Prolactin maintains parental responses and alters reproductive axis gene expression, but not courtship behaviors, in both sexes of a biparental bird

Prolactin, a hormone involved in vertebrate parental care, is hypothesized to inhibit reproductive hypothalamic-pituitary-gonadal (HPG) axis activity during parenting, thus maintaining investment in the current brood as opposed to new reproductive efforts. While prolactin underlies many parental behaviors in birds, its effects on other reproductive behaviors, such as courtship, remain unstudied. How prolactin affects neuropeptide and hormone receptor expression across the avian HPG axis also remains unknown. To address these questions, we administered ovine prolactin (oPRL) or a vehicle control to both sexes in experienced pairs of the biparental rock dove (Columba livia), after nest removal at the end of incubation. We found that oPRL promoted parental responses to novel chicks and stimulated crop growth compared to controls, consistent with other studies. However, we found that neither courtship behaviors, copulation rates nor pair maintenance differed with oPRL treatment. Across the HPG, we found oPRL had little effect on gene expression in hypothalamic nuclei, but increased expression of FSHB and hypothalamic hormone receptor genes in the pituitary. In the gonads, oPRL increased testes size and gonadotropin receptor expression, but did not affect ovarian state or small white follicle gene expression. However, the oviducts of oPRL-treated females were smaller and had lower estrogen receptor expression compared with controls. Our results highlight that some species, especially those that show multiple brooding, may be able to maintain mating behavior despite elevated prolactin. Thus, mechanisms may exist for prolactin to promote investment in parental care without concurrent inhibition of reproductive function or HPG axis activity.

Territorial Behavior of the White-necked Hawk (Buteogallus lacernulatus) and the Mantled Hawk (Pseudastur polionotus) in Eastern Brazil

ABSTRACT Studies of territorial and courtship behavior are lacking for many tropical raptors. From 2006 to 2009, using observations that were not time-limited, we studied the territorial and courtship behaviors of the White-necked Hawk (Buteogallus lacernulatus) and the Mantled Hawk (Pseudastur polionotus) in Rio Doce State Park in eastern Brazil. We observed White-necked Hawks and Mantled Hawks engaged in aerial displays on 67 and 13 occasions, respectively. Display behaviors performed by White-necked Hawks were characterized by 1–4 undulations followed by aerial swoops and spirals. Territorial and/or courtship behaviors of Mantled Hawks were characterized by the male and female performing thermal or horizontal gliding together and diving in spirals while frequently emitting a series of long and short whistles. This study presents the first formal descriptions of the aerial territorial/courtship displays of these rare forest-dwelling raptors.

Post-mating Refractoriness in Drosophila melanogaster Depends Upon Ecdysis Triggering Hormone Signaling

The decision to engage in courtship depends on external cues from potential mates and internal cues related to maturation, health, and experience. Hormones allow such information to be conveyed to distal tissues in a coordinated fashion. Here, we show Ecdysis-Triggering Hormone (ETH) is a regulator of male courtship in Drosophila melanogaster, and critical for mate choice and courtship inhibition after the completion of copulation. Preventing ETH release increases male-male courtship and decreases post-copulation courtship inhibition (PCCI). Such aberrant male courtship behavior in ETH-deficient males appears to be the consequence of inabilityto integrate pheromone cues into decision making. Silencing of ETH receptor (ETHR) in GR32A-expressing neurons leads to reduced ligand sensitivity and elevated male-male courtship. We find OR67D is critical for suppression of courtship after mating, and ETHR silencing in OR67D-expressing neurons, and GR32A-expressing neurons to a lesser degree, elevates post-copulation courtship. Finally, ETHR silencing in the corpus allatum increases post-copulation courtship; treatment of with juvenile hormone analog partially restores normal post-mating behavior. ETH, a stress-sensitive reproductive hormone, appears to coordinate multiple sensory modalities to guide Drosophila male courtship behaviors, especially after mating.

High-speed camera recordings uncover previously unidentified elements of zebrafish mating behaviors integral to successful fertilization

The mating behavior of teleost fish consists of a sequence of stereotyped actions. By observing mating of zebrafish under high-speed video, we analyzed and characterized a behavioral cascade leading to successful fertilization. When paired, a male zebrafish engages the female by oscillating his body in high frequency (quivering). In response, the female pauses swimming and bends her body (freezing). Subsequently, the male contorts his trunk to enfold the female’s trunk. This behavior is known as wrap around. Here, we found that wrap around behavior consists of two previously unidentified components. After both sexes contort their trunks, the male adjusts until his trunk compresses the female’s dorsal fin (hooking). After hooking, the male trunk slides away from the female’s dorsal fin, simultaneously sliding his pectoral fin across the female’s gravid belly, stimulating egg release (squeezing/spawning). Orchestrated coordination of spawning presumably increases fertilization success. Surgical removal of the female dorsal fin inhibited hooking and the transition to squeezing. In a neuromuscular mutant where males lack quivering, female freezing and subsequent courtship behaviors were absent. We thus identified traits of zebrafish mating behavior and clarified their roles in successful mating.

A neural hub that coordinates learned and innate courtship behaviors

Holistic behaviors often require the coordination of innate and learned movements. The neural circuits that enable such coordination remain unknown. Here we identify a midbrain cell group (A11) that enables male zebra finches to coordinate their learned songs with various innate behaviors, including female-directed calling, orientation and pursuit. Anatomical mapping reveals that A11 is at the center of a complex network including the song premotor nucleus HVC as well as brainstem regions crucial to innate calling and locomotion. Notably, lesioning A11 terminals in HVC blocked female-directed singing, but did not interfere with female-directed calling, orientation or pursuit. In contrast, lesioning A11 cell bodies abolished all female-directed courtship behaviors. However, males with either type of lesion still produced songs when in social isolation. Lastly, monitoring A11 terminals in HVC showed that during courtship A11 inputs to the song premotor cortex signal the transition from innate to learned vocalizations. These results show how a brain region important to reproduction in both birds and mammals coordinates learned vocalizations with innate, ancestral courtship behaviors.

Regulation of sexually dimorphic abdominal courtship behaviors in Drosophila by the Tlx/tailless-like nuclear receptor, Dissatisfaction

Sexually dimorphic courtship behaviors in Drosophila melanogaster develop from the activity of the sexual differentiation genes, doublesex (dsx) and fruitless (fru), functioning with other regulatory factors that have received little attention. The dissatisfaction gene (dsf) encodes an orphan nuclear receptor homologous to vertebrate Tlx and Drosophila tailless that is critical for the development of several aspects of female- and male-specific sexual behaviors. Here, we report the pattern of dsf expression in the central nervous system and show that the activity of sexually dimorphic abdominal interneurons that co-express dsf and dsx is necessary and sufficient for vaginal plate opening in virgin females and abdominal curling in males during courtship. We find that dsf activity results in different neuroanatomical outcomes in females and males, promoting and suppressing, respectively, female development and function of the DDAG neurons depending upon the sexual state of dsx expression. We posit that dsf and dsx interact to specify sex differences in the neural circuitry for dimorphic abdominal behaviors.

Changes in splicing and neuromodulatory gene expression programs in sensory neurons with pheromone signaling and social experience

Social experience and pheromone signaling in ORNs affect pheromone responses and male courtship behaviors in Drosophila, however, the molecular mechanisms underlying this circuit-level neuromodulation remain less clear. Previous studies identified social experience and pheromone signaling-dependent modulation of chromatin around behavioral switch gene fruitless, which encodes a transcription factor necessary and sufficient for male behaviors. To identify the molecular mechanisms driving social experience-dependent neuromodulation, we performed RNA-seq from antennal samples of mutant fruit flies in pheromone receptors and fruitless, as well as grouped or isolated wild-type males. We found that loss of pheromone detection differentially alters the levels of fruitless exons suggesting changes in splicing patterns. In addition, many Fruitless target neuromodulatory genes, such as neurotransmitter receptors, ion channels, and ion transporters, are differentially regulated by social context and pheromone signaling. Our results suggest that modulation of circuit activity and behaviors in response to social experience and pheromone signaling arise due to changes in transcriptional programs for neuromodulators downstream of behavioral switch gene function.

Gut microbiome modulates Drosophila aggression through octopamine signaling

Gut microbiome profoundly affects many aspects of host physiology and behaviors. Here we report that gut microbiome modulates aggressive behaviors in Drosophila. We found that germ-free males showed substantial decrease in inter-male aggression, which could be rescued by microbial re-colonization. These germ-free males are not as competitive as wild-type males for mating with females, although they displayed regular levels of locomotor and courtship behaviors. We further found that Drosophila microbiome interacted with diet during a critical developmental period for the proper expression of octopamine and manifestation of aggression in adult males. These findings provide insights into how gut microbiome modulates specific host behaviors through interaction with diet during development.

Male mate choice unresolved in the mangrove rivulus

Mate choice has the potential to drive phenotypic evolution because it can determine traits that increase an individual’s likelihood to reproduce (courtship behaviors, elaborate ornamentation). These traits, however, can also be detrimental for health or survival, often antagonizing the evolution of extreme phenotypes. Mangrove rivulus fish (Kryptolebias marmoratus) develop as self-fertilizing simultaneous hermaphrodites. Hermaphrodites overwhelmingly self-fertilize their eggs internally, but occasionally oviposit unfertilized eggs. Some individuals change sex to male after sexual maturity, essentially forgoing the reproductive assurance of selfing. In a continuing effort to understand how sex change to male is maintained this species, I designed an experiment to determine whether males act as choosers to increase their likelihood of finding unfertilized eggs for reproduction. I hypothesized that males would prefer to associate with younger hermaphrodites when given a dichotomous choice, as they lay a greater proportion of unfertilized eggs compared to older hermaphrodites. The males in this study did not show a preference for either the younger or older hermaphrodite but exhibited greater within individual variance across subtrials than among individual variation. I discuss alternative hypotheses concerning male mate choice in mangrove rivulus, which may illuminate hypotheses to be tested in this and other hermaphroditic species.