Postcopulatory sexual selection influences baculum evolution in primates and carnivores

Area of Science:

• Evolutionary biology
• Mammalian reproductive strategies
• Sexual selection

Background:

• The baculum's extreme morphological variability suggests sexual selection, yet its evolutionary path and adaptive function remain understudied.
• Understanding baculum evolution is crucial for comprehending mammalian reproductive diversity and sexual selection mechanisms.

Purpose of the Study:

• To reconstruct the evolutionary trajectory of the mammalian baculum using phylogenetic methods.
• To investigate the factors influencing baculum length evolution, particularly in primates and carnivores.
• To test the adaptive significance of the baculum in relation to reproductive strategies.

Main Methods:

• Bayesian phylogenetic framework utilizing Markov chain Monte Carlo (MCMC) methods.
• Reconstruction of ancestral baculum states across Mammalia.
• Comparative analysis of baculum length with testes mass, mating systems (polygamy), breeding seasonality, and intromission duration in primates and carnivores.

Main Results:

• The ancestral mammal lacked a baculum, but it was present in ancestral primates and carnivores.
• No correlation was found between testes mass and baculum length.
• Prolonged intromission duration, polygamy, and seasonal breeding were significant predictors of longer bacula in primates and carnivores.

Conclusions:

• The baculum is not solely driven by testes mass but is significantly influenced by reproductive strategies.
• Prolonged intromission and specific mating systems (polygamy, seasonal breeding) are key evolutionary drivers of baculum length.
• The baculum plays a crucial role in facilitating diverse reproductive strategies, especially in mammals with high postcopulatory sexual selection.