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Galanin Neuron Activation in Feeding, Parental Care, and Infanticide in a T Mouthbrooding African Cichlid Fish ⁎ Julie M

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Galanin Neuron Activation in Feeding, Parental Care, and Infanticide in a T Mouthbrooding African Cichlid Fish ⁎ Julie M Hormones and Behavior 126 (2020) 104870 Contents lists available at ScienceDirect Hormones and Behavior journal homepage: www.elsevier.com/locate/yhbeh Galanin neuron activation in feeding, parental care, and infanticide in a T mouthbrooding African cichlid fish ⁎ Julie M. Butler ,1, Erandi M. Herath, Arohan Rimal, Sarah M. Whitlow, Karen P. Maruska Department of Biological Sciences, Louisiana State University, United States of America ARTICLE INFO ABSTRACT Keywords: Galanin is a conserved neuropeptide involved in parental care and feeding. While galanin is known to mediate Offspring parental care and infanticide in rodents, its role in parental care and feeding behaviors in other taxa, particularly Parental care fishes, remains poorly understood. Mouthbrooding is an extreme form of parental care common in fishes in Starvation which caregivers carry offspring in their buccal cavity for the duration of development, resulting in obligatory Teleost starvation. In the cichlid fish Astatotilapia burtoni, females brood their young for ~2 wks and perform maternal care after release by collecting them into their mouth when threatened. However, females will cannibalize their brood after ~5 days. To examine the role of gal in feeding and maternal care, we collected mouthbrooding, fed, and starved females, as well as those displaying post-release maternal care and infanticide behaviors. Activation of gal neurons in the preoptic area (POA) was associated with parental care, providing the first link betweengal and offspring-promoting behaviors in fishes. In contrast, activation of gal neurons in the lateral tuberal nucleus (NLT), the Arcuate homolog, was associated with feeding and infanticide. Overall, these data suggest gal is functionally conserved across vertebrate taxa with POA gal neurons promoting maternal care and Arc/NLT gal neurons promoting feeding. 1. Introduction underlying the decision to cannibalize ones young, especially in fishes, the most diverse and speciose group of vertebrates. Parental care behaviors have evolved multiple times in animals and Teleost fishes display a diverse repertoire of parental care behaviors, play an evolutionarily significant role in species persistence by in- from the complete absence of parental care, to egg and nest defense, to creasing offspring survival Clutton-Brock,( 1991; Royle et al., 2012). A mouthbrooding (Blumer, 1982; Goodwin et al., 1998; Gross and parent's decisions on whether or not to engage in parental care beha- Sargent, 1985). Mouthbrooding is an extreme form of parental care in viors is influenced by both environmental and physiological factors, which one or both parents carry the developing young for the partial or because many parental behaviors come at costs to the caregiver as they full duration of development (Oppenheimer, 1970). This timeframe can shift their energy allocation from self-promoting to offspring-promoting range from days to weeks and often results in obligatory starvation. behaviors (Gross and Sargent, 1985; Liker and Székely, 2005; Manica, Animals are partially unable and/or unwilling to feed due to the phy- 2004; Nalepa, 1988; Smith and Wootton, 1995). When the costs of sical presence of the brood in their mouth, but the physiological and parental care outweigh the potential benefits or the environmental neural mechanisms associated with this obligatory starvation are poorly conditions interfere, animals can cease parental care and even engage understood. in infanticide, or the cannibalization of one's own young (Hausfater, Components of parental care and feeding neural circuitry are shared 1984). Infanticide is widespread across the animal kingdom, occurring and conserved across taxa (Fischer and O'Connell, 2017), with the neu- in diverse taxa from invertebrates to all vertebrate groups, and can be ropeptide galanin emerging as a candidate for mediating both parental performed by both male and female parents (Hausfater, 1984; Hrdy, care (Dulac et al., 2014) and feeding (Corwin et al., 1993; Crawley et al., 1979; Van Schaik and Janson, 2000). In teleost fishes, infanticide is 1990). Galanin is predominately found in the central nervous system and often a result of small brood size, decreased physical condition of the gastrointestinal tract of animals where it binds G-protein coupled Gal parent, and mate availability (Manica, 2002a; Manica, 2002b; Ochi, receptors. Teleost fish have four galanin receptors (galr1a, galr1b, galr2a, 1985; Petersen, 1990). But less is known about the neural mechanisms galr2b) that are found throughout the brain and in the testes of male Sea ⁎ Corresponding author at: 371 Jane Stanford Way, Gilbert 304, Stanford, CA 94305-5020, United States of America. E-mail address: [email protected] (J.M. Butler). 1 Present address: Biology Department, Stanford University, United States of America. https://doi.org/10.1016/j.yhbeh.2020.104870 Received 31 May 2020; Received in revised form 15 September 2020; Accepted 16 September 2020 0018-506X/ © 2020 Published by Elsevier Inc. J.M. Butler, et al. Hormones and Behavior 126 (2020) 104870 Fig. 1. Experimental protocol for collecting animals (A). Mouthbrooding females were identified on the first day of brooding in community tanks. Some females had their brood removed while others were allowed to retain their brood before being transferred to holding tanks (inset in A). Fed females were fed daily (yellow), but starved females were not (pink). Fed, starved, and brooding females (blue) were collected after 12 days. Females for the maternal care (purple) and infanticide (green) groups were collected after 14–18 days when they were displaying their respective behaviors. Hatched bar in (A) represents an overlap in collection timeframe between the maternal care and infanticide groups. Brains were stained for the neural activation marker pS6 (cyan) and gal (magenta), and co-labeled cells (white) were quantified (B). Scale bars represent 25 μm. nPPa: anterior part of the parvocellular preoptic area. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) bass Dicentrarchus labrax (Martins et al., 2014) and likely have different 2. Materials and methods functional roles (e.g. feeding, parental care, coloration; Eskova et al., 2020). Activation of galanin neurons in the medial preoptic area (mPOA) 2.1. Animals of rodents promotes parental care behaviors in both sexes while ablation of galanin mPOA neurons inhibits parental care and increases offspring- Adult Astatotilapia burtoni derived from a wild-caught stock from directed aggression (Wu et al., 2014). Parental poison frogs have more Lake Tanganyika, Africa in the 1970s were raised under laboratory galanin neurons than nonparental frogs, independent of sex, but in a conditions similar to their natural environment (~28 °C, pH 8.0, 12-h species-dependent manner (Fischer et al., 2019). Other work has found light/12-h dark cycle). Fish were fed daily with cichlid flakes that mPOA galanin neurons are activated during reproductive interac- (AquaDine, Healdsburg, CA, USA) and twice weekly with brine shrimp tions (Bakker et al., 2002; Tripp et al., 2020) and are involved in rat (Sally's Frozen Brine Shrimp, San Francisco, CA, USA). Prior to ex- sexual behavior (Bloch et al., 1996, 1993; Poggioli et al., 1992). In periments, fish were maintained in community aquaria in mixed sex midshipman fishes, POA galanin neurons are differentially activated in groups. Aquaria contained gravel at the bottom, halved terracotta pots type I males compared to type II males during courtship, but not during to serve as shelters, and several dominant, territorial males. All ex- nest defense (Tripp et al., 2020). In contrast to its role in parental care perimental protocols were approved by the Institutional Animal Care and reproduction in the POA, galanin neurons in the arcuate nucleus of and Use Committee (IACUC) at Louisiana State University, Baton mammals mediate feeding behavior by stimulating food intake (Corwin Rouge, LA, and were in accordance with the guidelines set forth by the et al., 1993; Crawley et al., 1990) and galanin promotes feeding beha- National Institutes of Health (NIH) Guide for the Care and Use of viors in goldfish (de Pedro et al., 1995; Volkoff and Peter, 2001). Because Laboratory Animals, 2011. of its involvement in both parental care behaviors and feeding, galanin is an excellent candidate for mediating the obligatory-starvation associated 2.2. Experimental procedures with mouthbrooding. The African cichlid fish Astatotilapia burtoni is an ideal system for To examine the role of the neuropeptide galanin in feeding and investigating how feeding and parental care neural circuitry intersect maternal care states, mouthbrooding females were collected from com- (Grone et al., 2012; Maruska and Fernald, 2018; Porter et al., 2017; munity tanks in the early brooding phase (within 24 h of brood onset) Renn et al., 2009). Females make a dramatic shift from self-feeding and transferred to 38 L experimental tanks. Each tank was divided in half immediately before spawning to obligatory starvation for the duration by a clear, acrylic barrier, and only one female was placed in each of brooding (~14 days). While mouthbrooding, females make critical compartment. Females were randomly assigned to one of five experi- decisions on a daily basis on whether to continue brooding and food- mental groups: mouthbrooding, fed, starved, post-release maternal care, restriction or to release or consume
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