Florida Largemouth Bass in Texas: an Exception to the Rule

Florida largemouth bass in Texas: an exception to the rule

Population genetic theory suggests that lineages introduced outside of their native range should show reduced fitness measured as survival, reproductive success, or growth.  These predictions have been shown to be true for numerous species, including largemouth bass Micropterus salmoides under various conditions. However the Texas Parks and Wildlife Department (TPWD) has been stocking Florida largemouth bass (FLMB; M. s. floridanus) since 1972 and the introduction of FLMB to Texas seems to be an exception to this rule.  Across reservoirs FLMB allele frequency increased from 0% prior to stocking, to 36% in 1992, to nearly 60% today.  The number of reservoirs yielding trophy bass (≥4.54 kg) increased from one before 1980 to 61 today.  Though FLMB genotypes constitute only 7% of the general population (3% native largemouth bass, 2% F₁, 88% F_x hybrids) they make up 51% (n=263) of trophy bass donated to TPWD (n=515).  No native largemouth bass has ever been donated.  The success of FLMB may be the result of competition in anthropogenically modified environments (i.e., Texas reservoirs), the fact that these environments more closely resemble the aquatic landscape of Florida than the lotic systems in which native largemouth bass evolved,  or the shared latitude unique to these geographic regions in North America.  Whatever the cause, introductions of FLMB to Texas, and subsequent hybridization with native largemouth bass, has not resulted in populations of maladaptive genotypes, poor survival, or reduced rates of growth.