Mensular discrimination between sympatric Peromyscus leucopodus and Peromyscus maniculatus in southern Illinois

Abstract

. 1997. Mensural discrimination between sympatric Peromyscus leucopus and P. maniculatus in southern Illinois. Acta Theriologica 42: 1-13.A total of 383 Peromyscus was collected from southern Illinois to determine morphological characteristics useful in identifying individuals as either P. leucopus (Rafinesque, 1818) or P. maniculatus (Wagner, 1845). Polyacrylamide gel electrophoresis of salivary amylase was used to positively identify all specimens. No univariate morphological character accurately discriminated between the two species because of a high degree of intraspecific variation. Stepwise discriminant function analysis of external characters correctly classified 97.9% of subadults to species. The most important external character was the tail length/body length ratio. This ratio was also the most important factor in discrimination of adults; the function correctly classified 98.6% of individuals. Considering skull measurements of adults, 9 cranial characters were needed to differentiate between the two species, with a correct classification of 98.9%. For old adults, all specimens were classified correctly using 5 cranial characters. There was no fast, easy, accurate method to discriminate between these species 100% of the time in the field.

Field Identification of the Mice <em>Peromyscus leucopus noveboracensis</em> and <em>P. maniculatus gracilis</em> in Central New York

“…We found both species to be polymorphic at the amylase locus. The alleles found in our study (Amy-1 76 and Amy-1 85 for P. maniculatus, and Amy-1 94 and Amy-1 100 for P. leucopus) were consistent with those found in previous studies (Aquadro and Patton 1980;Feldhamer et al 1983;Merriam et al 1989;Palas et al 1992;Kilpatrick et al 1994;Rich et al 1996;Sternburg and Feldhamer 1997;Bruseo et al 1999). Aquadro and Patton (1980) reported only the Amy-1 76 and the Amy-1 100 in their New York P. maniculatus and P. leucopus, respectively, but had assayed only four individuals of each species.…”

“…Although the ratio was larger for P. m. gracilis than P. l. noveboracensis in our study, the two species had ratios ≥ 1 (Table 1). In previous studies where head-body lengths were taken from dead specimens, the average tail to head-body ratios for both species were < 1, although P. l. noveboracensis had larger ratios than either P. m. bairdii or P. m. nubiterrae (Feldhamer et al 1983;Sternburg and Feldhamer 1997). We found that the tail to head-body ratio is not a diagnostic characteristic for the field identification of P. l. noveboracensis and P. m. gracilis in central New York as did Bruseo et al (1999).…”

“…We found that hind-foot length was not a reliable distinguishing characteristic for the two species as also suggested by others (Baker 1983;Feldhamer et al 1983;Palas et al 1992;Whitaker and Hamilton 1998). Ear lengths were more variable than other reported ranges, and have resulted from the difficulties measuring live mice in the field (Baker 1983;Feldhamer et al 1983;Sternburg and Feldhamer 1997).…”

“…Aquadro and Patton's (1980) approach has been employed successfully in various ecological studies of eastern Peromyscus to improve the accuracy of field identifications (Feldhamer et al 1983;Merriam et al 1989;Palas et al 1992;Garman et al 1994;Rand et al 1993;Kilpatrick et al 1994;Rich et al 1996;Sternburg and Feldhamer 1997;Bruseo et al 1999). Several researchers have concluded that identification of P. maniculatus and P. leucopus in northeastern North America can be reliably done only using molecular markers (Feldhamer et al 1983;Palas et al 1992;Kilpatrick et al 1994;Rich et al 1996;Sternburg and Feldhamer 1997). Because identification with salivary amylase is time consuming and requires an extensive laboratory analysis, a method for quick field identification would be beneficial for mark-recapture studies.…”

“…For identification of P. l. noveboracensis and P. m. gracilis, Garman et al (1994) developed a discriminantfunction equation with the tail-to-body length ratio as the independent variable, but they did not report the equation or its ability to discriminate between species. Feldhamer et al (1983) and Sternburg and Feldhamer (1997) constructed discriminant-functions using only external characteristics of P. l. noveboracensis and P. m. gracilis and classified 98.6% of the Peromyscus correctly. Their measurements, however, were taken from dead individuals and thus are more accurate than is possible with live mice.…”