Megupsilon aporus and Cyprinodon alvarezi: Observations in the field and laboratory behavior of two cyprinodontid fishes extinct in the wild

Authors: Robert K. Liu

Year: 2008 (xl)

Abstract

The speciose and fast-evolving Cyprinodontids have been, and continue to be, the subject of much phylogenetic research and management concern. Many species are endangered, and between 1971 and 1997, 7 species of Mexican Cyprinodon and the monotypic genus Megupsilon were extirpated in their habitats, although some are being maintained in captivity. For most of these species now extinct in the wild, as well as many still extant in the wild, nothing or little is known about their biology, especially behavior. Megupsilon and Cyprinoodon alvarezi, both from El Potosí, exemplify this lack of behavioral data. Discovered between 1948 and 1961, described in 1972, and extinct in the wild sometime after 1994 but with stocks maintained in captivity, Miller and Walters (1972) mention two unique behaviors of M. aporus, but nothing more has appeared regarding their behavior. In 1968, while finishing my dissertation on the comparative behavior of Cyprinodon, for about 10 months I kept and occasionally studied the laboratory behavior of about 40 specimens of these two species, and in 1972 I spent a day observing them in their then extant habitat. I report on those studies here, noting that Cyprinodon alvarezi behaves much like others of the C. eximius complex, but male M. aporus show Opercular Rotation (OR) and Jaw Nudging (JN), two behavioral acts not reported for any other New World Cyprinodontids except Floridichthys carpio, in which males exhibit a form of JN. OR may be very similar to Lowering Branchiostegal Membrane (LB), seen in Fundulus and in 3 genera of Old World cyprinodontids. Interestingly, JN also occurs in Fundulus, Adinia and at least 2 genera of Old World cyprinodontids. These and other observations will be discussed in relation to cyprinodontid phylogeny.