Vibrational Signals of African Stingless Bees

Insect. Soc. (2017) 64:415–424 DOI 10.1007/s00040-017-0564-9 Insectes Sociaux RESEARCH ARTICLE Vibrational signals of African stingless bees 1,2 1,2 3 1 K. Krausa • F. A. Hager • N. Kiatoko • W. H. Kirchner Received: 31 January 2017 / Revised: 21 March 2017 / Accepted: 12 April 2017 / Published online: 24 April 2017 Ó International Union for the Study of Social Insects (IUSSI) 2017 Abstract Many bee species produce thoracic vibrations in Introduction various contexts. Among the social stingless bees (Meli- ponini) pulsed thoracic vibrations are used to communicate Vibrational communication is the most ancient form of non- with nestmates. To date all studies on stingless bee vibra- chemical communication and widespread in arthropods and tional communication have been conducted in the many vertebrates (for review see: Cocroft and Rodrı´guez Neotropics. We, therefore, focused on six African stingless 2005; Hill 2008). However, it is probably the least known bee species of five genera: Meliponula, Hypotrigona, and least understood of all the sensory modes (Endler 2014). Liotrigona, Dactylurina, Plebeina. We analysed the signals’ Substrate vibrations are either used alone or in combination temporal patterns. Vibrational signals appear to play a role with other communication channels, such as chemical, in the recruitment of stingless bees. The degree of signal tactile or visual (Hill 2009). Arthropods make use of variation in the studied species was much lower than the vibrations in the context of mate location and identification, variation in the signals of Neotropical stingless bees. Fur- courtship and mating, maternal care, foraging, predation thermore, the inter-signal variation of the temporal patterns and predator avoidance (Hill 2009). exceeded intra-signal variation. This might reveal that the In social insects, the communication with nestmates is bees are able to modulate the temporal patterns and the crucial for their success. Intra-colonial communication is signals potential communicative value. Furthermore, for- primarily transmitted via chemical cues and signals aging activity correlates with pulse production in H. (Richard and Hunt 2013). However, in some cases vibra- gribodoi and M. bocandei, supporting the hypothesis that tional communication is used instead of chemical the vibrational signals are used in the context of foraging communication because it is more adequate and serves and recruitment. functions chemicals cannot (Hunt and Richard 2013). In drywood termites for example the resonance frequencies of Keywords African stingless bees Á a wood block are used to assess its size and attract nestmates Vibrational communication Á Foraging Á (Evans et al. 2005, 2007). The fungus growing Macrotermes Thoracic vibrations Á Temporal pattern termites tend to drum with their heads against the substrate and create a pulsed vibration when attacked. Workers respond by a fast retreat into the nest while other soldiers start to drum and thereby amplify and propagate the signal (Hager and Kirchner 2013;Ro¨hrig et al. 1999). In social & K. Krausa wasps, vibrations, induced by antennal drumming guide [email protected] caste development (Suryanarayanan et al. 2011). Within 1 Ruhr University Bochum, Universita¨tsstraße 150, 44780 ants the presence and use of stridulatory organs to produce Bochum, Germany vibrational signals is highly variable and has probably 2 Taita Taveta University, PO Box 635-80300, Voi, Kenya evolved multiple times (Golden and Hill 2016). Ants 3 African Bee Health Project, icipe-African Insect Science for stridulate to organise nest building (Pielstro¨m and Roces Food and Health, PO Box 30772-00100, Nairobi, Kenya 2012), to appeal help when buried (Markl 1965) and to 123 416 K. Krausa et al. recruit nestmates to food sources (Baroni-Urbani et al. that has led to the idea that information about the food 1988). source might be encoded in the signals temporal patterns Among the eusocial bees of the Apidae family (Apini, (Hrncir and Barth 2014). Early studies aimed to decode the Bombini and Meliponini), thoracic vibrations are employed message of the vibrational signals and suggested a relation to communicate with nestmates (for review see: Hrncir et al. of pulse duration and the distance to a food source (Esch 2006a). In honeybees (Apis mellifera), vibrational signals et al. 1965; Esch 1967; Nieh and Roubik 1998; Nieh et al. are very well studied. They are employed in the commu- 2003b) or its height above the ground (Nieh and Roubik nication among young queens (Grooters 1987; Michelsen 1998). However, more recent reinterpretations of the results et al. 1986a; Simpson 1964), used as stop signal for foragers suggest that the vibrations do not provide navigational (Michelsen et al. 1986b; Nieh 1993, for review see: information, but their occurrence and temporal patterns Michelsen 2014), might be employed in labour organization correlate with the net profitability during a foraging trip (Cao et al. 2007) and constitute an essential part of the (Hrncir et al. 2004; Hrncir 2009), which is determined by famous waggle dance communication (Esch 1961; Hrncir sugar concentration, solution flow, handling time, and the et al. 2011). The honeybees waggle dance comprises more presence of competitors (Hrncir and Barth 2014). than one information component; the dances attract nest- Barth et al. (2008) pointed out that the high variability mates to the dancer, reactivate and provide information found in vibrational signals produced by Melipona bees about the availability, location, profitability and olfactory foraging at a certain food source raises doubts about their characteristics of the food source (Gru¨ter and Farina 2009). capacity to carry precise information and does, therefor, not Acoustical signals of the waggle dance consist of several support a hypothesised referential communication. The pulses with a duration of about 20 ms and a frequency of honeybees’ referential communication system is very well 250–300 Hz (Michelsen et al. 1987). It has been suggested studied (Schu¨rch et al. 2015). Foragers encode food source that the acoustical components of the waggle dance encode information in the dances performed inside the hive (von the food source location. For example, the number of pulses Frisch 1965; Dyer 2002). Duration and angle of the dances increases with the distance of the food source (Wenner are proportional to the distance and direction of the food 1962). It was under discussion if the differences in the source. In each dance, waggle runs and thereby location number of produced pulses are due to the increasing dis- information are repeated. The waggle runs diverge in tance of the food source or due to its decreasing profitability duration and angle from each other. To obtain accurate that comes along with increasing distance. A more recent information, dance followers observe successive dances and study focuses on the influence of food source profitability on take an average (Tanner and Visscher 2008; von Frisch and the thoracic vibrations in honeybees. The authors do not find Jander 1957). Signal variability has been studied on dif- the number of pulses to vary with food profitability which ferent levels, ranging from variability between subspecies, indicates that pulse number could be a reliable indicator of the so-called dance dialects, to intra-individual and indi- the food source’s location and thereby supports earlier vidual variability. It has also been discussed that some intra- studies (Hrncir et al. 2011). dance variability in the indication of direction might be The usage of vibrational signals is thought to be an early adaptive (for review see: Dyer 2002). stage in the evolution of recruitment communication in Stingless bees show a remarkable diversity of life style Meliponini because solitarily foraging species, as well as and ecology. The study of Meliponini is promising to give species recruiting nestmates, make use of vibrational signals insights in the evolution of recruitment communication in (Kerr 1969; Lindauer and Kerr 1958). Beside a simple Apidae. Particularities of the habitat, such as the spatial and alerting of nestmates, a precise communication of the food temporal distribution of the food sources and competition source location benefits efficient exploitation of food sour- among species, may have had widely differing effects on the ces. For some stingless bee species, it is shown that they use evolution of communication systems in different species. visual odometry to measure height and distance of a food Only a small fraction of the more than 500 stingless bee source (Eckles et al. 2012; Hrncir et al. 2003). Furthermore, species has been studied in detail. Our knowledge on some species can communicate three-dimensional location vibrational communication is so far limited to only 14 of a food source (Lindauer and Kerr 1958, 1960; Nieh and Neotropical stingless bee species (Hrncir and Barth 2014). Roubik 1995, 1998; Nieh et al. 2003a; Nieh 2004). How- We wanted to test whether old-world species of stingless ever, it has not yet been clarified in which way location bees produce pulsed vibrational signals in a foraging con- information are shared with nestmates and to which extend text, similar to Neotropical Meliponini, and whether their vibrational signals are employed. In Meliponini, Lindauer vibrational signals potentially provide information for and Kerr (1958, 1960) were the first to observe pulsed nestmates. To include African stingless bee species into vibrational signals produced

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