Data from: Frogs with a southern drawl: Wide recognition space facilitates heterospecific aggression in territorial cricket frogs

Species recognition enables both females and males to make adaptive
behavioral decisions in sympatric zones. Research on species recognition
usually concentrates on how female mate choice prevents interspecies
matings. Male-male competition also plays an important role in
reproduction but is relatively understudied in the context of speciation.
The present study investigates the aggressive thresholds for species
recognition during male-male competition in northern and southern cricket
frogs: two sympatric “sibling” species of frogs that are distinguishable
based on advertisement calls. We conducted a field playback experiment
that presented synthetic calls to male northern cricket frogs (Acris
crepitans) that varied in temporal properties, spanning the range from
conspecific to heterospecific call properties. Males responded
aggressively to calls ranging from average conspecific calls to average
heterospecific calls, notably excluding extreme heterospecific calls. We
also modeled how optimal thresholds for species recognition depend on
local proportions of conspecific and heterospecific individuals, and
predicted as optimal the thresholds we measured under conditions of very
few heterospecifics. Overall, our results show that recognition space for
territorial aggression in male A. crepitans is larger than signal space,
and their thresholds for recognition would enable heterospecific
aggression. Such thresholds could be adaptive under social environments
dominated by conspecifics, or in noisy choruses in which males compete
with both conspecifics and heterospecifics to attract females by
minimizing acoustic interference from rivals.