In insects and frogs, a female’s preference for males who call first is well proven. These males are called leaders. Other calling males neighboring the leading male are called followers. Although the female preference for leaders has been studied thoroughly, its evolutionary origins are unknown. Here we examine a study testing whether mating with leading males gives a fitness benefit to females in Neoconocephalus ensiger katydids, and whether the leading trait is heritable.
Neoconocephalus ensiger, the sword-bearing conehead (Wiki Commons)
There are many evolutionary explanations for leader preference. One hypothesis is the idea that the preference for leaders existed in the female before the trait developed in the male. This is the pre-existing sensory bias hypothesis. Another hypothesis, addressed directly in this study, suggests that females gain a fitness benefit by mating with leading males. The authors predicted that this hypothesis would be supported.
For this study, males were collected as calling adults while females were collected as virginal nymphs. Leaders and followers were identified among the males. Females were then assigned randomly to mate with either leading or following males in consistent environmental conditions. After eggs were laid and hatched, male offspring were then categorized as either leaders or followers. They were also assessed for quality– including measurements of weight and body size. This process was then repeated after mating the new generation of katydids to create another generation.
Katydid eggs on a twig (Wiki Commons)
There were very few significant results in this study, though the insignificance of some tests proved quite interesting. The authors found that across generations, there was no evidence that producing leading calls was a heritable trait, disproving the hypothesis. Typically, heritability allows females an additional fitness benefit following the sexy-sons hypothesis: that the female’s ideal mate choice is a male whose genes produce sons that will have the most reproductive success. This is not the case here. Without heritability, there will be no coupling between the female preference and the male trait, which may weaken selection for leader preference over time. However, uncoupled fitness benefits exist, and may yet explain the evolutionary origin of leader preferences. It is also possible that the ability for the male to produce leading calls is due to its nutritional state. Clearly this leaves many questions to be answered, and has many implications for understanding the evolution of certain sexual preferences.
Sources:
Murphy, M. A., Gerhardt, H. C. and Schul, J. (2017), Leader preference in Neoconocephalus ensiger katydids: a female preference for a nonheritable male trait. J. Evol. Biol.. doi:10.1111/jeb.13188
