| << Chapter < Page | Chapter >> Page > |
Both H. glaber and C. damarensis experience a great reproductive skew , meaning only a few members of each species ever achieve reproductive success. This is part of the definition of eusociality. For naked mole-rats, less than 1% of the population ever reproduces, and for Damaraland mole-rats less than 8% ever reproduce (Jarvis et al. 1994). This begs the question of how these two mole-rat species suppress reproduction. The current belief is that naked mole-rats and Damaraland mole-rats suppress their workers through different mechanisms.
Using fractal dimension , which measures to what extent the burrow fills the area (Le Comber et al. 2002), Sichilima et al. (2008) investigated assumptions of the Aridity Food Distribution Hypothesis in Fukomys mechowii, a cooperatively breeding species of mole-rats. They examined burrow fractal dimension differences between the rainy season and the dry season, the relationship between fractal dimension and the number of colony members, and the relationship between fractal dimension and food mass in the burrow. They found that burrow fractal dimension increased with the number of colony members and during the rainy season, and that burrows with higher fractal dimensions had more food. This gives substantial support to the Aridity Food Distribution Hypothesis because it indicates that digging and burrowing is limited by energy demands during the arid season, one of the assumptions of the hypothesis. In addition, the risks of failing to find the patchily distributed food sources are reduced by greater numbers of foraging colony members (Sichilima et al. 2008). Similarly, Lovegrove and Wissel (1988) found foraging risks for solitary individuals in an environment with widely dispersed resources are high. Lovegrove also found, using math-based models, that the shift from solitary to group living is expected when there is a depression in the food density, which occurs when shifting from a mesic , or moderately moist, environment to an arid one (Lovegrove 1991), which falls in with the Aridity Food Distribution Hypothesis.
Naked mole-rats have no incest avoidance mechanism, unlike Damaraland mole-rats. Without those mechanisms there is no reason why workers should not breed with each other, yet they do not, suggesting that something must be preventing them. One possibility is that the queen shoves her workers (see [link] ), especially the larger ones who are more likely to breed eventually, to suppress reproduction (Jacobs and Jarvis 1996). Another is that some chemical or other social signal is given to suppress reproduction. Despite not knowing how exactly it is accomplished, it is known that when reproductively suppressed female mole-rats are removed from their colony and kept singularly their reproductive suppression is reversed (Faulkes and Abbott 1993, Clarke and Faulkes 1999). Since H. glaber do not avoid incest on their own, reproductive suppression is the sole method for maintaining the reproductive skew.
Notification Switch
Would you like to follow the 'Mockingbird tales: readings in animal behavior' conversation and receive update notifications?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|