The Co-evolution of Bullying Perpetration, Homophobic Teasing, and a School Friendship Network

Bullying and homophobic teasing behaviors
affect the lives of many school aged children, often co-
occur, and tend to peak in middle school. While bullying
and homophobic teasing behaviors are known to be peer

group phenomena, studies typically examine the associa-
tions at the individual or school levels. An examination of
these behaviors at the peer group level can aid in our
understanding of the formation and maintenance of peer
groups that engage in these forms of aggressive behavior

(selection), and the extent to which friends and the peer
group impact individual rates of these aggressive behaviors
(influence). In this longitudinal study, we assess the co-
evolution of friendship networks, bullying perpetration, and
homophobic teasing among middle school students (n =
190) using a Stochastic Actor-Based Model (SABM) for

longitudinal networks

A Conserved Role for Serotonergic Neurotransmission in Mediating Social Behavior in Octopus

Human and octopus lineages are separated by over 500 million years of evolution [1
, 2
] and show divergent anatomical patterns of brain organization [3
, 4
]. Despite these differences, growing evidence suggests that ancient neurotransmitter systems are shared across vertebrate and invertebrate species and in many cases enable overlapping functions [5
]. Sociality is widespread across the animal kingdom, with numerous examples in both invertebrate (e.g., bees, ants, termites, and shrimps) and vertebrate (e.g., fishes, birds, rodents, and primates) lineages [6
]. Serotonin is an evolutionarily ancient molecule [7
] that has been implicated in regulating both invertebrate [8
] and vertebrate [9
] social behaviors, raising the possibility that this neurotransmitter’s prosocial functions may be conserved across evolution. Members of the order Octopoda are predominantly asocial and solitary [10
]. Although at this time it is unknown whether serotonergic signaling systems are functionally conserved in octopuses, ethological studies indicate that agonistic behaviors are suspended during mating [11
, 12
, 13
], suggesting that neural mechanisms subserving social behaviors exist in octopuses but are suppressed outside the reproductive period. Here we provide evidence that, as in humans, the phenethylamine (+/−)-3,4-methylendioxymethamphetamine (MDMA) enhances acute prosocial behaviors in Octopus bimaculoides. This finding is paralleled by the evolutionary conservation of the serotonin transporter (SERT, encoded by the Slc6A4 gene) binding site of MDMA in the O. bimaculoides genome. Taken together, these data provide evidence that the neural mechanisms subserving social behaviors exist in O. bimaculoides and indicate that the role of serotonergic neurotransmission in regulating social behaviors is evolutionarily conserved.