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

In the early 1980s, sheepshead minnow Cyprinodon variegates 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. variegates and C. pecosensis .     

Temperature preferences and tolerances of three fish species inhabiting hyperthermal ponds on mangrove islands

The fish species Cyprinidon artifrons, Floridichthys carpio, and Gambusia yucatana inhabit shallow mangrove ponds off the coast of Belize. Portions of these ponds experience a diurnal temperature change from 26 °C at night to 40 °C and above during midday. Repeated field observations indicate Cyprinidon prefer the warmer (and much larger) portions of the ponds whereas the other two species stay in the cooler areas.The hypothesis that temperature is serving as a cue for partitioning within the ponds was supported by laboratory thermal gradient tests in which Cyprinidon preferred temperatures clearly higher than the other two species.The critical thermal maximum (CTM) was determined for the three species using members that had been acclimated to either a daily cycling temperature similar to that for the ponds, or to the mean of the 24-hour cycle (30 °C). Cyprinidon acclimated to the cycling temperature had a CTM of 45.5 °C, which apparently sets a new record for fish CTM. Acclimation to a constant 30 °C lowered the CTM to 43.7 °C. Floridichthys and Gambusia acclimated to the cycled temperature had CTMs of 43.9 and 43.3 °C respectively, and 42.5 and 42.6 °C for those acclimated to 30 °C.All three species appear to have the ability to tolerate the high temperatures throughout the ponds but only Cyprinidon utilize the whole pond during the day. This may help to explain the large populations of Cyprinodon found in these mangrove ponds compared to the other species.     

Description of a new species from Laguna Chichancanab,Yucatan, Mexico: <Emphasis Type="Italic">Cyprinodon suavium</Emphasis> (Pisces: Cyprinodontidae)

Cyprinodon suavium is a new species that belongs to the endemic species flock from Laguna Chichancanab, Yucatan, Mexico, which is proposed to have evolved by sympatric speciation in the lake during the last 8000years. C. suaviumis distinguished from all other known Cyprinodon species by a flattened and concave inter- and postorbital skull roof and a terminal mouth with distinctive thickened lips. The short gut length and dietary items found in the gut indicate that C. suavium is one of the carnivorous members of the flock.     

Evolutionary history of Ash Meadows pupfish (genus <Emphasis Type="Italic">Cyprinodon</Emphasis>) populations inferred using microsatellite markers

Pupfish (genus Cyprinodon) persist in a series of isolated warm springs in Death Valley. Here we describe an analysis of microsatellite variation at six loci for nine populations encompassing three distinct taxa. Levels of genetic variation within populations and the pattern of relatedness among populations are best explained by spring elevation. Springs at higher elevations harbored less variation and exhibited greater among population divergence than lower elevation springs. This pattern reflects regional paleohydrological history showing a declining water table over the last 20,000 years. Continuing decline of the water table, a trend accelerated by local ground water mining, portends a future of increasing isolation and declining within-population variation.     

Summer movements of desert pupfish among habitats at the Salton Sea

Summer movement behavior of native desert pupfish (Cyprinodon macularius Baird and Girard) was evaluated among various habitats around the Salton Sea, located in southern California. Agricultural drains, shoreline pools, and Salt Creek were sampled six times between June 28 and September 16, 1999. Collected pupfish were marked using fluorescent elastomer implants. Unique marks were used at each site. Movements were detected from locations of recaptured pupfish. Desert pupfish were found in 10 of 12 sites sampled. Of 3239 pupfish captured during the study, 278 were recaptures, including 27 recaptures at areas different from where they were initially marked. The best evidence of pupfish movements was in the southwestern area of the Salton Sea between a drain and a connected shoreline pool. Movements were also observed from lower Salt Creek into a shoreline pool at the mouth of the creek as the water level dropped. The use of the Salton Sea as a migration corridor between habitats was not documented during this short study. The marking technique was successful and showed promise for future mark and recapture studies of desert pupfish.     

Distribution,habitat and conservation status of desert pupfish (Cyprinodon macularius) in the Lower Colorado River Basin,Mexico

In order to better determine the currentstatus of desert pupfish populations (Cyprinodon macularius macularius) in the LowerColorado River Basin of Mexico, bimonthly fishsampling and habitat evaluations were carriedout from September 1996 to August 1997 in sixlocalities of Baja California and Sonora.Desert pupfish were collected using minnowseines and traps. Four sampling sites are inSonora, in shallow marginal habitats of theCiénega Santa Clara (Hunters' Camp, Outletof the Welton-Mohawk channel, El Doctor andFlor del Desierto) and two are in BajaCalifornia (Cerro Prieto and streams south ofCerro Prieto). The most abundant fish speciessampled was native desert pupfish (C.macularius, 59%) followed by sailfin molly(Poecilia latipinna, 19%), redbellytilapia (Tilapia cf. zilli, 10%) and western mosquito fish (Gambusiaaffinis, 7%). Significant temporalfluctuations in distribution and abundance ofdesert pupfish populations, as previouslyreported for these populations, was againdocumented. The main anthropogenic factorsaffecting distribution and abundance of desertpupfish populations in the Mexican portion ofthe Lower Colorado River Basin are progressivealteration of aquatic and riparian habitats, aswell as presence of exotic fishes that havecaused the displacement or elimination ofnative fish populations. Both habitat andpresence of the desert pupfish populations inthe study area are controlled by theperiodicity, quality and volume of dischargesinto the Mexican portion of the basin from theUnited States.     

Fish habitat associations in a spatially variable desert stream

White sands pupfish Cyprinodon tularosa were sampled with minnow traps along the length of Lost River, a highly variable desert stream in New Mexico, to evaluate if their abundance, median standard length ( L _S) and sex ratio values differed by microhabitat variables. Habitat measurements were made in a 4 m² area around the minnow trap. White Sands pupfish populations were primarily structured by L _S. As specific conductance and surface area increased, median size of fish decreased. Shallow areas with higher specific conductance were correlated with an increased number of fish.     

Fitness landscape of sympatric pupfishes a useful tool for visualizing speciation

Arguably the most useful model of evolution emerged from the mind of Sewall Wright when he invented the fitness landscape (Wright 1932 ). In a recent issue of Molecular Ecology, Martin & Feinstein ( 2014 ) investigate the genetics and demographic history of an adaptive radiation of pupfish on San Salvador Island. Since the founder species colonized the island 10 000 years ago, two descendent species have appeared and in several lakes all three species (a durophage, a scale‐eater, and the generalist ancestral form) coexist. The three species are thought to occupy three distinct fitness peaks. The durophage and generalists' peaks are close, whereas the scale‐eater's peak is predicted to be distant and separated from the other two by a deep valley. Consistent with this view, gene flow between the two species on close fitness peaks is greater than the gene flow between these two species and the third species on a more distant peak. Correspondingly, the inferred fitness landscape predicts progress towards speciation, with more limited separation of species on close peaks, and that speciation is more complete for the scale‐eater. The article provides an illustrative example of the power afforded by analysis of large numbers of SNPs for estimating key parameters underlying evolutionary divergence.     

Role of male-male competition and female choice in the development of breeding coloration in pupfish (Cyprinodon pecosensis)

The function of male breeding coloration and the conditionsunder which it is expressed were investigated using two experimentalprotocols that differed in the degree of control of social factors.In tank experiments, focal males were separated by opaque orclear partitions or allowed to interact freely without partitions.In lake experiments, males were introduced into opaque or clearenclosures in the lake from which they were collected. Thisdesign tested the relative importance of breeding substrate,social interactions with other males, and presence of femalesand juveniles on the expression of breeding coloration and agonisticand mating behavior in pupfish. Breeding coloration was notexpressed in the absence of conspecifics, even in the presenceof suitable breeding substrate, or in the presence of juveniles.Breeding coloration was poorly developed when only males werepresent, was more intense in the presence of females, and darkenedsignificantly after a spawning bout Males in clear enclosuresin their natural lake habitat were in visual contact with conspecificsof both sexes and developed more intense blue breeding colorationthan males in the tank experiments that were in visual contactonly with other males. Uncon-fined males with territories inthe lake developed the most intense breeding coloration. Breedingcoloration of male pupfish is a facultative trait that is welldeveloped when breeding females are present and plays a majorrole in the attraction and courtship of mates. However, maximumdevelopment of breeding coloration by territorial males suggeststhat intrasexual and intersexual selection act concordantlyon this trait.[Behav Ecol 7: 431-437 (1996)]     

Microsatellite DNA analysis of success in conserving genetic diversity after 33 years of refuge management for the desert pupfish complex

Refuge populations of Cyprinodon macularius and Cyprinodon eremus , the extant members of the endangered desert pupfish complex, have been maintained for up to 33 years in semi-natural refuges. We examined the success of the refuge program in maintaining diversity at four microsatellite DNA loci in 24 refuge populations of C. macularius and six of C. eremus that include, respectively, seven and four lineages representing original translocations from the wild. These lineages have been maintained with essentially no inoculations of genetic material from the wild and, except for one refuge, no intermixing of lineages. Comparison with wild-source populations showed marked declines in diversity within local refuges and within lineages, but relatively minor declines for the composite of all refuge populations for each species. In genetic makeup, the refuge populations generally clustered by lineage, indicating significant genetic drift early in lineage history. The results indicate that, with relatively minor adjustments in management, the refuge program can successfully preserve a large portion of the wild genetic diversity in the desert pupfish complex.