Morphological variation in intergrade pupfish populations from the Pecos River, Texas, U.S.A.

Abstract

In the early 1980s, sheepshead minnow Cyprinodon variegatus was introduced into the Pecos River, Texas, U.S.A. where it hybridized with the endemic Pecos pupfish C. pecosensis. By 1985, pupfish populations throughout approximately 300 km of the river consisted exclusively of individuals of hybrid origin (intergrades). There was significant (P<0·05) geographic variation in most morphological characters; the general pattern of variation was of a bidirectional cline centred near Pecos, Texas. At that site, morphology of intergrade populations resembled mostly that of the introduced species. Upstream and downstream from Pecos, morphology shifted progressively toward that typical of the native form. Intergrade populations were morphologically intermediate to the parental forms, showed a rapid approach to random assortment of characters, and generally exhibited greater morphological variability than occurred in either parent species. These observations and the consistent lack of bimodality in frequency distributions of a morphological hybrid index support the contention that intergrade populations comprise panmictic admixtures of C. variegatus and C. pecosensis. 1997 The Fisheries Society of the British Isles

Phylogeography of the banded killifish (Fundulus diaphanus): glacial races and secondary contact

“…Given that eastern reference samples were not fixed for the long X‐ src allele (Table I, mean = 0·91), the frequency in each sample was adjusted using a multiplicative factor of 1·1. Morphological similarity to the eastern type was estimated with a hybrid index calculated from the PC1 scores (Wilde & Echelle, 1997). The average of reference groups coordinates (west: sites 1 and 3; east: sites 18–20) were standardized to 0 and 1, respectively.…”

Understanding the establishment success of non‐indigenous fishes: lessons from population genetics

“…Rieseberg et al (1999) showed that this phenomenon, known as transgressive segregation, is commonly observed in hybrids. Nine out of 10 fish hybrids listed in Rieseberg et al (1999) showed evidence for transgressive segregation in at least some of the phenotypic traits including one example of hybridization between native and invasive species (Wilde & Echelle, 1997). Transgressive phenotypes were also detected in a mosaic hybrid zone between the native cyprinid Chondrostoma toxostoma (Vallot) and an invasive congener Chondrostoma nasus (L.) (Costedoat et al , 2005, 2007).…”

Morphologic comparisons of hatchery-reared specimens of Scaphirhynchus albus, Scaphirhynchus platorynchus, and S. albus�נS. platorynchus hybrids (Acipenseriformes: Acipenseridae)

“…Not all fish hybrids exhibit intermediacy between parental species (Leary et al., 1983), and the assumption that S. albus × S. platorynchus hybrids should be intermediate was questioned (Campton et al., 2000) and has no empirical basis. Additionally, genetically mediated morphologic variation can be expressed differently in fish hybrids relative to either parental species, and some hybrids may have more morphologic variability than either parental species (Wilde and Echelle, 1997). Even if most hybrids have intermediate (or near intermediate) index scores, some specimens may be indistinguishable from either parental species due to a particularly high or low index score.…”