Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Dr. Deby L. Cassill, Ph.D.

Committee Member

Michelle Green, Ph.D.

Committee Member

Michael Shamblott, Ph.D.

Committee Member

Noel Takeuchi, Ph.D.


Brood care, Maternal investment, Neurotransmitters, Social insects


The fire ant, Solenopsis invicta, is one of the most successful of the invasive eusocial invertebrates. The fire ant’s prolific reproductive capacity and its division of labor among five fertility castes are key factors to its successful invasion and global colonization across all continents except Antarctica. Although the rate of self-care and brood care by sterile S. invicta workers is well known, little is known about the rate of self-care and brood care by the other four fertility castes. In this study, I quantified the frequency and duration of behaviors by alate males, alate queens, newly mated queens, older mature queens, and sterile workers over six-hour periods (n = 12 individuals per caste). I found that newly mated queens and sterile workers engaged in brood care for the longest durations and at the highest frequencies. In contrast, alate males, alate queens, and older mated queens spent the majority of their time engaged in self-care behaviors. The social hormones, oxytocin and vasopressin, are found across the full spectrum of animal species including mammals, birds, reptiles, amphibians, fish, insects, and annelids. Oxytocin homologs play an essential role in reproductive processes including pair-bonding, mate selection, the induction of contractions during egg-laying and live mammalian birth and extended maternal care of offspring after hatch or birth. Inotocin, a homolog of oxytocin-vasopressin, has been characterized in social insects, but yet to be identified in S. invicta. Here, the S. invicta inotocin precursor mRNA was amplified using reverse transcriptase polymerase chain reaction (PCR) and confirmed by DNA sequencing. Using quantitative PCR, S. invicta inotocin precursor mRNA was expressed in newly mated queens. These findings provide valuable information to further investigate the physiological mechanisms driving brood care in a highly invasive species.

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