Auditory Brainstem Responses in Two Closely Related Peromyscus Species (Peromyscus leucopus and Peromyscus maniculatus)

Abstract

The genus Peromyscus has been extensively used as a model for ecological, behavioral, and evolutionary studies. We used auditory brainstem responses (ABRs), craniofacial morphology, and pinna measurements to compare characteristics that could impact the threshold, amplitude, and latency of ABRs in two wild-caught species, P. leucopus and P. maniculatus. We observed significant differences in craniofacial and pinna attributes between species, with P. leucopus exhibiting larger features and bigger overall size compared to P. maniculatus. ABR recordings showed similar hearing thresholds with peak sensitivity between 8 to 46 kHz for both species. We found that amplitude of ABR wave I and IV increased significantly with increasing intensity, while no main effect of species was detected. Latency of wave I and IV significantly decreased with increasing intensity in both species. Finally, we observed longer latencies of the binaural interaction component (BIC) at longer interaural time differences (ITDs) in P. leucopus, while no differences were observed across relative BIC amplitude between species. These results provide additional ABR related data that expands the use of both Peromyscus species as future models for auditory research.

Keywords: Auditory brainstem recording; Binaural hearing; Interaural timing difference (ITD); Peromyscus; Pinna.

Figure 1:

Map showing trapping site locations in Oklahoma. Packsaddle wildlife management area (WMA) sites are represented by pink triangles, James Collin wildlife management area (WMA) sites are represented by blue squares, and Payne County sites are represented by green circles.

Figure 2:

Morphological differences between P. leucopus and P. maniculatus. Pinnae, head, and body features (A) were evaluated between species (pink boxplot = leucopus, blue boxplot = maniculatus). Measurements JK show the inter pinnae distance, JN the nose to pinna distance, MK the pinna width, LM the pinna height, OP the tail length, and PQ the body length. Effective pinna diameter was calculated by taking the square root of pinna height multiplied by pinna width (MK/LM). Significant differences were observed for all features including Pinna width (B), Pinna length (C), Effective diameter (D), Nose to pinna distance (E), Inter pinna distance (F), Body length (G), Tail length (H), and Body mass (I). Peromyscus pictured is a wild caught P. leucopus captured in Payne County, Stillwater, Oklahoma. Image is presented only for demonstration of measurements.

Figure 3:

Figure 3A and 3B show auditory brainstem response patterns of a female P. leucopus (left) and a female P. maniculatus (right) determined with clicks of different intensities. Main waves I-V are identified in the 90 dB SPL example. Hearing range was measured across frequency (1–64 kHz) for both P. leucopus and P. maniculatus (Figure 3C). The vertical bars represent the standard error at each frequency. (Figure 3C). No significant main effects of frequency between species were found. Unfilled blue circles represent P. maniculatus while filled pink squares represent P. leucopus. Arrow in figure 3B shown how ampliture were calculated.

Figure 4:

Average amplitude of wave I and wave IV of auditory brainstem responses determined with clicks of different intensities (pink filled square = P. leucopus (n = 15), blue unfilled circle = P. maniculatus (n = 11)). The average wave IV/I amplitude ratio at each intensity is shown in figure 4E. The vertical bars represent the standard error at each point. Significant main effects of intensity on wave I and IV amplitude were detected for both species.

Figure 5:

Average peak latency of wave I and wave IV of auditory brainstem responses determined with clicks of different intensities (Pink filled squares = P. leucopus (n = 15), Blue unfilled circles = P. maniculatus (n = 11)). The average wave I-IV inter-peak latency at each intensity is shown in 5E. The vertical bars represent the standard error at each point.

Figure 6:

Binaural ABRs in wild P. leucopus (pink filled square) and P. maniculatus (blue unfilled circle). 6A, Shift in DN1 latency (ms) relative to ITD; reference latency at ITD = 0 is set to 0 ms. 6B, percentage relative DN1 amplitude relative to ITD normalized to the DN1 amplitude for ITD = 0 ms. Relative amplitude and latency of the DN1 BIC with varying ITD between − 2 to + 2 ms in 0.5 ms steps were measured. Significant main effects of ITD and species were detected in BIC shift in DN1 latencies between both species. No significant main effect of species was observed for relative amplitude of the BIC across ITDs. The vertical bars represent the standard error at each ITD.