About the author: Hannah Oswalt wrote this post as a part Dr. Stacy Krueger-Hadfield’s Evolutionary Biology course at the University of Alabama at Birmingham. Hannah is a doctoral student in Dr. Charles D. Amsler’s lab where she is investigating the effects of ocean acidification on macroalgae and amphipods around the western Antarctic Peninsula. She is excited to study these marine organisms and contribute to our understanding of how global climate change is affecting these unique organisms.
On a warm summer evening, you open your window and hear the melodious sounds of crickets gently chirping. To human ears, their chirps sound like a perfectly formed symphony, but do they sound this harmonious to female crickets?
Male crickets create their chirping sound by rubbing their front wings together. This sound acts as a romantic song to attract female crickets for mating but not every song is the same. Different species of crickets will often produce different chirps. This is fine when the species are not closely related. However, what happens when two closely related male crickets inhabit the same area? Do females get attracted to males of a different species?
Xu & Shaw (2019) explored whether the similar cricket species Laupala cerasinaand Laupala prunain the same area used different acoustic songs or different spacing of males. These two species are endemic to Hawaii and have calling songs characterized by trains of pulses. The frequency and pulse duration are similar between the species but each species has a distinctive pulse rate.
The methods were completed in two main steps. First, the question of location was determined by surveying calling males in three quadrants that covered different habitat types: closed canopy forest, open canopy forest, and tree fern-ginger patches. Male locations were marked with flags. Then, the species, calling site type, height of call position, and horizontal distance from neighbor were recorded for each cricket.
Next, acoustic differences were quantified by examining recordings of five males from each species for pulse rate, duration, frequency, and power spectra (distribution of acoustic power over the frequency range).
L. cerasina were found to have a significantly faster pulse rate, shorter pulse duration, and lower carrier frequency when compared to L. pruna (Figure 1). However, the power spectra between the species was found to be almost completely overlapping. Males were also shown to clump together in heterogeneous distributions, with L. cerasina usually calling from higher up.
The calls from each species were found to be similar enough that females are likely able to hear the songs from both species, possibly leading to interference when mating. A common response to such song similarity is often for males to separate from each other spatial. However, this was not observed. Males were found to cluster in heterogeneous groups in the same type of location and were usually found to be closer to males of the other species (Figure 2). The answer for this unusual multispecies male gathering might have a simple answer. Female crickets are often attracted to louder songs. More males calling together create a louder song to attract females. However, in comparison to clusters of same-species only, having mixed species groups still increases the volume of the songs but provides less competition among the males. This finding is a unique exception of previously found aggression between heterospecific males. In this case, male crickets do gather together to create a symphonic love song to attract mates.
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