Thesis Colloquium at CES on 16 May 2019 at 11:00 am titled "Condition dependent signalling and mating behaviour in the tree cricket Oecanthus henryi" by Sambita Modak from IISc
Male reproductive success can be driven by male mating effort in sexual signaling and in the benefits transferred to females during mating via nuptial gifts. Male mating effort, itself can be determined by various biotic and abiotic factors, such as nutrition quality, age, body size, mating status and temperature, contributing to the immediate condition of the male. In systems that involve long distance acoustic signaling by males for mate attraction, in addition to male mating effort, female motivation to acoustically localize a potential mate can also impact male reproductive success. Female motivation can again be governed by female condition. In my thesis, I studied the condition-dependent signaling and mating behaviour in an acoustically communicating tree cricket species, Oecanthus henryi. The first two chapters examine condition dependence of male mating effort in terms of male signaling and nuptial feeding respectively. In the second chapter, I also measured spermatophore attachment duration as a measure of male reproductive success. My results suggest that diet quality is an important factor in determining the male investment. Males reared on better quality adult diet had a higher lifetime and nightly signaling effort which would imply better mate attraction potential. In the mating behaviour, with increasing age males on high-quality diet had longer spermatophore attachment duration (SPAD) which can indicate higher sperm transfer and hence, higher fitness. Smaller males, received the least reproductive benefit in terms of SPAD across age and diet.
O. henryi males additionally exhibit a unique tool making behavior called baffling which increases their signal loudness. The gain in loudness is known to bestow a higher reproductive benefit (SPAD) to small males which are otherwise less preferred during mating. In the third chapter, we investigated the condition-dependence of this signaling strategy and found smaller males on better diet to have higher baffling probability. This result suggests that baffling is an energetically expensive alternate tactic used by the less preferred males possibly to improve their reproductive fitness.
In the final chapter of my thesis, I aimed to understand the effect of female dietary condition and mating status on female mate search and mating behaviour. Interestingly, female mating status and not diet turned out to be a key driving factor in this context. Despite a high remating propensity, mated females showed significantly low motivation to perform phonotaxis. Besides, both nuptial feeding duration and spermatophore attachment duration decreased in mated females. Thus, for a male it is more advantageous to mate with an unmated female. This highlights the importance of the proportion of virgin females in the wild population in relation to male reproductive success. Moreover, it could potentially determine sexual selection pressures in the system by introducing the additional competition in males for unmated females.