Simon K.A. Robson

Postnatal growth and development in the Mexican free-tailed bat (Tadarida brasiliensis mexicana) : birth size, growth rates and age estimation

Based on mark-recapture data, we quantified changes in body mass, length of forearm, and lengths of the total, proximal, and distal epiphyseal gaps of individual Mexican free-tailed bats (Tadarida brasiliensis mexicana) from birth to peak lactation. We used these data to develop empirical growth curves, derive growth rates, establish age-predictive equations, and compare growth parameters based on three nonlinear growth models. Length of forearm and body mass of neonates averaged 18.5 mm ? 0.7 (SD) and 3.2 g + 0.3, respectively. Mean body mass of pups increased linearly for the first 3 weeks, by which time they had achieved ca. 80% of the mean postpartum mass of adult females. Thereafter, body mass remained relatively stable until a small decrease in body mass was observed at the beginning of the 6th week when young first began to fly. The growth trajectory of the forearm also was linear for the first 3 weeks, but, thereafter, increased more slowly until average adult dimensions were reached in the 6th week. Length of total epiphyseal gap increased to its maximum size during the first 2 weeks and subsequently decreased in a linear fashion. Secondary centers of ossification appeared in the metacarpal and first phalanx of the fourth digit at ca. 14 days, thus, making it possible to quantify age-related changes in the proximal and distal epiphyseal gaps. The equation for estimating age based on length of the forearm is valid when this dimension is -39 mm, whereas the equation for estimating age based on length of the total epiphyseal gap is valid when length of the forearm is >39 mm. Together, these two equations make it possible to estimate the age of pups from 1 to 42 days of age in T. brasiliensis. Of the three nonlinear growth models (logistic, Gompertz, and von Bertalanffy), the logistic equation provides the best fit to the empirical curves for length of forearm and body mass.

Trail and Territorial Communication in Social Insects

The social properties of insect colonies are sometimes described in seemingly contradictory terms. As pinnacles of biological complexity they are superorganisms and their emergent, colony-level characteristics are often referred to in terms of their elaborate and sophisticated nature. Yet the mechanisms that mediate social interactions and group phenomena, after empirical or theoretical analysis, are simple and parsimonious. This complexity-mediated-by-simplicity paradigm provides a heuristic approach to the analysis of the basic behavioral characteristics of the individual members of an insect society and the regulatory mechanisms of cooperative response, which are the fundamental elements from which colony-level behavior is derived. Inevitably, the dissection and reconstruction of insect social organization involves semiochemicals, because the principal sensory modality of integration, social coordination, and assembly of colony-level patterns is olfaction.

Nonrandom search geometry in subterranean termites

[Extract] Studies of the organization of search in ants suggest that individual and colonylevel patterns are related to foraging ecology and may be adaptive [1, 2]. The organization of search in termites has received far less attention, in part because of their cryptic, subterranean foraging habits. Search in subterranean termites involves the construction of a gallery system, a series of branching tunnels in the soil that brings termites into contact with food. The organization of the gallery system might reflect the efficiency of colony search. In this paper we describe the nonrandom colony- level search pattern of the subterranean termite Reticulitermes ftavipes (Kollar), and suggest that it may be organized to minimize search redundancy.

Resource Assessment, Recruitment Behavior, and Organization of Cooperative Prey Retrieval in the Ant Formica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussi recruit nestmates to large anthropod prey and cooperatively transport the prey to the nest. The size of the group of ants retrieving prey is significantly correlated with the prey mass at the point at which the retrieval group reaches the nest entrance. To understand the mechanism involved in this “size matching” process, the regulation of retrieval group size was investigated by examining the modulatory role of trail pheromones in recruitment communication and the behavioral processes that might adjust retrieval group size to prey mass. Laboratory studies of hindgut, poison, and Dufours gland extracts showed that the contents of the hindgut, which was determined to be the source of trail pheromone, induced recruitment and orientation behavior in ants and regulated the recruitment response of ants in the absence of any other communication signal. However, chemical mass communication alone did not appear to explain the regulation of retrieval group size. Scout ants assess whether to collect prey individually or recruit nestmates to group-retrieve 100-, 200-, or 400-mg prey but did not vary group size in relation to either the prey mass or the presence of interspecific competitors once the decision to initiate group retrieval was made. The number of recruits leaving the nest was independent of these factors and first matched prey mass during prey transport, possibly through a process of differential individual response to immobile versus mobile prey items. Unpredictable factors such as prey resistance to movement and rapidly changing degrees of interspecific competition may preclude scouts from fine-tuning the retrieval group size before it reaches the prey.

The structure of a micro-bat community in relation to gradients of environmental variation in a tropical urban area

We investigated patterns of community structure (species composition, foraging activity, and nightly foraging patterns) of bats in relation to gradients of environmental variation in a tropical urban area. A total of 32 sites spread equally across eight habitat types were sampled in the city of Townsville, North Queensland, Australia. Each site was sampled on 3 non-consecutive occasions using automated AnaBat systems. Eleven species were confidently identified while a possible four more were identified only to the genus level. Ordination of environmental variables measured at these sites identified two distinct environmental gradients reflecting the degree of urbanisation and foliage density. With increasing urbanisation there was a decline in species richness and total foraging activity. We used regression trees to characterise foraging preferences of each species. This analysis suggested that only one species of Mormopterus was able to exploit the resources provided by urbanisation. This species foraged in areas with higher numbers of white streetlights. The remaining species of bats preferred to forage within close proximity to natural vegetation and with low numbers of streetlights. The density of vegetation in long-established suburbs did not substantially reverse the trend for urban areas to have fewer bat species than original habitats.

Key individuals and the organisation of labor in ants

In this chapter we examine the organisation of group behaviour at the level of the individual, and discuss the extent and significance of individual behavioural specialisation to group success. Studies of ants in which the behaviour of individuals as well as the group is recorded often reveal a high degree of individual specialisation in the absence of either age or morphological caste differences. Typically referred to as examples of elitism, idiosyncracy or specialisation, we incorporate these examples into a new classification, the key individual concept. This concept defines specialised individuals on the basis of their functional relationship to the behaviour of the group as a whole and indicates that a number of different organisational principles can underlie group behaviour. Some key individuals (catalysts) act to increase the activity level of other group members, whereas other key individuals (organisers) serve to ensure group cohesion and task completion. The demonstration that even large-scale process such as nest emigration can be organised by a subgroup of highly active individuals suggests that studies of group action might benefit from simultaneous analysis at both the individual and group level. Individuals may not always be behaviourally interchangeable, and individual behavioural specialisation, in the absence of age or caste differences, can be a significant component of group organisation.

Economy of Harem Maintenance in the Greater Spear-Nosed Bat, Phyllostomus hastatus

To investigate constraints on males associated with maintenance of harems, we used a time-energy approach to explore the relationship between temporal occupancy of roosts and nightly foraging activity in male and female greater spear-nosed bats, Phyllostomus hastatus. Harem males and females differed significantly in frequency and duration of nightly foraging bouts. Harem males spent less time away from their roost at night and departed and returned more frequently than did other members of the harem. Adult females and one subadult male foraged mostly during the first 2-3 h after sunset. Total time spent foraging by harem males, adult females, and a subadult male, averaged 98, 152, and 115 min per night, respectively. On average, harem males engaged in 7.2 randomly spaced foraging bouts per night, compared with 2.1 bouts for harem females and 2.0 bouts for a subadult male. Field metabolic rate, expressed on a mass-specific basis (ml CO2 g-1 h-1), averaged 3.4 ± 0.69 SD for harem males, 3.0 ± 0.85 for adult females, 1.9 ± 0.08 for a subadult male. These values varied predictably but did not differ significantly. Similarly, daily energetic expenditure, expressed on a whole-animal basis (kJ/day), averaged 168.6 ± 32.5 for harem males and 124.9 ± 38.9 for adult females but did not differ significantly. Because harem males allocate less time to nightly foraging activity compared with adult females, males should have more time and energy available for vigilance at the roost and/or the defense of females.

Single Nucleotide +1 Frameshifts in an Apparently Functional Mitochondrial Cytochrome b Gene in Ants of the Genus Polyrhachis

Twelve of 30 species examined in the ant genus Polyrhachis carry single nucleotide insertions at one or two positions within the mitochondrial cytochrome b (cytb) gene. Two of the sites are present in more than one species. Nucleotide substitutions in taxa carrying insertions show the strong codon position bias expected of functional protein coding genes, with substitutions concentrated in the third positions of the original reading frame. This pattern of evolution of the sequences strongly suggests that they are functional cytb sequences. This result is not the first report of +1 frameshift insertions in animal mitochondrial genes. A similar site was discovered in vertebrates, where single nucleotide frameshift insertions in many birds and a turtle were reported by Mindell et al. (Mol Biol Evol 15:1568, 1998). They hypothesized that the genes are correctly decoded by a programmed frameshift during translation. The discovery of four additional sites gives us the opportunity to look for common features that may explain how programmed frameshifts can arise. The common feature appears to be the presence of two consecutive rare codons at the insertion site. We hypothesize that the second of these codons is not efficiently translated, causing a pause in the translation process. During the stall the weak wobble pairing of the tRNA bound in the peptidyl site of the ribosome, together with an exact Watson–Crick codon–anticodon pairing in the +1 position, allows translation to continue in the +1 reading frame. The result of these events is an adequate level of translation of a full-length and fully functional protein. A model is presented for decoding of these mitochondrial genes, consistent with known features of programmed translational frameshifting in the yeast TY1 and TY3 retrotransposons.

Breeding system, colony and population structure in the weaver ant Oecophylla smaragdina

Weaver ants (Oecophylla smaragdina) are dominant ants in open forests from India, Australia, China and Southeast Asia, whose leaf nests are held together with larval silk. The species, together with its sole congener O. longinoda, has been important in research on biological control, communication, territoriality and colony integration. Over most of the range, only one queen has been found per colony, but the occurrence of several queens per nest has been reported for the Australian Northern Territory. The number of males mating with each queen is little known. Here we report on the colony structure of O. smaragdina using published and new microsatellite markers. Worker genotype arrays reflect the occurrence of habitual polygyny (more than one queen per colony) in 18 colonies from Darwin, Northern Australia, with up to five queens inferred per colony. Monogyny (one queen per colony) with occasional polygyny was inferred for 14 colonies from Queensland, Australia, and 20 colonies from Java, Indonesia. Direct genotyping of the sperm carried by 77 Queensland queens and worker genotypic arrays of established colonies yielded similar results, indicating that less than half of the queens mate only once and some mate up to five times. Worker genotype arrays indicated that queens from Java and the Northern Territory also often mate with more than one male, but less often than those from Queensland. A strong isolation‐by‐distance effect was found for Queensland samples. The variation uncovered means that O. smaragdina is a more versatile study system than previously supposed.

Bryophyte dispersal by flying foxes: a novel discovery

This research provides the first evidence of dispersal of bryophytes and associated microorganisms through ingestion by a highly mobile vertebrate vector, the spectacled flying fox (Pteropus conspicillatus). Bryophyte fragments were found in faeces collected at four P. conspicillatus’ camps in the Wet Tropics bioregion, northeastern Australia. These fragments were viable when grown in culture; live invertebrates and other organisms were also present. Our study has significantly increased understanding of the role of flying foxes as dispersal vectors in tropical forests.