Peromyscus sejugis Burt 1932

Bradley, Robert D., Francis, James Q., Platt II, Roy N., Soniat, Taylor J., Alvarez, Daysi & Lindsey, Laramie L., 2019, Mitochondrial Dna Sequence Data Indicate Evidence For Multiple Species Within Peromyscus Maniculatus, Special Publications of the Museum of Texas Tech University 70, pp. 1-59 : 25

Peromyscus sejugis Burt 1932

Peromyscus sejugis Burt, 1932:171 .

Holotype.— California Institute of Technology (catalog number 50,632); adult male; skin and skull. Original number W. H. Burt 3,530 .

Type locality.— Mexico: Baja California Sur; Santa Cruz Island , 25º 17’N, 110º 43’W; collected 23 January 1932.

Subspecies.— P. sejugis is monotypic.

Diagnosis.— Color of upperparts grayish with avellaneous and underparts white; tail bicolored with a narrow dorsal stripe. Skull arched antero-posteriorly; rostrum heavy; nasals broad, tapering posteriorly; relatively small auditory bullae ( Burt 1932). Average measurements ( Álvarez-Castañeda 2001): 160–197 mm; (= 184 mm) and a tail length that ranged between 65–94 mm; (= 85 mm). Larger in size than forms occurring on the mainland (specimens now assigned to P. gambelii ), especially in total length (184 mm versus 164 mm) and tail length (85 mm versus 75 mm).

Distribution.— Known only from the Santa Cruz and San Diego Islands, Gulf of California, Mexico.

Comparisons.— A member of the P. maniculatus species group. Burt (1932) associated P. sejugis with P. maniculatus and noted that it was larger in size compared to P. m. cooledgei (now P. gambelii ). The association with P. gambelii was confirmed based on phallic and allozyme data ( Hooper and Musser 1964; Avise et al. 1979). Avise et al. (1979) implied that P. sejugis is as different from P. maniculatus (now P. gambelii ) as it is from P. melanotis and P. polionotus . Hogan et al. (1997), Walker et al. (2006), and Greenbaum et al. (2017) reported low levels of mtDNA divergence between P. sejugis and P. maniculatus from Baja California but argued for retaining P. sejugis as a species based on unique morphometric and genetic characters (see Remarks below).

Cyt b sequences (this study) indicated that P. sejugis differs from P. gambelii , P. keeni , P. labecula , and P. sonoriensis by 2.05%, 3.97%, 4.42%, and 4.42%, respectively. Given the sample of one individual, within species genetic variation could not be determined.

Remarks.— A single sample was examined in this study that is assignable to P. sejugis . The specimen included herein was obtained from Mexico: Baja California Sur; Santa Cruz Island which is the type locality for P. sejugis .

Based on our examination of only a single individual, and the unclear phylogenetic results obtained herein due to the fact that our sample of P. sejugis was paraphyletic with samples representing P. gambelii , we defer to the findings and synopses offered in Walker et al. (2006) and Greenbaum et al. (2017) who opined that based on the available data, it was best to retain P. sejugis as a species. Specifically, they presented six reasons for continuing to recognize P. sejugis as a species separate from mainland forms of P. maniculatus (referred to P. gambelii by Greenbaum et al. 2017). First, morphological evidence presented by Burt (1932) and Álvarez-Castañeda (2001) depicted external and cranial differences between samples of P. sejugis and mainland forms. Second, Avise et al. (1974) reported allozymic differentiation between P. sejugis and mainland populations. Third, Smith et al. (2000), documented the appearance of a unique chromosomal inversion in P. sejugis . Fourth, Chirhart et al. (2005) reported a unique microsatellite allele in P. sejugis . Fifth, studies of mitochondrial DNA sequences ( Hogan et al. 1997; Walker et al. 2006; Cornejo-Latorre et al. 2017; Greenbaum et al. 2017) depicted samples of P. sejugis and P. maniculatus to form monophyletic clades, respectively. Sixth, given previous lines of evidence and based upon the insular and restricted distribution of P. sejugis ; as well as the surrounding conservation implications, demands careful treatment. Our data indicate that P. sejugis is allied closely with P. gambelii , similar to results generated in Greenbaum et al. (2017). Genetic distance data generated herein suggest these populations diverged from P. gambelii found on Baja California Sur approximately between 0.44 and 0.67 mya (see Fig. 3 ).

Figures

Figure 3. Time-calibrated ultrametric tree obtained from the BEAST analysis (Version 2.4, Bouckaert et al. 2014) of the mitochondrial cytochrome-b gene dataset. Scale bars at nodes represent the 95% highest posterior densities and numbers associated to each node are the estimated divergence times in million years ago.