Natural selection reinforces speciation in a radiation of neotropical rainforest plants

The importance of reinforcement, that is, natural selection that strengthens reproductive isolation between incipient species, remains controversial. We used two approaches to test for reinforcement in a species radiation of Neotropical gingers in the genus Costus. First, we conducted an intensive study of Costus pulverulentus and Costus scaber, two recently diverged species that co-occur and share hummingbird pollinators. The hummingbird pollinators transfer pollen between these Costus species, but hybrids are rarely found in nature. By performing pollinations between populations of C. pulverulentus and C. scaber from three sites across the species' geographic ranges, we find that pollen-pistil incompatibilities acting prior to fertilization have evolved only between locally sympatric populations, whereas geographically distant populations within the region of sympatry and allopatric populations remain fully interfertile. Second, we conducted a comparative study of isolating mechanisms across the genus. We find lower seed set due to pollen-pistil incompatibility between species pairs that co-occur and experience pollen transfer in nature compared to species pairs that are otherwise isolated, regardless of genetic distance. Taken together, these studies indicate that crossing barriers prevent potentially maladaptive hybridization and effectively reinforce the speciation process. Our results add to mounting evidence for reinforcement from animal studies and show that plant speciation may also involve complex mate recognition systems. Reinforcement may be particularly important in rapidly diverging lineages where ecological factors play a primary role in reproductive isolation, as may often be the case in tropical communities.     

A new sesquiterpene lactone from the roots of Saussurea lappa: structure-anticancer activity study

The dried roots of Saussurea lappa, called costus roots, are used in the traditional system of medicine for the treatment of cancer. In our investigation for the anticancer constituents from the hexane extract of this plant, a new sesquiterpene (1) was isolated along with the known compounds costunolide (2), β-cyclocostunolide (3), dihydro costunolide (4) and dehydro costuslactone (5). Their structures were established by the extensive spectroscopic analyses. In addition, costunolide and β-cyclocostunolide derivatives were synthesized using Michael-type addition reaction of NaOMe to the α-methylene-γ-lactone moiety. All the compounds were tested for their in vitro cytotoxic activity. Compound 1 exhibited potent cytotoxic activity and other compounds displayed moderate activity.     

Long Tongues and Loose Niches: Evolution of Euglossine Bees and Their Nectar Flowers1

I examined relationships between tongue length of orchid bees (Apidae: Euglossini) and nectar spur length of their flowers in the genera Calathea, Costus, and Dimerocostus using phylogenetically independent contrasts. Long‐tubed flowers have specialized on one or several species of long‐tongued euglossine bees, but long‐tongued bees have not specialized on long‐tubed flowers. Whereas long tongues may have evolved to provide access to a wider variety of nectar resources, long nectar spurs may be a mechanism for flowers to conserve nectar resources while remaining attractive to traplining bee visitors.     

Antidiabetic and antilipidemic effect of eremanthin from Costus speciosus (Koen.)Sm., in STZ-induced diabetic rats

The increasing prevalence of diabetes mellitus worldwide is an issue of major socio-economic concern. Diabetes mellitus is a complex and a multifarious group of disorders that disturbs the metabolism of carbohydrates, fat and protein. Medicinal plants play an important role in the management of diabetes mellitus especially in developing countries. Costus speciosus is widely used in Indian medicine to treat various diseases. Eremanthin was isolated from C. speciosus. The structure was identified using gas chromatography–mass spectrometry (GC–MS) analysis. Eremanthin was administered to streptozotocin (STZ) (50 mg/kg bw) induced diabetic male Wistar rats at different doses (5, 10, 20 mg/kg bw) for 60 days. Plasma glucose level was significantly (p < 0.05) reduced in a dose dependent manner when compared to the control. In addition, oral administration of eremanthin (20 mg/kg bw) significantly decreased glycosylated hemoglobin (HbA_1c), serum total cholesterol, triglyceride, LDL-cholesterol and at the same time markedly increased plasma insulin, tissue glycogen, HDL-cholesterol and serum protein. Eremanthin also restored the altered plasma enzyme (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase and acid phosphatase) levels to near normal. Results of this experimental study indicated that eremanthin possessed hypoglycemic and hypolipidemic activities and hence it could be used as a drug for treating diabetes.     

Effect of Costus spiralis (Jacq.) Roscoe Leaves,Methanolic Extract and Guaijaverin on Blood Glucose and Lipid Levels in a Type II Diabetic Rat Model

This study aimed to isolate and identify flavonoids with hypoglycemic activity in Costus spiralis leaves. The methanolic extract (ME) was rich in flavonoids, while the powdered leaves (PL) contained considerable amounts of macro‐ and microelements. Oral acute treatment of streptozotocin (STZ)‐induced diabetic rats for 18 h with the C. spiralis PL, ME and isolated guaijaverin (GUA) lowered glycemia, improved oral glucose tolerance and inhibited liver lipid peroxidation. GUA and ME lowered plasma levels of low‐density and non‐high density lipoproteins; GUA also lowered total cholesterol levels. PL, ME and GUA did not significantly alter the plasma levels of triglycerides, high‐density lipoproteins, very low‐density lipoproteins, creatinine and aspartate transaminase, and the total protein levels in the kidney and liver tissues. Therefore, C. spiralis leaves are promising raw materials and rich sources of bioactive flavonoids for the development of novel antidiabetic drugs due to their hypoglycemic, antidyslipidemic and antioxidant actions.     

Costus spiralis (Jacq.) Roscoe: A Novel Source of Flavones with α‐Glycosidase Inhibitory Activity

Costus spiralis, a plant used in traditional Brazilian medicine for the treatment of complications in diabetes, was investigated. Assay of hexane, ethyl acetate, methanol, and aqueous fractions obtained by partition of a crude methanol extract of dried leaves of C. spiralis revealed that AGI activity was confined to the ethyl acetate fraction. Purification of this fraction yielded schaftoside and isoschaftoside. The AGI activities of the two flavones were lower than, but comparable with, that of the anti‐diabetic drug acarbose. In contrast, the IC₅₀ value of the ethyl acetate fraction was 1.95‐, 2.34‐, and 2.22‐fold higher than those of acarbose, schaftoside, and isoschaftoside, respectively. The results demonstrate for the first time that schaftoside and isoschaftoside are responsible, in part, for the AGI activity of C. spiralis. Our study suggests that further investigations into C. spiralis may lead to the discovery of additional compounds with antihyperglycemic activity.     

Influence of Soil Variation on Diosgenin Content Profile in Costus speciosus from Indo-Gangetic Plains

Costus speciosus is a rich source of commercially important compound Diosgenin, distributed in different regions of India. The present investigation was aimed to quantify diosgenin through High Performance Thin Layer Chromatography in 34 germplasms of Costus speciosus and also to identify the superior sources and to correlate the macronutrients of rhizospheric soil. The starch content varied in microscopic examination and correlated inversely (r=−0.266) with diosgenin content. Findings revealed that the extraction process with acid hydrolysis yielded higher diosgenin content (0.15–1.88 %) as compared to non-hydrolysis (0.009–0.368 %) procedure. Germplasms from Uttar Pradesh (NBCS-4), Jharkhand (NBCS-39) and Bihar (NBCS-2) were identified as elite chemotypes based on hierarchical clustering analysis. The phosphorous content of respective rhizospheric soil correlated positively (r=0.742) with diosgenin content. Findings of present study are useful to identify the new agrotechniques. The elite germplasms can also be used as quality planting material for large scale cultivation in order to assure a sustained supply to the herbal drug industry.     

Accumulation of Cd2+ and Pb2+ in the suspension cultures of Agave amaniensis and Costus speciosus and the determination of the culture's growth and phytosteroid content

Cell suspension cultures of Agave amaniensis and Costus speciosus were grown in media containing Cd^{2 +} up to 25 and 20 mg l^–1, respectively, and Pb²⁺ up to 40 mg l^–1. The cultures hyper-accumulated Cd²⁺ up to 900 and 530 g g^–1 and Pb²⁺ up to 1390 and 1170 g g^–1 dry wt. in their respective biomasses. Increasing Pb²⁺ up to 30 mg l^–1 increased the biomass production and total sitosterol content of Costus speciosus by up to 1.7- and 1.3-fold, respectively.