Paleontology and Chronology of Two Evolutionary Transitions by Hybridization in the Bahamian Land Snail Cerion

The late Quaternary fossil record of the Bahamian land snail Cerion on Great Inagua documents two transitions apparently resulting from hybridization. In the first, a localized modern population represents the hybrid descendants of a 13,000-year-old fossil form from the same area, introgressed with the modern form now characteristic of the adjacent regions. In the second case, a chronocline spanning 15,000 to 20,000 years and expressing the transition of an extinct fossil form to the modern form found on the south coast was documented by morphometry of fossils dated by amino acid racemization and radiocarbon. Hybrid intermediates persisted for many thousands of years.     

Evaluation of similar-media scaling and a one-parameter model for estimating the soil water characteristic

Two simple methods for estimating the soil water characteristic curve from saturated soil water content, or even just the soil bulk density, plus one other measured point on the curve (such as the water content at a matric potential of –33 kPa) were evaluated. A similar-media scaling approach and the one-parameter model of Gregson et al. were compared for eight diverse soils from within the USA. The scaling method also requires knowledge of one complete curve to serve as a reference. The one-parameter model was extended to include the residual water content, and the soils were divided into three textural groups for the analysis. Visual comparison of the calculated vs. measured soil water content for both methods showed less scatter in the relationship to the 1:1 line, concomitant with smaller calculated error terms, for the one-parameter model. These results demonstrate that the one-parameter model is better than similar-media scaling in estimating soil water content.     

THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT III THE WATER BALANCE

The catchment of the Kingston Brook has an area of 57 km², mainly under pasture (56%) and arable crops (36%). Changes of soil water content, measured with a neutron probe from April 1969 to March 1973, were analysed to determine evaporation (summer only) and drainage. From measurements of rainfall and runoff, supplemented by Penman estimates of evaporation (in winter), water storage is estimated month by month. Annual mean values (mm) were: rainfall (559), evaporation (398), runoff (157). During the summer, the measured decrease in soil water storage contributed ca 100 mm to evaporation and drainage and there is evidence of delayed recharge (about 30 mm) during the winter. A linear relation between annual rainfall and annual runoff is interpreted in terms of (i) a fixed catchment storage (125 mm); (ii) a small and nearly constant winter evaporation (ca 49mm); (iii) summer evaporation of 125 mm from storage plus a constant fraction (0.57) of contemporary precipitation. Summer evaporation was restricted by the supply of rain in every year from 1969 to 1976. By estimation, 500 mm of summer rain is needed to maintain potential evaporation, and the deficit at which actual evaporation falls below the potential rate was about 40 mm. Replacing the pasture by cereals would increase runoff by about 10% because of the shorter growing season.     

MOVEMENT PATTERNS OF RIVERINE LITTER

Aspects of litter movement were looked at in a variety of ways. River bank clearances provided valuable information on litter accumulation and movement, showing a distinctive correlation between flood events and litter movement. Introduction of litter outside of channel deposition (diffuse sources) were limited in the study area in South Wales, UK. A rise in litter deposition occurred for some time after flood events, with the main accumulation occurring in the mid-bank zone. As only some litter types have an increased input during flood events e.g. sewage-derived material from combined sewer outfalls (CSO), accumulation of other litter types, e.g. plastic sheeting could be due to their distribution throughout the catchment. A positive correlation between litter stranding and vegetation was found. During high flows, (75.59 cumecs) litter is removed from sites with little restraining vegetation and deposited where stranding potential is high. Smaller items such as feminine hygiene products were more susceptible to stranding than larger plastic sheeting.     

Comparison of diets for the tropical spiny lobster Panulirus ornatus: astaxanthin-supplemented feeds and mussel flesh

The fast‐growing tropical lobster Panulirus ornatus is a good aquaculture candidate generating increased research to develop potential feeds. We conducted a 12‐week experiment, assessing growth, survival and tissue carotenoid levels of juvenile P. ornatus. Lobsters were fed either pelleted feeds supplemented with astaxanthin and containing 30, 60, 90 or 120 mg total carotenoid kg^?1; or one of two fresh mussel reference feeds – blue Mytilus edulis and green‐lipped Perna canaliculus. There was no clear dose response, in terms of growth rate, to increasing dietary astaxanthin content; mussel‐fed lobsters had inferior growth rates. Twelve‐week survival was unaffected by treatment. Whole lobster carotenoid (4.7, 16.7, 27.8 and 32.8 mg kg^?1, dry matter basis) increased with increasing dietary astaxanthin; pre‐treatment carotenoid was 22.2 mg kg^?1. Apparent total carotenoid content of the mussel‐fed lobsters was unexpectedly high because of interference by other pigments. High‐performance liquid chromatographic analysis of free astaxanthin levels varied from a pre‐treatment value of 7.3 mg kg^?1 to 2.0, 7.6, 12.5 and 23.6 mg kg^?1 with increasing dietary astaxanthin, and 3.5 (green‐lip) and 5.9 (blue) mg kg^?1 for the mussel‐fed lobsters. Although dietary astaxanthin, over the investigated range, did not affect growth rate or survival, there was a dose–response increase in tissue carotenoid content and darkening of the exoskeleton pigmentation, which may have important implications for immunocompetency and marketing. These implications are discussed in the context of pelleted feed development for this species.