Barriers to gene exchange in hybridizing field crickets: the role of male courtship effort and cuticular hydrocarbons

Luana S Maroja,David P Richardson,Elizabeth Hart,Zachary M Mckenzie,Joy Jing,Erica L Larson

doi:10.1186/1471-2148-14-65

Luana S Maroja, David P Richardson + Show 4 more

Open Access

https://doi.org/10.1186/1471-2148-14-65

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Abstract

BackgroundPre-zygotic barriers often involve some form of sexual selection, usually interpreted as female choice, as females are typically the choosier sex. However, males typically show some mate preferences, which are increasingly reported. Here we document previously uncharacterized male courtship behavior (effort and song) and cuticular hydrocarbon (CHC) profiles in the hybridizing crickets Gryllus firmus and G. pennsylvanicus. These two species exhibit multiple barriers to gene exchange that act throughout their life history, including a behavioral barrier that results in increased time to mate in heterospecific pairs.ResultsWe demonstrated that male mate choice (as courtship effort allocation) plays a more important role in the prezygotic behavioral barrier than previously recognized. In gryllids females ultimately decide whether or not to mate, yet we found males were selective by regulating courtship effort intensity toward the preferred (conspecific) females. Females were also selective by mating with more intensely courting males, which happened to be conspecifics. We report no differences in courtship song between the two species and suggest that the mechanism that allows males to act differentially towards conspecific and heterospecific females is the cuticular hydrocarbon (CHC) composition. CHC profiles differed between males and females of both species, and there were clear differences in CHC composition between female G. firmus and G. pennsylvanicus but not between the males of each species.ConclusionAlthough many barriers to gene exchange are known in this system, the mechanism behind the mate recognition leading to reduced heterospecific mating remains unknown. The CHC profiles might be the phenotypic cue that allow males to identify conspecifics and thus to adjust their courtship intensity accordingly, leading to differential mating between species.

Highlights

Pre-zygotic barriers often involve some form of sexual selection, usually interpreted as female choice, as females are typically the choosier sex
Time to mate Considering only the 73 out of 184 crosses that resulted in successful mating, time to mate (Figure 2) was influenced by the time to first call (F1,69 = 6.12, P = 0.01) and male species (F1,67 = 7.63, P = 0.006), G. firmus males mated faster (13.2 min for GF and 24.2 min for G. pennsylvanicus (GP)) and were more vigorous during courtship
Our results suggest that the prezygotic behavioral barrier, originally interpreted as female choice [22], may be strongly influenced by male courtship effort

Summary

Introduction

Pre-zygotic barriers often involve some form of sexual selection, usually interpreted as female choice, as females are typically the choosier sex. We document previously uncharacterized male courtship behavior (effort and song) and cuticular hydrocarbon (CHC) profiles in the hybridizing crickets Gryllus firmus and G. pennsylvanicus These two species exhibit multiple barriers to gene exchange that act throughout their life history, including a behavioral barrier that results in increased time to mate in heterospecific pairs. Pre-zygotic barriers to gene exchange can play a large role in reducing gene flow between species; these barriers act earlier in the life cycle and have the potential to restrict hybridization more than later acting barriers [1] Many of these barriers involve some form of sexual selection, usually interpreted as female choice, as females typically invest the most in the offspring [2] and tend to be choosier. We test if males are able to regulate courtship intensity depending on whether they encounter a conspecific or heterospecific female

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