THE EFFECT OF FOOD INTAKE ON MALE MATE-SEARCHING ACTIVITIES AND REPRODUCTIVE SUCCESS
1. Background and significance. Sexual selection has attracted considerable attention from behavioural and evolutionary ecologists since this theory was initially proposed by Charles Darwin. A myriad of studies have demonstrated that sexual selection is a potent evolutionary force driving the evolution of traits providing a reproductive advantage in the face of mating competition. However, the bulk of these studies focus on characteristics that are sexually selected for interference competition (i.e., fights between individuals) and/or mate choice, while overlooking other potentially important traits such as mate-searching activities. The dearth of knowledge about mate-searching is surprising because (1) finding mating partners is the initial step toward successful reproduction in non-social species, which comprises the majority of all animal species; and (2) because an individual’s investment in mate-searching activities typically correlates with reproductive success in systems where individuals engage in scramble competition to acquire mating partners (i.e., the first male that locates a female has a mating advantage). Further, traditional sexual selection theory holds that female reproductive success is constrained by energy intake, while male reproductive success is primarily limited by mate acquisition. However, recent evidence suggests that the energy invested by males in mating activities can be considerable. Although males invest relatively little energy in the production of gametes, mating activities such as mate-searching and mate-guarding, male-male combat for female acquisition, and courtship can be energetically costly. Thus, energy intake may strongly constrain and indirectly affect male reproductive success by enhancing mate acquisition. This study will provide an empirical test of the hypothesis that male reproduction can also be energy limited by investigating the causal links between food intake, investment in mate-searching, and reproductive success. These links remain largely unexplored, and this research may challenge a current paradigm of traditional sexual selection theory.
2. Objective and methods. I am conducting a food supplementation field study in a population of male Puff Adders (Bitis arietans), a viperid snake commonly found in South Africa. The objective of this study is to test the hypothesis that food intake affects a male’s investment in mate-searching activities and reproductive success. To accomplish this research, I use radiotelemetry (1) to track male adders and manipulate their energy intake by offering supplemental food (thawed striped mice) to half of the radiotracked males during a two-month period prior to the mating season (mid-January to mid-March), and (2) to quantify male adjustments in mate-searching activities in relation to energy intake (supplementally fed vs. unfed males) during the mating season (mid-March to mid-June). In addition, I will conduct DNA paternity analysis on the litters of female adders that were located by the radiotracked males to estimate the effect of energy intake on male reproductive success (e.g., the number of offspring fathered).
3. Why Puff Adders? Puff Adders are an excellent model system to conduct this research. First, their relatively limited mobility allows me to carefully quantify movement behaviour. Second, Puff Adders are sedentary ambush predators that can easily be approached in nature with little disturbance, which allows me to easily feed the radiotracked snakes. Third, the investment in mate-searching activities is male-biased, because males actively search for sexually receptive females during the breeding season. Finally, the mating system of Puff Adders is relatively simple because of the apparent lack of active female choice in snakes. Consequently, the potential for selection on male traits is strong and male intrasexual selection is likely the primary determinant of male reproductive success.