Researchers have made significant progress in understanding bird behavior and the reasons behind the persistence or disappearance of different mating systems throughout time.
A team from Rice University has gained fresh perspectives on the evolution of bird behavior, revealing why some mating systems continue to thrive while others decline over time. In a recent paper featured in the journal Evolution, researchers Rafael S. Marcondes and Nicolette Douvas explain that lekking—a mating approach where males attract females through displays without forming lasting relationships—is a stable evolutionary strategy. On the other hand, resource-defense polygamy, in which typically the male (but not exclusively) defends territories to draw in mates, is less stable and often shifts back to monogamy.
According to Marcondes, the lead author and a faculty fellow in ecology and evolutionary biology at Rice, “This research delves into how mating behaviors influence the survival of species while addressing bigger evolutionary questions. Our studies on birds reveal concepts that may also apply to other species.”
The research covered data from over 60% of the globe’s bird species—around 6,620 species—making it one of the most thorough analyses conducted to date.
Marcondes and Douvas adopted a rigorous methodology to examine the evolution of bird mating systems. Their classifications were drawn from credible sources like the “Handbook of Birds of the World,” categorizing species into three mating systems: monogamy (strong and long-term sociosexual bonds), resource-defense polygamy (weak and short-lived bonds), and lekking (no social bonds). They assessed the reliability and detail of these classifications using a scale from 1 to 3, highlighting a novel aspect of their study. Marcondes noted that while there’s much available on animal behavior, it’s often fragmented and inconsistently reported.
“We were among the first to organize that dispersed information and apply it on a broader scale,” Marcondes added.
For their evolutionary analysis, they utilized extensive family trees of species and applied stochastic character mapping to compensate for missing data. They also used advanced evolutionary models to explore dynamics of diversification and transitions among mating systems. This enabled them to model diversification rates, revealing links between mating systems and extinction/speciation rates, and to check if transitions adhered to predictable evolutionary sequences.
The research yielded several significant discoveries regarding the evolution of bird mating systems. Lekking, marked by intricate male displays and choosy females, proved to be notably stable, rarely evolving into other systems and often arising directly from monogamy instead of passing through polygamous forms. In contrast, resource-defense polygamy was found to be vulnerable, often reverting to monogamy, and linked to elevated extinction rates due to difficulties in managing parental care within this system. Monogamy, the most common mating strategy among birds, emerged as the most evolutionarily robust system, fostering strong sociosexual bonds that enhance parental investment and species survival.
“This study connects ecological insights with broader macroevolutionary frameworks,” Marcondes explained. “It illustrates how environmental factors, mating practices, and lineage evolution are interconnected over millions of years.”
Douvas, a senior premed student focusing on humanities, shared her thoughts on the study’s significance for her education at Rice and its influence on the field.
“Through statistical analysis and evolutionary modeling, we uncovered unexpected insights into the stability of lek mating behavior, a subject that hadn’t received much prior focus,” Douvas said. “One of the most intriguing findings was that lekking originated from monogamy, which challenged my earlier assumption that it stemmed from polygamy. This research not only deepened my comprehension of animal behavior but also enriched my understanding of the complexities of evolutionary trends. Participating in this interdisciplinary research has been an extraordinary experience, greatly enhancing my academic pursuits beyond the conventional realms of premed studies.”
