International Journal of Research Studies in Biosciences (IJRSB) Volume 3, Issue 6, June 2015, PP 43-53 ISSN 2349-0357 (Print) & ISSN 2349-0365 (Online) www.arcjournals.org ©ARC Page | 43 Correlation between Annual Immunity, Reproductive Success and Melatonin in a Nocturnal Owlet, Athene Brama Chandana Haldar*, Rakesh Verma, Sudipta Panshikar, Sanjeev Kumar Yadav Pineal Research Laboratory, Department of Zoology Banaras Hindu University, Varanasi, India *chaldar2001@yahoo.com Abstract: Seasonal fluctuations in immune system and reproduction are considered of great adaptive importance in mammals but such studies are lacking in avian, especially for any nocturnal bird. We accessed the seasonal variation in immune status of a tropical nocturnal owlet, Athene brama in relation with environmental factors and reproduction. For immune status we measured the total leukocyte count (TLC), percent lymphocyte count (%LC) and blastogenic response of peripheral blood mononucleated cell (PBMC) from blood. Maximum immune status and low gonadal activity (as measured by laprotomy) coincided with high circulating level of melatonin during the July and August months with prevailing monsoon condition in nature. Correlation analysis showed a less positive relation between melatonin and %SR of PBMC in both male and female owlets. However, a strong negative correlation was observed between testosterone, estradiol and %SR of PBMC. General immune status and melatonin level both showed an inverse relationship with gonadal activity suggesting that in this owlet melatonin is acting as immunostimulator and balancing immunity and reproduction. Hence, it could be suggested that in Indian spotted owlet, A. brama both immune and reproductive system might have coevolved sharing a bidirectional relationship to maintain physiological homeostasis. Keywords: Seasonal, Immune status, Melatonin, Reproduction, Owlet 1. INTRODUCTION The Indian spotted owlet, Athene brama is commonly known as “farmer‟s friend” because of its biological importance in predating on the field rodents, mice, lizards and other small pests of agricultural crops. The frequent use of herbicide and pesticide directly or indirectly influences immunity of these birds via the food chain [1]. The nature of the food always challenges the immunity and this could be the reason behind the decreasing number of many predator birds. Several studies on spotted owlet have inferred that habitat quality, prey abundance and weather are having drastic influence on reproduction [2],[3],[4]. However, only few studies were existing dealing with reproduction of birds in relation with immune capacity under natural condition [5],[6],[7],[8],[9],[10]. In addition owlets have to endure many stressors in their natural environments for e.g. food shortage, predator pressure, high parasite densities with season, and social pressure [11], [12], [13]. Evidence has accumulated that melatonin, a chemical messenger of photoperiod and phase response allows seasonal breeders to anticipate the changing seasons and make the necessary adjustments in advance of the actual breeding period [14]. It has been reported that melatonin, plays a pivotal role in seasonal adjustments of immunity in diurnal birds [9], [15]. Information is lacking for any nocturnal avian species where melatonin secretion is mostly progonodatropic in nature [11], [12], [13] but, has not correlated reproduction with immune function. In this regard the interplay of gonadal steroid – testosterone and melatonin could be of great interest because of their opposite functional nature towards immunity, testosterone acts as immune suppressor and gonado-stimulator while melatonin acts as immunostimulator and gonado-suppressor to maintain physiological and adaptive homeostasis in birds., We, therefore studied the correlation between peripheral gonadal steroid and melatonin in modulation of annual immune status of a nocturnal owlet, Athene brama.