Thesis Colloquium at CES on 17 January 2020 at 3:00 pm titled "Territorial and mating strategies of males in a lekking population of blackbuck (Antilope cervicapra)" by Jayabharathy Ranganathan from CES, IISc
Territoriality associated with lek-mating systems is unique in that males defend small, heavily clustered territories that lack resources usually thought to attract females, such as food and water. Females visit these male aggregations (leks) solely for the purpose of mating. Males compete intensively to defend mating territories and male mating success is typically highly skewed. Males in this system face the complex problem of making decisions on how much effort to allocate towards territory defence and mate attraction efforts versus maintenance activities and how to time this effort, as the duration of territory tenure in relation to the peak in number of females visiting the lek has important fitness consequences. Associated with the high variance in mating success, there is extensive variation in the behaviour of males holding territories on leks. In my thesis, I attempt to understand this variation in male lekking behaviour, by examining patterns of territorial investment in relation to patterns of expected payoffs, estimating underlying hormone correlates and analysing the social context of male territorial decisions. Using a lekking population of blackbuck (Antilope cervicapra) as a model system, I took an integrative approach to study the variation in male territorial and mating behaviour on lek.
In the first chapter, I investigated a principal blackbuck lek to understand the fine scale patterns of variation in male territorial investment and test whether they may arise from associated variation in mating benefits. I found that patterns of male investment in lek attendance, signalling and interactions closely track patterns in payoffs, supporting the hypothesis, that due to the large costs of lekking-related behaviour males should tailor their investment in this behaviour to predictable cues of mating benefits. Apart from responding to indirect spatial and temporal cues of potential mating benefits, males also appeared to modulate their lekking behaviour directly in response to a female visiting their territory.
In the second chapter, I examined relationships between lekking behaviour and testosterone and glucocorticoids on a blackbuck lek. I used a non-invasive technique of monitoring endocrine status by measuring concentration of hormone metabolite in blackbuck faeces using enzyme immunoassays. I found that time during the mating season predicted variation in faecal testosterone and cortisol metabolite concentration, but there was no clear relationship between testosterone/cortisol metabolite concentrations with distance from lek-centre.
In the third chapter, I examined the influence of local interactions on male behaviour by quantifying correlation of behaviours at the male neighbourhood level in the short-term (immediate) and long-term (over the mating season). I found that, in the short-term, neighbourhoods show correlated behaviour suggesting that males respond to the behaviour of neighbouring males when making decisions related to displays and how much time to spend on their territory. I found that, over the long-term, lekking male blackbuck appear to locally influence each other’s investment in intensive displays.
Overall my thesis findings indicate that male investment in high-cost signalling is sensitive to diverse factors, including fine-scale spatial and temporal patterns in potential mating benefits, immediate cues of mating benefits, and to social environment. My findings also suggest that taking an integrative approach and examining hormonal mechanisms may provide insights into trade-offs generating variation in costly male behaviour.