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Naked Mole-rat (Heterocephalus glaber) Fact Sheet: Behavior & Ecology

Activity Cycle

Rest in large groups

  • Colony active day and night (e.g., Brett 1991a)
    • Digging more common at night
  • Nonbreeders spend substantial time resting (Lacey et al. 1991; Lacey and Sherman 1991)
    • Huddle together during periodic rest breaks; often sleep in a large “dogpile,” up to 4 individuals deep (Tucker 1981; Lacey et al. 1991; Patterson 2016)

Burrows

Structure

  • Burrow system composed of chambers and tunnels (Patterson 2016)
  • Chamber functions (Jarvis and Sale 1971; Maree and Faulkes 2016, except as noted)
    • Nesting: care of young and food storage
      • Usually lined with peels of root vegetables and other fibrous materials (Hill et al. 1957)
    • Latrines: where urination and defecation occur
  • Tunnel functions (Jarvis and Sale 1971; Brett 1991a)
    • Movement between chambers
    • Connection of nest chambers and shallow foraging areas
    • Soil removal from burrow
  • Tunnels can extend 3 km (2 mi) or more (Patterson 2016)
  • T-shaped tunnel junctions allow mole-rats to back in and reverse direction (Hill et al. 1957; Lacey et al. 1991)
  • Tunnel structure influenced by food type and location (Jarvis and Sale 1971; Brett 1991a; Patterson 2016)
    • Extensive branching where food is concentrated
  • After use, shallow foraging burrows sealed off from main burrow system (Brett 1991a; Patterson 2016)

Digging

  • Most digging is cooperative (Hill et al. 1957; Lovegrove 1989; Brett 1991a; Patterson 2016, and as noted)
    • Most intense after rain softens soil, allowing for easier, more rapid expansion of burrow system
  • Teeth and forelimbs used for excavation (Jarvis and Sale 1971; Tucker 1981)
    • Brace body with forelimbs
  • Diggers form a chain (Jarvis and Sale 1971; Lacey and Sherman 1991; Patterson 2016, except as noted)
    • More dominant individuals excavate at front of chain (Brett 1986)
      • Periodically relieved by individual behind
    • Workers in middle of chain scrape and push soil under body (with front limbs, then hind limbs)
      • Soil eventually passed to individual at tunnel exit
    • Often a larger individual is at end of chain (Braude 1991; Lacey et al. 1991)
      • Expels soil from burrow using backwards kicks
  • Digging activity leaves volcano-shaped soil mounds (molehills) aboveground (Drake-Brockman 1910, as cited by Hamilton 1928; Jarvis and Sale 1971; Braude 1991; Jarvis and Sherman 2002)
    • A colony of 85 to 90 mole-rats can produce 400 to 500 molehills (a displacement of about 3,600 to 4,500 kg/7,900 to 9,900 lbs of soil)
    • Holes on surface quickly covered to prevent snakes from entering (Jarvis and Sherman 2002)
  • Individuals in managed care observed to place woody materials behind front teeth while digging in substrates that produce fine dust (Shuster and Sherman 1998)
    • Described as “tool use”
    • May help to prevent choking, or inhaling fine dust or shards of sharp materials
    • Not yet known if a similar behavior occurs in wild populations

Nesting

  • Carry nesting material in teeth or sweep it to nest using hind feet (Lacey and Sherman 1991)

Movements and Dispersal

Colony distribution

  • Local distribution
    • Colonies often adjacent or interconnected (Brett 1991b)
      • Naked mole-rats have limited dispersal ability
    • A colony of 60 to 90 individuals may occupy a burrow system of 0.5 to 3 km (0.3 to 2 mi) (Patterson 2016)
  • Regional distribution
    • Patchy; colonies not often near each other (Patterson 2016)
    • Size of colony and proximity to nearby colonies influenced by food density

New colony formation

  • Triggered by queen’s death or physical division of burrow system (e.g., tunnel collapse (Brett 1991b; Patterson 2016)
    • Nonbreeding individuals may remain sealed off in new colony to gain breeding status

Active dispersal

  • Litters may include rare “disperser morphs” (O’Riain et al. 1996; O’Riain 1996; Braude 2000)
    • Active individuals, with fat reserves
      • May be of either sex
      • Travel aboveground 200 to 300 m (600 to 1,000 ft) or farther to mate with members of other colonies or start new colonies
      • Reduces inbreeding, promotes genetic mixing

Social Behavior

Highly social within colony

  • One of the few eusocial vertebrates (caste system) (Jarvis 1981; Faulkes and Bennett 2013; Maree and Faulkes 2016; Patterson 2016)
    • Characteristics (Jarvis 1981; Faulkes and Bennett 2001)
      • Reproductive division of labor
      • Overlapping generations
      • Cooperative care of young
    • Examples of eusocial insects: honey bees, termites (Lacey and Sherman 1991)
  • Naked mole-rats live in highly organized colonies of extended family groups (Brett 1991b; Maree and Faulkes 2016; Patterson 2016)
    • Typically 40 to 80 (range: 10 to 295) individuals per colony
  • Majority of individuals work but do not breed (Lacey and Sherman 1991)
    • Nonbreeders gather food, defend the burrow, care for young, and provide other support to the colony
    • Often referred to as “subordinates” (sexually immature adults)
  • Dominance hierarchy based on body size (Brett 1991b; Lacey and Sherman 1991; Clarke and Faulkes 1998; Patterson 2016, except as noted)
    • Only largest individuals in colony breed
    • Duties of workers shift as they grow in size: from burrow maintenance and care of young to digging, searching for food, and burrow defense
    • Larger individuals have better access to resources (e.g., food)
    • Larger individual moves over the top of smaller individual when 2 individuals meet in tight tunnel spaces (Lacey et al. 1991)
  • See Lacey et al. (1991) for descriptions of social behaviors
  • See Reproduction

Communication

Tactile communication

  • Shoving behavior reinforces dominance hierarchy (Reeve and Sherman 1991; Jacobs and Jarvis 1996; van der Westhuizen et al. 2006) and possibly several other functions (Reeve and Sherman 1991; Reeve 1992; Stankowich and Sherman 2002)

Smell and scent marking

  • Colony members identify one another by a unique “colony scent” (Reeve and Sherman 1991; O’Riain and Jarvis 1997; Jarvis and Sherman 2002)
    • Scent acquired during huddling, grooming, and when individuals roll in latrine chamber
    • Pups recognize queen by scent before eyes open (Jarvis 1991)
    • Also see Agonistic Behavior and Defense

Vocalizations

(Pepper et al. 1991; Credner et al. 1997; Patterson 2016, and as noted)

  • Naked mole-rats very vocal (Pepper et al. 1991)
  • Many types of calls (at least 18); one of the largest vocal repertoires of any rodent (Judd and Sherman 1996)
    • Greeting/contact
    • Mating
    • Aggressive
    • Distress
  • Juveniles have distinct vocalizations (Pepper et al. 1991)
  • Uses of high-pitched calls (Judd and Sherman 1996)
    • To bring foragers to location of newly discovered food sources
    • To solicit food or copulations
    • As alarm (defense of burrow)
  • Functions of chirps (Yosida et al. 2007)
    • Reduce conflict
    • Strengthen association between colony members
    • Resolution of dominance hierarchy conflicts
  • Vocalizations may also communicate:
    • Body size/dominance
    • Individual identity

Agonistic Behavior and Defense

Threat detection

  • Sensitive to vibrations (Hill et al. 1957)
    • Remain still if detect movement nearby

Strictly territorial

  • Aggressive towards naked mole-rats of other colonies (e.g., O’Riain and Jarvis 1997)
  • Aggressive towards separated colony members that have lost distinct colony scent (O’Riain and Jarvis 1997; Clarke and Faulkes 1999)
  • Nonbreeding individuals defend colony against intruders and predators (Hill et al. 1957; Brett 1991b; Lacey and Sherman 1991; O’Riain and Jarvis 1997; Patterson 2016)
    • Worker gives alarm call when intruder detected
    • Larger-bodied defenders block tunnel to prevent intruder from entering nest
      • Advance and retreat together, in unison
      • Gape and snap teeth
      • Give hiss or trill vocalizations

Confrontation within a colony

  • Colony members compete for resources (Patterson 2016, and as noted):
    • Food (Schieffelin and Sherman 1995)
    • Access to dig sites
    • Breeding status, especially among females (Jarvis 1991)
      • Male–male aggression infrequent in established colonies (Clarke and Faulkes 1998)
      • Agonistic behavior (physical contests) suppresses reproduction in subordinate individuals (e.g., Margulis et al. 1995)
  • Dominance often asserted through open-mouth gaping, accompanied by hiss and chirp vocalizations (Lacey et al. 1991; Patterson 2016, and as noted)
    • Additional behaviors (rarely cause injury)
      • Tugging skin of opponent (Schieffelin and Sherman 1995)
      • Shoving (Reeve and Sherman 1991; Margulis et al. 1995; Jacobs and Jarvis 1996; O’Riain 1996; Clarke and Faulkes 1998; Clarke and Faulkes 2001; Stankowich and Sherman 2002)
        • Breeding adults—particularly queen—shove pups
          • Most frequent during weaning
        • Queen shoves large and high-ranking individuals
      • Tetany
        • After being shoved by breeding female, subordinate individual lies still with feet in air for several minutes
      • Biting
  • Same-sex fighting between subordinates to gain breeding status (Margulis et al. 1995; Clarke and Faulkes 1997; Smith et al. 1997; Ciszek 2000; Clarke and Faulkes 2001, and as noted)
    • Occurs after queen’s death (females) or during new colony formation (both sexes)
    • Often results in injury or death (Jarvis 1991; Lacey et al. 1991)
      • Competitors shove and bite each other
  • Juveniles wrestle and spar by interlocking incisors (“tooth fencing”) (Lacey et al. 1991)
    • Also grip and drag each other through tunnels
    • Behavior ceases in adulthood

Other Behaviors

Grooming and self-care

  • Mole-rats groom themselves, not each other (Tucker 1981; Alexander 1991)
  • Clean feet, head, and body with incisors (Lacey et al. 1991)
  • Sharpen incisors by grinding edges of top and bottom teeth together (Lacey et al. 1991)

Ecological Role

Ecosystem engineer

  • Hill et al. (1957) suggest burrowing by naked mole-rats allows rain and air to penetrate soil more deeply; promotes plant growth
  • Burrowing activities of 2 other African mole-rat species shown to increase mineral levels in soil, and change plant species composition and richness (Hagenah and Bennett 2013)
    • Also affected aboveground plant biomass

Interspecies Interactions

Relationship with humans

  • Naked mole-rats live in very dry regions with little development and little agriculture (Maree and Faulkes 2016)
    • Known to eat some types of crops (e.g., cassava, sweet potatoes)—but not a significant agricultural pest (Maree and Faulkes 2016)
  • Atypical, highly developed social system is of much interest to biologists (Patterson 2016)
  • Many adaptations and aspects of life history are of interest to medical/drug researchers (Patterson 2016; Mulatu 2018, and as noted)
    • Long lifespan/anti-aging traits (O’Connor et al. 2002; Dammann and Burda 2006; Edrey et al. 2011; Evfratov et al. 2014; Holtze et al. 2016; Lewis and Buffenstein 2016; Zou et al. 2020)
      • Good health maintained into late adulthood (O’Connor et al. 2002; Edrey et al. 2011)
    • Tolerance of hypoxia (condition of inadequate oxygen supply)
    • Resistance to cancer (Liang et al. 2010; Jiang et al. 2016)
      • Cases reported from managed care populations (Delaney et al. 2016)
    • Insensitivity to certain types of pain (Park et al. 2008)
    • Genes as a biomedical resource (Keane et al. 2014)

Locomotion

Digging

  • Large incisor teeth, primarily lower incisors, used for digging; also front feet (Tucker 1981)
    • Lip folds and bristles around mouth prevent soil from being swallowed (see Tucker 1981, p. 57)
  • Also see Burrows

Running

  • Can run both forward and backward very quickly (Tucker 1981; Lacey et al. 1991; Chris Faulkes, personal communication, 2019)
  • Climb over each other when passing in tunnels (Tucker 1981)

Swimming

  • Capable swimmers (Hamilton 1928)
    • “Dog paddle” strokes; scull with tail

Sweet Slumber

Naked mole-rat sleeping on back

Nonbreeding workers often rest while lying on their backs.

Colony members often sleep in a large "dogpile," up to 4 individuals deep.

Image credit: © Josh More/Flickr. Some rights reserved, CC BY-NC-ND 2.0.

Molehill Mounds

Naked mole-rat expels soil from burrow (molehill)

Naked mole-rats are known for forcefully kicking soil out of the tunnel exit during excavation (also known as "volcanoing").

Diggers work together by forming a chain, and then scaping and pushing soil to the tunnel exit.

Image credit: © Markus Lilje/iNaturalist. Some rights reserved, CC-BY-NC-ND 4.0.

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