Aging brains and social behavior in an invertebrate model: neuromodulation and neuroanatomy of task attendance across the worker lifespan of the ant Pheidole dentata
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1
Boston University, Department of BIology, United States
Social insects provide powerful systems to explore evolutionary theories of aging and examine the neurobiological underpinnings of behavioral development. Little is understood, however, about the neural processes associated with social role differentiation and behavioral decline across the worker lifespan. Studies describe extensive neuroplasticity underlying age- and subcaste- related division of labor in workers, including the neuromodulation of honeybee foraging behavior and cellular correlates of behavioral roles in paper wasps. As workers of the ant Pheidole dentata mature, the brain undergoes synaptic restructuring, neuropil growth in the mushroom bodies and other brain compartments, and increases in monoamine titers. These neural changes occur as behavioral repertoires expand and minor workers improve in task efficiency. How brains change in association with task performance across the worker lifespan remains unknown.
We measured task performance in behaviorally mature (>20 days) minor workers to address how behaviors critical to colony function change from adult eclosion to death. We found that minors exhibited suites of behavioral traits and could be categorized to nurse or forager phenotypes. Foragers show positive phototaxis, readily attack live prey and transport dead prey, and exhibit high rates of locomotion, while nurses show opposite responses to the same task stimuli. Brood-care assays show that nurses perform significantly more nursing acts per approach than foragers. To understand the neuromodulation of social roles, we measured serotonin (5HT) and dopamine (DA) brain titers using high performance liquid chromatography (HPLC). Foragers showed significantly higher levels of both amines than nurses. Treating foragers with the competitive antagonist α-methyltryptophan (AMTP), which depletes 5HT, or elevation of 5HT with the precursor 5-hydroxytryptophan (5HTP) in nurses was not sufficient to change responses to live prey. Two models could explain this social role differentiation. First workers could reach behavioral maturity and then progress from nurses to foragers. Alternatively, nurses and foragers could belong to the same age group but be physiologically differentiated, either stably or with rapid task switching. To assess the role of age in the differentiating nurses and foragers, task attendance was assayed in behaviorally mature (20 days), midlife (45 days), and old (95 days) minor workers, which can live up to 140 days in the lab. Midlife and old workers had higher locomotion rates than mature workers, but predatory behavior was generally low in all age groups.
In addition to neuromodulators, neuroanatomical age-associated changes, including apoptotic cell death in neurons and/or glia could contribute to patterns of task attendance from maturity to death. Our approach allows an assessment of sensorimotor function, which can be linked to neural decline to provide empirical evidence to test aging and senescence theories, while examining lifespan division of labor.
Keywords:
Aging,
Apoptosis,
Behavioral Development,
Neuromodulation,
Serotonin,
social insects
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for participant symposium and student poster award)
Topic:
Social Behavior
Citation:
Giraldo
YM,
Rusakov
A,
Kordek
A and
Traniello
JF
(2012). Aging brains and social behavior in an invertebrate model: neuromodulation and neuroanatomy of task attendance across the worker lifespan of the ant Pheidole dentata.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00346
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Ms. Ysabel M Giraldo, Boston University, Department of BIology, Boston, MA, 02215, United States, ygiraldo@bu.edu