Parallel evolution in Marquesan partulid land snails

Partulid land snails of the genus Samoana inhabiting the Marquesas Islands of French Polynesia exist as two distinct types, the 'thick-shelled' and 'thin-shelled' species. The two types differ in size, shell-thickness, pigmentation of the shell and mantle, stickiness of the mucus, and length of the tentacles. A study of variation in allozymes indicates that the species form a monophyletic group, within which the differences between the two types have twice evolved independendy, once in the northern islands and at least once in the south. In the Society Islands the two suites of characters are found in both Partula and Samoana , where there is evidence of at least four other independent derivations of the two types. The thin-shelled species consistendy tend to occur at the higher altitudes (above 200 m). These cases of parallel evolution argue strongly that the complexes of associated characters have arisen through natural selection.     

Heterostyly and Pollen-tube Interactions in Luculia gratissima (Rubiaceae)

Observations on the floral biology of Luculia gratissima (Rubiaceae)showed that this species is distylous with complementary positioningof anthers and stigmas in the two floral forms. Unusual featuresof distyly in this species include the larger size of the corolla,the stigma surface and the stigmatic papillae in the thrum flowerscompared to the pin ones. Stigmatic surfaces have similar secretionsbut they appear more copious in thrum than pin. The floral dimorphismwas accompanied by a very effective self-incompatibility systemand no seed was set on selfing. Seed number per capsule on crossingwas significantly greater in thrum flowers compared to pin.Incompatible pollen tubes were inhibited within 24 h at thebase of the stigma/top of the style in both morphs. Amputationof this region of the gynoecium removed the self-incompatibilityreaction in thrum but not pin flowers. Pollination with a mixtureof compatible and incompatible pollen and sequential pollinationwith self followed by cross pollen showed that there were interactionsbetween the two types of pollen tube. The presence of compatibletubes was found to cause the excessive swelling of the pollen-tubetip of the incompatible ones. The incompatible tubes did notappear to have any effect on the growth of compatible ones. Luculia gratissima, distyly, floral biology, self-incompatibility, pollen-tube interactions     

ASSESSMENT OF POTENTIAL BIAS WITH SNOWSHOE HARE FECAL PELLET-PLOT COUNTS

Abstract: The fecal pellet-plot method has been used extensively for snowshoe hare (Lepus americanus) population studies across the species' range, but potential biases associated with the technique have not been addressed adequately. We studied hare pellet-plots in northern Idaho to quantify pellet decomposition rates across environmental gradients, and conducted feeding trials on captive hares to assess the role of diet on pellet production rates. We found that across our study area pellet numbers tended to be higher on plots with high vegetative cover, which likely was a reflection of hare habitat choice rather than lesser pellet decomposition in such habitat. A pellet decomposition experiment indicated that pellet persistence was negatively related to moisture level, and that pellets produced by hares during summer decomposed more quickly than those from winter. We found that only 19% of fecal pellets collected from plots located across northern Idaho were produced by hares during winter. There was a correlation between pellet numbers from plots that were pre-cleared 1 year earlier and estimated numbers of hares on 6 study areas. A similar correlation was lacking for pellet counts from uncleared plots, implying that hare population estimation via pellet-plot counts should involve plot pre-clearing. In captive studies, juvenile hares produced slightly fewer pellets per day per gram of food ingested than adults, but pellet production was similar across diets comprised of 10 different browse species. We conclude that for our study area the fecal pellet-plot method may be subject to notable pellet decomposition bias, and therefore recommend that use of the method elsewhere across the species' range be preceded by assessment of both the pellet-hare density relationship and pellet decomposition rates across habitats.     

Hybridization between tetraploid species of Alopecurus L. (Poaceae): chromosome behaviour of natural and artificial hybrids

The meiotic behaviour of plants from mixed populations of Alopecurus pratensis × A. geniculatus and of A. pratensis × A. arundinaceus ( 2n = 4×(= 28) is reported together with observations on some artificially produced hybrids. This meiotic behaviour is correlated with the degree of hybridity as shown by the hybrid index values of the plant. In A. pratensis × A. geniculatus hybrids there are marked differences between populations in the degree of meiotic disturbance and in one population there was an almost complete breakdown of meiosis. Alopecurus pratensis × A. arundinaceus hybrids show fairly regular meiotic pairing but in most plants there are a few univalent chromosomes at metaphase I. Artificially produced hybrids of A. pratensis × A. aequalis gave meiotic configurations that suggest that the genomes of the parent species are very similar. Taken together with the results from artificially produced hybrids of A. pratensis × A. geniculatus , it is suggested that bivalent-promoting mechanisms reduce multivalent formation both in the species and the hybrids. The interaction of different genotypes involved in the control of meiosis may account for the variation in meiotic behaviour in the different populations of hybrids. Pollen fertility is reduced in most populations of hybrids and likely to be an important factor permitting introgressive hybridization.     

Biometry of Cenomanian–Turonian placoliths: a proxy for changes of fertility and surface‐water temperature?

Most publications discussing Cenomanian–Turonian calcareous nannofossils focus on abundance fluctuations across the boundary interval. So far, there have been no studies that deal with the influence of palaeoenvironmental changes on the size of common Cenomanian–Turonian nannofossil taxa. The genera Biscutum, Broinsonia, Prediscosphaera, Retecapsa and Watznaueria have therefore been analysed from 19 samples of Cenomanian–Turonian age from the Goban Spur, northeast Atlantic. The genus Biscutum shows a slight decrease of mean length from 4.14 μm in the Cenomanian to 3.94 μm in the Turonian. Broinsonia is marked by a decrease from 6.07 μm in the Cenomanian to 5.64 μm in the Turonian. On the other hand, Prediscospheara increases in size from 4.98 μm in the Cenomanian to 5.61 μm in the Turonian. Two genera (Retecapsa, Watznaueria) show no significant changes in their mean length. The mean size of Biscutum is perhaps controlled by nutrients, where larger specimens may have preferred the more fertile palaeoenvironment of the Late Cenomanian. The size decrease of Biscutum in the Turonian is probably related to reduced nutrient availability. The genus Prediscosphaera spp., may have favoured low‐fertility conditions, as its mean size increases in the Turonian. A worldwide decline of the frequency of Broinsonia spp. during the Cenomanian–Turonian transition implies that this genus is not solely controlled by the nutrient content. The size of Broinsonia spp. may have been therefore influenced by the latest Cenomanian warming event. The increase in sea‐surface temperature may have been unfavourable for Broinsonia spp. as reflected by decreasing mean size and frequency. □Calcareous nannofossils, biometry, morphometry, Oceanic Anoxic Event 2.     

Improvement of persistence and yield of Italian ryegrass (Lolium multiflorum) through pesticide use

The present two field experiments, involving plots of Italian ryegrass sown in 1976, 1980 and 1984 confirmed results of earlier work in which the yield and persistence of Italian ryegrass was greatly increased by the application of pesticide. A range of pesticide treatments were used. The responses to application of permethrin applied three times per year average 8% for the three years of the first experiment and 5% for the five years of the second experiment. Such responses appeared cost-effective, but the overall environmental impact of such applications is not known.