The Preble's meadow jumping mouse: subjective subspecies, advocacy and management

Abstract

I read with concern the letters to the editor regarding the Preble’s meadow jumping mouse Zapus hudsonius preblei in which Martin (2006) criticized Ramey et al. (2005) for questioning the subspecies designation and the editor for a failed peer review, and Crandall (2006) defended his editorship. However, the debate over the subspecies status of the Preble’s meadow jumping mouse does not properly acknowledge the subjectivity of the subspecies category. Designation of subspecies status is inherently subjective and this should be openly admitted by both sides of the debate. Accusations of advocacy in this issue are spurious because applied fields such as wildlife conservation or agriculture have inherent advocacy for management objectives. As discussed below, I suggest management units of intraspecific groups should be based on geography, not subjective judgements of subspecies status or genetic diffentiation. The subspecies status of this mouse has been discussed extensively (Ramey et al., 2005, 2006; Crandall, 2006; Martin, 2006; Vignieri et al., 2006) because it has been listed as threatened under the Endangered Species Act (ESA). Briefly, the Preble’s mouse was designated a subspecies with limited descriptive morphological data. There are no diagnostic characters that unequivocally distinguish it from conspecifics. It does not have monophyletic mitochondrial DNA. It may be geographically isolated from, and have different allele frequencies than, con-specific populations. Sample sizes and locations studied are probably small relative to population numbers. The allele frequency differences are for DNA loci that are usually considered selectively neutral. There are no data documenting local adaptation, but it is possible. Given the lack of quantitative criteria for naming subspecies the Preble’s mouse could be considered a legitimate subspecies, or not a legitimate subspecies. My concerns center on the lack of appreciation of the subjectivity of subspecies and on misunderstanding of the nature of advocacy and management in the context of the Preble’s mouse. It is well established that the subspecies category is subjective (reviewed by Cronin, 1993, 2006; Geist, O’Gara & Hoffmann, 2000; Zink, 2004). This includes other cases involving the ESA (e.g. Cronin, 1997; Zink et al., 2000) and recognition of this could have avoided much of the debate over the Preble’s mouse. The following quotes are telling: ‘Most of the prominent commentators on the theory of speciation have been careful to emphasize the inherently subjective and even arbitrary nature of racial limits.’ ‘. . . we are convinced that the subspecies concept is the most critical and disorderly area of modern systematic theory . . .’ (Wilson & Brown, 1953). Wilson and Brown note the synonymy of the terms subspecies and geographical race. It is noteworthy that Krutzsch (1954) named the Preble’s subspecies in the year following Wilson & Brown’s (1953) classic critique of subspecies. Krutzsch’s analysis was typical of many at the time, with few specimens and a qualitative subspecies designation. ‘. . . because so many characters show independent patterns of geographic variation, and because so many loci are polymorphic and vary in allele frequency from one population to another, some combination of characters will distinguish every population from all others so there is no clear limit to the number of subspecies that can be recognized.’ (Futuyma, 1986, pp. 108–109). ‘. . . present applications of the subspecies concept are uneven, frequently undocumented and lead to no improvement of either evolutionary theory or practical taxonomy.’ (Vanzolini, 1992, p. 189). ‘Widespread species thus can be divided into any number of different sets of ‘subspecies’ simply by selecting different characteristics on which to base them.’ ‘As . . . with other species, geographic variation . . . does not allow Homo sapiens to be divided into natural evolutionary units. That basic point . . . has subsequently been demonstrated in a variety of organisms . . . and use of the subspecies (or race) concept has essentially disappeared from the mainstream evolutionary literature.’ (Ehrlich, 2000: 49, 291).