Sex differences in aggression: Differential roles of 5-HT2, neuropeptide F and tachykinin

Abstract

Despite the conserved function of aggression across taxa in obtaining critical resources such as food and mates, serotonin’s (5-HT) modulatory role on aggressive behavior appears to be largely inhibitory for vertebrates but stimulatory for invertebrates. However, critical gaps exist in our knowledge of invertebrates that need to be addressed before definitively stating opposing roles for 5-HT and aggression. Specifically, the role of 5-HT receptor subtypes are largely unknown, as is the potential interactive role of 5-HT with other neurochemical systems known to play a critical role in aggression. Similarly, the influence of these systems in driving sex differences in aggressive behavior of invertebrates is not well understood. Here, we investigated these questions by employing complementary approaches in a novel invertebrate model of aggression, the stalk-eyed fly. A combination of altered social conditions, pharmacological manipulation and 5-HT2 receptor knockdown by siRNA revealed an inhibitory role of this receptor subtype on aggression. Additionally, we provide evidence for 5-HT2’s involvement in regulating neuropeptide F activity, a suspected inhibitor of aggression. However, this function appears to be stage-specific, altering only the initiation stage of aggressive conflicts. Alternatively, pharmacologically increasing systemic concentrations of 5-HT significantly elevated the expression of the neuropeptide tachykinin, which did not affect contest initiation but instead promoted escalation via production of high intensity aggressive behaviors. Notably, these effects were limited solely to males, with female aggression and neuropeptide expression remaining unaltered by any manipulation that affected 5-HT. Together, these results demonstrate a more nuanced role for 5-HT in modulating aggression in invertebrates, revealing an important interactive role with neuropeptides that is more reminiscent of vertebrates. The sex-differences described here also provide valuable insight into the evolutionary contexts of this complex behavior.

Resource limitation, intra‐group aggression and brain neuropeptide expression in a social wasp

“…These two peptides have been associated with regulating feeding-related processes in insects (Ament et al, 2011;Huang et al, 2011;Kwok et al, 2005;Nässel, 2002;Pabla & Lange, 1999;Van Wielendaele et al, 2013). Additional work has linked these peptide genes to aggression behaviour in expansive animal taxa (Asahina et al, 2014;Bubak et al, 2019;Howe et al, 2016;Pavlou et al, 2014). Here, we saw an increase in expression of these genes paired with both an increase in nutritional status and elevated aggression.…”

“…The neuropeptide hormone Neuropeptide F (NPF) is another example of a canonical nutrient signalling gene, widely distributed through both the central nervous and digestive systems, and is involved in the regulation of feeding across a wide variety of taxa. There is evidence from Drosophila that NPF modulates aggression as well as food-seeking behaviour (Bubak et al, 2019;Dierick & Greenspan, 2007). NPF may serve to signal to an individual its own nutritional status, which can in turn affect behavioural outcomes, including their degree of cooperation or aggression.…”

“…NPF may serve to signal to an individual its own nutritional status, which can in turn affect behavioural outcomes, including their degree of cooperation or aggression. Similarly, the neuropeptide Tachykinin has been implicated in regulating aggression in many insect groups (Asahina et al, 2014;Bubak et al, 2019;Howe et al, 2016;Pavlou et al, 2014), as well as foraging behaviour in honeybees (Brockmann et al, 2009). Thus, neuropeptides such as insulin-like peptides, NPF and Tachykinin are excellent candidates as molecular intermediaries between nutrient signalling and aggressive behaviour in social insects.…”

Disruption of serotonin biosynthesis increases resistance to striped stem borer without changing innate defense response in rice

“…In insects, serotonin regulates or modulates a wide variety of processes, such as feeding, 57,58 growth, 59,60 reproduction, 59 aggression, 61,62 and circadian. 63 In addition, peripheral tissue localized serotonin also modulates immunity 64 and gut microbial homeostasis.…”

Exploring the Sexual Dimorphism of Crustacean Neuropeptide Expression Using Callinectes sapidus as a Model Organism

“…One major class of molecules contributing to signaling within the nervous and neuroendocrine system is neuropeptides. These short-chain amino acid sequences with diverse structures are released from neurons to act as both local messengers between neurons and long-range circulating hormones released from the neuroendocrine tissue. − Due to their important and diverse roles in the nervous system, studying these signaling peptides could provide insights into differences between the neurological functions of females and males. − …”