epigeous fungus-growing termite nests in a dry deciduous forest in Karnataka, India. In this environment, Odontotermes obesus produces cathedral shaped mounds. Their density, shape (height and volume) and soil physicochemical properties were analyzed in ferralsol and vertisol environments. No significant difference was observed in O. obesus mound density (n = 2.7 mound ha(-1) on average in the vertisol and ferralsol areas). This study also showed that O. obesus has a limited effect on soil physical properties. No differences in soil particle size, pH, or the C:N ratio and base saturation were measured whereas the C and N contents were reduced and CEC was higher in termite nest soils in both environments. Clay mineralogical composition was also measured, and showed the presence of higher amounts of smectite clays in termite nest soils, which thus explained the increasing CEC despite the reduced C and N content. However, the main difference was the shape of the termite mounds. The degradation of the nests created a hillock of eroded soil at the base of termite mounds in the vertisol while only a thin layer of eroded soil was observed in the ferralsol. The increased degradation of termite mounds in the vertisol is explained by the presence of smectites (2:1 swelling clays), which confer macroscopic swelling and shrinking characteristics to the soil. Soil shrinkage during the dry season leads to the formation of deep cracks in the termite mounds that allow rain to rapidly penetrate inside the mound wall and then breakdown unstable aggregates. In conclusion, it appears that despite a similar abundance, termite mound properties depend to a large extent on the soil properties of their environments. (C) 2015 Elsevier B.V. All rights reserved.

Evolution of social behaviour in the primitively eusocial wasp Ropalidia marginata: do we need to look beyond kin selection?

Ropalidia marginata is a primitively eusocial wasp widely distributed in peninsular India. Although solitary females found a small proportion of nests, the vast majority of new nests are founded by small groups of females. In suchmultiple foundress nests, a single dominant female functions as the queen and lays eggs, while the rest function as sterile workers and care for the queen's brood. Previous attempts to understand the evolution of social behaviour and altruism in this species have employed inclusive fitness theory (kin selection) as a guiding framework. Although inclusive fitness theory is quite successful in explaining the high propensity of the wasps to found nests in groups, several features of their social organization suggest that forces other than kin selection may also have played a significant role in the evolution of this species. These features include lowering of genetic relatedness owing to polyandry and serial polygyny, nest foundation by unrelated individuals, acceptance of young non-nest-mates, a combination of well-developed nest-mate recognition and lack of intra-colony kin recognition, a combination of meek and docile queens and a decentralized self-organized work force, long reproductive queues with cryptic heir designates and conflict-free queen succession, all resulting in extreme intra-colony cooperation and inter-colony conflict.