Biodiversity of sweetpotato (iPomoea batatas,Convolvulaceae) in Southern Mexico

Between 1987 and 1992 the phytogeographic region of southern Mexico was explored during three collecting trips made in search of cultivated and wild germplasm of the sweetpotato (Ipomoea batatas). The first trip was made in 1987, when we collected wild species in Ipomoea section Batatas found in the southeastern and southwestern regions of Mexico. A second trip was made in 1990, when we collected accessions of the cultivated species as well as wild species in the southeast, southwest and northeast. The third and final trip was oriented at identification, characterization and collecting seeds in the ecological niches ofI.tabascana andI.umbraticola. As a result of the three trips we collected 165 accessions of cultivated and wild germplasm with populations dispersed in 147 localities in 15 states of the Mexican region: Veracruz, Tabasco, Campeche, Chiapas, Oaxaca, Yucatán, Guerrero, Michoacán, San Luis Potosí, Hidalgo, Querétaro, Tamaulipas, Guanajuato, Puebla and México. Of the total accessions some 64 (38.3%) were of the cultivated species including nine accessions of feral material, and 103 accessions (61.7%) were of wild species made up of 59 accessions of seven species in the section Batatas, 37 of other species in the family Convolvulaceae, and seven yet to be determined. We have identified the largest genetic biodiversity in six localities of five states: Tabasco, Oaxaca, Michoacán, San Luis Potosí, and Puebla. Biodiversity maintenance in this region is associated with the day-of-the-dead festivities.     

Genetic population structure and call variation in a passerine bird, the satin bowerbird, Ptilonorhynchus violaceus

Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. One hypothesis to explain this variation is that it is associated with geographic isolation among populations and therefore should follow a vicariant pattern similar to that typically found in neutral genetic markers. Alternatively, if environmental selection strongly influences vocalizations, then genetic divergence and vocal divergence may be disassociated. This study compared genetic divergence derived from 11 microsatellite markers with a metric of phenotypic divergence derived from male bower advertisement calls. Data were obtained from 16 populations throughout the entire distribution of the satin bowerbird, an Australian wet-forest-restricted passerine. There was no relationship between call divergence and genetic divergence, similar to most other studies on birds with learned vocalizations. Genetic divergence followed a vicariant model of evolution, with the differentiation of isolated populations and isolation-by-distance among continuous populations. Previous work on Ptilonorhynchus violaceus has shown that advertisement call structure is strongly influenced by the acoustic environment of different habitats. Divergence in vocalizations among genetically related populations in different habitats indicates that satin bowerbirds match their vocalizations to the environment in which they live, despite the homogenizing influence of gene flow. In combination with convergence of vocalizations among genetically divergent populations occurring in the same habitat, this shows the overriding importance that habitat-related selection can have on the establishment and maintenance of variation in vocalizations.     

Diatom Succession and Interaction in Littoral Periphyton and Plankton

Periphyton and plankton samples were collected at four littoral stations in a relatively shallow, eutrophic lake (Elk Lake, B.C., Canada) over a six month period from August 1967 to January 1968. The most abundant planktonic diatoms demonstrated a pattern of seasonal succession typical of temperate lakes, and all were present in the periphyton. This pattern was identical at all stations:Fragilaria crotonensis was dominant from August to October,Asterionella formosa in November and December, andMelosira italica (plusM. varians) in January.F. virescens, although never dominant, peaked in October. Periphyton communities were dominated byAchnanthes minutissima, Cocconeis placentula, F. crolonensis andF. virescens. Considerable station variation in successional patterns occurred over different exposure periods; station differences were least in those samples immersed for monthly intervals, and greatest in those immersed for a cumulative four-month period. Interaction between the phytoplankton and periphyton was illustrated by the occurrence of species common to both habitats. A decrease in cell numbers and percent abundance of these species in planktonic populations coincided with their increase in the periphyton, a relationship which appeared dependent on the breakdown of thermal stratification in November. For example, following turnover,F. crotonensis andA. formosa settled out of the plankton and correspondingly increased in percent abundance in the periphyton. This interdependence was less evident in the four-month samples, whereA. minutissima andC. placentula dominated throughout the entire period and appeared to out-compete the more typical planktonic components for diminishing substrate area. Species interaction or competition was accentuated as exposure duration and periphyton total cell standing crops increased and species diversity decreased, and appeared to account in part, for station differences in successional patterns.     

Somatic hybrids between Solanum bulbocastanum and potato: a new source of resistance to late blight

 Solanum bulbocastanum, a wild, diploid (2n=2x=24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tuberosum PI 203900 (2n=4x=48) yielded hexaploid (2n= 6x=72) somatic hybrids that retained the high resistance of the S. bulbocastanum parent. RFLP and RAPD analyses confirmed the hybridity of the materials. Four of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC₁ progeny segregated for resistance to the US8 genotype (A-2 mating type) of P. Infestans. Resistant BC₁ lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field-plot in Wisconsin, to which no fungicide was applied, two of the BC₁ lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-blight epidemic. In contrast, under these same conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. These results indicate that effective resistance to the late-blight fungus in a sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and that this resistance can then be further transmitted into potato breeding lines by sexual crossing. Received: 27 October 1997 / Accepted: 11 November 1997     

Historical stocking data and 19th century DNA reveal human‐induced changes to native diversity and distribution of cutthroat trout

Many species are threatened with extinction and efforts are underway worldwide to restore imperilled species to their native ranges. Restoration requires knowledge of species' historical diversity and distribution. For some species, many populations were extirpated or individuals moved beyond their native range before native diversity and distribution were documented, resulting in a lack of accurate information for establishing restoration goals. Moreover, traditional taxonomic assessments often failed to accurately capture phylogenetic diversity. We illustrate a general approach for estimating regional native diversity and distribution for cutthroat trout in the Southern Rocky Mountains. We assembled a large archive of historical records documenting human‐mediated change in the distribution of cutthroat trout (Oncorhynchus clarkii) and combined these data with phylogenetic analysis of 19th century samples from museums collected prior to trout stocking activities and contemporary DNA samples. Our study of the trout in the Southern Rocky Mountains uncovered six divergent lineages, two of which went extinct, probably in the early 20th century. A third lineage, previously declared extinct, was discovered surviving in a single stream outside of its native range. Comparison of the historical and modern distributions with stocking records revealed that the current distribution of trout largely reflects intensive stocking early in the late 19th and early 20th century from two phylogenetically and geographically distinct sources. Our documentation of recent extinctions, undescribed lineages, errors in taxonomy and dramatic range changes induced by human movement of fish underscores the importance of the historical record when developing and implementing conservation plans for threatened and endangered species.     

Lipoprotein(a) in women twins: heritability and relationship to apolipoprotein(a) phenotypes.

Lp(a) is a unique lipoprotein consisting of an LDL-like particle and a characteristic protein, apo(a). Increased levels of Lp(a) constitute a risk factor for coronary heart disease. Variation in the size of the apo(a) protein is a phenotype controlled by the apo(a) gene on chromosome 6 and is related to Lp(a) plasma levels. Based on 169 MZ and 125 DZ adult female twin pairs, this study's purpose was to estimate the proportion of the variation in Lp(a) levels that is due to genetic influences and to determine the extent to which the apo(a) locus explains this heritability. Lp(a) levels were significantly more similar in MZ twins than in DZ twins: mean co-twin differences were 3.9 +/- 5.7 mg/dl and 16.0 +/- 19.9 mg/dl (P less than .001), respectively. Intraclass correlations were .94 in MZ twins and .32 in DZ twins, resulting in a heritability estimate of .94 (P less than .001). Heritability was then calculated using only co-twins with the same apo(a) phenotype: the heritability estimate decreased to .45 but was still highly significant (P less than .001). Therefore, on the basis of heritability analysis of women twins, Lp(a) levels are almost entirely genetically controlled. Variation at the apo(a) locus contributes to this heritability, although other genetic factors could be involved.     

Forward chemical genetic screens in Arabidopsis identify genes that influence sensitivity to the phytotoxic compound sulfamethoxazole

The rise of high mountain chains is widely seen as one of the factors driving rapid diversification of land plants and the formation of biodiversity hotspots. Supporting evidence was reported for the impact of the rapid rise of the Andean mountains but this hypothesis has so far been less explored for the impact of the “roof of the world”. The formation of the Himalaya, and especially the rise of the Qinghai–Tibetan Plateau in the recent 20 million years, altered the monsoon regimes that dominate the current climates of South East Asia. Here, we infer the hypothesis that the rise of Himalaya had a strong impact on the plant diversity in the biodiversity hotspot of the Southwest Chinese Mountains. Our analyses of the diversification pattern of the derived fern genus Lepisorus recovered evidence for changes in plant diversity that correlated with the strengthening of South East Asian monsoon. Southwest China or Southwest China and Japan was recovered as the putative area of origin of Lepisorus and enhancing monsoon regime were found to shape the early diversification of the genus as well as subsequent radiations during the late Miocene and Pliocene. We report new evidence for a coincidence of plant diversification and changes of the climate caused by the uplift of the Himalaya. These results are discussed in the context of the impact of incomplete taxon sampling, uncertainty of divergence time estimates, and limitations of current methods used to assess diversification rates.     

Seasonal changes in the effects of arginine vasotocin and stretch on Anolis uterine contractions in vitro

We determined the effects of acute stretch on spontaneous and arginine vasotocin (AVT)-driven contractions of the Anolis carolinensis uterus in vitro. Whole uteri from reproductively inactive females (October) were placed in a bath of oxygenated 32 degrees C Anolis "Ringer's." Two initial tensions were utilized, 1.5 g or 15 g, the latter being an estimate of the tension on the wall of a uterine compartment. Uteri were then exposed to either saline or AVT (50 ng/ml), and spontaneous or AVT-driven contractions were recorded for 20 min with the use of a strain gauge and physiograph. A similar experiment was performed on uteri from reproductively active females in the summer (June). Our results indicate that the effects of acute stretch and AVT on uterine contractility were qualitatively similar in summer and fall. That is, AVT induced a tonic contraction; stretch decreased the duration of the tonic contraction; the saline-treated uteri exhibited spontaneous rhythmic contractions; AVT increased the amplitude of the rhythmic contractions, but only at the lower tension; there were no effects of AVT on the timing (contraction interval, duration, rest interval) of the rhythmic contractions; and stretch increased the frequency of the rhythmic contractions. Season greatly influenced the magnitude of these contractile phenomena. Uteri tested during the breeding season exhibited greater distensibility, an increase in the amplitude and duration of the AVT-driven tonic contraction, and an increase in the frequency of both spontaneous and AVT-driven rhythmic contractions because of a decrease in both contraction duration and rest interval.(ABSTRACT TRUNCATED AT 250 WORDS)