Hierarchical auditory perception for species discrimination and individual recognition in the music frog

The ability to discriminate species and recognize individuals is crucial for reproductive success and/or survival in most animals.However,the temporal order and neural localization of these decision-making processes has remained unclear.In this study,event-related potentials(ERPs)were measured in the telencephalon,diencephalon,and mesencephalon of the music frog Nidirana daunchina.These ERPs were elicited by calls from 1 group of heterospecifics(recorded from a sympatric anuran species)and 2 groups of conspecifics that differed in their fundamental frequencies.In terms of the polarity and position within the ERP waveform,auditory ERPs generally consist of 4 main components that link to selective attention(N1),stimulus evaluation(P2),identification(N2),and classification(P3).These occur around 100,200,250,and 300 ms after stimulus onset,respectively.Our results show that the N1 amplitudes differed significantly between the heterospecific and conspecific calls,but not between the 2 groups of conspecific calls that differed in fundamental frequency.On the other hand,the N2 amplitudes were significantly different between the 2 groups of conspecific calls,suggesting that the music frogs discriminated the species first,followed by individual identification,since N1 and N2 relate to selective attention and stimuli identification,respectively.Moreover,the P2 amplitudes evoked in females were significantly greater than those in males,indicating the existence of sexual dimorphism in auditory discrimination.In addition,both the N1 amplitudes in the left diencephalon and the P2 amplitudes in the left telencephalon were greater than in other brain areas,suggesting left hemispheric dominance in auditory perception.Taken together,our results support the hypothesis that species discrimination and identification of individual characteristics are accomplished sequentially,and that auditory perception exhibits differences between sexes and in spatial dominance.

Identification of Three Common Loliginidae Squid Species in the South China Sea by Analyzing Hard Tissues with Geometric Outline Method

The hard tissues of squid can provide important information for species identification. In this study, we used statolith and beak to identify three squid species including Uroteuthis duvaucelii, Loliolus beka, and U. edulis in the South China Sea. Because of the highly overlapping habitat and similar body morphology of the three squid species, we explored four different ways to identify them, by using statolith, upper beak, lower beak and a combination of statolith and beak. An outline geometric morphometric method and stepwise discriminant analysis were used to evaluate the most suitable method for the identification. We found that the combination of statolith and beak had the highest cross validation rate that was 75.0%, 87.5% and 88.7% for U. duvaucelii, L. beka and U. edulis, respectively. Using two beaks had similar results and the lowest cross validation rate was 60.0%, 50.0%, and 73.7% for the upper beak, 46.9%, 58.5% and 75.3% for the lower beak of U. duvaucelii, L. beka and U. edulis, respectively. Analyzing with the statolith had moderate cross validation which was 72.2%, 80.0%, and 87.7% for U. duvaucelii, L. beka and U. edulis, respectively. From the results it is suggested when the entire body of a squid is available, a combination of statolith and beak should be used for the identification. When only one hard tissue is available, species identification can be subjected to large errors.