Sociales

Sampling methods (Altmann, 1974; Martin & Bateson, 1993) employed in this study were:

focal observation - one or more subjects were observed for a specific amount of time while recording all instances of behaviour on a checksheet or an event recorder;

scan sampling - one or more subjects are scanned at regular intervals and the behavioural state of each individual at the sampling point is recorded. In this study all colony members were scanned at one hour intervals and the relevant behaviours recorded on a checksheet;

ad libitum sampling - recording as much as possible of all relevant behaviours of a group of subjects. In this study rare but important events, such as sexual behaviour, were recorded using this method.

2.2.2 Ethogram

Lacey and colleagues have constructed an ethogram for naked mole-rats (Lacey et al., 1991). They described 72 non-vocal behaviours grouped into 17 categories based upon presumed functional similarity. What follows is not a complete ethogram, but instead a subset of behaviours from the full behavioural repertoire which were recorded during this study. Behavioural labels defined by Lacey et al.,

(1991) are italicised and are followed by a description of the behaviour. Behaviours are grouped according to presumed functional similarity.

Seven types of agonistic behaviours were recorded. I have additionally included passing behaviour here, as it is essentially a contest over right of way. The agonistic behaviours recorded were:

open-mouth gaping - animals stand face to face with muzzles almost touching and top and bottom incisors separated, and air rapidly inhaled and exhaled to produce a hissing sound (Pepper eta l., 1991).

incisor fencing - animals stand face to face with their mouths at right angles and their incisors locked together. The animals may then shove back and forth and rock their heads from side to side with the incisors locked together (see Plates 3 & 4).

batting - animals simultaneously swat at each other's muzzles with their forepaws.

biting - the jaws of one animal close around the body of another.

shoving - animals stand face to face with their muzzles pressed together. One animal then moves forward pushing the other backward.

tugging - one animal grabs the skin of another with its incisors and pulls backward.

tetany - an individual doubles up and lies still, often with its feet in the air. This behaviour is usually a response to being shoved or gaped at by the breeding female.

passing - animals moving through the tunnel system may pass side by side, or more commonly, one over the other. Individuals may pass one another while moving forward or backwards (Plate 1).

Naked mole-rats transport a wide variety of materials (eg food, debris, nesting material). All four transport behaviours were recorded in this study:

mouth carrying - item is held with the incisors and carried of the floor.

dragging - an item is held with the incisors and dragged along the floor, usually backwards.

sweeping - while moving backwards, loose items (substrate, food etc) are kicked backwards.

backward kicking - back legs are synchronously lifted and kicked upward while the animal remains stationary. In contrast to sweeping, material is propelled both vertically and horizontally while the animal remains stationary.

Digging behaviours are frequently observed in captive colonies whether appropriate substrate (soil, sand, etc) is available or not. Three digging behaviours were recorded:

gnawing - the incisors are scraped along the substrate.

backshoveling - forelegs are synchronously lifted, moved forward and down onto the substrate. This behaviour propels material underneath and behind the animal.

foreleg digging - one foreleg is brought forward and scraped against the substrate then returned to its initial position. This action is repeated rapidly using alternate forelegs.

Naked mole-rats exhibit behaviours associated with grooming their own bodies. Three auto grooming behaviours were recorded:

- cleaning the incisors with the forefeet.

- wiping the face and muzzle with both forefeet. - scratching the face and muzzle with both forefeet.

All sexual behaviours were recorded whenever observed. The three mating behaviours recorded were:

backing - queen backs up to a male, exhibiting a lordosis-like posture that exposes her genitalia.

mounting - approaching the queen from behind, the male typically braces his front legs against the sides of the tunnel system and exhibits a peddling-like motion of the hind legs he attempts to bring his genitals into contact with the queens.

copulating - pelvic thrusting by the male after contact between his genitals and the queens.

2.2.3 Recording method

Behaviours were recorded either on a checksheet or using a computer as an event recorder. A checksheet was used to record behaviour during breeding female and breeding male removal experiments. On each checksheet the frequency of agonistic behaviours initiated or received by the focal animal was recorded, as well as the identity of interactors. In addition to seven agonistic behaviours recorded (see ethogram, below), the frequency that the focal animal passed over, or under, other colony members was recorded on checksheets. Ad libitum observations of unexpected events were recorded on checksheets as narratives.

A desktop PC and a hand-held Psion Organiser were used as event recorders to record the behavior of individuals during odour and social preference trials, respectively. Computers have many advantages over checksheets in recording behavioural events. Behaviours can be scored on a more accurate time base and, due to the efficient way of recording, more rapidly occurring streams of events can be recorded than with checksheets. More importantly for odour and social preference trials, durations as well as frequencies of behaviours can be recorded. The ObserverA^TA™ a software package for Video Tape Analysis of behaviour for Windows (Noldus Information Technology, Utrecht, Holland), was installed on a 33 MHz 486 desktop personal computer (PC). The software was then configured by specifying the research design, independent variables, the subjects under investigation, the events to be scored and the keys they will be linked to on the computer. All odour and social preference trials were filmed and recorded with a time-code onto VHS format video tapes. To achieve this, a video camera mounted on a tripod, positioned above the test apparatus, was connected to a video recorder (VCR) by a A.E.C. 8/18/28 VITC time-code generator (Adrienne Electronics Corporation, Las Vegas, USA). The VITC is a video time code generator which writes time codes to the video tape in a Vertical Interval Time Code format, allowing the time code to be read at any playback speed. The advantage of video tape analysis using a time-code generator is that coding behaviour can be carried out at different VCR playback speeds while maintaining a proper time reference. Behavioural sequences can thus be registered at a speed adjusted to the particular behaviour studied. Video recordings of trials were replayed on a jog/shuttle VCR connected to a PC and the frequency and duration of relevant behaviours were recorded using The Observer/VTA. The advantage of using a jog/shuttle VCR is that videos could be analysed frame by frame if necessary while maintaining a proper time reference. Behaviours were recorded by clicking on the appropriate Observer Windows icon when the behaviour was observed.

A Psion Organiser IILZ64 (R.S. Components, Corby, England) was used as a hand-held event recorder (8 x 14 x 3cm) for social preference trials. The Organiser was fitted with a 32Kb rampak (allowing extra data storage) and a datapak containing the event-recording software for the Psion Organiser. Configurations designed for social preference trials were exported via the Comms Link from the desktop PC to the Psion Organiser. During trials the frequencies and durations of relevant behaviours were recorded by pressing the appropriate keys on the keypad. After trials, observation data files were exported from the Psion Organiser to the desktop PC using the Comms link for data storage and analysis.