Modeling the variations in male optimal strategies to maximize reproductive success in relation to female spatial predictability

TOURMENTE, MAXIMILIANO; TAMARIT, F.; CHIARAVIGLIO, MARGARITA

Punta del Este

Congreso; 150 years of Darwin´s Evolutionary theory South American Celebration; 2009

Universidad de La República

Sperm competition is recognized as an important evolutive force which promotes numerous adaptations in the males, tending to increase paternity proportion. Snakes have several reproductive features which reduce potential for female monopolization and increase male gonad investment. These features suggest that sperm competition could be a significant evolutive mechanism in snake reproduction. Previous evidence and theories denote two fundamental expenditure sources in the reproductive energetic budget of male snakes: (1) mate searching effort, which is determined by female spatial predictability and influences the amount of potential matings, and (2) sperm production, which determines how successful can these matings be in terms of paternity proportion. In order to elucidate the selective pressures that influence the energetic decisions of male snakes, we used cellular automata to construct a numeric model of the variations of male reproductive success in relation to female spatial distribution in a sperm competition context. To simulate the effect of differential energy investment between mate search displacement and semen production, the model was constructed using a gradient of energy allocation of total energetic budget for one of the expenditure sources and the complementary proportion for the other. Additionally, the mean value of the lowest probability of finding a female in which males accumulate their maximum reproductive success, were calculated foreach expenditure strategy. Results suggest that when female encounter probability is low, males that allocate higher proportions of energy to displacement accumulate higher reproductive success. On the contrary, when female encounter becomes more probable, the higher accumulated reproductive success goes to males with high proportion of total energy allocated to sperm production. We predict that mating systems differing in female spatial predictability would impose divergent selective pressures to the maximization of male reproductive success, determining divergent optimum energy allocation strategies. In mating systems relying on prolonged mate searching, selection would favor males that allocate high amounts of energy to displacement. Conversely, mating systems similar to explosive aggregations would favor an increase in energy allocation to sperm production due to high female spatial predictability.