Black Bass Classification Revisited

By Dave Votaw

Identifying bass isn't as simple as largemouth, smallmouth, spot!

While reading the November 2010 issue of Bass Master magazine recently, my attention was drawn to the article “Men on a Mission” announcing the successful completion of the Bass Slam by twelve fishermen.  The Bass Slam Challenge, initiated by Bass Master in 2009, requires anglers to catch an “average” specimen of each species in the black bass genus Micropterus.  There is no time limit, although these first twelve anglers accomplished the Challenge in just one year.  My first thought was to take on the challenge in 2011 and do it with a fly rod (and I’m not the only Fly Fish Ohio staffer who had the same idea, so look for a report on the Bass Slam fly rod challenge at FlyFishOhio.com this year).  However, my second thought was ‘how many fish did these guys have to catch?’  For 2010 they needed only eight, but I knew the black bass classification was in a state of flux, and indeed in 2010 a new species, the Alabama spotted bass, was added to the genus (Bass Master 2010). 

The genus Micropterus was first described in 1802 by Lacepede and the classification has continued to evolve since.  Fisheries scientists never seem to tire of examining the relationships among these economically important species of game fish.  Not until 1949 was the largemouth bass added to Micropterus unifying the known major species of the genus – M. dolomieu, punctulatus, and salmoides – for the first time (Bailey and Hubbs, 1949).  The most recent additions as distinct species in the genus are the shoal bass (M. cataractae) in 1999 (Williams and Burgess, 1999), and in 2010 the Alabama spotted bass (M. punctulatus henshalli).  Presumably the Alabama spot will receive a new Linnaean classification that does not imply it to be a subspecies of M. punctulatus, the spotted bass, as they are not closely related.

Ecological and management studies on the major species of Micropterus are extensive due to the economic importance of these species.  However the phylogenetic relationships among the nine species have not been elucidated until recently through molecular genetic analysis; typically morphological characteristics are used in taxonomy and tend to result in great debate on species identification among fishermen, especially considering the variety of common and regional names used for sport fish and their changing palettes of coloration from one geographic area to another.  Kassler et al. (2002) assessed the genetic relationships among the species and subspecies recognized in Micropterus using techniques to analyze morphological variation, variation in the nuclear genome, and variation in mitochondrial DNA (mtDNA).  For the morphological analysis, 14 meristic characteristics (characteristics that are countable structures occurring in series, eg., dorsal rays, scales on the lateral line) were used to differentiate Micropterus species.  Employing discriminant function analysis, 86% of the 313 specimens examined were classified correctly.  The authors concluded that “… classification rates were reasonably high for all species except M. coosae, which overlapped greatly with M. treculi.”

Allozyme protein analysis of nuclear genome material using electrophoresis produced two definitive conclusions:  the genetic distinction between M. salmoides and M. floridanus; and a lack of distinctiveness between M. dolomieu and the Neosho subspecies M. dolomieu velox.  Florida strain largemouth and Northern largemouth have not only allelic differences at several allozyme loci, they also exhibit large mtDNA sequence differences, as well as distinct morphological differences.  With regard to M. dolomieu velox, the Neosho smallmouth bass, Kassler et al. (2002) conclude that the status of the Neosho smallmouth bass remains to be explored, and that further analysis using multiple techniques need to be conducted before a complete understanding of smallmouth bass taxonomy can be achieved.  These conclusions reflect Stark and Echelle’s (1998) allozyme research that found evidence of three different lineages of M. dolomieu in the Missouri, Arkansas, and Oklahoma Ouachita uplands.  Kassler et al. also note a high level of divergence between M. punctulatus and M. punctulatus henshalli; in addition to being geographically separated, they are morphologically and genetically different, indicating that the Alabama spot is not closely related to M. punctulatus, but rather is most closely related M. coosae, the redeye bass. 

Kassler et al. summarize the phylogenetic relationships among the nine species of Micropterus in the following figure illustrating four lineages based on the genetic analyses discussed.

 

Summary of phylogenetic relationships based on mtDNA analyses (Kassler et al., 2002)

 As the figure shows, all nine species of Micropterus have a single common ancestor; these species are believed to be ‘recently’ evolved, meaning hybridization in the wild is possible despite the fact that they are separate, distinct species. Hybridization has been demonstrated in the laboratory.  Maladaptive genes can be introduced into a species or subspecies when different species are mixed through a stocking program, resulting in hybridization and a loss of genetic fitness in the resident stock.  This maladaptation takes the form of a breakdown in the genetic makeup that evolved over time through natural selection.  Wildlife managers need to know the genetic structure of species, particularly how distantly related they are, to be able to make responsible decisions that protect the genetic resources of the species involved.  Little of this data is currently available. 

Within Micropterus, the most well known example illustrating the need for species-specific genetic information is the ill-conceived introduction of Florida strain largemouth bass into populations of native M. salmoides (Phillip et al., 2002).  Fisheries managers expected bigger largemouth bass to result from hybridization of the two species now known to be genetically distinct, but improvement was not found and a loss in the genetic fitness of the resident largemouth bass population that evolved in a region uninhabited by M. floridanus took place.  The widespread distribution of smallmouth bass into non-native regions has also led to the loss of genetic integrity in populations of M. treculi (Guadalupe bass) and M. punctulatus.  Development of further genetic information regarding the relationships among game fish species will help stop the growing erosion of genetic resources found in Micropterus and other game fish taxonomic groups. 

References:

 

Bass Master. 2010.  Men on a mission.  Vol. 43(10):26-31.

 

Kassler TW et al. 2002.  Molecular and morphological analyses of the black basses:  Implications for taxonomy and conservation.  Am Fish Soc Symposium 31:291-322.

 

Philipp DP et al. 2002.  Mixing stocks of largemouth bass reduces fitness through outbreeding depression. Am Fish Soc Symposium 31:349-363.

 

Stark WJ and Echelle AA. 1998. Genetic structure and systematics of smallmouth bass, with emphasis on interior highlands populations.  Trans Am Fish Soc 127:393-416.

 

Williams JD and Burgess GH. 1999.  A new species of bass, Micropterus cataractae (Teleostei: Centrarchidae) from the Appalachicola river basin in Alabama, Florida, and Georgia.  Bull Fl Mus of Nat Hist.