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ABSTRACT-We provide the first description of behavior in the Catarina pupfish (Megupsilon aporus). Aggressive, courtship, and spawning behaviors resemble those of other North American cyprinodontids. However, M. aporus differs from others in the group in absence of breeding territoriality in males. Male M. aporus often perform opercular rotation during aggressive displays and jaw-nudging during courtship, behaviors that, among other North American cyprinodontids, are absent or known only in Floridichthys. Some unusual features of behavior (lack of territoriality) and morphology (dwarfism; absence of pelvic fins) in M. aporus might have been shaped by interaction with a cohabitant, the Potosi pupfish Cyprinodon alvarezi.
RESUMEN-Proporcionamos la primera descripcíon del comportamiento en el cachorrito enano del Potosí (Megupsilon aporus). El comportamiento de agresi ón, cortejo y desove se asemeja a el de otros cyprinodóntidos norteamericanos. Sin embargo, M. aporus difiere de los demás al carecer la territorialidad en machos reproductores. Machos de M. aporus frecuentemente muestran una rotaci ón opercular durante exhibiciones agresivas y un empuj ón mandibular durante el cortejo, comportamientos que, entre los cyprinodóntidos norteamericanos, están ausentes o son conocidos solamente en Floridichthys. Algunas de las características inusuales del comportamiento (falta de la territorialidad) y morfología (enanismo; ausencia de aletas pélvicas) de M. aporus podrían haber sido conformadas por la interaccíon con un cohabitante, Cyprinodon alvarezi.
The monotypic genus Megupsilon, which appears to be >7,000,000 years old (Echelle, 2008), is extinct in the wild and virtually unknown except for comments on its demise (Contreras and Lozano, 1996) and studies of its systematic relationships (Parenti, 1981; Parker and Kornfield, 1995; Costa, 1997; Echelle et al., 2005). The genus, represented by M. aporus (Catarina pupfish), once occupied a small spring system near El Potosí, Nuevo Léon, Mexico, where it co-occurred with another endemic pupfish, Cyprinodon alvarezi (Potosi pupfish). By 1994, both species were extinct in the wild as a result of overmining of groundwater and drying of habitats (Contreras and Lozano, 1996).
The continued existence of M. aporus is extremely precarious. Until recently, two lineages initiated separately with wild-caught individuals >20 years ago were being maintained by private aquarists and university personnel in Mexico, Germany, and the United States (A. Valdez, pers. comm.). In the summer of 2012, the two lineages consisted of only one population each, one...