A redescription of Moina hutchinsoni, a rare cladoceran (Branchiopoda : Anomopoda) found in remnants of a Mexican saline lake, with notes on its life history

摘要

Moina hutchinsoni Brehm, 1937, a nearctic anomopod cladoceran, was observed in shallow ephemeral ponds of the former Texcoco Lake, near Mexico City, Mexico. The type material, from Lake Winnemucca, Nevada, was considered lost; additional topotypic material could not be obtained from that locality because the site is completely dry. The species is redescribed herein based on specimens from Texcoco Lake and Border Lake, Nebraska. Specimens from these localities were compared to study the morphological variability of this species; differences were found in the cuticular hair patterns on head, body, antennules, and second antennae, in the number of feathered setae on the postabdomen, and in the structure of pectens in claws. The life cycle of this rare species was analyzed in the laboratory. In culture, diet consisted of the microalgae Ankistrodesmus falcatus (freshwater) and Chlorella sp. (marine); both algae were consumed by the cladoceran. Culture temperature ranged between 15degrees and 20degreesC, and salinity range was 5-25 g L-1. Cultured specimens were significantly larger than those from field populations. Lower temperatures correlated with a delayed first reproduction and with a longer inactive time between succeeding clutches. The wide thermal and salinity ranges tested during culturing, plus the ability of these animals to consume algae not normally found in its natural environment, suggest a euryecious character of this species in laboratory conditions that contrasts with the affinity of natural populations for high-salinity habitats. The lifespan of this species is longer than that of other moinids; it may be the longest-lived species within the Moinidae. The average clutch size ranged from 12 to 24.8 neonates; optimal environmental conditions differed for number of neonates and maximum clutch size. Loss of the natural environments (saline lakes) where this rare species has been recorded, both in Mexico and U.S.A., suggests an endangered status of this cladoceran.